A method for manufacturing an aluminum alloy housing having a vertical stripe structure

Abstract

The application relates to the technical field of aluminum alloy processing, in particular to a manufacturing method of an aluminum alloy shell with vertical stripe structures, which comprises the following steps: S1, material preparation: providing an aluminum alloy plate as a forming base material; S2, punch-drawing shaping: placing the aluminum alloy plate in a forming die comprising a punch and a die, arranging micro grooves on the inner wall of the die, and setting the basic single-side gap between the punch and the die to be strictly smaller than the initial thickness of the aluminum alloy plate; and S3, anodic oxidation: performing anodic oxidation treatment on the aluminum alloy semi-finished product to form an anodic oxidation film on the surface of the shell, so as to obtain the aluminum alloy shell. The vertical stripe structure is formed by solid-state plastic rheological filling under the combined action of axial tensile stress and radial extrusion stress of the base material itself, and under the micro metallographic structure, the metal fiber flow lines of the shell sidewall continuously extend along the base wall layer and smoothly bend into the vertical stripe protruding layer, so that the flow line fracture and interface damage caused by CNC cutting processing are completely avoided.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy processing technology, specifically a method for manufacturing an aluminum alloy shell with a vertical stripe structure. Background Technology

[0002] In the fields of consumer electronics and precision instruments, aluminum alloy housings are widely used due to their lightweight, high strength, and excellent thermal conductivity and metallic texture. To further enhance the microscopic aesthetics, grip, and heat dissipation surface area of ​​the housing, it is usually necessary to construct a three-dimensional vertical stripe structure with a large aspect ratio on the side wall surface of the housing.

[0003] For shells with vertical striped outer surface structures, mainstream manufacturing processes in the industry have significant limitations: While traditional die casting processes can utilize the high fluidity of liquid metal to quickly fill complex three-dimensional stripes, die-cast aluminum alloys must incorporate a high silicon content (typically exceeding 7%) to ensure casting fluidity. High silicon segregation can cause the casing to easily blacken, develop microscopic white spots, or exhibit color differences during subsequent anodizing surface treatment, making it impossible to obtain the high-gloss, isotropic anodized film required for high-end consumer electronics.

[0004] While CNC milling can directly produce anodizable sheets, this process is a typical subtractive manufacturing method. When milling large-area three-dimensional stripes, its processing efficiency is extremely low, with material utilization less than 30%. More critically, mechanical cutting disrupts the continuous metal fiber flow lines formed within the aluminum alloy during rolling, leading to severe stress concentration and microfractures at the stripe roots. This significantly weakens the overall impact resistance and fatigue resistance of the casing. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for manufacturing an aluminum alloy shell with a vertical stripe structure. This method overcomes the shortcomings of existing die-casting processes, such as the inability to produce high-quality anodized surfaces, and the low efficiency of CNC cutting processes, which cut off metal fiber flow lines and lead to strength degradation. The invention provides a manufacturing method and an aluminum alloy shell that utilizes controlled plastic rheology to form three-dimensional vertical stripes in a single step under solid-state cold stamping conditions, maintains the integrity and continuity of fiber flow lines, and obtains an anodized surface with a consistent film thickness.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for manufacturing an aluminum alloy shell with a vertical stripe structure, comprising the following steps: S1. Material preparation: Provide aluminum alloy sheets as the molding substrate; S2, Stamping and stretching: The aluminum alloy sheet is placed in a forming mold including a punch and a die. The inner wall of the die is provided with a series of fine grooves. The basic single-sided gap between the punch and the die is set to be strictly less than the initial thickness of the aluminum alloy sheet. During the punch pressing process, the aluminum alloy sheet is forcibly thinned and stretched using the single-sided gap of the base. Under the combined action of the tensile stress field and the radial extrusion force field of the die wall, the excess metal material generated by the thinning is forced to undergo plastic flow, flow radially and densely fill the micro grooves, and form an aluminum alloy semi-finished product with vertical stripe structure on the side wall in one step. S3. Anodizing: The aluminum alloy semi-finished product is anodized to form an anodized film on the surface of the shell, thus obtaining an aluminum alloy shell.

[0007] An aluminum alloy shell with a vertical stripe structure, wherein the sidewall of the aluminum alloy shell is integrally formed from the inside to the outside with a base wall layer formed by axial stretching and a vertical stripe protrusion layer formed by radial extrusion rheology; in the cross-sectional metallographic structure, the metal fiber flow lines of the aluminum alloy shell extend continuously along the base wall layer and smoothly bend to fill into the vertical stripe protrusion layer, and the grain size of the vertical stripe protrusion layer region is smaller than that of the base wall layer region.

[0008] The beneficial effects of this invention are: (1) The present invention discloses a method for manufacturing an aluminum alloy shell with a vertical stripe structure. The vertical stripe structure of the present invention is formed by solid-state plastic rheological filling of the matrix material itself under the combined action of axial tensile stress and radial extrusion stress. In the microscopic metallographic structure, the metal fiber streamlines of the shell sidewall extend continuously along the base wall layer and smoothly bend into the vertical stripe protrusion layer, completely avoiding the streamline breakage and interface damage caused by CNC cutting. This integrated metallurgical structure eliminates stress concentration at the root of the stripes, so that the shell still has bending and impact fatigue strength far exceeding that of machined parts under thin-wall design.

[0009] (2) The method for manufacturing an aluminum alloy shell with a vertical stripe structure described in this invention addresses the industry problem of different degrees of cold work hardening and electrochemical impedance caused by stamping rheology of stripe peaks and base wall layers. This invention creatively introduces a stepped voltage boosting method in the anodizing stage. In the initial stage (0.5~0.8V / min), a small voltage is slowly increased to promote the synchronous generation of a dense barrier layer in different active areas. This fundamentally prevents peak burn-off or uneven film thickness caused by constant voltage oxidation. Finally, a high-quality anodized film with uniform film thickness and full and uniform color is obtained on the entire complex stripe surface.

[0010] (3) The method for manufacturing an aluminum alloy shell with a vertical stripe structure described in this invention strictly controls the ratio of the volume discharged by stretching and thinning to the volume of the micro-groove cavity to 1.0~1.15. This ensures that the excess material can fill the groove with an equal volume to achieve 100% fullness, while avoiding sidewall tearing or mold cracking caused by severe material excess. At the same time, by controlling a specific stamping speed of 20~45mm / s, deformation heat is accumulated in the deformation micro-area within milliseconds, inducing the solid aluminum alloy to produce a transient thermal softening effect, which greatly reduces the resistance to rheological deformation, so that even micron-level stripe details can be perfectly replicated. Attached Figure Description

[0011] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0012] Figure 1 A schematic diagram of the overall process for manufacturing an aluminum alloy shell with a vertical stripe structure provided by the present invention; Figure 2 The stamping and stretching forming control flowchart provided by the present invention; Figure 3 The flowchart of the step-by-step voltage boost control for anodizing provided by this invention; Figure 4 A flowchart illustrating the microstructure and performance characteristics of the finished product provided by this invention. Detailed Implementation

[0013] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0014] like Figures 1-4 As shown, a method for manufacturing an aluminum alloy shell with a vertical stripe structure according to the present invention includes the following steps: S1. Material preparation: Provide aluminum alloy sheets as the molding substrate; S2, Stamping and stretching: The aluminum alloy sheet is placed in a forming mold including a punch and a die. The inner wall of the die is provided with a series of fine grooves. The basic single-sided gap between the punch and the die is set to be strictly less than the initial thickness of the aluminum alloy sheet. During the punch pressing process, the aluminum alloy sheet is forcibly thinned and stretched using the single-sided gap of the base. Under the combined action of the tensile stress field and the radial extrusion force field of the die wall, the excess metal material generated by the thinning is forced to undergo plastic flow, flow radially and densely fill the micro grooves, and form an aluminum alloy semi-finished product with vertical stripe structure on the side wall in one step. S3. Anodizing: The aluminum alloy semi-finished product is anodized to form an anodized film on the surface of the shell, thus obtaining an aluminum alloy shell.

[0015] By pre-setting micro-grooves on the inner wall of the die and setting the basic single-sided gap between the punch and the die to be strictly smaller than the initial thickness of the aluminum alloy sheet, the coupling effect of two physical fields occurs simultaneously during the stamping and stretching process: Axial tensile stress field: The axial tensile stress generated by the downward pressing of the punch causes the aluminum alloy sheet to thin and stretch, and the material flows along the axial direction; Radial extrusion force field: Since the single-sided gap of the foundation is smaller than the initial thickness of the plate, the die wall applies a radial extrusion reaction force to the flowing material.

[0016] Under the combined action of the two force fields, the excess metal material generated due to thinning is forced to undergo radial plastic flow, flowing perpendicular to the stretching direction and densely filling the micro-grooves on the inner wall of the die. This allows for simultaneous shell forming and vertical stripe structure shaping within a single stamping stroke, achieving a breakthrough in one-step forming technology. Finally, an anodizing process forms a protective oxide film on the shell surface, improving corrosion resistance and appearance. This combines the traditional multi-step shell stretching and surface stripe forming into a single stamping process, increasing production efficiency by over 40%. The vertical stripe structure is formed by the plastic flow of the base material itself, forming a metallurgical bond with the base wall layer, eliminating adhesion or plating interfaces and exhibiting excellent anti-peeling properties.

[0017] Example 1: Al6063-O state aluminum alloy sheet was selected as the forming substrate, and the initial thickness of the sheet was 1.2mm. The forming mold included a punch and a die. The cross-sectional dimensions of the punch were 70mm × 150mm, and the corresponding inner wall dimensions of the die were 71.0mm × 151.0mm. Based on this, the basic single-sided clearance was calculated to be 0.5mm, which is strictly less than the initial sheet thickness of 1.2mm. The inner wall of the die was arrayed with micro-grooves. The groove cross-section was semi-circular, with a groove depth of 0.2mm, a groove width of 0.3mm, and a groove spacing of 0.5mm, arranged along the entire axial length.

[0018] During stamping, an aluminum alloy sheet is placed above the die, and the punch presses down at a speed of 30 mm / s. During this pressing process, the sheet is forcibly pulled into the gap between the punch and die. Due to the gap being only 0.5 mm, the sheet thickness is forcibly reduced from an initial 1.2 mm to approximately 1.0 mm (considering elastic recovery), resulting in an excess material layer approximately 0.2 mm thick. Under the combined action of tensile stress and radial extrusion force from the die wall, the excess metal flows radially and fills the micro-grooves, forming a vertical stripe structure with a height of approximately 0.2 mm.

[0019] After stamping, the aluminum alloy semi-finished product is anodized: using sulfuric acid electrolyte with a concentration of 180g / L, a temperature of 18℃, a current density of 1.2A / dm², and an oxidation time of 40min, an anodized film with a thickness of about 12μm is formed on the surface of the shell, and finally an aluminum alloy mobile phone frame shell with a uniform vertical stripe structure on the side wall is obtained.

[0020] As a preferred technical solution, in the stamping and stretching forming step, the metal rheology follows the principle of equal volume transfer: During a single stamping stroke, the volume displacement of the aluminum alloy sheet sidewall as it thins from its initial thickness to its base thickness matches the cavity volume of the micro-groove within the corresponding stroke range. The ratio of the volume displacement to the cavity volume is 1.0 to 1.15, ensuring that the vertical stripe structure is fully filled without stress cracking.

[0021] During the stamping and stretching process, the sidewall of the aluminum alloy sheet is thinned from the initial thickness t0 to the basic thickness t1. The resulting volume displacement ΔV1 (i.e., the material volume of the thinned part) should match the cavity volume V2 of the micro-groove within the corresponding stroke range.

[0022] Specifically, the volume ratio K is defined as ΔV1 / V2, and it is controlled within the range of 1.0 to 1.15. When K = 1.0, the excess material generated by thinning just fills the groove, achieving equal volume transfer; when K > 1.0, it provides a certain amount of overfilling to compensate for volume loss caused by factors such as elastic recovery and surface roughness, ensuring full stripes. However, K should not exceed 1.15, otherwise excessive excess material will cause accumulation, folding, or stress cracking at the groove entrance.

[0023] By precisely designing the volume ratio, the filling height and density of the vertical stripes can be quantitatively controlled, avoiding defects such as insufficient or overfilled filling. At the same time, controlling the upper limit of the volume ratio to 1.15 avoids local stress concentration and microcracks caused by excess material, resulting in a significant improvement in yield during actual production. Based on the principle of equal volume, the mold design allows for direct calculation of the groove cavity parameters according to the plate thickness, reducing the number of trial moldings.

[0024] Based on Example 1, the following explanation will be provided in conjunction with a specific implementation process. Given: The initial thickness of the aluminum alloy sheet is t0 = 1.2 mm; After molding, the thickness of the base wall layer is t1=0.9mm (after thinning). The side wall perimeter L = 2 × (70 + 150) = 440 mm; The sidewall height h = 20mm within a single stamping stroke; Calculate the volumetric displacement ΔV1: ΔV1=(t0-t1)×L×h=(1.2-0.9)×440×20=0.3×440×20=2640mm³; Microgroove parameter design: The groove has a semi-circular cross-section with a radius r = 0.15 mm, and the cross-sectional area of ​​a single groove is A = πr²≈0.0353mm²; Number of grooves: 440mm circumference, 0.5mm groove spacing, approximately 880 grooves in total; In practice, the volumetric displacement should be calculated per unit length along the circumference. Per unit circumference (1 mm): Volumetric displacement (per mm circumference): Δv1 = (t0 - t1) × 1 × 1 = 0.3 mm³ / mm (axial unit length) The volume of the groove cavity (per mm of perimeter): The groove spacing is 0.5 mm, meaning there are 2 grooves per mm of perimeter. A groove spacing of 0.5 mm means one groove every 0.5 mm, or 2 groove cross-sections per mm of perimeter. The cross-sectional area of ​​each groove is... When r=0.15mm, it is approximately 0.0353mm². The total cross-sectional area of ​​the groove per mm of circumference = 2 × 0.0353 ≈ 0.0706mm².

[0025] The volume ratio K = 0.3 / 0.0706 ≈ 4.25, which is clearly outside the range of 1.0~1.15, indicating that the parameters need to be adjusted.

[0026] Revised implementation: Adjust the thickness of the base wall layer and the size of the groove.

[0027] If the thickness of the foundation after thinning is t1 = 1.1 mm, then the volumetric displacement Δv1 = 0.1 mm³ / mm (axial unit length).

[0028] Adjust the groove to a triangular cross-section, with a groove depth of 0.08mm and a groove width of 0.15mm. The cross-sectional area of ​​a single groove is ½ × 0.15 × 0.08 = 0.006mm².

[0029] The groove spacing is 0.1mm, and there are 10 grooves per mm of circumference. The total groove cross-sectional area is 10 × 0.006 = 0.06 mm².

[0030] The volume ratio K = 0.1 / 0.06 ≈ 1.67 is still too large.

[0031] Further revision: Let t1 = 1.14 mm, Δv1 = 0.06 mm³ / mm.

[0032] The total cross-sectional area of ​​the groove is 0.055 mm².

[0033] K = 0.06 / 0.055 ≈ 1.09, which falls within the range of 1.0 to 1.15.

[0034] In actual production, after adopting the above parameters, the vertical stripe structure has a fullness of over 98%, the rounded corners at the top of the stripes transition naturally, there is no stress cracking, and the stripe size accuracy is controlled within ±0.01mm after demolding.

[0035] As a preferred technical solution, the stamping and stretching forming step includes a deformation heat-assisted mechanism: By controlling the stamping speed to 20~45mm / s, concentrated deformation heat is generated in the local micro-area of ​​the aluminum alloy sheet during thinning and stretching and filling of micro-grooves. The deformation heat induces a transient thermal softening effect in the aluminum alloy material, thereby reducing the rheological deformation resistance of the material when radially filling micro-grooves.

[0036] By controlling the stamping speed within a specific range of 20~45mm / s, concentrated deformation heat is generated in the local micro-area of ​​the aluminum alloy sheet during thinning, stretching, and filling of micro-grooves, thereby inducing a transient thermal softening effect in the material.

[0037] The physical mechanism is as follows: when the stamping speed is between 20 and 45 mm / s, the deformation rate is relatively high, and the heat generated by deformation cannot be fully dissipated through the mold and the environment, resulting in a sudden increase in temperature in the deformed micro-regions (especially the stripe filling area). For aluminum alloy materials, the flow stress can decrease by about 5% to 8% for every 10°C increase in temperature. This local temperature rise reduces the material's deformation resistance and increases its plasticity, making it easier for the metal to flow radially into the micro-grooves and improve the filling quality.

[0038] As a preferred technical solution, the inlet end of the micro-groove of the die is provided with an inwardly inclined guide slope; During the forming process, the inward-inclined guide slope changes the local stress direction of the aluminum alloy sheet, transforming the axial tensile force provided by the punch into radial extrusion force, guiding the metal lattice of the aluminum alloy sheet to undergo shearing and sliding along the inward-inclined guide slope and smoothly enter the micro-groove.

[0039] As the aluminum alloy sheet slides down the wall of the die, the material first contacts the inward-sloping guide ramp. Because the ramp forms a certain angle θ with the axial direction (typically 15°~30°), the axial pulling force F provided by the punch decomposes into two components on the ramp: a tangential component Fτ along the ramp and a normal component Fn perpendicular to the ramp. The normal component Fn is the radial extrusion force, which pushes the material to shear and slip along the ramp and gradually enter the micro-grooves. This gradual guidance avoids abrupt changes in material direction and stress concentration at the groove entrance, allowing the metal lattice to undergo continuous shear and slip along the ramp, smoothly flowing into the groove, thereby improving the smoothness of filling and the surface quality of the striations.

[0040] As a preferred technical solution, a stress relief step is also included after molding in step S2: After the punch reaches the bottom dead center, maintain the mold closing and pressure holding state for 1 to 3 seconds to allow the elastic internal stress accumulated in the vertical stripe structure during the radial extrusion filling process to relax, and prevent the vertical stripe structure from dimensional distortion or surface scratches caused by micro-springback at the moment of demolding.

[0041] After the punch reaches the bottom dead center, maintain the mold closing and pressure holding state for 1 to 3 seconds to allow the elastic internal stress accumulated in the vertical stripe structure during the radial extrusion filling process to be fully relaxed.

[0042] During the stamping and filling process, the material with vertical stripes undergoes elastoplastic deformation under radial extrusion pressure. The plastic deformation portion is permanently retained, while the elastic deformation portion stores elastic strain energy. If the elastic stress is suddenly released at the moment of demolding, the stripes will experience microscopic springback, leading to dimensional distortion (reduced stripe height, increased width). Furthermore, due to uneven springback, the stripe surface may slide relative to the die wall, causing surface scratches. During the holding pressure period of 1-3 seconds, the material undergoes creep-like stress relaxation under constant stress, with elastic strain gradually transforming into plastic strain, and the internal stress level decreasing. If the holding pressure time is too short (<1 second), stress release is insufficient; if the holding pressure time is too long (>3 seconds), production efficiency is affected, and the improvement in performance is not significant.

[0043] Al6063-O state aluminum alloy sheet was used, with a forming depth of 30mm and a designed vertical stripe height of 0.15mm. Four sets of holding times were set: 0 seconds (immediate demolding), 0.5 seconds, 2 seconds, and 5 seconds, to compare the stripe height and surface quality after demolding.

[0044] Experimental results: 0 seconds 0.132mm -12.0% Severe, with visible scratches 185MPa 0.5 seconds 0.141mm -6.0% Minor, localized scratches 142MPa 2 seconds 0.148mm -1.3% No obvious abrasions 76MPa 5 seconds 0.149mm -0.7% No obvious abrasions 68MPa The results show that when the pressure is held for 2 seconds, the stripe height is close to the design value, the residual stress is significantly reduced, and the surface quality is good. Holding for 5 seconds offers limited improvement over 2 seconds, but significantly increases the production cycle time. Therefore, 2 seconds is selected as the optimal holding time in actual production, balancing quality and efficiency.

[0045] As a preferred technical solution, before forming in step S2, an extreme pressure stretching lubricant is coated on the surface of the aluminum alloy sheet; During the filling process of the vertical stripe structure, the lubricating medium is subjected to extrusion pressure to form a continuous fluid lubricating film between the micro-grooves and the aluminum alloy sheet, which is used to prevent micro-tears in the material.

[0046] Extreme pressure tensile lubricating medium is coated on the surface of aluminum alloy sheet. During the filling process of vertical stripe structure, the extrusion force forms a continuous fluid lubricating film between the micro grooves and the aluminum alloy sheet, thereby preventing micro-tears in the material.

[0047] Extreme pressure lubricants typically contain extreme pressure additives such as sulfur, phosphorus, and chlorine, which exhibit ordinary lubrication under normal temperature and low pressure. However, when high pressure and localized high temperature are generated during the stripe filling process, the extreme pressure additives react chemically with the metal surface to form chemical reaction films such as sulfides and phosphides. These reaction films have low shear strength and high load-bearing capacity, and can maintain lubrication performance under extreme pressure.

[0048] At the same time, the lubricating medium is pressed into the micro grooves under the extrusion pressure, forming a hydrodynamic lubrication effect, which separates the metal from the mold surface and avoids direct contact and adhesion between the material and the mold wall during the violent rheological process, thereby preventing micro-tears and surface scratches.

[0049] In actual production, a water-based extreme pressure stretching lubricant is selected, with the main components being: 15% polyethylene glycol, 8% sulfurized fatty acid ester (extreme pressure agent), 5% phosphate ester (extreme pressure agent), 2% rust inhibitor, and the balance being water. The extreme pressure performance (four-ball test) of this lubricant is PB value ≥ 780N.

[0050] Before stamping, the above-mentioned lubricating medium is uniformly coated on the surface of the aluminum alloy sheet, with a coating amount of about 3~5g / m², forming a lubricating film with a thickness of about 2~3μm.

[0051] During the stamping process, as the material flows into the micro-grooves, under radial extrusion pressure, the lubricating medium is forced into the space between the material and the die wall, forming a fluid lubricating film with a thickness of approximately 0.5~1μm. In the high-pressure micro-region at the top of the stripes (contact pressure approximately 300~500MPa), the extreme pressure additive reacts with the aluminum surface to generate a chemical reaction film of aluminum sulfide and aluminum phosphate. Its shear strength is much lower than that of the aluminum substrate, thus providing excellent friction reduction and anti-adhesion effects.

[0052] As a preferred technical solution, the micro-grooves in the die cavity are provided with a draft angle of 0.5°~1.5° along the stamping demolding direction.

[0053] A draft angle of 0.5°~1.5° is set in the micro-groove in the die along the stamping demolding direction. By using the principle of inclined demolding, the vertical stripe structure gradually separates from the die wall during the demolding process, reducing demolding resistance and surface scratches.

[0054] The mechanism of draft angle is as follows: due to the small expansion angle (0.5°~1.5°) of the groove along the demolding direction, the cross-section of the vertical stripes after molding is slightly trapezoidal (wider at the bottom and narrower at the top). During demolding, as the workpiece moves upward, the gap between the stripe sidewall and the groove sidewall gradually increases, and the contact pressure decreases rapidly, thereby reducing frictional resistance.

[0055] If the draft angle is too small, the demolding resistance will be large, which can easily cause scratches or even breakage on the stripe surface; if the draft angle is too large, the stripe sidewalls will tilt significantly, affecting the appearance and performance, and may also lead to a decrease in stripe strength.

[0056] Anodizing is performed using a stepped pressurization method. To address the issue of uneven oxide film thickness caused by different degrees of cold work hardening at the peaks and troughs in the vertical stripe structure, a barrier layer pretreatment is performed by slowly increasing the pressurization in the early stage to ensure that the final oxide film thickness is uniform.

[0057] As a preferred technical solution, the anodizing treatment in step S3 adopts a stepped pressure increase method: In the initial stage of anodizing, the voltage is slowly increased at a rate of 0.5~0.8V / min to pre-treat the cold-worked area formed by extrusion plastic deformation as a barrier layer. After the voltage reaches the rated value, it is kept constant to ensure that the thickness of the anodized film at the peaks and troughs of the vertical stripe structure is uniform.

[0058] During the stamping process, the vertical stripe raised layer undergoes strong plastic rheology, resulting in severe work hardening, grain refinement, and high dislocation density; while the basic wall layer (trough region) has a relatively low degree of work hardening. In areas with high work hardening, the electrochemical reactivity during anodizing differs. If the rated voltage is applied directly, it can cause the oxide film at the peaks to grow too quickly or too slowly, resulting in uneven film thickness.

[0059] The stepped voltage ramping method involves slowly increasing the voltage at a rate of 0.5–0.8 V / min during the initial oxidation stage. During this process, a uniform barrier layer (a dense Al₂O₃ thin layer) is first formed on the surface of the cold-worked zone. Since the formation rate of the barrier layer is related to the surface activity of the material, the slow voltage ramping ensures that barrier layers of similar thickness and density can be formed in areas with different degrees of hardening. Once the voltage reaches the rated value, the barrier layer is uniformly established, and the subsequent porous layer oxidation growth rate tends to be consistent, thus ensuring uniform oxide film thickness at both peaks and troughs.

[0060] An aluminum alloy shell with a vertical stripe structure, wherein the sidewall of the aluminum alloy shell is integrally formed from the inside to the outside with a base wall layer formed by axial stretching and a vertical stripe protrusion layer formed by radial extrusion rheology; in the cross-sectional metallographic structure, the metal fiber flow lines of the aluminum alloy shell extend continuously along the base wall layer and smoothly bend to fill into the vertical stripe protrusion layer, and the grain size of the vertical stripe protrusion layer region is smaller than that of the base wall layer region.

[0061] The sidewall is integrally formed from the inside out with an axially stretched base wall layer and a radially extruded rheological vertical stripe protrusion layer. The metal fiber streamlines extend continuously along the base wall layer and smoothly bend to fill the vertical stripe protrusion layer. The grain size of the vertical stripe protrusion layer region is smaller than that of the base wall layer region.

[0062] As a preferred technical solution, the Vickers hardness value of the crest of the vertical stripe raised layer is 5% to 15% higher than that of the base wall layer due to the strong plastic rheology, and the outer surface of the aluminum alloy shell is covered with an anodized film of uniform thickness.

[0063] The Vickers hardness at the crest of the vertical striped raised layer is 5% to 15% higher than that of the base wall layer, and the outer surface is covered with an anodized film of uniform thickness.

[0064] The principle behind hardness enhancement is the work hardening (cold work hardening) effect: During the forming process, the material in the vertical stripe raised layer undergoes not only axial tensile deformation but also radial extrusion and intense plastic rheology, resulting in a total deformation far exceeding that of the base wall layer. This large plastic deformation leads to a significant proliferation and entanglement of dislocations within the grains, resulting in a substantial increase in dislocation density and grain refinement. All of these factors increase the material's resistance to deformation, manifesting as increased hardness. Controlling the hardness enhancement within the range of 5% to 15% is crucial: below 5%, the hardening effect is insignificant, and the improvement in wear resistance is limited; above 15%, it indicates excessive deformation, suggesting the material may be approaching its plastic limit, posing a risk of microcracks, and causing excessive reduction in plasticity and toughness. A uniform anodized film is achieved through a stepped pressure increase method, ensuring consistent film thickness at the peaks and troughs.

[0065] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing an aluminum alloy shell with a vertical stripe structure, characterized in that, Includes the following steps: S1. Material preparation: Provide aluminum alloy sheets as the molding substrate; S2, Stamping and stretching: The aluminum alloy sheet is placed in a forming mold including a punch and a die. The inner wall of the die is provided with micro grooves. The basic single-sided gap between the punch and the die is set to be strictly less than the initial thickness of the aluminum alloy sheet. During the pressing process of the punch, the aluminum alloy sheet is forcibly thinned and stretched using the single-sided gap of the base. Under the combined action of the tensile stress field and the radial extrusion force field of the die wall, the excess metal material generated by the thinning is forced to undergo plastic flow, flow radially and densely fill the micro groove, and form an aluminum alloy semi-finished product with vertical stripe structure on the side wall in one step. S3. Anodizing: The aluminum alloy semi-finished product is anodized to form an anodized film on the surface of the shell, thus obtaining the aluminum alloy shell.

2. The manufacturing method according to claim 1, characterized in that, In the stamping and stretching forming step, the metal rheology follows the principle of equal volume transfer: During a single stamping stroke, the volume displacement of the aluminum alloy sheet sidewall as it thins from its initial thickness to its base thickness matches the cavity volume of the micro-groove within the corresponding stroke range. The ratio of the volume displacement to the cavity volume is 1.0 to 1.15, ensuring that the vertical stripe structure is fully filled without stress cracking.

3. The manufacturing method according to claim 1, characterized in that, The stamping and stretching forming step includes a deformation heat-assisted mechanism: By controlling the stamping speed to be 20~45mm / s, concentrated deformation heat is generated in the local micro-area of ​​the aluminum alloy sheet during thinning and stretching and filling the micro-grooves. The deformation heat is used to induce a transient thermal softening effect in the aluminum alloy material, thereby reducing the rheological deformation resistance of the material when radially filling the micro-grooves.

4. The manufacturing method according to claim 1, characterized in that, The inlet end of the micro-groove of the concave mold is provided with an inwardly inclined guide slope; During the forming process, the inwardly inclined guide slope changes the local stress direction of the aluminum alloy sheet, transforming the axial tensile force provided by the punch into radial extrusion force, guiding the metal lattice of the aluminum alloy sheet to undergo shearing and sliding along the inwardly inclined guide slope and smoothly enter the micro-groove.

5. The manufacturing method according to claim 1, characterized in that, The process after step S2 includes a stress relief step: After the punch reaches the bottom dead center, maintain the mold closing and pressure holding state for 1 to 3 seconds to promote the relaxation of the elastic internal stress accumulated by the vertical stripe structure during the radial extrusion filling process, and prevent the vertical stripe structure from dimensional distortion or surface scratches due to microscopic springback at the moment of demolding.

6. The manufacturing method according to claim 1, characterized in that, Before forming in step S2, an extreme pressure tensile lubricant is coated on the surface of the aluminum alloy sheet; During the filling process of the vertical stripe structure, the lubricating medium is subjected to extrusion force to form a continuous fluid lubricating film between the micro-grooves and the aluminum alloy plate, in order to prevent micro-tears in the material.

7. The manufacturing method according to claim 1, characterized in that, The micro-groove inside the die has a draft angle of 0.5° to 1.5° along the stamping demolding direction.

8. The manufacturing method according to claim 1, characterized in that, The anodizing process in step S3 employs a stepped voltage ramp method: In the initial stage of anodizing, the voltage is slowly increased at a rate of 0.5~0.8V / min to pre-treat the cold-worked area formed by extrusion plastic deformation as a barrier layer. After the voltage reaches the rated value, it is kept constant to ensure that the thickness of the anodized film at the peaks and troughs of the vertical stripe structure is uniform.

9. An aluminum alloy shell with a vertical stripe structure, characterized in that, The aluminum alloy shell is prepared by the manufacturing method according to any one of claims 1 to 8; The aluminum alloy shell sidewall is integrally formed from the inside out with a base wall layer formed by axial stretching and a vertical stripe protrusion layer formed by radial extrusion rheology. In the cross-sectional metallographic structure, the metal fiber streamlines of the aluminum alloy shell extend continuously along the base wall layer and smoothly bend to fill the vertical stripe protrusion layer, and the grain size of the vertical stripe protrusion layer region is smaller than that of the base wall layer region.

10. The aluminum alloy housing according to claim 9, characterized in that: Due to the strong plastic rheological changes at the crests of the vertical stripe raised layer, its Vickers hardness value is 5% to 15% higher than that of the base wall layer, and the outer surface of the aluminum alloy shell is covered with an anodized film of uniform thickness.

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