High-density edge metal alloy die castings, die casting method, die casting device and applications

Abstract

The application discloses a metal alloy die casting with high compact edge, a die casting method, a die casting device and application, and belongs to the technical field of die casting forming. In the edge area of the die casting, the number of pore clusters in each square millimeter is not more than 0.5, the number of pores in each cluster is not more than 3, the average distance of pores outside the cluster is not less than 50 mu m, and the equivalent size of all pores is not more than 0.4 mm. The pores include shrinkage porosity and gas hole type, the number ratio of which is 1: (0.1-0.5), and the proportion of the gas hole type pores is not more than 30%. After the die casting is subjected to anodic oxidation treatment, the color difference DE between the edge and the matrix is less than 0.8. The application solves the problem of anodic oxidation color difference caused by the pore difference between the edge and the matrix of the die casting, guarantees the appearance consistency and structural reliability of the product, and can be used in the fields of high appearance requirements such as consumer electronics and automobiles.

Description

Technical Field

[0001] This invention belongs to the field of die casting technology, specifically relating to a high-density edge metal alloy die casting part, a die casting method, a die casting device, and its application. Background Technology

[0002] Die casting, as a highly efficient and near-net-shape metal parts manufacturing process, is widely used in high-end manufacturing fields such as consumer electronics casings, automotive parts, and robotic mechanical components. In these applications, the surface quality and microstructural uniformity of the edge areas often determine the performance and aesthetics of the final product. This is especially true for alloy die castings that require anodizing, where the anodizing effect and consistency between the edge and base areas become key indicators for evaluating product quality.

[0003] In traditional die casting processes, the edge areas of castings often exhibit inherent defects such as inhomogeneous microstructure and insufficient density. These defects primarily stem from the solidification characteristics of molten metal within the mold cavity and uneven pressure distribution. Specifically, after molten metal is injected into the mold cavity, a solidified layer first forms in the edge area that contacts the low-temperature mold wall. Because traditional die casting typically lacks a pressurization system or uses a uniform pressurization system, the edge areas cannot receive sufficient feeding pressure. Simultaneously, due to their large heat dissipation area and rapid cooling rate, the edge areas are prone to forming coarse dendritic crystal structures and exhibiting high and uneven internal pore density.

[0004] This microstructural inhomogeneity is amplified dramatically during the anodizing process. Due to significant differences in pore density, grain size, and impurity content between the edge and substrate regions, the growth rate and structure of the anodized film exhibit marked variations across different areas. In actual production, this difference often manifests as a visible "yin-yang" phenomenon, where a noticeable color difference occurs between the edge and substrate regions, severely degrading the product's appearance. For high-end consumer electronics products, this color difference is almost impossible to completely eliminate through subsequent processing, leading to a significant decrease in product yield and a substantial increase in costs.

[0005] Therefore, there is an urgent need to develop a die-casting technology that can control the microstructure of the edge region and improve the porosity distribution, so as to solve the technical problems of low density and large color difference in the edge region of metal alloy die-casting parts.

[0006] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0007] This invention provides a metal alloy die casting with high-density edges, a die casting method, a die casting apparatus, and an application, which at least solves the technical problems of low density in the edge area of ​​metal alloy die castings and large color difference in anodizing.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a metal alloy die casting with a high-density edge, wherein at least in the edge region, the number of pore clusters per square millimeter does not exceed 0.5, and the number of pores in each cluster does not exceed 3; the average spacing between pores outside the pore clusters is not less than 50 μm; and the equivalent size of all pores does not exceed 0.4 mm. The porosity includes shrinkage porosity and gas porosity. The ratio of shrinkage porosity to gas porosity in the metal alloy die casting is 1:(0.1~0.5), and the total number of gas porosity in the edge region accounts for no more than 30% of the total number of porosity in the edge region. After anodizing, the color difference ΔE between the edge area and the base area of ​​a metal alloy die casting is less than 0.8.

[0009] Furthermore, the average grain size of the edge region of the metal alloy die casting is 10μm~50μm, and the standard deviation of the grain size is no greater than 10μm.

[0010] Furthermore, the deviation in average grain size between the edge region and the base region of the metal alloy die casting is less than 10%.

[0011] Furthermore, the proportion of dendrites in the edge region of the metal alloy die casting is no more than 1%.

[0012] Furthermore, the impurity content in the edge area of ​​the metal alloy die casting is no more than 0.5%.

[0013] Furthermore, the surface roughness Ra of the edge region of the metal alloy die casting is no greater than 1.5 μm.

[0014] Furthermore, the metal alloy is an aluminum alloy, magnesium alloy, titanium alloy, stainless steel, copper alloy, nickel alloy, or zinc alloy.

[0015] Furthermore, the metal alloy is a 6-series or 7-series aluminum alloy.

[0016] In a second aspect, the present invention provides an application of the metal alloy die casting of the first aspect in the manufacture of structural parts for electronic devices, transportation vehicles, robots, medical devices, industrial equipment, or new energy equipment.

[0017] Thirdly, the present invention provides a die-casting method for preparing a metal alloy die-casting part with high-density edges as described in the first aspect, comprising: The molten metal is filled into the mold cavity; When the molten liquid in the mold cavity begins to solidify, the mold cavity is pressurized to discharge excess molten liquid from the overflow port on the mold cavity; the ratio between the volume of excess molten liquid and the volume of the mold cavity is not less than 0.1.

[0018] Furthermore, the die-casting method also includes auxiliary heating of the edge of the mold cavity after the excess melt has been completely drained, with a heating temperature of 400℃~480℃ and a heating time of 5s~30s.

[0019] Furthermore, pressurizing the mold cavity includes pressurizing the mold cavity multiple times, with the pressure of each subsequent pressurization increasing by 20% to 40% compared to the pressure of the previous pressurization, and the pressure of the last pressurization being 40% to 200% greater than the pressure of the first pressurization.

[0020] Furthermore, the ratio between the volume of excess melt and the volume of the mold cavity is in the range of 0.1 to 0.5.

[0021] Furthermore, the step of filling the mold cavity with molten liquid includes first filling the molten liquid at a first flow rate, and then second filling the molten liquid at a second flow rate higher than the first flow rate; The volume of excess melt and the volume of the mold cavity satisfy the following relationship:

[0022] In the formula, The volume of excess melt; This refers to the volume of the mold cavity; This is the first proportionality constant, and its value ranges from 0.1 to 0.2; This is the temperature difference between the melt and the mold, and its value ranges from 300℃ to 350℃. The mold temperature, with a value ranging from 300℃ to 420℃; The first flow velocity is defined as 2 m / s, and its value range is no greater than 2 m / s.

[0023] Fourthly, the present invention provides a die-casting apparatus for implementing the die-casting method of the third aspect, comprising a mold and a pressurizing mechanism; a mold cavity is formed inside the mold, and an overflow port is provided on the mold cavity; the pressurizing mechanism is disposed on the mold and is used to pressurize the molten liquid in the mold cavity so that excess molten liquid is discharged from the overflow port; The overflow port is circumferentially located on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity.

[0024] Furthermore, the die-casting apparatus also includes a heating mechanism, which is mounted on the mold and is used to provide auxiliary heating to the edge of the mold cavity after the excess melt has been completely drained.

[0025] Furthermore, the die-casting apparatus also includes an injection mechanism for first filling the molten metal at a first flow rate and then second filling the molten metal at a second flow rate higher than the first flow rate.

[0026] The beneficial effects of this invention are as follows: The high-density edge metal alloy die casting provided by this invention overcomes the bottleneck of low edge quality in traditional die castings by achieving synergistic matching in defect control, microstructure, and surface properties of its edge region. The porosity of the edge region of this die casting exhibits a controlled morphology and gradient distribution, limiting not only the number of pore clusters per unit area, the number of pores within a cluster, and the average spacing between pores, but more importantly, specifying the ratio of shrinkage-type pores to gas-type pores and the upper limit of the proportion of gas-type pores. This specific morphology, ratio, and distribution of the pore structure minimizes the difference in microscopic pore morphology and density between the edge and the substrate. Since the formation and coloring of the anodic oxide film are extremely sensitive to microscopic defects on the substrate material surface, this highly controlled and uniform edge porosity state allows the edge region and the substrate region to exhibit nearly identical electrochemical and optical responses during the oxidation process, thus achieving a seamless and uniform appearance in the final visual result. This solves the problem of obvious color difference that inevitably occurs at the edges of traditional die castings due to disordered pore distribution, high density, and significant differences from the substrate.

[0027] The uniform and fine microstructure at the edges contributes to the high density of the die-cast parts. The average grain size in the edge region of the die-cast parts of this invention is fine and concentrated, with minimal deviation from the matrix structure, while the proportion of dendritic grains is effectively suppressed. This highly consistent grain structure from the edge to the matrix means that the material achieves homogenization of properties at the microscale, eliminating internal stress concentration or local performance collapse caused by abrupt changes in microstructure, and ensuring stable and predictable mechanical response and dimensional stability of the parts under complex working conditions.

[0028] Building upon this core effect, the edge region of this die-cast part also possesses excellent comprehensive physical properties. The specific low-defect porosity structure itself constitutes a dense and uniform reinforced edge, endowing this region with higher structural integrity and load-bearing reliability. Furthermore, the edge of this die-cast part also features uniform and fine grain size, an extremely low dendrite ratio, low impurity content, and good surface roughness. These characteristics, combined with the core porosity control, ensure that the edge of the die-cast part meets high-quality requirements not only in visual appearance but also in microstructure, mechanical properties, and surface quality. This makes it suitable for use as structural components in high-end consumer electronics housings, precision automotive parts, and other products with stringent requirements for both appearance and performance.

[0029] This invention not only achieves control over product appearance and other indicators, but also provides an optimized die-casting method and die-casting apparatus for producing such a product. The method combines pressurization and feeding with impurity removal by pressurizing the mold cavity and controlling overflow. The accompanying die-casting apparatus ensures the accuracy and repeatability of pressure application through an independent pressurization mechanism. The optimized die-casting method and apparatus guarantee that the aforementioned superior product performance can be stably and efficiently achieved in large-scale production. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 These are comparative photographs of the gold content of the edge regions of the die-cast parts in Embodiment 1 and Comparative Example 1 of the present invention. Figure 2 Metallographic microscope image of the metal alloy die casting provided in Embodiment 12 of the present invention; Figure 3 Metallographic microscope image of the metal alloy die casting provided in Embodiment 16 of the present invention; Figure 4 This is a photograph of the appearance of the edge area of ​​the die-cast part after anodizing, according to Embodiment 1 of the present invention. Figure 5 These are comparative photos of the appearance of the edge area and the base area of ​​the die-cast part after anodizing, as shown in Embodiment 16 of the present invention. Figure 6 These are comparative photos of the appearance of the edge area and the base area of ​​the die-cast part after anodizing, as shown in Comparative Example 1 of this invention. Figure 7 This is a three-dimensional structural diagram of the mold provided in Embodiment 1 of the present invention; Figure 8 This is a side view of the mold provided in Embodiment 1 of the present invention; Figure 9 Metallurgical microscope image of typical porosity; Figure 10 Metallurgical microscope image of a typical shrinkage-type pore.

[0032] Explanation of reference numerals in the attached figures: 10. Mold cavity; 20. Liquid inlet; 30. Overflow outlet. Detailed Implementation

[0033] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0035] In traditional die-casting processes, the edge regions experience rapid cooling and often lack sufficient feeding pressure, leading to the accumulation of defects such as shrinkage porosity and gas porosity. These edge porosity defects not only affect the mechanical properties of the product but, more seriously, cause uneven coloring during anodizing, resulting in visible uneven surfaces. This invention aims to achieve precise and uniform control of porosity distribution in edge regions by synergistically controlling the number of pore clusters per unit area, the number of pores within each cluster, and the average pore spacing.

[0036] In this invention, the term "edge region" refers to a region extending inward from the outer contour edge of the die-cast part at a certain distance. Specifically, the range of the edge region can be 1mm to 5mm inward from the outer contour edge, preferably 2mm to 3mm, and more preferably 2mm. Those skilled in the art will understand that, depending on the size, shape, and specific application requirements of the die-cast part, the specific range of the edge region can be appropriately adjusted within the range of 1mm to 5mm. As long as the adjusted region still reflects the microstructure feature control effect described in this invention, it should fall within the protection scope of this invention.

[0037] This invention provides a metal alloy die casting with a high-density edge, wherein at least in the edge region, the number of pore clusters per square millimeter does not exceed 0.5, and can be 0.5, 0.49, 0.48, 0.45, 0.42, 0.4, 0.38, 0.35, 0.32, 0.3, 0.28, 0.25, 0.22, 0.2, 0.18, 0.15, 0.12, 0.1, 0, and any value between them.

[0038] This invention controls the morphology and distribution of pore clusters in edge regions. First, it is necessary to clarify the meaning of "pore cluster" in the context of this patent: "Pore cluster" specifically refers to a localized defect aggregate formed by two or more pores at a microscopic scale, where the minimum distance between their edges is less than 20 μm. This definition is based on the following two considerations: First, when two or more pores are too close (<20 μm), their stress fields will significantly overlap, greatly increasing the risk that this area will become a preferred path for microcrack initiation and propagation; second, such closely adjacent pores are highly likely to merge through narrow matrix bridges during subsequent heat treatment or use, evolving into a macroscopic defect with a size far exceeding the allowable range, severely damaging the structural integrity of the material. Therefore, the "pore cluster" defined in this invention essentially aims to identify and control defect aggregation morphologies with high hazard and high merging risk.

[0039] Based on this, the present invention, through extensive process verification and performance testing, controls the number of pore clusters per square millimeter in the edge region to no more than 0.5. When the number of clusters per unit area exceeds 0.5 per mm... 2 This means that high-risk defect clusters are distributed too densely. Even if the number of pores within a single cluster is small, the densely distributed clusters form a microscopic network of weak points throughout the edges. During anodizing, these dense clusters can lead to uneven local growth of the oxide film, causing abnormal current density distribution, resulting in visible, uneven color variations on the darker and lighter sides. Controlling the cluster density to an extremely low level is fundamental to ensuring that the edge regions exhibit a high degree of consistency with the substrate during electrochemical treatment.

[0040] The number of pores in each cluster shall not exceed 3, and can be either 3 or 2.

[0041] This invention controls the number of pores within each pore cluster to no more than three, aiming to directly constrain the complexity within the cluster. If a cluster contains more than three pores, such as four, five, or more, and its overall spacing meets the definition of a cluster with a spacing of less than 20 μm, such a large number of pores severely disrupts the material continuity of that local area, forming a micro-porous defect structure. During anodizing, this highly complex defect structure, as a whole, causes severe and irregular interference to the wetting of the oxide solution, current conduction, and oxide film growth, easily forming dark spots or color difference areas that are more pronounced than those of a single cluster. Controlling the upper limit of the number of pores within a cluster to three, and working in conjunction with a cluster density limit, ensures that even if a very small number of clusters exist, their harmfulness is controllable and will not directly lead to macroscopic appearance failure.

[0042] The average spacing between pores outside the pore cluster is not less than 50 μm, and can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, larger, or any value in between.

[0043] This invention controls the average spacing between pores outside of pore clusters to be no less than 50 μm. The aim is to regulate the distribution of pores in a non-clustered state (i.e., isolated or widely spaced pores) and prevent them from exhibiting negative clustering-like effects due to excessive density. The 50 μm average spacing threshold is determined based on the principles of material micromechanics and surface treatment. First, from a mechanical performance perspective, when the average spacing between pores is less than 50 μm, even if they are not defined as "pore clusters" (i.e., spacing ≥ 20 μm), the stress field influence zones between these relatively isolated defects have a high probability of overlapping. Under load, these overlapping stress fields will mutually promote each other, significantly increasing the tendency for local plastic deformation and microcrack connection, weakening the overall load-bearing capacity and fatigue life of the edge areas. Second, from the perspective of the anodizing process, the growth of the oxide film depends on the uniform electrochemical reaction on the substrate surface. If the pore distribution is too dense, the resulting microporous network will severely interfere with the flow and distribution of the electrolyte on the surface, causing current lines to twist and concentrate among numerous defect points. This uneven electrochemical environment causes differences in growth rate and structure between densely porous and relatively intact regions of the oxide film, ultimately manifesting as visible, large-area unevenness in light and dark areas or color. Therefore, controlling the average pore spacing to a level of not less than 50 μm ensures sufficient matrix spacing between defects. This not only blocks harmful mechanical and electrochemical interactions between defects but also provides a relatively uniform reaction substrate at the microscale for the anodic oxidation process, contributing to a uniform appearance.

[0044] The equivalent size of all pores shall not exceed 0.4 mm, and may be 0.4 mm, 0.35 mm, 0.3 mm, 0.25 mm, 0.2 mm, 0.15 mm, 0.1 mm, smaller, or any value in between. Preferably, the depth does not exceed 0.3 mm, and can be 0.3 mm, 0.25 mm, 0.2 mm, 0.15 mm, 0.1 mm, smaller, or any value between them.

[0045] This invention controls the equivalent size of all pores to not exceed 0.4 mm (defined as the diameter of a circle with the same projected area), and preferably the depth to not exceed 0.3 mm. This direct constraint on the size of individual pores aims to eliminate macroscopic and critical defects that may dominate failure or appearance defects at the source. The upper limit of the equivalent size takes into account the critical impact of defects on mechanical properties. Pores that are too large can themselves become significant stress concentration sources, easily becoming direct crack initiation points under dynamic or impact loads, seriously threatening the reliability of structural components. Simultaneously, during the oxidation process, the electric field distribution, solution exchange, and gas exhaust conditions inside and outside excessively large pores are drastically different from those on flat surfaces, easily leading to abnormal oxide film growth at these locations (such as excessive thickness, looseness, or inability to form), thus forming independent, clearly identifiable dark or bright spots, disrupting the overall color uniformity. Pores with greater depth, even with small surface openings, will present unique problems during anodizing due to their longitudinal structure. Excessively deep pores can hinder the sufficient inflow and renewal of the oxidizing solution, leading to incomplete oxidation at the bottom of the pore or the formation of dead zones. This can easily cause color inconsistencies with the surface or a decrease in corrosion resistance in these areas. By synergistically controlling the equivalent size and depth of the pores, the aspect ratio of the pores is effectively limited, ensuring that even if pores exist within the allowable range, their morphology remains relatively smooth, avoiding the introduction of uncoordinated local extreme conditions in subsequent surface treatments.

[0046] In summary, this invention achieves precise control of microscopic defects in the edge region by comprehensively controlling indicators such as the number of pore clusters, the number of pores within the clusters, the pore spacing, and the pore size and depth, thus fundamentally solving the problem of uneven anodizing in the edge region.

[0047] Porosity includes shrinkage porosity and gas porosity. The ratio of shrinkage porosity to gas porosity in metal alloy die castings is 1:(0.1~0.5), which can be (1:0.1), (1:0.2), (1:0.3), (1:0.4), (1:0.5) and any value between them. The total number of pores in the edge region shall not exceed 30% of the total number of pores in the edge region, and may be 30%, 28%, 25%, 22%, 20%, 18%, 15%, 12%, 10%, 8%, 5%, 2%, 0%, or any value between them.

[0048] It is understood that porosity is mainly classified into shrinkage porosity and gas porosity based on its formation and morphology. Shrinkage porosity is usually formed due to insufficient compensation for volume shrinkage during alloy solidification. It is irregular in shape, dendritic, or torn, with rough inner walls, and is often located at hot spots or thick-walled areas during the last solidification of the casting. This invention defines shrinkage porosity as having a major axis / minor axis ratio of not less than 1.5, reflecting its characteristic of extending along grain boundaries or in a specific direction. Gas porosity is mainly formed by the precipitation of gases (air, hydrogen, etc.) in the melt during solidification or by entrainment during mold filling. It is mostly circular or elliptical in shape, with smooth inner walls, and is often distributed inside or near the surface of the casting. This invention defines gas porosity as having a major axis / minor axis ratio of less than 1.5 and a relatively regular shape.

[0049] Shrinkage porosity is a pore structure with a major axis / minor axis ratio of not less than 1.5. The major axis / minor axis ratio of shrinkage porosity can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, higher, or any value between them. A porosiform pore is a pore structure with a major axis / minor axis ratio of less than 1.5. The major axis / minor axis ratio of a porosiform pore can be 1.4, 1.3, 1.2, 1.1, 1, or any value between them. Understandably, because the length of the major axis must not be less than the length of the minor axis, the lower limit of the major axis / minor axis ratio of a porosiform pore is 1.

[0050] This invention not only controls the overall quantity and distribution of pores, but also implements graded control over the ratio of these two types of pores, and specifically controls the upper limit of the proportion of porosity in key areas. Specifically, this invention limits the ratio of shrinkage porosity to porosity in the metal alloy die casting (covering both edge and base areas) to 1:(0.1~0.5), meaning that the number of porosity pores is relatively small throughout the entire die casting, approximately 10% to 50% of the shrinkage porosity; simultaneously, it further controls the proportion of porosity pores in the edge area to no more than 30% of the total number of pores in that area. The purpose of these settings is to ensure the overall and local uniformity of anodizing coloring.

[0051] Understandably, shrinkage-type pores and porosity-type pores differ fundamentally in their formation, morphology, and electrochemical response during anodizing. Shrinkage-type pores originate from insufficient solidification and feeding, exhibiting irregular morphology and rough inner walls, and are mostly found on fresh metal surfaces. During anodizing, the oxide film can grow relatively uniformly along the rough inner walls or fill the gaps through sealing, resulting in a diffuse scattering effect on light and making it difficult to form abrupt color difference boundaries. Conversely, porosity-type pores are mostly formed by gas entrainment during molding or gas evolution during solidification, exhibiting near-spherical or elliptical shapes with smooth inner walls. These pores are highly susceptible to retaining oxide inclusions (double oxide films) entrained during molding. Electrochemically, these residues act as insulating or weakly bonded regions, hindering the full wetting of the oxidizing solution and the expulsion of gas from the pores, leading to localized electric field distortion and abnormally concentrated current density. During the oxide film growth stage, weak oxide zones with abnormal thickness or loose structure are easily formed around the pores; during the coloring stage, this area is extremely sensitive to thin film optical interference and is the core cause of macroscopic visible color difference.

[0052] This invention controls the ratio of shrinkage porosity to pore size in the overall casting to be 1:(0.1~0.5), macroscopically ensuring that the overall defect morphology of the die casting is dominated by relatively controllable shrinkage porosity, which helps promote overall densification. Based on this, for edge areas with high cooling rates and where gas is easily entangled at the end of the filling process, this invention further controls a stricter upper limit for the proportion of pores (≤30%). Edge areas are the most critical areas for anodizing appearance inspection, and their tolerance for microscopic defects is much lower than that of the matrix. By controlling the overall proportion of pores to prevent them from becoming dominant, and further controlling the pore types and porosity in edge areas, the probability of highly hazardous pores accumulating in key appearance areas can be minimized. This effectively blocks local electrochemical response anomalies caused by regularly shaped pores and internal wall inclusions, thereby reducing the risk of significant color differences from the source of pore type.

[0053] Specifically, if the proportion of porosity in the edge region exceeds 30%, even if the total number of pores in the overall die-cast part does not exceed the limit, the accumulated electric field distortion and optical interference effects at the edge may quickly exceed the human eye's perception threshold for color uniformity. In this case, visible spots, dark edges, or color differences between the two sides are very likely to appear in the edge region after anodizing. Therefore, this specific ratio and its upper limit help to promote the production of die-cast parts with high appearance consistency in this invention.

[0054] After anodizing, the color difference ΔE between the edge area and the base area of ​​the metal alloy die casting is less than 0.8, and can be 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, smaller, or any value between them.

[0055] It is understood that color difference ΔE is a comprehensive index defined by the International Commission on Illumination (CIE) to quantify the perceptual difference between two colors. When ΔE is less than 1.0, the human eye can usually hardly perceive the difference; while ΔE less than 0.8 indicates an extremely high degree of color matching, almost to the point of being visually indistinguishable. For high-end consumer electronics and automotive trim parts, ΔE less than 0.8 is the critical value for meeting stringent appearance quality inspection standards. This invention controls the color difference ΔE between the edge and the substrate of the die-cast part after anodizing to less than 0.8, which is the most direct macroscopic performance test standard for the comprehensive effect achieved by all the aforementioned microstructural controls.

[0056] From an optical mechanism perspective, the color of anodic oxide films mainly originates from the absorption of light by the film layer and the thin-film interference effect. Even minute changes in the thickness of the oxide film can lead to a significant shift in the wavelength of the interference light, resulting in a color difference visible to the naked eye. The low-density, fine, dispersed, and predominantly shrinkage-type porous structure ensures that the electrochemical activity, current distribution, oxide solution wetting, and reaction rate of the edge regions during anodizing are highly similar to those of the substrate region, thus growing oxide films with extremely similar thickness, porosity, and microstructure.

[0057] The interference, absorption, and reflection of light by this oxide film are almost uniform at the edges and the substrate, ultimately presenting a seamless and uniform color visually. Die-cast parts prepared using the technical solution of this invention achieve a high degree of consistency between the edges and the substrate in the anodized appearance, completely solving the common problems of white edges, dark edges, or uneven surfaces in traditional die-cast parts. If ΔE exceeds 0.8, even with a small number of micropores, it means that the difference in oxide film thickness between the edges and the substrate exceeds the threshold of human visual perception, usually due to uncontrolled agglomerated pores or severe grain size differences in the edge region.

[0058] Furthermore, the average grain size of the edge region of the metal alloy die casting is 10μm~50μm, and can be 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm and any value between them; The standard deviation of the grain size is no greater than 10 μm, and can be 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, smaller, and any value in between.

[0059] Grain size is a microstructural parameter that directly affects the mechanical properties (such as strength and toughness) of metallic materials. Therefore, this invention controls the grain size of the microstructure in the edge region. An average grain size of 10 μm to 50 μm falls into the category of fine-grained microstructure. Fine grains mean a greater number of grain boundaries, which can more effectively hinder dislocation movement, thereby significantly improving the yield strength and hardness of the material. More importantly, during the anodizing process, grain size directly affects the micro-roughness and gloss of the oxide film. Controlling the grain size below 50 μm ensures uniform oxide film growth and a smooth, bright surface. Simultaneously, controlling the standard deviation of the grain size to no more than 10 μm aims to ensure a concentrated and relatively uniform grain size distribution in the edge region, avoiding an inhomogeneous microstructure composed of coarse and fine grains. A uniform and fine grain structure not only benefits the stability of mechanical properties but also provides a good matrix condition for obtaining a uniform surface treatment effect.

[0060] Understandably, the influence of grain size on the growth behavior of anodic oxide films stems primarily from the difference in electrochemical activity between grain boundaries and the interior of the grain. At grain boundaries, the atomic arrangement is more disordered, and the energy state is higher, typically exhibiting higher reactivity during anodic oxidation than within the grain, resulting in a faster oxide film growth rate. When the grain size is too large, the number of grain boundaries per unit area decreases significantly, leading to noticeable differences in the growth rate of the oxide film across different grain regions. This difference manifests macroscopically as uneven gloss or slight color variations. Conversely, when the grain size is controlled within the range of 10 μm to 50 μm, the grain boundary distribution is sufficiently dense and uniform, causing the growth rate of the oxide film to tend to be consistent across the entire surface, thus achieving uniform film thickness and optical properties.

[0061] Furthermore, the standard deviation of grain size is a statistical parameter characterizing the uniformity of the microstructure. Even if the average grain size falls within the ideal range, a large standard deviation still indicates the presence of numerous anomalous grains with sizes deviating from the average. These anomalous grains may be products of localized cooling rate fluctuations, compositional segregation, or heterogeneous nucleation. During anodizing, anomalously large grains exhibit different oxidation behavior from their surrounding areas due to their low grain boundary density, forming microscale difference zones. When the size and distribution of these difference zones reach a certain level, their cumulative optical effects become perceptible to the human eye, manifesting as localized abnormal gloss or slight color differences. Therefore, controlling the standard deviation to no more than 10 μm aims to ensure the homogeneity of the microstructure from a statistical distribution perspective, eliminating potential appearance risks caused by grain size dispersion.

[0062] It should also be noted that the control of grain size in the edge region is synergistically related to the porosity control indicators mentioned above. Fine-grained microstructures generally imply a high nucleation rate and controlled growth rate during solidification, which helps suppress the formation and growth of shrinkage-type pores. Simultaneously, a uniform grain distribution facilitates the uniform transmission of pressure during solidification, reducing localized insufficient feeding caused by microstructural inhomogeneity. Therefore, grain size control not only directly affects mechanical properties and appearance but also indirectly supports the achievement of preceding indicators such as pore density and pore type ratio.

[0063] Furthermore, the deviation in average grain size between the edge region of the metal alloy die casting and the base region of the metal alloy die casting is less than 10%, and can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0, and any value between them.

[0064] It is understood that this invention controls the average grain size of the edge region and the matrix region of the die-cast part to be highly similar, further enhancing the overall uniformity of the product's microstructure. In traditional die casting, due to the significant difference in cooling conditions between the edge and the center, the edge grains are often much smaller than the matrix (rapid cooling leads to a high nucleation rate), resulting in obvious microstructural differences. This microstructural difference can also lead to uneven performance and anodized color difference. Because grains of different sizes may have different grain boundary densities, crystal orientations, and local chemical compositions, they affect the local behavior of anodizing. By controlling the average grain size deviation between the edge and the matrix, it can be ensured that the basic structural unit scale of the material is basically consistent from the matrix to the edge. This greatly promotes the homogenization of the material's macroscopic properties, making the reflection behavior of light consistent across the entire product surface, and ensuring uniform oxide film thickness, thus eliminating visual color difference.

[0065] Specifically, the impact of grain size deviation on the uniformity of anodic oxide film growth mainly stems from the difference in electrochemical activity at grain boundaries. At grain boundaries, the atomic arrangement is more disordered, and the energy state is higher, typically exhibiting higher reactivity in the anodic oxide electrolyte than within the grains, resulting in a faster oxide film growth rate. When the grain size deviation between the edge region and the substrate region is large, the grain boundary density in the two regions will differ significantly, leading to different growth rates of the oxide film at the edge and in the substrate, ultimately forming an oxide film layer of inconsistent thickness. This thickness difference causes a shift in the wavelength of reflected light through thin-film interference, macroscopically manifesting as a color difference perceptible to the naked eye.

[0066] Furthermore, when the average grain size deviation between the edge and the substrate exceeds 10%, the difference in grain boundary density between the two regions will cause the difference in anodic oxide film thickness to exceed the human visual perception threshold. Specifically, if the edge grain size is significantly smaller than the substrate, the grain boundary density in the edge region is too high, the oxide film growth rate is too fast, and a thicker oxide film is easily formed, resulting in a darker hue after coloring, i.e., the dark edge phenomenon. Conversely, if the edge grain size is significantly larger than the substrate, the grain boundary density in the edge region is too low, the oxide film growth rate is too slow, and a thinner oxide film is easily formed, resulting in a lighter hue after coloring, i.e., the white edge phenomenon. Therefore, controlling the deviation within 10% helps to maintain consistency in the appearance of the anodized edge and the substrate.

[0067] Furthermore, controlling grain size deviation is crucial for the uniformity of the product's mechanical properties. Significant differences in grain size between the edge and the matrix can lead to mismatches in strength, toughness, and fatigue performance between the two regions. When the part is under load, stress concentration is likely to occur at the edge-matrix interface, becoming a preferred path for crack initiation and propagation. Controlling the deviation to within 10% ensures a smooth transition of mechanical properties from the edge to the matrix, improving the overall structural reliability and service life of the product.

[0068] Furthermore, the dendritic ratio in the edge region of the metal alloy die casting is no more than 1%, and can be 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0, or any value between them. This dendritic ratio refers to the percentage of grain area with distinct secondary dendrite arm characteristics in the cross-section of the edge region observed under a metallographic microscope, relative to the total grain area.

[0069] Understandably, dendrites are a common non-equilibrium structure in alloy solidification. Their well-developed dendritic arms displace solute elements into the intergranular space, causing severe microsegregation. Under die-casting conditions, especially when the melt is significantly undercooled or the cooling rate is uneven, well-developed dendrites are prone to form. The edge regions, due to direct contact with the low-temperature mold wall, experience a much higher cooling rate than the matrix region, theoretically making them highly susceptible to chilled dendrite formation. Without intervention in the solidification process, the proportion of dendrites in the edge regions is typically much higher than 1%. The presence of dendrites implies the existence of secondary dendritic arms within the grains, resulting in irregular grain shapes. The interdendritic regions are often enriched with solute elements and impurities, and are also prone to shrinkage porosity. A higher proportion of dendrites is usually accompanied by poorer mechanical properties (especially plasticity and toughness) and poorer chemical composition uniformity.

[0070] Specifically, the impact of dendrites on the appearance of anodized surfaces mainly stems from the electrochemical potential difference between the interdendritic segregation zone and the dendritic arm matrix. In the anodizing electrolyte, the dissolution rates of the solute-rich interdendritic regions and the solute-poor dendritic arm regions differ, leading to inconsistent oxide film thickness. When the proportion of dendrites is high, this microscopic thickness difference accumulates macroscopically, manifesting as uneven gloss or color difference. This invention controls the proportion of dendrites in the edge region to be no more than 1%, requiring the edge region to exhibit a predominantly equiaxed crystalline structure. This microstructure, dominated by equiaxed crystals, exhibits better grain isotropy, fewer internal defects, and more uniform composition, thus providing an ideal matrix for obtaining a high-strength, high-toughness, and uniform anodized surface. When the proportion of dendrites exceeds a threshold, it means that the solidification mode in the edge region has shifted to obvious directional growth, and the resulting component segregation will be difficult to compensate for by subsequent anodizing processes, easily leading to visible uneven surfaces between the edge and the matrix. Therefore, controlling the proportion of dendrites to an extremely low level helps to eliminate electrochemical inhomogeneities in the edge region from the solidification source.

[0071] Furthermore, the impurity content in the edge region of the metal alloy die casting is no more than 0.5%, and can be 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.05%, 0, or any value between them. This impurity content refers to the percentage of non-metallic inclusions in the cross-section of the edge region observed under a metallographic microscope or scanning electron microscope.

[0072] The impurities referred to here mainly include non-metallic inclusions such as oxides, sulfides, and silicates, which are incorporated into the melt during smelting, transfer, or filling. Specifically, in the die-casting process, the main sources of impurities include: the oxide film (double oxide film) formed when molten aluminum comes into contact with air during smelting; refractory material particles that peel off from the crucible or runner during melt transfer; mold release agent residues that are drawn in by turbulence during filling; and incompletely melted high-melting-point compounds in the alloy raw materials. Impurity phases typically have high hardness, poor plasticity, and weak bonding with the metal matrix, making them weak points in the material and prone to becoming the origin of crack initiation and propagation, significantly reducing the material's mechanical properties (especially fatigue strength and ductility).

[0073] From the perspective of anodizing appearance, the impact of impurity content on the color uniformity of the edge area mainly stems from the following three mechanisms: First, the standard electrode potential of metallic inclusions differs significantly from that of the aluminum alloy substrate, forming micro-galvanic corrosion cells in the anodizing electrolyte. This leads to abnormally concentrated or dispersed current density around the inclusions, resulting in an oxide film growth rate inconsistent with the substrate. Second, hard inclusions do not participate in the film-forming reaction during oxidation, forming insulating islands or weak interfaces in the oxide film, disrupting the film continuity and causing abnormal light scattering at these locations. Third, some inclusions (such as sulfides and silicates) may selectively dissolve in the anodizing electrolyte, leaving micropores or defects on or inside the oxide film, becoming uneven adsorption sites for colorants. During anodizing, the impurity phase may have different electrochemical properties than the base metal, leading to localized oxide film failure, defects, or color differences.

[0074] Furthermore, when the impurity content in the edge region exceeds 0.5%, the number of inclusions per unit area will increase significantly, and the cumulative effect of the above three mechanisms will exceed the human eye's perception threshold for color uniformity. Specifically, after anodizing, the edge region often exhibits scattered black or white spots, or even a noticeably dirty appearance, failing to meet application standards in fields with high aesthetic requirements. Therefore, controlling the impurity content is more helpful in ensuring the structural reliability and surface treatment purity of edge regions with high density and high aesthetic requirements.

[0075] Furthermore, controlling impurity content is also crucial for the corrosion resistance of products. The interface between non-metallic inclusions and the base metal is often the preferential entry channel for corrosive media, and interfacial corrosion is prone to occur in humid or salt spray environments, leading to a reduction in product service life. Controlling the impurity content to below 0.5% can significantly reduce the number of such corrosion-sensitive interfaces, improving the overall corrosion resistance and reliability of the product.

[0076] Furthermore, the surface roughness Ra of the edge region of the metal alloy die casting is no greater than 1.5 μm, and can be 1.5 μm, 1.4 μm, 1.3 μm, 1.2 μm, 1.1 μm, 1.0 μm, 0.9 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm and any value between them.

[0077] It should be noted that the surface roughness Ra value can be obtained by measuring the arithmetic mean deviation of the profile on a flat surface in the edge area of ​​the die casting using a contact surface profilometer, in accordance with the GB / T1031-2009 standard.

[0078] Surface roughness Ra is the arithmetic mean deviation used to assess the degree of surface micro-profile undulation. The surface roughness of die castings is directly affected by the surface condition of the mold cavity, the melt filling method, and the solidification process. Traditional die casting may result in wrinkles, cold shuts, or sticking marks on the casting surface due to turbulence, melt adhesion, or poor venting, leading to a relatively high surface roughness. Under conventional die casting process conditions, the surface roughness Ra of the edge region of aluminum alloy die castings is typically in the range of 2.0 μm to 5.0 μm. This is mainly due to the rapid cooling rate and decreased melt fluidity in the edge region, resulting in insufficient adhesion between the melt and the mold cavity surface. This invention requires the surface roughness Ra of the edge region to be no greater than 1.5 μm, reflecting the emphasis on near-net-shape forming capability and original surface quality of the die casting. Lower surface roughness means that the edges of the casting after demolding have a better finish, which not only improves the visual and tactile quality of the product, but also reduces micro-stress concentration points, which is beneficial to improving fatigue strength. At the same time, it provides a more uniform and flat base for subsequent surface treatments such as anodizing, which helps to form an oxide film with uniform thickness and dense structure, thereby obtaining a brighter and more uniform coloring effect.

[0079] Specifically, the 1.5 μm surface roughness threshold is determined based on the growth characteristics of anodic oxide films and the principle of optical interference. Typically, the thickness of anodized aluminum alloy films ranges from 5 μm to 25 μm. When the surface roughness Ra of the substrate exceeds 1.5 μm, the ratio of the height difference between the surface micro-peaks and valleys to the oxide film thickness is too high, leading to significant fluctuations in the thickness distribution of the oxide film at the microscale. This thickness fluctuation causes a shift in the wavelength of reflected light through thin-film interference, macroscopically manifesting as uneven gloss or slight color difference. Conversely, when the surface roughness Ra is controlled below 1.5 μm, the height difference between the surface micro-peaks and valleys is sufficiently small relative to the oxide film thickness, allowing the oxide film to uniformly cover the substrate surface and form a film layer with consistent optical properties.

[0080] Furthermore, surface roughness control is also crucial for the corrosion resistance and assembly performance of products. Higher surface roughness means more microscopic gaps and depressions, which are prone to trapping corrosive media in humid or salt spray environments, becoming preferential initiation points for pitting or crevice corrosion. Controlling the Ra value to within 1.5 μm can significantly reduce the number of such corrosion-sensitive sites, improving the overall corrosion resistance of the product. Simultaneously, for the edges of die-cast parts that need to be assembled with other components (such as the mating surface between the mobile phone frame and the screen), lower surface roughness ensures tighter contact and more uniform stress distribution, improving assembly accuracy and product reliability.

[0081] Furthermore, the metal alloy is an aluminum alloy, magnesium alloy, titanium alloy, stainless steel, copper alloy, nickel alloy, or zinc alloy. Even further, the metal alloy is a 6-series or 7-series aluminum alloy.

[0082] It is understood that this invention has broad applicability to various types of metal alloys, and its microstructure can appear in a variety of alloy systems, including aluminum alloys, magnesium alloys, titanium alloys, stainless steel, copper alloys, nickel alloys, and zinc alloys. This invention is particularly suitable for aluminum alloy die castings, especially 6-series (Al-Mg-Si series, such as 6061, 6082) and 7-series (Al-Zn-Mg-Cu series, such as 7075) aluminum alloys. These two types of aluminum alloys are heat-treatable aluminum alloys, possessing high strength, good machinability, and certain corrosion resistance, making them ideal materials for consumer electronics, automotive structural parts, and other fields. However, due to issues such as solidification range, hot cracking tendency, and reactivity with mold materials, obtaining high-density, high-performance die castings is difficult, and achieving a high-quality anodized surface is even more challenging. This invention, through the aforementioned series of controls on the edge microstructure, makes it possible to produce 6-series or 7-series high-strength aluminum alloy parts suitable for anodizing using die casting processes. This invention selects 6-series or 7-series aluminum alloys, breaking through their technical bottlenecks in the die-casting field, especially in applications with high appearance requirements, thereby effectively utilizing their excellent comprehensive performance potential. The technical solution of this invention provides a feasible path for the die-casting application of these two types of high-performance aluminum alloys, enabling die-cast parts to not only achieve mechanical properties close to forged or extruded materials, replacing forging or CNC machining, but also to meet stringent appearance consistency requirements, and to be applied at low cost to structural components with high appearance requirements such as mobile phone frames and tablet shells.

[0083] It is understood that 6-series and 7-series aluminum alloys are preferred applications of this invention with commercial value, but the principles of this invention can also be applied to other metal alloys (such as magnesium alloys, zinc alloys, etc.), and this invention does not have any particular limitations.

[0084] This invention provides an application of the above-mentioned metal alloy die casting parts in the manufacture of electronic equipment structural parts, transportation vehicle structural parts, robot structural parts, medical device structural parts, industrial equipment structural parts, or new energy equipment structural parts.

[0085] Preferably, metal alloy die castings can be used in the manufacture of consumer electronics housings, precision automotive parts, humanoid robot mechanical components, or medical components.

[0086] Consumer electronics casings (such as the frames of mobile phones and laptops) have extremely high requirements for material appearance consistency, surface quality, lightweight, structural strength, and the ability to form complex structures. The die-cast parts of this invention exhibit minimal color difference between the edges and the substrate, low surface roughness, high density, and excellent mechanical properties, perfectly meeting these requirements. Precision automotive components (such as structural brackets and decorative parts) also require good strength, durability, and appearance quality. Especially with the trend towards lightweighting, the application of aluminum alloy die-cast parts is becoming increasingly widespread, and the high performance and uniform appearance of the products of this invention give them a competitive advantage. Humanoid robot mechanical components require lightweight, high-strength, wear-resistant materials that can withstand complex stresses. The die-cast parts of this invention, by controlling grain size and impurities, achieve an excellent combination of mechanical properties. Medical components (such as device casings and non-implantable structural parts) require high purity, surface integrity, and biocompatibility of materials. The low impurity content and good surface quality of this invention make this possible. Therefore, the die-cast parts of this invention can be applied in high-end fields, possessing significant technological value and market potential.

[0087] It should be noted that the core of this invention's protection of the high-density edge die-castings lies in their unique microstructural characteristics, rather than being entirely limited to a specific manufacturing process. Microstructural characteristics (such as pore cluster density, grain size, dendrite ratio, etc.) are the essential factors determining the final performance and appearance of the die-castings, while the manufacturing process is merely a means to achieve these microstructural characteristics. Regardless of the manufacturing method used, any metal alloy die-casting possessing the specific microstructural characteristics described in this invention should be considered within the scope of protection of this invention. Manufacturing methods include, but are not limited to: employing different melt-filling strategies based on timing or path; using local pressurization methods based on different principles such as mechanical, hydraulic, or pneumatic pressure; controlling the solidification sequence through special mold cooling design combined with pressure intervention; and performing appropriate local solid-state thermomechanical treatment (such as warm forging, rolling) after conventional die casting to further eliminate edge defects, or combinations thereof. However, despite the existence of multiple possible implementation paths, this invention provides a preferred die-casting method. After extensive experimental verification, an optimal process window has been determined, enabling the stable and efficient achievement of the aforementioned stringent microstructural control indicators. To better realize and explain in detail how to efficiently and reliably produce the die-cast parts of this invention, an optimized and verified die-casting method embodiment is provided below, along with its technical details and principles. This embodiment not only demonstrates the specific operational steps for realizing the product of this invention, but also reveals the intrinsic relationship between process parameters and microstructure evolution, providing reproducible technical guidance for those skilled in the art.

[0088] This invention provides a die-casting method for preparing metal alloy die-casting parts with high-density edges, comprising: The molten metal is filled into the mold cavity; When the molten liquid in the mold cavity begins to solidify, at least the edge of the mold cavity is pressurized to discharge excess molten liquid from the overflow port on the mold cavity; the ratio between the volume of excess molten liquid and the volume of the mold cavity is not less than 0.1, and can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, higher, and any value between them.

[0089] Preferably, the ratio between the volume of excess melt and the volume of the mold cavity is in the range of 0.1 to 0.5, and can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and any value between them. More preferably, the ratio between the volume of excess melt and the volume of the mold cavity is in the range of 0.1 to 0.2.

[0090] This invention controls the volume ratio of "excess melt" (i.e., the molten metal that ultimately enters the overflow channel and venting channel). Based on the flow dynamics and solidification behavior of molten metal within the mold cavity, this invention determines a critical proportional relationship between excess melt and the mold cavity volume. This ratio helps improve the internal density and surface integrity of the die-cast part. Specifically, the role of excess melt is to directionally expel the cold sludge, oxide inclusions, and entrained gas formed at the filling front due to contact with the low-temperature mold wall during the final stage of filling, using continuously injected clean melt. In traditional die-casting processes, the overflow channel is often conservatively designed, with its volume typically only accounting for 3% to 5% of the cavity volume, mainly serving only to passively receive the cold front and venting the end. However, this invention significantly increases this ratio to no less than 0.1 (i.e., more than 10%), and controls it within the preferred range of 0.1 to 0.5. This parameter setting, which is significantly higher than industry norms, is not simply an increase in volume, but rather based on die-casting filling dynamics, thermodynamic balance, and edge microstructure control, thereby achieving the core objectives of this invention: high-density edges and color-difference-free anodizing.

[0091] Understandably, during die casting filling, regardless of how smoothly the flow rate is controlled, heat exchange inevitably occurs the instant the molten front contacts the mold, forming a solidified or semi-solidified layer with lower temperature, poorer fluidity, and rich in oxides. During die casting filling, the molten material flowing at the very front is of extremely poor quality. As this portion of the molten material flows through the pressure chamber, runner, and cavity, it entrains residual air from within the cavity. Furthermore, because it is constantly in contact with the low-temperature mold wall, it experiences the greatest heat loss, has the lowest temperature, and is rich in pre-solidified broken oxide scale and nascent coarse grains. If the overflow ratio is too low, it means that the volume of molten material used for flushing and replacement is insufficient to completely push this portion of the cold, sludge-laden molten material at the front into the overflow channel. If the residual cold, sludge-laden molten material remains inside the casting or near the surface, it will cause defects such as cold shuts, flow marks, and porosity, and significantly reduce the mechanical properties and density of the casting. In conventional processes with small overflow designs, this inferior melt often stagnates at the edges of the product or at the end of the filling process, inevitably leading to high porosity, numerous inclusions, and a loose microstructure in the edge areas. This invention requires an overflow rate of at least 10% of the cavity volume. This volume level ensures that not only the contaminated melt at the very front, but also the melt in the transition zone behind it, which contains some impurities, can be completely pushed out of the overflow port. This means that what ultimately remains and solidifies at the product edge is the fresh melt that was originally located in the later part of the flow channel, at a higher temperature, with higher purity, and without component segregation. This overfilling replacement mechanism avoids the generation of edge defects from the source of the material and is more conducive to obtaining a pure microstructure consistent with the matrix.

[0092] It should be noted that the large overflow displacement mechanism is more conducive to stabilizing the pore microstructure and anodized color difference index required by this invention. Specifically, the cold molten metal that is forcibly discharged is the main carrier of porosity (formed by gas entrapment and residual double oxide film). Through large-scale overflow flushing, the gas and oxide inclusions in the melt in the edge area are cleaned, thereby strictly suppressing the number of the most harmful porosity to a low level, stabilizing the ratio of shrinkage porosity to porosity to pores at 1:(0.1~0.5), and ensuring that the proportion of porosity in the edge area does not exceed 30%. At the same time, the continuously flowing high-temperature pure melt significantly delays the rapid solidification at the edge, allowing the melt to remain in a shrinkable state for a longer period of time, providing sufficient time for subsequent pressure shrinkage. This allows the pores generated by solidification shrinkage to be fully compressed and isolated, preventing them from connecting and merging to form complex defects, thereby controlling the pore cluster density, the number of pores within the cluster, and the equivalent size. Ultimately, this edge microstructure, dominated by isolated, rough-walled, shrinkage-type pores with strictly controlled pore types, exhibits electrochemical activity and current distribution highly consistent with the substrate during anodizing. The oxide film can grow uniformly on the inner wall of the pores or effectively seal them, eliminating local coloring anomalies and optical interference differences caused by pore enrichment and inner wall insulation, thus ensuring the appearance consistency of color difference between the edges and the substrate.

[0093] Understandably, one of the core problems of existing technologies is the color difference in anodizing between the edge and the substrate, and one source of this color difference is the difference in grain size caused by the different cooling rates of the two. Due to their large surface area and strong chilling effect in the mold, the edge area typically cools too quickly, easily forming a chilled layer or fine grain band. When the overflow ratio is increased to above 0.1, a large amount of continuously flowing high-temperature excess molten liquid releases heat to the edge mold wall as it flows through the edge region into the overflow port. This dynamic heating effect significantly increases the local temperature of the edge mold, reduces the drastic temperature difference between the edge molten liquid and the mold, and thus mitigates the tendency for the edge to chill. This allows the edge region to achieve a solidification cooling rate closer to that of the substrate region, promoting the consistency of grain size between the edge and the substrate, and thermodynamically avoiding microstructural differences between the anodized and anodic surfaces.

[0094] Building upon this, the present invention further provides a preferred overflow ratio range of 0.1 to 0.5. This range is designed to ensure an optimal balance between process effectiveness, mold design rationality, and production costs. When the overflow ratio is too low, as mentioned earlier, the amount of molten metal available for venting gas and cold slag is insufficient, making it difficult to consistently ensure adequate purification of the cavity under all process conditions. This increases the risk of porosity or inclusions in the casting, leading to a decrease in yield. Conversely, when the overflow ratio is too high, although a larger overflow may technically contribute to the purification effect, it leads to a significant decrease in metal utilization and an increase in raw material costs. Furthermore, an excessively large overflow requires the design of a larger overflow channel (cavity), which not only places higher demands on the spatial layout and structural strength of the mold design, increasing the difficulty and cost of mold manufacturing, but may also increase the processing burden of subsequently removing overflow waste, reducing production efficiency. Therefore, the range of 0.1 to 0.5 defines a reasonable operating range that is technically effective in ensuring quality and economically feasible in production.

[0095] Based on this, the present invention further specifies a preferred ratio range of 0.1 to 0.2. Controlling the overflow ratio within the range of 0.1 to 0.2 allows for a more stable production of high-quality castings with low porosity and uniform microstructure. An overflow rate of 0.1 to 0.2 is sufficient to discharge the small amount of molten cold front generated in the final stage, while avoiding energy consumption and material waste caused by excessive overflow. This preferred range reflects the optimized choice between high quality and high efficiency in the process of the present invention, contributing to the realization of stable, large-scale production.

[0096] It is important to note that maintaining a ratio of excess molten liquid volume to mold cavity volume of no less than 0.1 is a mandatory requirement for achieving the desired technical effect in the preferred die-casting method of this invention, constituting the fundamental safety boundary of the process scheme. The formula provided below regarding the specific functional relationship between the excess molten liquid volume and mold cavity volume is merely a preferred dynamic control strategy. In other words, those skilled in the art, when implementing the preferred die-casting method of this invention, must first ensure that the excess molten liquid volume ratio meets the mandatory requirement of no less than 0.1. Based on this, to obtain better process matching and casting quality consistency, a more precise excess molten liquid volume ratio can be determined using this formula according to specific process conditions (such as temperature difference and flow rate). If the ratio calculated by the formula is lower than 0.1, the lower limit of 0.1 should be followed to ensure that it remains within the safe process window. This control logic, using absolute values ​​as a baseline and empirical formulas as optimization guidance, effectively improves the universality and reliability of the method of this invention.

[0097] Furthermore, the step of filling the mold cavity with molten liquid includes first filling the molten liquid at a first flow rate, and then second filling the molten liquid at a second flow rate higher than the first flow rate; The volume of excess melt and the volume of the mold cavity satisfy the following relationship:

[0098] In the formula, The volume of excess melt; This refers to the volume of the mold cavity; The first proportionality constant has a value range of 0.1 to 0.2, and can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, and any value between them; The temperature difference between the melt and the mold ranges from 300℃ to 350℃, and can be 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, and any value between them. The temperature is the mold temperature, and its value ranges from 300℃ to 420℃. It can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, or any value between them. The first flow velocity is defined as follows, and its value is no greater than 2 m / s. It can be 2 m / s, 1.9 m / s, 1.8 m / s, 1.7 m / s, 1.6 m / s, 1.5 m / s, 1.4 m / s, 1.3 m / s, 1.2 m / s, 1.1 m / s, 1.0 m / s, 0.9 m / s, 0.8 m / s, 0.7 m / s, 0.6 m / s, 0.5 m / s, 0.4 m / s, 0.3 m / s, 0.2 m / s, 0.1 m / s, or any value between them.

[0099] This invention derives the above-mentioned empirical model based on the thermodynamic and fluid dynamic mechanisms of the filling process. This model quantitatively describes the intrinsic relationship between the minimum theoretical excess melt volume required to obtain a high-quality casting and the temperature difference between the melt and the mold, the absolute temperature level of the mold, and the first filling flow rate.

[0100] The core of the relationship proposed in this invention lies in determining the theoretical minimum excess melt volume ratio related to process conditions. The value calculated on the right side of the formula represents the critical lower limit of the ratio of excess melt volume to cavity volume that needs to be achieved under specific temperature differences, mold temperatures, and first flow rates to ensure that the cold molten melt and entrained gas at the filling front can be effectively discharged from the cavity, thereby obtaining a casting with a dense interior and intact surface.

[0101] Understandably, the use of a greater than or equal to relationship in the formula is to clearly define that, in the actual implementation of the method of this invention, the volume ratio of excess melt actually used must be at least equal to or greater than the value calculated by this formula. As long as this condition is met, the most basic process requirement for cavity purification through overflow is achieved. This ensures that, under different temperature differences, mold temperatures, and first flow rate process combinations, the volume of excess melt dynamically meets the verified minimum standard. This invention does not impose an upper limit on the actual volume ratio of excess melt. Technically speaking, as long as the overflow system capacity of the mold allows, increasing the overflow flow rate generally will not damage but will only more thoroughly remove impurities. Therefore, the overflow ratio in actual production can be selected and optimized based on a trade-off between technical effectiveness and economic costs (metal loss, energy consumption).

[0102] Understandably, the constant in the relation This was determined through extensive repeatable die-casting experiments under baseline and adjacent process conditions, and by statistical analysis of the actual excess melt volume ratio corresponding to the obtained high-quality castings. Under the premise of satisfying other core process conditions of this invention, By controlling the quality within this range, the goals of low porosity, no surface defects, and uniform microstructure can be achieved more stably.

[0103] Understandably, the temperature term in the relational expression adopts... The form of represents the physical significance of relative thermal shock intensity. Among them, molecules... Represents the driving force for heat exchange between the molten metal and the mold; the denominator The mold temperature level was introduced as a benchmark.

[0104] Understandably, the overflow rate is related to the temperature difference between the melt and the mold. The relationship is directly proportional because the greater the temperature difference, the higher the heat flux density at the moment of contact between the molten metal and the mold, the faster the cooling rate at the solidification front, and the thicker the layer of cold, viscous molten metal that forms per unit time, which is typically lower in temperature and higher in viscosity, and may be rich in oxides. To effectively remove this increased cold molten metal from the casting body, the overflow rate for flushing and displacement needs to be increased accordingly. The volume of excess molten metal is related to the mold temperature. The inverse relationship exists because mold temperature not only affects the temperature difference but also independently influences the flow behavior of the molten liquid. When the mold temperature... At lower temperatures, even with temperature differences Similarly, the cooling effect of the mold on the molten metal is more pronounced. Low-temperature molds cause a rapid increase in the viscosity of the molten metal front, increasing flow resistance and thus requiring more power to push the cold contaminant out. Furthermore, lower... This means the mold's thermal capacity is at a low level, resulting in higher heat absorption efficiency and exacerbating the temperature drop at the molten front. Therefore, it implies that the mold temperature... Under lower operating conditions, the present invention requires a larger volume of excess melt to replenish the heat loss at the front edge with sufficient superheated melt, avoid incomplete filling, and provide stronger hydrodynamics to ensure the discharge of impurities.

[0105] Understandably, the reason for using the ratio of temperature difference to mold temperature is... Rather than a single parameter, this ratio constructs a dimensionless thermal index, taking into account temperature difference. and mold temperature A single temperature difference cannot fully reflect the intensity of cooling, and the same temperature difference has different effects on the viscosity of the melt at different mold temperatures. By using a ratio, the formula can adaptively evaluate the actual cooling intensity under different mold temperature settings, thereby achieving precise matching of the excess melt volume.

[0106] Understandably, the exponent of the temperature term in the formula is 0.5 (square root), reflecting the nonlinear effect of the temperature difference on the rate of formation of the cold sludge layer at the solidification front. This aligns with the fundamental laws of heat conduction and solidification kinetics. According to Fourier's law of heat conduction and the theory of solidified layer growth, the thickness of the solidified shell or the cooling depth is generally proportional to the square root of the temperature difference. Since one of the main functions of the excess melt volume is to displace the cold sludge layer formed during cooling, the required overflow volume is closely related to the thickness of this cold sludge layer. Given that the amount of cold sludge layer formed is related to the square root of the temperature difference, the proportion of excess melt volume used for rinsing should naturally also be positively correlated with the square root of the temperature difference. This exponent setting makes the formula more consistent with physical reality, avoiding overestimation or underestimation that might result from a linear relationship.

[0107] Understandably, the exponent of the second term in the equation is -1, reflecting another mechanism by which the first flow rate affects the filling process and overflow requirements. When the first flow rate decreases (i.e., filling slows down), the melt flow is smoother, and air entrapment within the cavity is significantly reduced, which is advantageous. However, slower filling also means a longer residence time of the melt within the cavity, increasing overall heat loss, and potentially causing a more pronounced drop in the temperature of the melt front. To maintain sufficient hydrodynamics during the longer filling time, pushing the potentially increased viscous resistance due to temperature drop and the continuously generated small amount of cold melt at the front towards and out of the overflow port, a sufficient melt flow rate is needed to provide continuous flushing. Therefore, the volume ratio of excess melt needs to be compensated for by a negative correlation with the first flow rate; that is, the slower the filling, the larger the required minimum volume ratio of excess melt.

[0108] Understandably, the "2" in the second term of the relation is a normalization reference value, corresponding to... The characteristic process parameter value. The unit of "2" is m / s, which is taken from the upper limit of the first flow rate of the present invention (≤2m / s), and is used as the normalization benchmark for this parameter, so that the term in the formula related to the first flow rate becomes a dimensionless factor.

[0109] Using this formula, those skilled in the art can calculate the required minimum excess melt volume ratio based on specific process conditions. For example, when die-casting an aluminum alloy structural part, the process parameters are set as follows: mold temperature The melt temperature is 700℃, and the temperature difference between the melt and the mold is... First flow velocity Substitute the values ​​into the formula to calculate ( This yields a minimum a / b ratio of 0.15, meaning the minimum theoretical excess melt volume ratio is approximately 0.15. The excess melt volume is approximately 115% of the cavity volume, which helps to obtain higher quality die-cast parts. If the mold temperature is increased to... The temperature difference between the melt and the mold With other parameters remaining constant, the calculated minimum a / b ratio is approximately 0.13. This represents the ratio of temperature difference to mold temperature. As a relative indicator of thermal shock intensity, it can more accurately characterize overflow demand than a single temperature parameter. In actual production, the final overflow rate can be determined based on different calculation results and economic considerations.

[0110] In summary, this relationship links core thermodynamic parameters with fluid dynamic parameters, jointly determining the minimum process parameters required to achieve effective cavity purification. It replaces the traditional, crude experience-based approach of fixing the overflow ratio, achieving adaptive and scientific matching of excess melt volume with specific process conditions. This dynamic control model reflects the systematic and precise nature of the invention's process, and is more conducive to the stable production of high-quality die-cast parts under a wide range of process parameter combinations.

[0111] In this invention, the velocity of the first flow rate in the first filling is no greater than 2 m / s, and can be 2 m / s, 1.9 m / s, 1.8 m / s, 1.7 m / s, 1.6 m / s, 1.5 m / s, 1.4 m / s, 1.3 m / s, 1.2 m / s, 1.1 m / s, 1.0 m / s, 0.9 m / s, 0.8 m / s, 0.7 m / s, 0.6 m / s, 0.5 m / s, 0.4 m / s, 0.3 m / s, 0.2 m / s, 0.1 m / s, and any value between them.

[0112] Preferably, the velocity of the first flow velocity is not greater than 1.0 m / s. More preferably, the velocity of the first flow velocity is not greater than 0.5 m / s. Even more preferably, the velocity of the first flow velocity is not greater than 0.3 m / s.

[0113] In this invention, the "first flow velocity" specifically refers to the flow velocity of the molten metal at the inlet cross-section at the instant it enters the mold cavity through the inlet during the first filling stage. This invention controls the first flow velocity during the first filling stage, effectively achieving laminar flow filling and eliminating turbulence and air entrapment. Traditional die-casting processes, in pursuit of filling efficiency, often employ high-speed jets (typically much higher than 2 m / s), causing the molten metal to generate strong inertial and shear forces upon entering the mold cavity, rapidly transforming the flow state into disordered turbulence. This turbulence not only tears apart the molten metal front, breaking up air within the mold cavity and entraining it into the melt to form bubbles that are difficult to expel, but also violently erodes the surface of the thin solidified layer that has already formed in contact with the low-temperature mold wall, causing this solidified layer to shift and accumulate, resulting in macroscopic black streaks and watermarks on the product surface. This invention sets the upper limit of the first flow velocity to no more than 2 m / s precisely to suppress the generation of this destructive flow from the inlet. When the molten metal enters the mold cavity smoothly at a speed not exceeding 2 m / s, its Reynolds number decreases significantly, allowing the flow pattern to transition from turbulent to laminar or steady flow. This velocity threshold makes subsequent smooth filling possible. Building upon this, the proposed optimal range reflects a deeper understanding of the low-speed concept. The lower the velocity, the weaker the inertial force of the molten metal, the gentler the flow, and the less disturbance it causes to the gas inside the mold cavity and the mold surface. For example, in fields with extremely high surface finish requirements, such as consumer electronics casings, using an extremely low filling speed of ≤0.3 m / s can almost completely eliminate surface defects caused by flow impact.

[0114] In this invention, the "second flow rate" specifically refers to the flow velocity of the molten metal across the cross-section of the inlet at the instant it enters the mold cavity through the inlet during the second filling stage. Its definition is consistent with the first flow rate to ensure the comparability of process parameters and the linearity of control.

[0115] Preferably, the second flow rate is greater than the first flow rate, and the pressure acting on the melt in the second filling is increased by 10% to 30% compared with the first filling. This pressure can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or any value between them.

[0116] Understandably, in a die-casting system, the pressure acting on the molten metal is the driving force that propels its flow and determines its flow rate (second flow rate). Controlling the pressure acting on the molten metal during the second filling is, in essence, also an indirect regulation of the molten metal flow rate during the second filling stage. Specifically, the second flow rate is the overall flow rate of the molten metal as it completes filling the remaining portion of the cavity under increased pressure. Specifically, because this invention employs a smooth inlet channel with a cross-sectional area variation within ±10% (gateless design), it eliminates the traditional narrow gate structure, preventing drastic pressure loss or velocity amplification within the channel. This means that the pressure applied by the injection mechanism can be directly transmitted to the mold cavity in a highly linear and predictable manner. Therefore, controlling the second filling pressure is equivalent to directly controlling the driving force on the molten metal within the cavity, avoiding the nonlinear pressure transmission problem caused by the gate effect in traditional processes.

[0117] This invention controls the second flow rate to be greater than the first flow rate, and the pressure acting on the molten liquid during the second filling is increased by 10% to 30% compared to the first filling. The purpose is to ensure the integrity of the filling while effectively promoting the dynamic overflow process, thereby achieving the directional discharge of gas inside the cavity and the cold molten liquid at the leading edge. The first filling stage establishes a laminar flow field at a low speed (first flow rate) to avoid air entrapment and surface erosion; while the second filling stage, without disrupting the established laminar flow field, provides sufficient kinetic energy to drive the molten liquid to complete the remaining filling, and exerts a stable pushing effect on the gas, cold molten liquid, and floating oxide inclusions accumulated at the leading edge of the molten liquid and near the overflow port, discharging them out of the cavity through the overflow port.

[0118] Furthermore, the die-casting method also includes auxiliary heating of the edge of the mold cavity after the excess melt has been completely drained. The heating temperature is 400℃~480℃, which can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃ and any value between them; the heating time is 5s~30s, which can be 5s, 10s, 15s, 20s, 25s, 30s and any value between them.

[0119] Understandably, the auxiliary heating refers to a localized temperature compensation operation performed on the mold portion corresponding to the edge area of ​​the mold cavity after the excess melt has been completely discharged through the overflow port and before the die casting has completely solidified. This auxiliary heating can be achieved through heating rods, induction heating coils, or localized heat radiation devices installed on the mold. Its purpose is to dynamically control the cooling rate of the edge portion during the critical solidification time of the edge region, thereby optimizing the formation process of the edge microstructure.

[0120] Understandably, the heating temperature range of 400℃~480℃ is based on a comprehensive consideration of the solidification characteristics of aluminum alloys, the heat resistance of mold materials, and the appearance requirements of anodizing. Specifically, the lower limit of 400℃ is the critical value at which the auxiliary heating can produce an actual heat conduction effect. When the heating temperature at the edge of the mold is below 400℃, since the mold steel itself is already in the working temperature range of 300℃~420℃ during the die casting process, the excessively low auxiliary heating temperature cannot form an effective temperature gradient, and the heat transfer rate to the edge of the casting is insufficient, making it difficult to have a substantial impact on the edge solidification behavior and failing to achieve the technical objective of slowing down the edge cooling rate. The upper limit of 480℃ is the critical value to prevent the risk of remelting or sticking to the mold at the edge of the casting. When the heating temperature exceeds 480℃, approaching or exceeding the solidus temperature of some aluminum alloys (approximately 475℃~550℃), it may cause local remelting of the solidified edge shell, destroying the formed dense structure. Simultaneously, high temperatures exacerbate thermal fatigue in the mold steel, reducing mold life and increasing the adhesion tendency between the casting and the mold surface, affecting demolding quality and dimensional accuracy. Therefore, the temperature range of 400℃~480℃ represents an optimized balance between ensuring effective thermal compensation and avoiding structural damage.

[0121] Furthermore, the heating time range of 5s to 30s is based on the synergistic optimization of the solidification kinetics at the edge of the die-casting part and the production cycle. Specifically, the lower limit of 5s is the shortest time to ensure effective heat transfer during the heating process. Heat needs a certain thermal diffusion time to transfer from the mold heating element to the edge of the casting. If the heating time is too short, the heat will not be fully transferred to the solidification front at the edge of the casting before the heating process ends, thus failing to regulate the solidification behavior. The upper limit of 30s is a reasonable limitation considering the efficiency of the die-casting production cycle. One of the core advantages of die-casting is its high production efficiency; a single die-casting cycle typically ranges from 30s to 120s. If the auxiliary heating time exceeds 30s, it will significantly extend the production cycle, reduce production efficiency, and increase the energy cost per unit product. Simultaneously, excessively long heating times may lead to overheating in the edge region, causing grain coarsening or localized component segregation, which in turn damages the uniformity of the edge microstructure. Therefore, the time range of 5s to 30s represents a reasonable operating window between ensuring sufficient heat transfer and maintaining production efficiency.

[0122] Understandably, the auxiliary heating step is synergistically related to the overflow control process described above. Specifically, this auxiliary heating can regulate grain growth. In the aforementioned process, the purification and initial densification of the melt in the edge region are achieved by using an excess melt ratio of not less than 0.1. However, the edge region, due to its direct contact with the mold wall and large heat dissipation area, naturally has a higher cooling rate than the matrix region. Without auxiliary heating, the edge may rapidly descend below the solidification line due to quenching, causing the dendrite skeleton to quickly overlap and close the feeding channels, making it difficult for subsequent pressurization to be effectively transmitted to the microscopic shrinkage porosity region, easily forming dense pore clusters and large-sized shrinkage porosity. The introduction of the auxiliary heating step further regulates the edge solidification behavior from a thermodynamic perspective, based on overflow impurity removal and pressure feeding. Specifically, after the excess melt is discharged, the edge region is still in a semi-solid or just completed solidification state. At this time, local auxiliary heating can slow down the subsequent cooling rate of the edge region, allowing the edge to achieve a solidification time closer to that of the matrix region. This homogenization of the cooling rate and extension of the solidification time ensures that the semi-solid melt maintains sufficient fluidity and compressibility for a longer period. The delayed solidification process provides additional time for the entrained gases to rise and escape. Combined with the source purification through large overflow, the final residual porosity is significantly reduced, stably achieving a shrinkage porosity to porosity ratio of 1:(0.1~0.5) and a porosity percentage of ≤30%. This controlled pore morphology and distribution, along with the uniform grain structure, further contributes to the absence of significant color difference after anodizing.

[0123] Furthermore, the specific effects of the auxiliary heating step on the microstructure of the edge region are reflected in the following three aspects: First, auxiliary heating reduces the cooling rate of the edge region, reduces the nucleation undercooling, and makes the growth rate of edge grains more consistent with that of the matrix, which helps to control the deviation of the average grain size between the edge and the matrix; Second, the slower cooling rate is conducive to the formation of equiaxed crystals rather than the directional growth of dendritic crystals, which helps to control the proportion of dendritic crystals in the edge region; Third, auxiliary heating allows the edge region to be held at a higher temperature for a longer time, which is more conducive to the relaxation of solidification shrinkage stress.

[0124] Understandably, if the auxiliary heating temperature is below 400℃ or the heating time is less than 5 seconds, the thermal compensation effect is insufficient, the cooling rate in the edge region remains significantly higher than that of the substrate, the feeding channels close prematurely, and the pores cannot be effectively compressed and instead become densely aggregated. The density, size, and porosity of the pore clusters can easily increase significantly, making it difficult to achieve consistent control of the grain size between the edge and the substrate, and color differences may still occur after anodizing. If the auxiliary heating temperature exceeds 480℃ or the heating time exceeds 30 seconds, it may cause overheating in the edge region, leading to grain coarsening, local remelting, or mold damage, which in turn impairs the edge density and appearance quality, while reducing production efficiency. Therefore, a temperature range of 400℃ to 480℃ and a time range of 5 seconds to 30 seconds can maximize the improvement effect of auxiliary heating on the uniformity of the edge microstructure and the precise control of pore morphology without compromising other performance indicators.

[0125] It should also be noted that the timing of the auxiliary heating step—after the excess melt has been completely drained—is of significant process importance. Heating before the excess melt has drained may reduce the viscosity of the melt in the edge areas, affecting the overflow and impurity removal effect, and could even cause drained impurities to flow back into the mold cavity. Heating after the die casting has completely solidified means that the microstructure has already formed, and heating can only relieve stress, not regulate the solidification behavior. Therefore, performing auxiliary heating within the time window after the excess melt has drained and before complete solidification maximizes its intervention in the solidification process without compromising the overflow and impurity removal objective.

[0126] It should also be noted that the timing for determining when excess molten metal has been completely drained can be monitored based on the amount of molten metal injected. Since the volume of the mold cavity is a fixed, known value, and the target excess molten metal ratio is preset (e.g., 0.1~0.5), this can be determined by monitoring the total amount of molten metal injected into the mold cavity. Specifically, when the total volume of injected molten metal reaches (1+x) times the volume of the mold cavity (where x is the target excess ratio), it can be determined that the excess molten metal has been completely drained.

[0127] In summary, the auxiliary heating step, as an optional optimized process in the die-casting method of this invention, works in conjunction with core processes such as overflow control and differentiated pressure application to further improve the control of the microstructure in the edge region from a thermodynamic perspective. Through precise control of the heating temperature (400℃~480℃) and heating time (5s~30s), high-quality die-cast parts with uniform edge and matrix microstructure and no color difference during anodizing can be stably obtained under large-scale production conditions.

[0128] Furthermore, pressurizing the mold cavity includes pressing the mold cavity multiple times, with the pressure of each subsequent pressurization increasing by 20% to 40% compared to the pressure of the previous pressurization, which can be 20%, 25%, 30%, 35%, 40%, or any value between them; and the pressure of the last pressurization is 40% to 200% greater than the pressure of the first pressurization, which can be 40%, 60%, 80%, 100%, 120%, 140%, 160%, 180%, 200%, or any value between them.

[0129] In the early stages of solidification, the melt has good fluidity, and relatively low pressure is sufficient for feeding. However, as solidification progresses, a dendritic framework gradually forms, significantly increasing the melt's flow resistance. If a constant pressure is maintained, the effective feeding pressure will decrease due to the increased resistance, leading to insufficient feeding in the later solidification stages and the formation of shrinkage porosity. This invention employs multiple pressurizations to match the applied pressure gradient with the increase in flow resistance during the melt's solidification process, ensuring that the melt receives sufficient driving force for densification throughout the entire solidification range.

[0130] Specifically, the pressure increase of each subsequent pressurization is controlled within the range of 20% to 40%, an optimized range determined based on the rheological properties of semi-solid metals. If the increase is less than 20%, the pressure increment is insufficient to overcome the increased flow resistance due to the increased solid fraction. Subsequent pressurization cannot be effectively transmitted to the solidification front, resulting in a weak feeding effect and difficulty in eliminating the micro-shrinkage porosity formed later, leading to insufficient porosity in the edge region. More importantly, insufficient pressure increase will cause the feeding channels between semi-solid dendrites to close prematurely. Isolated micropores are prone to interconnecting and merging during subsequent solidification, resulting in an excessive number of pore clusters per square millimeter and an excessive number of pores within each cluster. A stepped pressurization of 20% to 40% can continuously apply uniform extrusion force to the forming dendritic network, forcibly compressing and separating pores that might otherwise connect and merge, thereby controlling the pore cluster density and the number of pores within the cluster. If the pressure increase exceeds 40%, the excessive pressure jump may impact the already formed primary solidified shell, leading to excessive grain fragmentation or microcracks, and even causing flash at the mold parting surface, affecting the dimensional accuracy and surface roughness of the casting. A stepped pressure increase of 20% to 40% can smoothly compensate for pressure loss due to solidification shrinkage, avoiding uneven microstructure caused by excessive pressure fluctuations, and helping to control the standard deviation of grain size in edge regions.

[0131] Furthermore, controlling the pressure of the final pressurization to be 40% to 200% higher than the first pressurization is logically related to the single pressurization ratio and the number of pressurization cycles. The lower limit of the total pressurization amplitude of 40% corresponds to the upper limit of the single pressurization ratio of 40%, aiming to confirm that at least two effective pressurizations have been performed. Specifically, the first pressurization is the initial pressurization. If two pressurizations are performed, and the second pressurization is set at the maximum single increase of 40%, the final pressure will be 40% higher than the first. Therefore, setting the lower limit of the total pressurization to 40% parameterally locks in at least two stages including the first initial pressurization and the second pressurization, ensuring the actual execution of the multiple pressurization process and avoiding insufficient feeding due to insufficient pressurization cycles. The higher total pressure at the end of solidification can penetrate deep into the dendrite interstices, strongly compressing the residual liquid phase, effectively limiting the expansion of shrinkage porosity and controlling its equivalent size. Meanwhile, the continuously increasing high pressure environment significantly improves the solubility of residual gases in the melt and inhibits gas expansion and escape, forcing the final retained pore morphology to be mainly irregular shrinkage-type due to mechanical compression, while reducing the proportion of more harmful near-spherical porosity. If the total pressurization increase is less than 40%, it may mean that only a single pressurization was performed or the second pressurization increase was too small, failing to form an effective pressure gradient to drive impurity discharge and densification.

[0132] The 200% upper limit on the total pressurization rate limits the maximum number of pressurization cycles to balance process effectiveness and production feasibility. Based on a single pressurization rate of 20% to 40%, if each pressurization cycle accumulates at the minimum increment of 20%, approximately six pressurization cycles are required to reach a total increase of 200% (i.e., the final pressure is three times the initial pressure). Therefore, the 200% upper limit implicitly controls the number of pressurization cycles within a reasonable range of 2 to 6. If the total pressurization rate exceeds 200%, it means too many pressurization cycles or excessively large single increments, which will lead to overly complex process control, difficulty in implementing mold structures, and excessively long pressurization sequences that will severely slow down production cycles. The 40% to 200% range represents a balance between ensuring high density, process economy, and equipment feasibility, contributing to stable, large-scale production.

[0133] It should also be noted that the specific number of pressurization cycles can be adjusted within the above-mentioned logical range according to the wall thickness of the casting, the type of alloy, and the mold cooling conditions. As long as the requirements of the single pressurization ratio and the total pressurization ratio are met, the technical objective of this invention can be achieved. For example, for thinner edge areas, two pressurization cycles can be used, with a single pressurization increase of 40% and a total increase of 80%; for thicker or more complex areas, three or more pressurization cycles can be used, with a single pressurization increase of 20% to 30% and a total increase of 100% to 150%. This flexible process window design enhances the applicability and stability of the method of this invention on different product structures, and can stably obtain metal alloy die castings with high-density edges and a color-difference-free anodized appearance under different process conditions.

[0134] Understandably, this multi-stage pressurization method, in conjunction with the overflow control and temperature control processes described above, jointly constructs a highly dense microstructure in the edge region. Multiple pressurizations not only reduce porosity but also help refine the grains. The periodic increase in pressure can disturb the temperature and solute fields at the solidification front, inhibiting excessive dendrite growth and promoting the formation of equiaxed crystals, thereby controlling the dendritic ratio and average grain size in the edge region. This controlled pore morphology eliminates local electric field distortions and optical interference anomalous sources during the anodizing process. The edge region exhibits electrochemical activity and film formation rate highly consistent with the substrate during oxidation, and the oxide film thickness difference is compressed to the nanometer scale, effectively reducing the color difference between the edge and the substrate after anodizing.

[0135] Optionally, the holding time after each pressurization is 5s to 20s, which can be 5s, 8s, 10s, 12s, 15s, 18s, 20s and any value between them.

[0136] Understandably, the solidification process of molten metal within the mold cavity is not instantaneous, but rather a dynamic process in which the solid fraction gradually increases over time. Setting the holding time after each pressurization to 5-20 seconds is based on a balance between pressure transmission efficiency and production cycle time. If the holding time is less than 5 seconds, the pressure has not been fully transmitted to the solidification front, and the molten metal does not have enough time to densify and fill under pressure, resulting in a weak feeding effect. If the holding time exceeds 20 seconds, although it is beneficial for densification, it will significantly prolong the die-casting production cycle, reduce production efficiency, and increase energy costs. The 5-20 second time window ensures that each pressure level can effectively act on the semi-solid melt, completing sufficient stress relaxation and plastic deformation within the semi-solid paste region. This allows isolated pores outside the cluster to be evenly dispersed, effectively controlling their average spacing and further preventing stress superposition and electrochemical coupling effects between defects.

[0137] This invention provides a die-casting apparatus for implementing a die-casting method, including a mold and a pressurizing mechanism; a mold cavity is formed inside the mold, and an overflow port is provided on the mold cavity; the pressurizing mechanism is disposed on the mold and is used to pressurize the molten liquid in the mold cavity so that excess molten liquid is discharged from the overflow port; wherein, the overflow port is disposed circumferentially on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity.

[0138] The die-casting apparatus of this invention overcomes the structural limitations of traditional die-casting equipment. By introducing a controllable multi-stage pressurization mechanism in conjunction with a large-proportion overflow system, it solves the technical problems of insufficient density and uneven microstructure in the edge region. In traditional die-casting equipment, there is usually no dedicated pressurization mechanism, and the pressure on the mold cavity cannot be dynamically adjusted to adapt to changes in flow resistance during molten solidification. Because the edge region dissipates heat quickly and solidifies early, dynamically increased pressure is required to effectively suppress shrinkage porosity and gas formation. This invention, by setting up a pressurization mechanism with multi-stage pressurization capabilities, allows the edge region to receive multiple incremental pressure compensations during solidification, ensuring the density and uniformity of the microstructure in this region.

[0139] Furthermore, the pressurizing mechanism is configured to apply multiple pressures to the mold cavity, with each subsequent pressurization pressure adjustable to increase by 20% to 40% compared to the previous pressurization, and the final pressurization pressure adjustable to increase by 40% to 200% compared to the first pressurization. Understandably, this multi-stage pressure regulation capability is designed to match the rheological changes during the solidification process of the melt. As solidification progresses, the formation of dendritic skeletons leads to increased flow resistance. The device ensures that the feeding driving force at each stage can overcome the current flow resistance and compact the micropores by progressively increasing the pressure. If the device can only provide a constant pressure or the pressure increase is too small, it cannot effectively eliminate the shrinkage porosity generated during later solidification; if the pressure increase is too large or the number of pressurizations is too high, it may place an excessive load on the mold structure. The pressurizing mechanism of this invention achieves a stable output of this specific pressure gradient through the control of a hydraulic or mechanical drive source, which helps to obtain highly dense edges.

[0140] Furthermore, the overflow port is circumferentially disposed on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity, which can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% and any value between them.

[0141] To better achieve the aforementioned overflow function, the overflow port design of this invention differs significantly in area from that of traditional die-casting processes. In the prior art, the main function of the overflow port is often understood as passively containing cold, contaminated metal and a small amount of gas; its total opening area is typically small, often accounting for less than 10% of the surface area of ​​the mold cavity sidewall. In contrast, this invention preferably requires the overflow port area to account for 15% to 25% of the surface area of ​​the mold cavity sidewall. This larger area percentage is more conducive to adapting to the core process of this invention.

[0142] Understandably, the overflow behavior in this invention is not a simple passive containment, but an active, quantitative flushing process. As mentioned above, this method controls the lower limit of the total overflow, and its lower limit value (not less than 0.1) and its preferred implementation range (0.1~0.5, more preferably 0.1~0.2) are generally higher than the overflow of conventional processes. To accommodate this larger planned overflow, a preferred matching scheme is to provide it with an overflow channel with stronger flow capacity to ensure that at the end of the filling period, this portion of the melt rich in impurities and gases can be quickly, smoothly, and unimpededly discharged from the cavity, avoiding throttling or back pressure at the overflow port.

[0143] In this invention, the "area of ​​the overflow port" refers to the sum of the effective cross-sectional areas of the channels through which the molten liquid flows from inside the mold cavity to the external overflow system; the "surface area of ​​the sidewall of the mold cavity" refers to the actual total area of ​​the vertical or inclined surfaces around the mold cavity that form the product shape, excluding the bottom and top surfaces of the mold cavity (i.e., the plane where the parting surface is located). This invention controls the area of ​​the overflow port to account for 15% to 25% of the sidewall surface area of ​​the mold cavity, aiming to ensure that the flow capacity of the overflow system matches the cavity volume and heat dissipation surface area, thus meeting the requirements for rapid venting and slag removal under large overflow flow while ensuring the overall strength of the mold structure.

[0144] Specifically, this invention provides two typical implementations of the overflow port structure: The first embodiment is an independent overflow port structure, which can be a bi-splitting mold where the upper and lower mold mating surfaces are perpendicularly abutting. In this structure, the mold cavity is jointly enclosed by the upper and lower molds, and the outer walls of the upper and lower molds are usually set as vertical surfaces. When the mold is closed, the outer walls of the upper and lower molds abut each other perpendicularly to form a closed cavity sidewall. The overflow port is manifested as multiple independent through holes opened on the mold sidewall, preferably located in the upper region of the upper mold sidewall, so as to utilize the gas rising characteristics for venting. In this embodiment, the "area of ​​the overflow port" is the sum of the opening cross-sectional areas of each independent through hole at the inner wall of the cavity; the "surface area of ​​the mold cavity sidewall" corresponds to the total surface area of ​​the sidewalls of the cavity formed by the upper and lower molds after they are closed. Therefore, the area ratio in this embodiment refers to the ratio of the total cross-sectional area of ​​the independent overflow port through holes to the total surface area of ​​the cavity sidewalls formed by the upper and lower molds. This structure is easy to process and clean, and is suitable for castings with regular shapes and uniform overflow requirements.

[0145] The second implementation is a continuous overflow edge structure, which can be an insert-type mold with a vertical upper mold, an inclined lower mold, and the upper mold inserted into the lower mold. In this structure, the sidewall of the lower mold is designed as an inclined surface, and the sidewall of the upper mold is a vertical surface. When the mold is closed, the upper mold is inserted downward into the lower mold, and a fitting gap is formed between the end face of the upper mold and the inclined sidewall of the lower mold. At this time, the overflow port no longer appears as an independent through hole, but as a continuous overflow edge (i.e., the fitting gap between the end face of the upper mold and the sidewall of the lower mold) circumferentially arranged at the top of the lower mold. After the molten metal is filled, the excess molten metal and gas overflow evenly from this ring gap at the top of the lower mold. In this implementation, the "area of ​​the overflow port" is the cross-sectional area of ​​the annular channel of the continuous overflow edge; the "surface area of ​​the mold cavity sidewall" mainly corresponds to the surface area of ​​the sidewall of the lower mold (because the main sidewall of the cavity is surrounded by the inclined surface of the lower mold, and the upper mold mainly forms the top). Therefore, the area ratio in this implementation refers to the ratio of the cross-sectional area of ​​the continuous overflow edge at the top of the lower mold to the surface area of ​​the sidewall of the lower mold cavity. This continuous overflow edge structure eliminates the dead zone between independent overflow ports, allowing the gas and cold molten sludge at the molten front to be discharged evenly and synchronously along the entire circumference of the cavity. It is particularly suitable for complex castings with extremely high requirements for airtightness and surface quality.

[0146] Regardless of the implementation method used, the present invention controls the ratio of the overflow port area to the cavity sidewall surface area to be between 15% and 25%. For the first implementation method, if the ratio is below 15%, the total flow area of ​​the independent through holes is insufficient, which can easily lead to a throttling effect under large overflow flow processes, resulting in poor venting or back pressure at the overflow port. If the ratio is above 25%, the effective support area of ​​the upper and lower mold sidewalls decreases, weakening the mold strength and increasing the risk of mold expansion. For the second implementation method, if the ratio is below 15%, the gap between the continuous overflow edges is too narrow, which is not conducive to the smooth discharge of cold melt and can easily cause premature solidification and blockage of the overflow edges. If the ratio is above 25%, it means that the upper mold insertion depth is too shallow or the lower mold sidewall is too thin, which will also affect the guiding accuracy and structural rigidity of the mold. Therefore, the range of 15% to 25% is a balance point between fluid dynamics flow requirements and mold mechanical strength, which helps to ensure the stable implementation of the two-stage filling and large overflow process of the present invention.

[0147] Furthermore, the die-casting apparatus also includes a heating mechanism mounted on the mold, used to provide auxiliary heating to the edges of the mold cavity after the excess melt has been completely drained. Understandably, the heating mechanism can be a heating rod embedded in the mold, an induction heating coil, or a localized heat radiation device, configured to raise the temperature of the edge mold to 400°C~480°C and maintain it for 5s~30s. This functional module is introduced to compensate for the excessively rapid cooling rate in the edge region. Traditional die-casting apparatuses lack localized heating capabilities, leading to the formation of coarse dendrites or fine grain bands at the edges due to rapid cooling, resulting in a significant difference in microstructure from the matrix. The apparatus of this invention uses a heating mechanism to dynamically compensate for the temperature at the edges during the critical solidification window, slowing down the cooling rate and promoting consistency in grain size between the edges and the matrix. This controls the average grain size deviation between the edges and the matrix to within 10%, thereby contributing to achieving a color difference ΔE of less than 0.8 after anodizing.

[0148] Furthermore, the die-casting apparatus also includes an injection mechanism for first filling the molten metal at a first flow rate and then second filling the molten metal at a second flow rate higher than the first flow rate.

[0149] Understandably, the injection mechanism is the power component of the die-casting device, and its filling strategy directly determines the flow state of the molten metal within the mold cavity and the final internal quality of the casting. This invention employs a segmented filling strategy, combining first and second filling stages, aiming to balance the contradiction between filling smoothness and mold filling integrity. Traditional die casting often uses a single high-speed filling method. Although the filling speed is fast, it easily generates turbulence within the mold cavity, causing the molten metal to trap air and form porosity defects. Especially in edge areas, high-speed impacts can exacerbate mold wear and increase the risk of mold sticking. This invention achieves controllable optimization of the filling process by controlling the flow rate in stages.

[0150] Specifically, a lower initial flow rate is used in the first filling stage. A lower flow rate helps achieve laminar filling, significantly reducing the risk of air entrapment caused by turbulence as the molten metal flows through the runner and cavity. In the initial filling stage, a large amount of air exists within the cavity. If the flow rate is too high, the air is easily trapped inside the molten metal, forming pores. By controlling the initial flow rate, for example, to no more than 2 m / s, it can be ensured that the gas within the cavity is orderly discharged from the parting surface or venting groove, establishing a stable temperature and flow field foundation for subsequent solidification. Furthermore, a lower flow rate reduces the erosion of the mold cavity walls by the molten metal, extending mold life, and reduces localized temperature fluctuations caused by frictional heat, which is beneficial for controlling the standard deviation of grain size in the edge region to be no greater than 10 μm.

[0151] Based on this, the second filling stage employs a second flow rate higher than the first flow rate. When the cavity is filled to a certain proportion, such as 70% to 90%, the remaining space is small. At this point, the main purpose of increasing the flow rate is to provide sufficient kinetic energy to drive the excess melt through the overflow port. As mentioned earlier, this invention requires that the excess melt volume ratio be not less than 0.1, and the overflow port area account for 15% to 25% of the sidewall surface area. If the second flow rate is too low, the melt may not be able to completely fill the cavity or effectively push the cold sludge melt into the overflow tank due to the decrease in temperature and increase in viscosity at the leading edge, resulting in residual impurities in the edge area. A higher second flow rate ensures that the filling and overflow rinsing process is completed before the melt solidifies, and the dynamic pressure effect of the fluid is used to completely remove the cold sludge layer at the leading edge, thereby helping to control the porosity ratio of the edge area to below 30%.

[0152] This segmented flow rate control works closely in conjunction with the overflow calculation formula described earlier. The first flow rate in the formula is a key parameter that directly affects the required minimum overflow ratio. A lower first flow rate reduces initial air entrapment, lowering the basic requirement for overflow venting; while a higher second flow rate ensures that the melt has sufficient fluidity to complete the displacement at the calculated overflow ratio. The combination of these two factors avoids the high porosity risk associated with high-speed filling and overcomes the cold shut or incomplete filling defects caused by low-speed filling. This slow-then-fast filling method, combined with subsequent differentiated pressurization processes, effectively controls the number of pore clusters in the edge region and the number of pores within each pore cluster.

[0153] The present invention will now be described in further detail with reference to specific embodiments, but these are exemplary and do not limit the scope of protection of the present invention in any way.

[0154] Example 1 A high-density edge aluminum alloy die-casting part is prepared by the following method: The 7075 aluminum alloy is melted to form a liquid, the temperature of which is 700℃ and the temperature of the mold is 380℃. The molten liquid is filled into the mold cavity, and the area of ​​the overflow port accounts for 20% of the side wall surface area of ​​the mold cavity. The overflow port is a continuous overflow edge structure and is set along the circumferential direction of the top of the lower mold. The filling process is divided into two stages: the first filling stage is carried out at a flow rate of 1 m / s, and the second filling stage is carried out at a flow rate of 1.3 m / s. As the molten metal in the mold cavity begins to solidify, the entire mold cavity is pressurized multiple times to allow excess molten metal to drain from the overflow port. Specifically, a total of three pressurizations are performed: the first pressurization pressure is 10 MPa, the second pressurization pressure is 13 MPa (30% higher than the first), and the third pressurization pressure is 17 MPa (30% higher than the second and 70% higher than the first). The holding time after each pressurization is 10 seconds. Control the volume of excess melt to approximately 0.2 (i.e. 20%) of the mold cavity volume, and discharge the excess melt through the overflow port; After the excess melt is completely drained, the edge of the mold cavity is subjected to auxiliary heating at a temperature of 450°C for 15 seconds. The die-cast part was then removed from the mold.

[0155] After standard pretreatment, the die-cast parts are subjected to 20V DC constant voltage anodizing in sulfuric acid electrolyte at 20℃ for 30 minutes.

[0156] Example 2 The die-casting method in this embodiment is the same as that in Embodiment 1, except that: after the excess melt is completely drained, the edge of the mold cavity is subjected to auxiliary heating at a temperature of 400°C for 15 seconds.

[0157] Example 3 The die-casting method in this embodiment is the same as that in Embodiment 1, except that: after the excess melt is completely drained, the edge of the mold cavity is subjected to auxiliary heating at a temperature of 480°C for 15 seconds.

[0158] Example 4 The die-casting method in this embodiment is the same as that in Embodiment 1, except that: after the excess melt is completely drained, the edge of the mold cavity is not subjected to auxiliary heating.

[0159] Example 5 The die-casting method in this embodiment is the same as in Embodiment 1, except that the mold cavity is pressurized twice. The first pressurization pressure is 10 MPa, and the second pressurization pressure is 14 MPa (40% increase over the first, for a total increase of 40%). The holding time after each pressurization is 10 seconds.

[0160] Example 6 The die-casting method in this embodiment is the same as in Embodiment 1, except that the mold cavity is pressurized three times. The first pressurization pressure is 10 MPa, the second pressurization pressure is 12 MPa (20% higher than the first), and the third pressurization pressure is 14.4 MPa (20% higher than the second and 44% higher than the first). The holding time after each pressurization is 10 seconds.

[0161] Example 7 The die-casting method in this embodiment is the same as in Embodiment 1, except that the mold cavity is pressurized four times. The first pressurization pressure is 10 MPa, the second pressurization pressure is 14 MPa (40% increase from the first), the third pressurization pressure is 19.6 MPa (40% increase from the second), and the fourth pressurization pressure is 27.4 MPa (40% increase from the third and 174% increase from the first). The holding time after each pressurization is 10 seconds.

[0162] Example 8 The die-casting method in this embodiment is the same as that in embodiment 1, except that after the molten liquid is filled, a uniform pressure (10MPa) is applied to the entire mold cavity for a single pressure holding, without multiple pressure application steps, and the pressure holding time after pressure application is 10s.

[0163] Example 9 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the volume of excess melt is controlled to be approximately 0.1 (i.e. 10%) of the mold cavity volume.

[0164] Example 10 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the volume of excess melt is controlled to be approximately 0.5 (i.e. 50%) of the mold cavity volume.

[0165] Example 11 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the volume of excess melt is controlled to be approximately 0.6 (i.e. 60%) of the mold cavity volume.

[0166] Example 12 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the 6082 aluminum alloy is melted to form a molten liquid.

[0167] Example 13 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the AZ91D magnesium alloy is melted to form a molten liquid.

[0168] Example 14 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the area of ​​the overflow port accounts for 25% of the side wall surface area of ​​the mold cavity.

[0169] Example 15 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the area of ​​the overflow port accounts for 15% of the side wall surface area of ​​the mold cavity.

[0170] Example 16 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the ratio of the volume of excess melt to the volume of the mold cavity is calculated and determined according to the formula:

[0171] Among them, take Temperature difference between melt and mold mold temperature First flow velocity The calculated ratio is approximately 0.18.

[0172] Example 17 The die-casting method in this embodiment is the same as that in embodiment 1, except that the overflow port is an independent overflow port structure. Specifically, an overflow port is provided on the upper part of each side wall of the mold cavity. The overflow port is circular in shape, and the area of ​​the overflow port accounts for 20% of the surface area of ​​the side wall of the mold cavity.

[0173] Comparative Example 1 The die-casting method in this comparative example is the same as that in Example 1, except that the volume of excess melt is controlled to be approximately 0.05 of the mold cavity volume.

[0174] Test case The following performance tests were performed on the die-cast parts obtained in all embodiments and comparative examples: 1. Porosity analysis of the edge region: Metallographic specimens were taken from the edge region of the die-cast part (within 2 mm of the outer edge). After grinding, polishing, and etching, at least 5 different fields of view were observed using a high-magnification optical microscope. Image analysis software was used to statistically analyze: the number of pore clusters per square millimeter (defined as a cluster with a pore spacing <20 μm); the maximum number of pores within a single cluster; the average spacing of pores outside the cluster; the equivalent diameter (area equivalent circle diameter) of all pores; and the number and ratio of shrinkage porosity pores (major axis / minor axis ratio ≥1.5) and gas porosity pores (major axis / minor axis ratio <1.5).

[0175] 2. Analysis of different pore shapes: Metallographic specimens were cut from the die-cast parts, ground, polished, and etched, and then observed using a high-magnification optical microscope at at least five different fields of view. Image analysis software was used to statistically analyze the number of shrinkage porosity (major axis / minor axis ratio ≥ 1.5) and gas porosity (major axis / minor axis ratio < 1.5). Calculate the ratio of shrinkage porosity to gas porosity in metal alloy die castings, and calculate the proportion of the total number of gas porosity in the edge region to the total number of pores in the edge region.

[0176] 3. Edge-to-substrate color difference (ΔE) test: After the die-cast parts undergo standard anodizing treatment, the L*, a*, and b* values ​​of the edge area and adjacent substrate area (more than 5 mm from the edge) are measured using a spectrophotometer, and the total color difference (ΔE) is calculated.

[0177] 4. Microstructure analysis: Metallographic specimens were taken from the edge area of ​​the die-cast part. Using an optical microscope and image analysis software, the average grain size and standard deviation of grain size were statistically analyzed according to the ASTM E112 standard. The dendritic ratio (area percentage) was evaluated.

[0178] 5. Impurity content analysis: Using a scanning electron microscope (SEM) equipped with EDS, area scanning analysis was performed in the edge region to assess the area percentage of non-metallic inclusions as the impurity content.

[0179] 6. Surface roughness (Ra) test: Using a contact surface profilometer, the arithmetic mean deviation Ra of the profile is measured on a flat surface in the edge region of the die casting.

[0180] Based on the above testing methods, the examples and comparative examples were tested, and the resulting performance data are summarized in Table 1.

[0181] Table 1

[0182] As shown in Table 1, the metal alloy die castings prepared in the embodiments of the present invention meet all the requirements of the present invention in terms of the microstructure of the edge region. Example 1, as the baseline example, uses a complete combination of process parameters and represents the technical effect of the preferred technical solution of the present invention. The process parameters of most examples are within the preferred range, and their performance is similar to that of Example 1, demonstrating the stability of the process window of the present invention. Although a few examples lack some preferred features or their process parameters are at the boundary of the preferred range, their product performance is still within the scope of protection claimed by the present invention; only some indicators are close to the upper limit. This indicates that preferred features such as auxiliary heating, multiple pressurization, overflow ratio, and overflow port area have a promoting effect on obtaining the optimal effect. In contrast, Comparative Example 1 lacks the core process feature of the present invention (overflow ratio below 0.1), and all performance indicators do not meet the requirements of the present invention. The overall data trend shows that the present invention, through the synergistic effect of process features such as overflow ratio control, multiple step pressurization, and auxiliary heating, can effectively regulate the microstructure of the edge region of the die casting, significantly reduce the density of pore clusters, improve grain uniformity, and inhibit dendritic crystal formation, ultimately achieving a high degree of appearance consistency between the edge and the substrate after anodizing.

[0183] To further demonstrate the technical effectiveness of the present invention, the following analysis will be conducted in conjunction with specific experimental test results and images.

[0184] like Figure 1 As shown, Figure 1 These are comparative photographs of the gold content of the edge areas of the die-cast parts in Embodiment 1 and Comparative Example 1 of the present invention. Figure 1 The right half of the image represents Example 1, and the left half represents Comparative Example 1. The right half (Example 1) shows sparse, fine, and dispersed pores in the edge region, with no obvious pore clusters. The photograph shows a uniform, fine equiaxed crystalline structure in the edge region, with an average grain size of approximately 25 μm. The grain size distribution is concentrated, and the proportion of dendritic crystals is extremely low. The left half (Comparative Example 1) shows a large number of dense pores in the edge region, with multiple pores clustered together, and larger pores present. The photograph shows uneven grain size in the edge region, with coarse dendritic crystals present, and locally abnormally large grains formed due to rapid cooling, resulting in poor microstructure uniformity.

[0185] like Figure 2 As shown, Figure 2 Metallographic microscope images of the metal alloy die-casting part provided in Embodiment 12 of the present invention. From... Figure 2 The metallographic structure reveals fine and uniform grains in the edge region, with an average grain size of approximately 26 μm, a small standard deviation in grain size, a dendritic proportion of approximately 0.55%, and sparse porosity without obvious clustering. This result indicates that the die-casting method of the present invention is applicable not only to 7-series aluminum alloys but also to 6-series aluminum alloys (such as 6082 alloy). Although 6-series and 7-series aluminum alloys differ in solidification range, strengthening phase precipitation behavior, and fluidity, the present invention, through the synergistic effect of overflow ratio control, multiple step pressurization, and auxiliary heating, can effectively adapt to the solidification characteristics of different alloy systems. In Example 12, using 6082 aluminum alloy melt, a microstructure quality comparable to that of 7-series alloys was still obtained. This verifies the universality of the process scheme of the present invention, indicating that this technical solution can overcome the limitations of alloy composition and provide a universal solution for high densification and high appearance consistency of die-cast parts of different series of aluminum alloys.

[0186] like Figure 3 As shown, Figure 3 Metallographic microscope images of the metal alloy die-casting part provided in Embodiment 16 of the present invention. From... Figure 3 The metallographic structure shows that the grains in the edge region are fine and uniform, with a small average grain size and sparse porosity, and the microstructure is similar to that of Example 1. This result indicates that the overflow ratio calculation formula provided by this invention can adaptively determine the required minimum overflow rate according to specific process conditions (temperature difference, flow rate, mold temperature), achieving a scientific match between the overflow rate and process parameters. The overflow ratio calculated using the formula ensures effective discharge of cold molten sludge at the filling front, avoiding edge defects caused by insufficient overflow, while also avoiding material waste and increased production costs due to excessive overflow. Figure 3The metallographic structure verified the practicality and accuracy of the overflow ratio calculation formula, providing an operable guidance method for those skilled in the art to determine reasonable overflow under different process conditions.

[0187] like Figure 4 As shown, Figure 4 The images show the appearance of the die-cast part's edge and substrate after anodizing in Example 1. The images show that after anodizing, the edge area of ​​the die-cast part has a uniform color, with no color difference perceptible to the naked eye. Furthermore, testing showed that the surface roughness Ra of the entire edge area of ​​the die-cast part is no greater than 1.5 μm.

[0188] like Figure 5 As shown, Figure 5 These are comparative photographs showing the appearance of the edge region and the base region of the die-cast part after anodizing, as described in Embodiment 16 of the present invention. Figure 5 As can be clearly seen, the die-cast parts prepared using the method of this invention exhibit a highly consistent appearance between their edge and substrate regions after anodizing. Both surfaces are smooth and flat, without any visible defects, and there is no obvious color difference boundary between the edge and the substrate. This macroscopic appearance result directly verifies the effectiveness of the technical solution of this invention, indicating that by controlling the porosity distribution, grain size, and impurity content in the edge region, consistency in the electrochemical oxidation response between the edge and the substrate has been successfully achieved, meeting the technical requirement of a color difference ΔE less than 0.8.

[0189] like Figure 6 As shown, Figure 6 These are comparative photographs showing the appearance of the edge region and base region of the die-cast part after anodizing in Comparative Example 1 of the present invention. Compared with the embodiments, Comparative Example 1 shows a significant decrease in the quality of the die-cast part due to the excessively low proportion of excess melt. Figure 6 It can be observed that obvious surface defects exist in both the edge region and the substrate region of Comparative Example 1, including microcracks, pore aggregation, and discoloration caused by uneven oxidation.

[0190] Figure 7 and Figure 8 The specific embodiments of the continuous overflow edge structure in the mold of the present invention are shown from both a three-dimensional perspective and a side view. For example... Figure 7 and Figure 8As shown, the overflow port 30 is not a traditional independent through hole, but a continuous annular channel set on the top side of the lower mold. Multiple overflow ports 30 are connected around the circumference of the mold cavity 10 to form a complete overflow edge. When the upper and lower molds are closed, this continuous overflow edge cooperates with the upper mold to form a complete venting and slag removal channel around the top of the cavity. The advantages of this structural design are: First, it eliminates the venting dead angle that may exist between independent overflow ports, allowing the gas and cold molten sludge at the front of the molten metal to be discharged evenly and synchronously along the entire circumference of the cavity; Second, the overflow stalk formed on the casting by the continuous overflow edge is complete and continuous, which is convenient for subsequent one-time removal by special tooling, improving post-processing efficiency; Third, the large cross-sectional area of ​​the overflow edge ensures that the flow rate of the molten metal through the overflow port 30 can still be kept at a low level under high overflow flow process, maintaining a laminar or steady flow state, and achieving truly stable rinsing.

[0191] like Figure 9 As shown in the figure, a typical vesicular pore is displayed, which is circular or elliptical in shape, with smooth inner walls and a major axis / minor axis ratio of less than 1.5, which conforms to the morphological characteristics of vesicular pores.

[0192] like Figure 10 As shown in the figure, a typical shrinkage-type pore is displayed. It has an irregular shape, is dendritic or torn, has a rough inner wall, and has a major axis / minor axis ratio of not less than 1.5, which is consistent with the morphological characteristics of shrinkage-type pores.

[0193] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A metal alloy die-casting part with high-density edges, characterized in that, The metal alloy die casting shall have at least 0.5 pore clusters per square millimeter in the edge region, and no more than 3 pores in each cluster; the average spacing between pores outside the pore clusters shall not be less than 50 μm; and the equivalent size of all pores shall not exceed 0.4 mm. The pore cluster is a local defect aggregate formed by two or more pores at the microscale when the minimum distance between their edges is less than 20 μm. The equivalent size of the pore is the diameter of a circle with the same projected area as the pore. The pores include shrinkage pores and gas pores. The ratio of shrinkage pores to gas pores in the metal alloy die casting is 1:(0.1~0.5), and the total number of gas pores in the edge region accounts for no more than 30% of the total number of pores in the edge region. After anodizing, the color difference ΔE between the edge region and the base region of the metal alloy die casting is less than 0.

8.

2. The high-density edge metal alloy die-casting part according to claim 1, characterized in that, The average grain size of the edge region of the metal alloy die casting is 10μm~50μm, and the standard deviation of the grain size is not greater than 10μm.

3. The high-density edge metal alloy die-casting part according to claim 2, characterized in that, The deviation in average grain size between the edge region of the metal alloy die casting and the base region of the metal alloy die casting is less than 10%.

4. The high-density edge metal alloy die-casting part according to claim 1, characterized in that, The dendritic ratio in the edge region of the metal alloy die casting is no greater than 1%.

5. The high-density edge metal alloy die-casting part according to claim 1, characterized in that, The impurity content in the edge region of the metal alloy die casting is no more than 0.5%.

6. The high-density edge metal alloy die-casting part according to claim 1, characterized in that, The surface roughness Ra of the edge region of the metal alloy die casting is no greater than 1.5 μm.

7. The high-density edge metal alloy die-casting part according to claim 1, characterized in that, The metal alloy is an aluminum alloy, magnesium alloy, titanium alloy, stainless steel, copper alloy, nickel alloy, or zinc alloy.

8. The high-density edge metal alloy die-casting part according to claim 7, characterized in that, The metal alloy is a 6-series or 7-series aluminum alloy.

9. The application of a metal alloy die-casting part as described in any one of claims 1 to 8 in the manufacture of structural parts for electronic devices, transportation vehicles, robots, medical devices, industrial equipment, or new energy equipment.

10. A die-casting method for preparing a metal alloy die-casting part with high-density edges as described in any one of claims 1 to 8, characterized in that, include: The metal alloy is melted to form a liquid and then filled into the mold cavity; When the molten liquid in the mold cavity begins to solidify, the mold cavity is pressurized to discharge excess molten liquid from the overflow port on the mold cavity; The ratio between the volume of the excess melt and the volume of the mold cavity is not less than 0.

1.

11. The die-casting method according to claim 10, characterized in that, The die-casting method further includes, after the excess melt is completely drained, auxiliary heating of the edge of the mold cavity, with a heating temperature of 400℃~480℃ and a heating time of 5s~30s.

12. The die-casting method according to claim 10, characterized in that, Pressurizing the mold cavity includes pressing the mold cavity multiple times, wherein the pressure of each subsequent pressurization is 20% to 40% higher than the pressure of the previous pressurization, and the pressure of the last pressurization is 40% to 200% higher than the pressure of the first pressurization.

13. The die-casting method according to claim 10, characterized in that, The ratio between the volume of the excess melt and the volume of the mold cavity is in the range of 0.1 to 0.

5.

14. The die-casting method according to claim 10, characterized in that, The step of filling the mold cavity with molten metal includes first filling the mold cavity with molten metal at a first flow rate and then second filling the mold cavity with molten metal at a second flow rate higher than the first flow rate; The volume of excess melt and the volume of the mold cavity satisfy the following relationship: In the formula, The volume of excess melt; This refers to the volume of the mold cavity; This is the first proportionality constant, and its value ranges from 0.1 to 0.2; This is the temperature difference between the melt and the mold, and its value ranges from 300℃ to 350℃. The mold temperature, with a value ranging from 300℃ to 420℃; The first flow velocity is defined as 2 m / s, and its value range is no greater than 2 m / s.

15. A die-casting apparatus for carrying out the die-casting method as described in any one of claims 10 to 14, characterized in that, include: A mold having a mold cavity inside, and an overflow port provided on the mold cavity; A pressurizing mechanism, disposed on the mold, is used to pressurize the molten liquid in the mold cavity, so that excess molten liquid is discharged from the overflow port; The overflow port is circumferentially disposed on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity.

16. The die-casting apparatus according to claim 15, characterized in that, The die-casting apparatus also includes a heating mechanism disposed on the mold, used to provide auxiliary heating to the edge of the mold cavity after the excess melt has been completely discharged.

17. The die-casting apparatus according to claim 15, characterized in that, The die-casting apparatus further includes an injection mechanism for first filling the molten metal at a first flow rate and then second filling the molten metal at a second flow rate higher than the first flow rate.

Images