High-fluidity anodized aluminum alloy as well as preparation method and application thereof

Abstract

The invention belongs to the field of novel die-casting aluminum alloys, and discloses a high-fluidity anodized aluminum alloy and a preparation method and application thereof. The alloy is prepared from the following components in percentage by mass: 0.05 to 0.75 percent of Si, 0.2 to 2.0 percent of Mg, 0.2 to 3.5 percent of Mn, 0.3 to 0.5 percent of In, 0.01 to 0.3 percent of Sn, 0.1 to 0.9 percent of Fe, 0.05 to 0.15 percent of Zr, 0.03 to 0.15 percent of La, 0.03 to 0.8 percent of Zn, 0.03 to 0.2 percent of Cu, 0.03 to 0.15 percent of Ce and the balance of Al and inevitable impurities. In the alloy, Mn-Mg is synergistically used as a strengthening framework, In / Sn / Cd has melt rheology and anti-cracking modification functions, and Ir / Cd-Sc / Er nanophase synergistically regulates and controls oxidation homogeneity. The alloy has excellent fluidity, high strength and low hot crack tendency, the yield strength in the die-casting state is larger than or equal to 170 MPa, the technical contradiction of the mobile phone integrated die-casting structure in the aspects of ultra-thin wall mold filling, multi-anchor-point heat crack resistance, heat treatment-free strengthening and high-quality anode appearance is solved, the yield is high, and the cost is low. The method is suitable for manufacturing complex thin-wall components in the consumer electronics field such as mobile phone shells.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new die-casting aluminum alloys, and particularly relates to a high-fluidity anodized aluminum alloy as well as a preparation method and application thereof. BACKGROUND

[0002] In the design and manufacturing of 3C products, especially the metal structural parts of smart phones, lightweight structure, component integration and high-end surface treatment have become the key direction to improve product competitiveness. Currently, the industry generally adopts the process route of manufacturing and assembling the middle plate and the frame separately. Among them, the middle plate, as an internal support, is mainly formed by high-pressure die casting of ADC12 and other aluminum-silicon alloys. Such alloys, with high silicon content, are suitable for thin-walled complex components due to their excellent high-temperature fluidity. However, ADC12 usually contains a high proportion of silicon and copper, with silicon content ranging from 9.5% to 12% and copper content usually between 1.5% and 3.5%. During anodizing, these elements are prone to form intermetallic compounds such as silicon-rich phase and copper-rich phase, resulting in uneven oxide film thickness, poor continuity, abnormal color development, local dark spots or grayness, and other defects, making it difficult to meet the strict requirements of surface quality for appearance parts.

[0003] To meet the appearance and performance requirements of the frame, 6061 and other aluminum-magnesium-silicon deformed aluminum alloys are usually used, which are formed by extrusion and CNC machining. Although this process can achieve good anodizing effect and surface consistency, the material utilization rate is low, the processing cycle is long, and the cost is high. Then the die-casting middle plate and the machined frame need to be connected by welding, which not only prolongs the production cycle, but also introduces the welding heat-affected zone, residual stress and potential galvanic corrosion risk, affecting the reliability and life of the overall structure.

[0004] Therefore, it is an urgent technical demand in the industry to develop a new type of aluminum alloy that can be integrally die-cast and has good anodizing performance. The core difficulty lies in how to synergistically optimize the alloy composition, solidification process and surface treatment process to achieve high fluidity required for die casting and chemical uniformity required for anodizing at the same time. High silicon content can improve fluidity, but will seriously damage the quality of the oxide film; while aluminum-magnesium-silicon alloys suitable for oxidation have problems such as insufficient die-casting fluidity, high tendency to thermal cracking, poor filling capacity, etc. SUMMARY

[0005] The present application aims at the above challenges, by multi-scale component design, such as regulating the proportion of main elements such as silicon, magnesium, copper, etc., adding trace grain refinement and phase regulation elements, and optimizing the die casting process parameters to control the cooling rate and solid phase transformation, while developing a matching anodic oxidation process, which systematically solves the core bottleneck of poor oxidation film quality of die casting aluminum alloy, and provides a feasible material basis and process path for efficient, low-cost and high-performance manufacturing of intelligent mobile phone middle frame and middle plate integrated structure.

[0006] The present application aims at the above challenges, by multi-scale component design, such as regulating the proportion of main elements such as silicon, magnesium, copper, etc., adding trace grain refinement and phase regulation elements, and optimizing the die casting process parameters to control the cooling rate and solid phase transformation, while developing a matching anodic oxidation process, which systematically solves the core bottleneck of poor oxidation film quality of die casting aluminum alloy, and provides a feasible material basis and process path for efficient, low-cost and high-performance manufacturing of intelligent mobile phone middle frame and middle plate integrated structure.

[0007] The present application aims at the above challenges, by multi-scale component design, such as regulating the proportion of main elements such as silicon, magnesium, copper, etc., adding trace grain refinement and phase regulation elements, and optimizing the die casting process parameters to control the cooling rate and solid phase transformation, while developing a matching anodic oxidation process, which systematically solves the core bottleneck of poor oxidation film quality of die casting aluminum alloy, and provides a feasible material basis and process path for efficient, low-cost and high-performance manufacturing of intelligent mobile phone middle frame and middle plate integrated structure. The present application aims at the above challenges, by multi-scale component design, such as regulating the proportion of main elements such as silicon, magnesium, copper, etc., adding trace grain refinement and phase regulation elements, and optimizing the die casting process parameters to control the cooling rate and solid phase transformation, while developing a matching anodic oxidation process, which systematically solves the core bottleneck of poor oxidation film quality of die casting aluminum alloy, and provides a feasible material basis and process path for efficient, low-cost and high-performance manufacturing of intelligent mobile phone middle frame and middle plate integrated structure. A high-fluidity anodized aluminum alloy, the composition of the alloy is, in mass percentage: Si 0.05-0.75%, Mg 0.2-2.0%, Mn 0.2-3.5%, In 0.3-0.5%, Sn 0.01-0.3%, Fe 0.1-0.9%, Zr 0.05-0.15%, La 0.03-0.15%, Zn 0.03-0.8%, Cu 0.03-0.2%, Ce 0.03-0.15%, the balance being Al and unavoidable impurities.

[0008] In some examples, the mass ratio of Mn to Mg is (1.5-2.5):1.

[0009] In some examples, it also includes Cd 0.02-0.05%, preferably, the mass ratio of In to Cd is (1.5-2.5):1.

[0010] In some examples, it also includes Sc 0.03-0.3% and Er 0.05-0.15%, preferably, the mass ratio of Sc to Er is (1-2):1.

[0011] In some examples, it also includes Ir 0.05-0.1%.

[0012] In some examples, it also includes Cd 0.02-0.05%, Sc 0.03-0.3% and Er 0.05-0.15%.

[0013] In some examples, it also includes Cd 0.02-0.05%, Ir 0.05-0.1%.

[0014] In some examples, it also includes Cd 0.02-0.05%, Ir 0.05-0.1%, Sc 0.03-0.3% and Er 0.05-0.15%.

[0015] In some examples, Ir 0.05-0.1%, Sc 0.03-0.3% and Er 0.05-0.15% are further included.

[0016] In some examples, Cd 0.02-0.05% is further included, the total content of In, Sn and Cd is 0.33-0.85%, and the mass ratio of In / (Sn+Cd) is (1.0-2.5):1.

[0017] In some examples, the individual content of the impurity elements is ≤0.05%, and the total content is ≤0.1%.

[0018] The above features can be combined arbitrarily without conflict.

[0019] The second aspect of the present application provides: The preparation method of the high-fluidity anodized aluminum alloy of the first aspect of the present application comprises the following steps: Raw material preparation: weigh the raw materials according to the alloy ratio; Alloying: after melting all the required raw materials, an alloy melt is obtained, and the temperature is controlled at 710-740°C during the alloying process; Refining and degassing: refine and degas the alloy melt at 710-740°C; Die casting: transfer the treated melt to a die casting machine for die casting to obtain a die casting.

[0020] In some examples, before die casting, 0.02-0.05% of a hot crack inhibitor accounting for the total mass of the alloy melt is added to the alloy melt, and the hot crack inhibitor is an Al-3V-2Ti-0.5B intermediate alloy.

[0021] The above features can be combined arbitrarily without conflict.

[0022] The third aspect of the present application provides: A die-cast aluminum alloy piece is obtained by anodizing the high-fluidity anodized aluminum alloy of the first aspect of the present application after die casting, or by anodizing the die casting obtained by the preparation method of the second aspect of the present application, and the anodizing process comprises: Pretreatment of the aluminum alloy die casting, including water washing, degreasing and neutralization; Electrolytic treatment of the pretreated aluminum alloy die casting in an acid solution, wherein sodium lignosulfonate is added as a corrosion inhibitor; Sealing treatment of the workpiece after electrolytic treatment.

[0023] In some examples, the electrolytic treatment is performed at a voltage of 39.5-40.5 V for 18-40 min at a constant temperature of 18-22℃.

[0024] In some examples, the concentration of sodium lignosulfonate in the acid solution is 5-10 g / L.

[0025] In some examples, the acid solution comprises 150 ± 10 g / L of sulfuric acid, 18 ± 2 g / L of oxalic acid, and 7.5 ± 1 g / L of sodium lignosulfonate.

[0026] In some examples, the hole sealing treatment comprises hot water sealing and subsequent fluorosilane solution immersion and solidification.

[0027] In some examples, the hot water sealing is performed at 70 ± 5℃ for 10 ± 2 min, followed by water washing.

[0028] In some examples, the mass ratio of alkoxy silane to perfluorooctyl triethoxysilane in the fluorosilane solution is (3-5):1, preferably 4:1.

[0029] In some examples, the die-cast aluminum alloy part is a mobile phone, a tablet frame, or a die-cast part with an integrated middle plate.

[0030] The above features can be combined arbitrarily without conflict.

[0031] The beneficial effects of the present application are: The high-flow anodized aluminum alloy of some examples of the present application, while abandoning the high-silicon route to ensure the quality of anodization, simultaneously achieves: Perfect filling of ultra-thin wall with a thickness of less than 0.2 mm and a multi-groove structure; Thermal cracking rate at the root of multiple anchor points ≤0.2%; Anodized film without color difference (ΔE <1.0); Yield strength > 170 MPa and aging time ≤10 min.

[0032] The high-flow anodized aluminum alloy of some examples of the present application, in view of the harsh requirements of integrated die-cast structure with ultra-thin wall thickness, complex geometry, T6-free heat treatment, and high-quality anodization, designs the following multi-component synergistic alloy system: Mn-Mg synergistic as a strengthening framework: The content of Mn is controlled at 0.2-3.5%, the content of Mg is controlled at 0.4-2.0%, and the mass ratio of Mn / Mg is controlled at 1.5-2.5. This design makes the content of Mn close to the Al-Mn eutectic point (~1.8%), and in the process of die casting rapid solidification, most of Mn is dissolved in the α-Al matrix, the matrix strength is significantly improved by using the solid solution strengthening effect of Mn, and the best fluidity near the eutectic composition is considered, so the contradiction between high strength and high fluidity is solved. The content of Si is limited to be less than or equal to 0.7%, so that the Si is combined with Mg preferentially, and a dispersed β''(Mg2Si) strengthening phase is formed in situ after die casting, so that the matrix strength of the die casting is provided immediately, and the problem of insufficient strength of the traditional die casting aluminum alloy is avoided.

[0033] In / Sn / Cd melt rheology and crack resistance modification function: In view of the problems of melt filling and hot cracking in the root area of the super-thin wall (<0.3 mm) and multi-anchor point of the integrated die-casting structure, the content of elements indium (In), tin (Sn) and cadmium (Cd) is accurately controlled in the range of 0.3-0.5%, 0.01-0.3% and 0.02-0.05% respectively. Under this accurate ratio, In, Sn and Cd cooperatively construct a multi-element low-melting-point eutectic system with intermetallic compound InSn4 as the structural core and Cd element. The eutectic temperature of the system is significantly lower than that of the aluminum matrix. The key role of the design is that at the end of die casting filling: when the α-Al dendritic skeleton is initially formed, the above-mentioned multi-element low-melting-point organization (with InSn4 as the core) distributed in the interdendritic region can still maintain a semi-molten liquid state. These liquid phases can effectively fill the micro shrinkage holes caused by solidification shrinkage, realize the end liquid feeding of the super-thin wall area, and ensure perfect filling; at the same time, the semi-molten liquid film as a high-efficiency stress buffer layer relaxes the thermal stress concentrated in the interdendritic region due to solidification shrinkage through plastic flow, thereby effectively inhibiting the initiation of hot cracks. The present invention reveals and utilizes the unique synergistic effect of In / Sn / Cd: the multi-element low-melting-point eutectic network formed by them is significantly superior to any combination of two elements or known binary eutectic system in terms of melt feeding capacity and thermal stress relaxation effect. It is particularly key and unexpected to find that when the mass ratio of indium (In) to cadmium (Cd) is accurately controlled in the range of (1.5-2.5):1, the system's resistance to hot cracking shows a significant synergistic peak. The control of the total amount of elements is also crucial, too low will result in insufficient effective liquid phase, which cannot fully realize the feeding and relaxation effect; too high will easily form a continuous brittle eutectic network, which seriously damages the ductility of the casting. The range provided by the present invention achieves the best balance.

[0034] Ir / Cd-Sc / Er nano-phase synergistic regulation of oxidation homogeneity: To achieve a color difference-free anodic oxide film (ΔE < 1.0), this invention introduces two components, Ir / Cd and Sc / Er, to construct a multi-level nano-synergistic regulation mechanism. This mechanism, based on the functional complementarity and mutual reinforcement between the two component precipitates, systematically improves the uniformity of the oxide film. The specific mechanisms of action are as follows: First, the combined addition of Sc and Er forms coherent L12-type Al3(Sc,Er) nanoparticles, which act as heterogeneous nucleation sites for α-Al during solidification, refining the matrix grains to 10–30 μm. This refinement significantly increases the total grain boundary area, not only stabilizing the grain boundary structure and reducing the tendency for preferential corrosion, but more importantly, providing a structural basis for the highly dispersed distribution of the Ir / Cd nanophase.

[0035] Secondly, Ir and Cd synergistically form nanoscale IrIn3 and Cd-containing intermetallic compound phases during the smelting process. This phase has an electrochemical potential close to that of the aluminum matrix and exhibits high inertness during anodic oxidation. Its core function lies in forming a large number of uniform and stable electrochemical sites at the microscopic level, relying on the diffusely distributed substrate provided by Sc / Er, thereby effectively suppressing the "current hotspots" and excessive corrosion caused by local concentration of oxidation current.

[0036] The synergy between Ir / Cd and Sc / Er manifests as functional coupling and enhancement: the Sc / Er phase creates conditions for a uniform distribution of the Ir / Cd phase through grain refinement; the Ir / Cd phase, in turn, suppresses localized corrosion through potential homogenization, compensating for the shortcomings of the Sc / Er phase in electrochemical regulation. Together, they significantly improve the uniformity and consistency of oxide film growth, keeping ΔE stably below 1.0.

[0037] The preparation methods of some examples of this invention are based on a deep understanding of the hot crack formation mechanism: hot cracking is essentially caused by the contraction of the residual liquid film between dendrites under the action of surface tension in the later stage of solidification. When the feeding channel is isolated and the liquid film breaks to form isolated droplets, it cannot compensate for the intergranular separation caused by tensile stress. The TiB2 phase in conventional Al-Ti-B refining agents mainly acts on nucleation in the early stage of solidification and has a limited effect on the liquid film behavior in the later stage of solidification. This invention adds the hot cracking inhibitor Al-3V-2Ti-0.5B master alloy to the melt, utilizing the extremely high thermal stability (melting point > 2800℃) and chemical inertness of the VB2 phase, so that it exists stably in the interdendritic liquid phase throughout the entire solidification process. The numerous dispersed VB2 nanoparticles exert a significant pinning and dragging effect on the liquid film, effectively delaying the shrinkage and isolation process of the liquid film and maintaining the continuity of the feeding channel. This significantly reduces the tendency for hot cracking caused by insufficient feeding, making it particularly suitable for solving the cracking problem at multiple anchor points and thin-thickness joints in integrated die-cast mobile phone parts. Tests have shown that it can reduce hot cracking sensitivity by more than 30%.

[0038] The preparation methods of some examples of this invention, an integrated strengthening process: implementing multi-stage stepped pressure aging during the heat straightening process; Phase 1: Hold at 170-190℃ for 3-5 minutes under 20-25MPa pressure, introducing a dislocation density ≥10. 14 / cm 2 This accelerates the precipitation of Mg2Si; Second stage: Reduce the pressure to 16-20MPa and hold for 3 minutes to eliminate local stress; Third stage: Reduce pressure to 12-16MPa and hold for 2 minutes to stabilize dimensions; The total aging time is ≤10 minutes, and the tensile strength is greater than 250MPa and the elongation is greater than 6% at the same time.

[0039] This invention, through a novel alloy design approach of "low silicon manganese magnesium substrate - melt rheological modification - synergistic regulation of nanophases," combined with the exclusive processes of "VB2 pinning for thermal crack resistance" and "multi-stage pressure aging," systematically overcomes the contradictions of high material flow / high strength / oxidizability in the integrated die casting of electronic products, such as mobile phones. It also innovates in forming (ultra-thin walls / zero thermal cracking), efficiency (short-time high-efficiency strengthening), and appearance (color difference-free anodizing), providing a full-chain technical solution for the high-performance, high-yield, and high-aesthetic manufacturing of consumer electronic structural components. Attached Figure Description

[0040] Figure 1 This is a comparison of the macroscopic appearance of different die-cast parts, with the conventional middle plate on the left and the integrated die-cast part of frame / middle plate of Example 1 on the right. The component of the present invention on the right avoids the potential quality risks (such as incomplete welding, deformation, and residual stress) caused by welding / assembly in the traditional solution on the left, and significantly simplifies the production process.

[0041] Figure 2 This is a comparison of the macroscopic appearance of the mobile phone mid-plate die-casting parts prepared by Example 1 (right) and Comparative Example 1 (left). It can be seen that the sample of Comparative Example 1 (without In / Sn elements) shows severe thermal cracks at the root; the sample of Example 1 of this invention shows that the same part is intact and without defects.

[0042] Figure 3 This is a comparison chart of the spiral flowability test results of the alloys in Example 1 (right) and Comparative Example 1 (left). The spiral filling length of the alloy in Example 1 is significantly longer than that in Comparative Example 1, indicating that it has better flowability.

[0043] Figure 4This is a high-magnification SEM+EDS elemental distribution map of Example 1 of the present invention. In Example 1, elements such as In and Sn are highly overlapped and significantly enriched between α-Al dendrites, which directly confirms the formation of a low-melting-point multi-element eutectic phase. At the same time, Sc and Er elements are uniformly dispersed in the matrix, which proves the existence of Al3(Sc,Er) nano-reinforcing phase.

[0044] Figure 5 This is a macroscopic comparison of the anodized surface effects of Example 1 (right) and Comparative Example 2 (left) of the present invention. The sample of Comparative Example 2 (without Ir / Cd elements) shows obvious cloud spots and color differences on the surface; the sample of Example 1 of the present invention has a uniform and bright surface color.

[0045] Figure 6 The SEM microstructure of the sample obtained in Example 1 of this invention is shown. The alloy exhibits uniform and fine α-Al equiaxed crystals (grain size 10-30 μm), and at the grain boundaries, low-melting-point eutectic phases (bright white) formed by elements such as In and Sn are uniformly distributed in a fine, discontinuous manner. Detailed Implementation

[0046] The first aspect of the present invention provides: A high-flowability anodized aluminum alloy, comprising, by mass percentage: Si 0.05–0.75%, Mg 0.2–2.0%, Mn 0.2–3.5%, In 0.3–0.5%, Sn 0.01–0.3%, Fe 0.1–0.9%, Zr 0.05–0.15%, La 0.03–0.15%, Zn 0.03–0.8%, Cu 0.03–0.2%, Ce 0.03–0.15%, with the balance being Al and unavoidable impurities.

[0047] In some instances, the mass ratio of Mn to Mg is (1.5–2.5):1.

[0048] In some instances, it also includes 0.02% to 0.05% Cd, preferably, the mass ratio of In to Cd is (1.5 to 2.5):1.

[0049] In some instances, Sc 0.03–0.3% and Er 0.05–0.15% are also included, with the preferred mass ratio of Sc to Er being (1–2):1.

[0050] In some instances, Ir is also included at 0.05% to 0.1%.

[0051] In some instances, it also includes Cd 0.02–0.05%, Sc 0.03–0.3% and Er 0.05–0.15%.

[0052] In some instances, it also includes Cd 0.02–0.05% and Ir 0.05–0.1%.

[0053] In some instances, it also includes Cd 0.02–0.05%, Ir 0.05–0.1%, Sc 0.03–0.3% and Er 0.05–0.15%.

[0054] In some instances, it also includes Ir 0.05–0.1%, Sc 0.03–0.3% and Er 0.05–0.15%.

[0055] In some instances, it also includes 0.02-0.05% Cd, the total content of In, Sn and Cd is 0.33-0.85%, and the mass ratio of In / (Sn+Cd) is (1.0-2.5):1.

[0056] In some instances, the individual content of the impurity element is ≤0.05%, and the total content is ≤0.1%.

[0057] These features can be combined arbitrarily as long as they do not conflict with each other.

[0058] A second aspect of the present invention provides: The method for preparing the high-fluidity anodized aluminum alloy according to the first aspect of the present invention includes the following steps: Raw material preparation: Weigh the raw materials according to the alloy ratio; Alloying: After melting all the required raw materials, an alloy melt is obtained. During the alloying process, the temperature is controlled at 710-740℃. Refining and degassing: Refining and degassing of the alloy melt at 710℃~740℃; Die casting: The processed melt is transferred to a die casting machine for die casting to obtain a die casting part.

[0059] In some instances, prior to die casting, 0.02 to 0.05% by weight of a hot crack inhibitor, which is an Al-3V-2Ti-0.5B master alloy, is added to the alloy melt.

[0060] These features can be combined arbitrarily as long as they do not conflict with each other.

[0061] To achieve better surface treatment results, the inventors further developed a compatible surface treatment to address the common problems encountered by conventional anodizing processes, such as early selective corrosion, oxide film powdering, and insufficient corrosion resistance, due to the presence of multiple low-melting-point active elements like In, Sn, and Cd. A third aspect of this invention provides: A die-cast aluminum alloy part is obtained by die-casting the high-fluidity anodized aluminum alloy described in the first aspect of the present invention and then anodizing it, or by preparing a die-cast part according to the preparation method described in the second aspect of the present invention and then anodizing it, wherein the anodizing process includes: Pre-treatment of aluminum alloy die castings by water washing, degreasing, and neutralization; The pretreated aluminum alloy die casting is placed in an acid solution for electrolytic treatment, wherein sodium lignosulfonate is added to the acid solution as a corrosion inhibitor. The workpiece after electrolytic treatment is then sealed.

[0062] Sodium lignosulfonate, as a key early corrosion inhibitor, works by preferentially and selectively adsorbing its sulfonic acid groups and benzene rings onto the microscopic regions exposed by low-melting-point active elements such as In, Sn, and Cd, forming a dense, dynamic adsorption protective film instantly in the early stages of oxidation. This adsorption film effectively blocks free H₂. + The preferential attack on active sites significantly delays their rapid dissolution, thereby fundamentally eliminating local over-corrosion (i.e., "powdering") caused by microscopic unevenness of composition, laying the foundation for the subsequent formation of a uniform thickness and smooth substrate of colorless anodic oxide film.

[0063] The voltage, temperature, and treatment time of the electrolytic treatment can be adjusted according to the treatment effect. In some cases, the voltage is set to 39.5-40.5V and the electrolytic treatment is carried out at a constant temperature of 18-22℃ for 18-40 minutes.

[0064] In some instances, the concentration of sodium lignosulfonate in the acid solution is 5–10 g / L.

[0065] In some instances, the acid solution is composed of 150 ± 10 g / L sulfuric acid, 18 ± 2 g / L oxalic acid, and 7.5 ± 1 g / L sodium lignosulfonate.

[0066] Composite sealing and surface protection enhancement: To meet the stringent requirements of consumer electronics products for durable appearance and resistance to daily wear and tear, a two-step composite sealing process is adopted: Preliminary sealing: First, use 70℃ hot water to seal the holes for 10 minutes to initially seal the macroscopic pores of the oxide film using the hydration reaction.

[0067] In some instances, the sealing process includes hot water sealing followed by impregnation and curing with a fluorosilane solution.

[0068] In some instances, the hot water sealing process specifically involves heat sealing the holes at 70±5℃ for 10±2 minutes, followed by water rinsing.

[0069] In some instances, the mass ratio of alkoxysilane to perfluorooctyltriethoxysilane in the fluorosilane solution is (3-5):1, preferably 4:1.

[0070] Functional Enhancement Sealing: The substrate is then impregnated with a fluorosilane composite solution (alkoxysilane to perfluorooctyltriethoxysilane mass ratio of (3-5):1, concentration 8-10%), and finally cured at 80℃. The introduction of perfluorooctyl groups significantly reduces surface energy, while the alkoxysilanes form strong covalent bonds (Si-O-Al) with the matrix, ultimately constructing a covalently cross-linked Si-O-Si three-dimensional network structure on the surface. This composite film not only increases the surface contact angle to >110°, giving it superhydrophobic properties, but also effectively resists the penetration of corrosive media such as sweat and cosmetics. Its wear resistance is more than 3 times higher than that of single hot water sealing or conventional nickel salt sealing processes, ensuring the product's appearance quality throughout its entire lifecycle.

[0071] In some instances, the die-cast aluminum alloy parts are integrated die-cast parts for the frame and middle plate of mobile phones and tablets.

[0072] These features can be combined arbitrarily as long as they do not conflict with each other.

[0073] The following disclosure provides many different implementations or examples for different ways of implementing the present invention.

[0074] The present invention will now be described in detail with reference to embodiments, comparative examples and experimental data. However, this is not intended to identify the key or decisive elements of the invention or to limit the scope of protection.

[0075] The technical solution of the present invention will be further illustrated below with examples. In order to obtain products with more stable quality, the impurities in each example are controlled below 0.10%.

[0076] The present invention will be further illustrated below by way of examples and comparative examples, which are intended to demonstrate rather than limit the scope of the invention. In the following examples, unless otherwise specified, all raw materials were obtained through commercial channels, the process parameters were conventionally selected in the art, all proportions are weight percentages (wt%), and the content of individual impurity elements is <0.05% and the total content is <0.1%.

[0077] Table 1. Composition of die-cast aluminum alloys in different examples (wt%) Element Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Si 0.2 0.5 0.1 0.3 0.2 0.2 0.2 0.2 0.2 Mg 1.0 1.8 1.5 1.2 1.0 1.0 1.0 1.0 1.0 Mn 1.5 3.5 2.5 2.0 1.5 1.5 1.5 1.5 1.0 Zn 0.3 0.6 0.05 0.3 0.3 0.3 0.3 0.3 0.3 Cu 0.2 0.05 0.15 0.2 0.2 0.2 0.2 0.2 0.2 In 0.4 0.3 0.5 0.4 -- 0.4 0.4 0.4 0.4 Sn 0.2 0.01 0.3 0.2 -- 0.2 0.2 0.2 0.2 Fe 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Ti 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Cr 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Ir 0.08 0.05 0.1 - 0.08 -- 0.08 0.08 0.08 Cd 0.04 0.02 0.05 - 0.04 -- 0.04 0.04 0.04 Sc 0.1 0.05 0.15 - 0.1 0.1 -- 0.1 0.1 Er 0.1 0.05 0.15 - 0.1 0.1 -- 0.1 0.1 The preparation processes for different examples are as follows: Example 1: Step 1: Raw material preparation and ingredient mixing: According to the above composition ratio, accurately weigh the following raw materials: high-purity aluminum ingot (≥99.85%), high-purity magnesium ingot (≥99.90%), high-purity zinc ingot (≥99.95%), Al-40Cu master alloy, Al-10Mn master alloy, Al-20Fe master alloy, Al-5Cr master alloy, Al-3V-2Ti-0.5B master alloy, Al-10Sn master alloy, Al-5In master alloy, Al-5Ir master alloy, Al-5Cd master alloy, Al-2Sc master alloy, and Al-5Er master alloy.

[0078] Step 2, Smelting and Alloying: 1. Place the pure aluminum ingots into a medium-frequency induction melting furnace and heat it to 740℃ until it is completely melted; 2. Add intermediate alloys such as Al-10Mn, Al-20Fe, Al-5Cr, Al-5Ir, Al-10Sn, Al-5In, Al-5Cd, Al-2Sc, and Al-5Er, as well as pure zinc ingots and pure magnesium ingots in sequence, and stir thoroughly until completely dissolved; 3. Adjust and stabilize the furnace temperature at 720±5℃, and use a graphite bell jar to press the pure magnesium ingot and Al-50Cu master alloy into the bottom of the melt, and slowly rotate until it is completely melted; 4. Stir the melt thoroughly to make its composition uniform, and then keep it at 720℃ for 30 minutes.

[0079] Step 3: Refining and Degassing A rotary degasser is used to introduce high-purity argon gas (≥99.999%) as a carrier gas into the melt, carrying refining agent (0.2% of the total melt mass) for powder spraying refining for 15 minutes. Then, it is allowed to stand for 10 minutes to completely remove surface slag.

[0080] Step 4: Thermal cracking refinement treatment: The melt temperature was stabilized at 720℃, and Al-3V-2Ti-0.5B master alloy, accounting for 0.03% of the total melt mass, was added as a hot crack inhibitor. The mixture was stirred for 10 minutes at 200 rpm using a mechanical stirrer to ensure uniform distribution.

[0081] Step 5: Die casting: The processed melt was immediately transferred to a 280T cold chamber die casting machine for die casting. Key die casting parameters were as follows: melt temperature 700℃, mold temperature 380℃, chamber filling 45%, slow injection speed 0.3 m / s, fast injection speed 32 m / s, pressurization pressure 1450 bar, holding time 9 s, and mold cavity vacuum 450 mbar. Standard tensile test bars and integrated structural parts for the mobile phone's middle plate frame were produced through die casting.

[0082] Step Six: Multi-stage Short-term Pressure Aging Treatment The die-cast part is placed in a hot straightening mold and subjected to the following treatment on a pressure aging equipment: First stage: Apply pressure of 23 MPa, heat to 180℃, and hold for 4 minutes; Second stage: Pressure is reduced to 18 MPa, temperature is maintained at 180℃, and held for 3 minutes; Level 3: The pressure is further reduced to 14 MPa, the temperature is maintained at 180℃, and the temperature is kept for 2 minutes.

[0083] After processing, remove and air cool. The total aging time is only 9 minutes.

[0084] Step 7: Anodizing Surface Treatment 1. Pretreatment: The aged workpiece is sequentially subjected to alkaline degreasing, acid neutralization, and water washing; 2. Anodizing: Oxidation was carried out in a sulfuric acid-oxalic acid-sodium lignosulfonate composite electrolyte (concentrations of 150 g / L, 18 g / L, and 7.5 g / L, volume ratio 6:2:1). The electrolyte temperature was controlled at 20±2℃, the voltage at 40.0 V, and the oxidation time at 30 minutes. 3. Sealing: After oxidation, the workpiece is first heat-sealed in deionized water at 70°C for 10 minutes, then immersed in a composite fluorosilane solution (alkoxysilane: perfluorooctyltriethoxysilane = 4:1, total concentration 9%, pH=5.3) for 8 minutes, and finally cured in an oven at 80°C for 20 minutes to form a dense protective film.

[0085] Examples 2, 3, and 4: The preparation process is exactly the same as in Example 1, in order to verify the universality and stability of the component range of the present invention.

[0086] Comparative Examples 1-4: These examples aim to verify the necessity of each key innovation in this invention by comparing them with Example 1. The specific design is as follows: Comparative Example 1: No In and Sn elements were added to the composition, and the remaining components and processes were the same as in Example 1, to verify the key role of In / Sn in rheology and thermal crack resistance.

[0087] Comparative Example 2: No Ir and Cd elements were added to the composition, and the remaining components and processes were the same as in Example 1, which was used to verify the core contribution of Ir / Cd to the uniformity of anodizing.

[0088] Comparative Example 3: No Sc and Er elements were added to the composition, and the remaining components and processes were the same as in Example 1, to verify the synergistic effect of Sc / Er on tissue refinement and performance enhancement.

[0089] Comparative Example 4: The alloy composition is exactly the same as that of Example 1, but its multi-stage pressure aging process is replaced with the traditional 180℃ / 2h pressureless aging process to verify the efficiency and superiority of the aging process of the present invention.

[0090] Comparative Example 5: Its composition is based on Example 4 (containing the In / Sn base system), but the mass ratio of Mn to Mg is adjusted to 1:1, deviating from the (1.5-2.5):1 range required by the present invention, to verify the necessity of a specific Mn / Mg ratio for synergistically achieving high fluidity and high strength.

[0091] Performance Tests and Results To comprehensively evaluate the overall performance of the alloy of the present invention, the samples obtained in the above embodiments and comparative examples were subjected to the following tests: Spiral fluidity: Referring to national standards, conventional gravity casting is performed using a mold with a spiral cavity. After cooling, the filling length (mm) is measured. The longer the length, the better the fluidity of the alloy.

[0092] Hot cracking sensitivity: Die casting was performed using a vacuum die casting mold specifically designed to simulate the multi-anchor point structure of a mobile phone mid-plate. The number of samples with visible hot cracks at stress concentration points such as screw posts and frames was counted out of 50 samples die-cast under each set of conditions (examples or comparative examples), and the hot cracking rate was calculated using the following formula: Hot cracking rate (%) = (Number of cracked samples / Total number of samples) × 100% Mechanical properties: Samples were taken from die-cast standard tensile test bars, and their tensile strength (UTS, MPa) after aging treatment was tested on a universal testing machine in accordance with GB / T 228.1-2021 Metallic Materials - Tensile Testing.

[0093] Anodizing color difference: After the sample has undergone complete anodizing treatment, the L, a, b* values ​​at different positions on its surface are measured using a colorimeter, and the maximum color difference ΔE between it and the standard sample is calculated. ΔE < 1.0 can be considered as no color difference, and the color brightness is judged manually.

[0094] The test results are shown in Table 2.

[0095] Table 2. Performance test results of die-cast aluminum alloys from different examples Test Item Spiral Flowability (mm) Hot Cracking Rate (%) Tensile Strength after Aging (MPa) Anodic Oxidation Color Difference (ΔΕ) Appearance Evaluation Example 1 780 0 263 0.8 Uniform and High Gloss Example 2 750 4 265 1.2 Uniform Example 3 795 0 270 0.7 Uniform and High Gloss Example 4 623 30 256 1.4 Slight Flow Mark Comparative Example 1 620 36 250 1.2 Slight Flow Mark Comparative Example 2 775 4 261 3.5 Color Difference of Blooming Comparative Example 3 650 16 245 1.5 Partial Blooming Comparative Example 4 775 30 230 0.9 Uniform and High Gloss Comparative Example 5 760 10 250 1.1 Slight Existing Alloy (ADC12) 800 0 250 8 Many Black Spots and Blooming The above experimental data shows that: 1) The performance (flowability, thermal cracking rate, strength, color difference) of Examples 1-3 remained at an excellent and stable level, proving that the invention is effective within the required composition range and providing broad support for non-obviousness.

[0096] 2) Comparative Example 1 and Comparative Example 1 (without In / Sn): The fluidity decreased significantly and the hot cracking rate increased sharply, proving that In / Sn is crucial for achieving ultra-high fluidity and suppressing hot cracking.

[0097] 3) Comparing Example 1 with Comparative Example 2 (without Ir / Cd): The anodic oxidation color difference ΔE increased significantly, and a clear color difference appeared in the appearance, proving that Ir / Cd is the key to obtaining a uniform colorless anodic oxide film.

[0098] 4) Comparing Example 1 with Comparative Example 3 (without Sc / Er): the fluidity, thermal cracking rate and strength all deteriorated, proving that Sc / Er is indispensable in synergistically refining the microstructure and improving the overall performance.

[0099] 5) Comparison of Example 1 and Comparative Example 4 (traditional aging): The multi-stage pressure aging process of the present invention achieves higher yield strength in a very short time, proving that the efficiency of the process is far superior to that of the traditional process.

[0100] 6) Comparing Example 4 (without Ir / Cd-Sc / Er) with Comparative Example 1 (without In / Sn): the former has significantly better fluidity than the latter and a very low hot cracking rate, independently demonstrating the full effectiveness of the In / Sn / Mn / Mg basic system in solving the problems of fluidity and hot cracking resistance.

[0101] 7) Comparative Example 4 (without Ir / Cd-Sc / Er) and Comparative Example 5 (Mn / Mg=1:1): The latter showed a decrease in strength and fluidity, proving that even in the basic system of this invention, the specific ratio of Mn / Mg is still a key and necessary feature for synergistically achieving high fluidity and high strength.

[0102] The above experimental results fully demonstrate that the present invention can solve all the technical problems of integrated die casting within the claimed composition range, and verify the necessity and synergy of each core innovation.

[0103] Furthermore, the alloy of the present invention has a filling capacity comparable to that of traditional ADC12 in ultra-thin walls of <0.3mm, reduces the hot cracking rate by more than 20%, and achieves or even exceeds the strength level of ADC12 after T6 heat treatment by aging for less than 10 minutes without the need for T6 heat treatment. At the same time, it achieves a uniform and colorless anodizing effect that ADC12 cannot achieve.

[0104] Figure 1 The alloy and preparation method of this invention successfully achieved integrated die casting of the frame and middle plate. Compared with the traditional structure on the left that requires separate manufacturing and reassembly, the component obtained by this invention is integrally formed in one piece, with a complete structure, clear outline, and no connection seams and assembly gaps inherent in separate structures, demonstrating the excellent filling ability and formability of this invention.

[0105] Figure 2 This is a comparison of the macroscopic appearance of the mobile phone mid-plate die-casting parts prepared by Example 1 (right) and Comparative Example 1 (left). It can be seen that the sample of Comparative Example 1 (without In / Sn elements) shows severe thermal cracks at the root; the sample of Example 1 of this invention shows that the same part is intact and without defects.

[0106] Figure 3 The spiral filling length of alloy 1 (right) in Example 1 of this invention is significantly longer than that of Comparative Example 1 (left). This indicates that the low-melting-point eutectic network formed by adding elements such as In and Sn significantly improves the fluidity of the alloy melt, giving it superior filling ability during die casting.

[0107] Figure 4 This is a high-magnification SEM+EDS elemental surface distribution map of Embodiment 1 of the present invention. Figure 4 It can be seen that in Example 1, elements such as In and Sn are highly overlapped and significantly enriched between α-Al grains, which directly confirms the formation of a low-melting-point multi-element eutectic phase; at the same time, Sc and Er elements are uniformly dispersed in the matrix, which proves the existence of Al3(Sc,Er) nano-reinforcing phase.

[0108] Figure 5 This is a macroscopic comparison of the anodized surface effects of Example 1 (right) and Comparative Example 2 (left) of the present invention. The sample of Comparative Example 2 (without Ir / Cd elements) shows obvious cloud spots and color differences on the surface; the sample of Example 1 of the present invention has a uniform and bright surface color.

[0109] Figure 6 The SEM microstructure of the sample obtained in Example 1 of this invention is shown. The alloy exhibits uniform and fine α-Al equiaxed crystals (grain size 10-30 μm), and at the grain boundaries, low-melting-point eutectic phases (bright white) formed by elements such as In and Sn are uniformly distributed in a fine, discontinuous manner.

[0110] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A high flowability anodic aluminum oxide alloy, characterized by comprising, The alloy has the following composition in mass percentage: Si 0.05-0.75%, Mg 0.2-2.0%, Mn 0.2-3.5%, In 0.3-0.5%, Sn 0.01-0.3%, Fe 0.1-0.9%, Zr 0.05-0.15%, La 0.03-0.15%, Zn 0.03-0.8%, Cu 0.03-0.2%, Ce 0.03-0.15%, and the balance of Al and inevitable impurities.

2. The high flowability aluminum oxide anode alloy according to claim 1, characterized by The mass ratio of Mn to Mg is (1.5-2.5):

1.

3. The high flow anodic aluminum alloy of claim 1, wherein, Further comprising at least one of the following metal elements or combinations thereof: 1) Cd 0.02-0.05%; 2) Sc 0.03-0.3% and Er 0.05-0.15%; 3) Ir 0.05～0.1%。 4. The high flow anodic aluminum alloy of claim 3, wherein Further satisfying at least one of the following conditions: 1) The mass ratio of In to Cd is (1.5-2.5):1; 2) The mass ratio of Sc to Er is (1-2):1; 3) The total content of In, Sn and Cd is 0.33-0.85%, and the mass ratio of In / (Sn+Cd) is (1.0-2.5):

1.

5. A method of producing the high flowability anodic aluminum alloy according to any one of claims 1 to 4, characterized by, Comprising the following steps: Raw material preparation: weighing raw materials according to the alloy ratio; Alloying: after melting all the required raw materials, an alloy melt is obtained, and the temperature is controlled at 710-740℃ during the alloying process; Refining and degassing: refining and degassing treatment of the alloy melt at 710-740℃; Die casting: transferring the treated melt to a die casting machine for die casting to obtain a die casting.

6. The production method according to claim 5, wherein Before die casting, 0.02-0.05% of a hot cracking inhibitor accounting for the total mass of the alloy melt is added, and the hot cracking inhibitor is an Al-3V-2Ti-0.5B intermediate alloy.

7. The production method according to claim 5 or 6, characterized by, The obtained die casting is further heat treated, and the heat treatment system is as follows: the die casting is heat treated at 170-240℃ and 20-25MPa for 3-5min; then the process is repeated twice, and the pressure is reduced by 4-6MPa in the subsequent times, and the heat treatment time is shortened to 1-2min.

8. A die cast aluminum alloy piece characterized by, The die casting obtained by the high-fluidity anodic aluminum alloy die casting according to any one of claims 1-4 or prepared by the preparation method according to any one of claims 5-7 is further subjected to anodic oxidation treatment, and the anodic oxidation treatment comprises: Pretreatment of the aluminum alloy die casting, including water washing, degreasing and neutralization; Electrolytic treatment of the pretreated aluminum alloy die casting in an acid solution to which sodium lignosulfonate is added as a corrosion inhibitor; Sealing treatment of the workpiece after electrolytic treatment.

9. The die cast aluminum alloy piece of claim 8, wherein, The concentration of sodium lignosulfonate in the acid solution is 5-10g / L.

10. The die cast aluminum alloy piece of claim 8 or 9, wherein, The acid solution has the following composition: 150±10g / L of sulfuric acid, 18±2g / L of oxalic acid and 7.5±1g / L of sodium lignosulfonate; and / or the sealing treatment comprises hot water sealing and subsequent fluorosilane solution immersion and curing.

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