High-surface-quality die-casting aluminum alloy for thin-wall part and preparation method thereof

Abstract

The invention belongs to the field of new materials, and discloses a high-surface-quality die-casting aluminum alloy for a thin-wall part and a preparation method of the high-surface-quality die-casting aluminum alloy. The die-casting aluminum alloy is prepared from the following components in percentage by weight: 0.05 to 0.5 percent of Si, 0.1 to 0.8 percent of Mg, 0.8 to 3.2 percent of Mn, 0.05 to 0.5 percent of Zn, 0.01 to 0.25 percent of Cu, 0.3 to 0.5 percent of Bi, 0.1 to 0.3 percent of Sb, 0.1 to 0.6 percent of Fe, 0.03 to 0.15 percent of Yb, 0.01 to 0.03 percent of Y, 0.01 to 0.3 percent of Sc, 0.05 to 0.2 percent of Zr, 0.01 to 0.03 percent of Eu, 0.03 to 0.3 percent of Sr, 0.01 to 0.15 percent of La, 0.01 to 0.15 percent of Ce and the balance of Al and inevitable impurities. Through the synergistic effect of multi-element rare earth elements (Sc, Yb, Y and Eu) and Bi / Sb, the liquidity, the solidification behavior and the surface quality of the low-silicon aluminum alloy are remarkably improved, the flow line and hot crack defects are effectively restrained, meanwhile, the high mechanical property (the tensile strength is larger than or equal to 180 MPa, the yield strength is larger than or equal to 130 MPa, and the percentage elongation after fracture is larger than or equal to 8%) and the excellent anodic oxidation uniformity are achieved, and the low-silicon aluminum alloy has the good application prospect. The die-casting die is particularly suitable for die-casting forming of ultrathin-wall parts.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new materials, and particularly relates to a high-surface-quality die-casting aluminum alloy for thin-walled parts and a preparation method thereof. BACKGROUND

[0002] Aluminum alloy has become the first choice for complex thin-walled parts, such as notebook computer shells and internal structural parts, due to its excellent specific strength, thermal conductivity and good surface treatment performance. The die casting process provides an efficient and economical production way for realizing complex structure and thin-walled integrated molding. The mechanical properties of high-silicon system die-casting aluminum alloy are good, and the surface quality of die casting is high, but the congenital defect of darkening of anodic oxidation cannot be avoided. At present, the requirements for appearance and texture of consumer electronic products are increasingly strict, so that low-silicon (silicon content <0.5%) die-casting aluminum alloy capable of obtaining bright and uniform anodized film becomes an inevitable choice for high-end applications. However, when the low-silicon aluminum alloy is applied to large-size, ultra-thin-walled (0.8-1.6 mm) components such as notebook computers, the serious flow line defects have become the core technical bottleneck restricting the yield improvement.

[0003] The root cause of this problem lies in the inherent contradiction of material properties. First, in order to obtain excellent anodic oxidation surface quality, the silicon content must be reduced to a very low level, but this directly leads to insufficient strength of the alloy matrix. In order to make up for the strength defects, manganese, magnesium, copper, zinc and other strengthening elements must be added. However, the addition of these elements significantly changes the solidification characteristics of the alloy, often leading to decreased melt fluidity, increased viscosity, and expanded paste solidification interval. Or introduce a single rare earth element (such as Sc or Ce) for improvement, although it may have some benefits in certain aspects (such as grain refinement), but it cannot systematically and cooperatively regulate the core contradiction between paste zone liquid film shrinkage and smoothness of feeding channels, resulting in poor application effect on large thin-walled parts.

[0004] When filling notebook computer shells and other components with large projection areas and multiple chambers, the melt flow is long and the flow path is complex. When the low-silicon alloy melt flows through the thin-walled area, a very thin 'paste zone' is formed at the front of the melt. This paste zone has low strength and a wide interval. When the subsequent melt cannot effectively and continuously feed and fuse this area, the dendritic network in the paste zone will be pulled apart under thermal stress, forming microcracks. These microcracks are macroscopically manifested as permanent flow line marks on the surface of the component (see FIG. 1). Figure 1 Therefore, the key to solving the flow line problem lies in how to stabilize the liquid film at the solidification front and ensure its continuous fusion and feeding throughout the filling process.

[0005] It is particularly pointed out that such flow lines are not significant on small components such as mobile phone middle frames, but are particularly prominent on large thin-walled parts such as notebook computers. This is because the filling time required by large parts is longer, the heat loss of the melt is more serious, and the flow stability is more difficult to maintain. These flow line defects are clearly visible in the as-cast state, and are reduced after pretreatment such as polishing and sandblasting, but in the subsequent anodizing process, due to the difference in film growth rate and thickness between the defect area and the normal area, the flow lines will be amplified and even strengthened in the form of color difference, matte band or bright-dark stripes, ultimately resulting in unqualified product appearance.

[0006] The prior art mainly alleviates flow lines by optimizing die casting process parameters such as increasing mold temperature and injection speed, but the effect is limited and easy to cause other defects. Therefore, there is an urgent need in the art for a new alloy design scheme that can start from the material itself, fundamentally improve the melt flowability and inhibit the generation of flow lines while ensuring excellent anodizing performance of low-silicon aluminum alloys. The purpose of the present application is to solve this specific technical problem by innovative component design, and to provide a low-silicon die casting aluminum alloy solution with high surface quality, good mechanical properties and excellent filling capacity. SUMMARY

[0007] The purpose of the present application is to overcome at least one deficiency of the prior art and provide a high-surface-quality die-casting aluminum alloy for thin-walled parts and a preparation method thereof.

[0008] The technical scheme adopted by the present application is: In a first aspect, the present application provides: A high-surface-quality die-casting aluminum alloy for thin-walled parts, having a chemical mass composition of: Si 0.05-0.5 %, Mg 0.1-0.8 %, Mn 0.8-3.2 %, Zn 0.05-0.5 %, Cu 0.01-0.25 %, Bi 0.3-0.5 %, Sb 0.1-0.3 %, Fe 0.1-0.6 %, Yb 0.03-0.15 %, Y 0.01-0.03 %, Sc 0.01-0.3 %, Zr 0.05-0.2 %, Eu 0.01-0.03 %, Sr 0.03-0.3 %, La 0.01-0.15 %, Ce 0.01-0.15 %, and the balance being Al and unavoidable impurities.

[0009] In some examples, the individual content of the impurity elements is ≤0.05 %, and the total content is ≤0.1 %.

[0010] In a second aspect, the present application provides: The preparation method of the high-surface-quality die-casting aluminum alloy of the first aspect of the present application comprises the following steps: S1) Raw material preparation and melting: raw materials are prepared according to the alloy composition ratio, and the raw materials are melted, alloying is carried out at 710-740 ℃, and an alloy melt is obtained; S2) Refining and degassing: the alloy melt is subjected to refining and degassing treatment at 710-740 ℃, and the hydrogen content of the melt is controlled to be ≤0.12 ml / 100g Al; S3) Die casting: the treated melt is transferred to a die casting machine for die casting to obtain a die casting.

[0011] In some examples, in the step S2, 0.02-0.04% of nano Y2O3 particles based on the total mass of the melt are added to the melt, and the shear dispersion is uniform.

[0012] In some examples, during the die casting process, a three-stage speed curve is used for injection: low-speed filling in the initial stage, the speed is 0.2-0.3 m / s; medium-speed filling in the middle stage, the speed is 0.6-0.8 m / s; high-speed filling in the final stage, the speed is 1.2-1.5 m / s.

[0013] In some examples, during the die casting process, the injection pressure is 80-120 MPa.

[0014] In some examples, during the die casting process, the holding pressure is 60-80 MPa.

[0015] In some examples, during the die casting process, the vacuum degree of the mold cavity is reduced to 100-300 mbar through the mold vacuum system before and / or at the end of the melt filling.

[0016] In some examples, the die casting is subjected to T5 or T6 heat treatment.

[0017] In some examples, the T5 heat treatment system is: aging treatment at 180-220 ℃ for 4-10 hours; the T6 heat treatment system is: solid solution treatment at 510-520 ℃ for 2-3 hours, followed by water quenching or air cooling, and then aging treatment at 160-180 ℃ for 6-8 hours.

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

[0019] The third aspect of the application provides: A die-cast thin-wall part is prepared from the high-surface-quality die-cast aluminum alloy of the first aspect of the application, or is prepared by the preparation method of the second aspect of the application and is further subjected to anodic oxidation treatment.

[0020] In some examples, the wall thickness of the die-cast thin-wall part is not more than 2 mm.

[0021] In some examples, the wall thickness of the thin-walled die casting part is 0.8-1.6 mm.

[0022] In some examples, the thin-walled die casting part is an electronic product shell or skeleton structure.

[0023] The beneficial effects of the present application are: The high-surface-quality die casting aluminum alloy of some examples of the present application, by reasonably adjusting alloying elements, wherein the first functional group: "grain boundary and liquid film stabilizing group" (Sc-Yb-Y), the core goal of this group of elements is to strengthen the dendrite skeleton and liquid film strength at the end of solidification. The Sc-Yb-Y ternary combination realizes intracrystalline-grain boundary synergistic stabilization. Sc elements form Al3Sc nanoparticles that are coherent with the α-Al matrix, which acts as an efficient heterogeneous nucleation core at the early stage of solidification, greatly increasing the nucleation rate and obtaining ultra-fined equiaxed crystals. Fine grains mean a more developed grain boundary network, which is conducive to dispersing solidification shrinkage stress. Yb and Y elements mainly play a role in the interdendritic mushy zone, and the high-melting-point intermetallic phases (such as Al3Yb, Al3Y) formed by Yb and Y elements are enriched at the solid-liquid interface, which has a significant pinning and dragging effect on dendrite growth. This effect not only refines the secondary dendrite arms, but more importantly, it can significantly enhance the liquid film root structure strength, thereby resisting the tearing of the liquid film caused by solidification shrinkage and inhibiting the initiation of flow patterns and micro-cracks. More importantly, Y elements can change the morphology and distribution of impurity Fe phases by forming τ1-Al8Cu4Y phases. Yb and Sc can further form Al3(Sc, Yb, Y) multi-element composite phases with core-shell structure, which significantly suppresses grain boundary migration and grain growth. This multi-element combination forms a crack-resistant and surface quality improvement system superior to single or binary element addition through intracrystalline refinement, grain boundary strengthening, and phase structure stabilization. The second functional group: "mushy zone feeding behavior control group" (Eu-Bi-Sb), the core goal of this group of elements is to maintain the smoothness of the feeding channel under the premise of maintaining the stability of the liquid film. Eu and Bi / Sb combination precisely controls the mushy zone feeding behavior: the addition of Eu aims to control the phase composition at the end of solidification, and promote the formation of low-melting-point phases (such as Al2Eu). The phase adheres to the grain boundary to form a continuous liquid film, which is beneficial to the flow of liquid metal between dendrites and "heals" the micro-cracks formed. The addition of Bi and Sb elements aims to form low-melting-point eutectic phases such as Al-Bi and Al-Sb with the aluminum matrix. The essential role of these phases is to widen the solidification temperature range of the alloy and lower the solidification endpoint temperature. The three work together to form a multi-level feeding network that maintains the channel in a wide temperature range and precisely lubricates the end temperature with Eu, which enhances the filling capacity of the melt to micro-shrinkage.

[0024] The preparation method of the high surface quality die casting aluminum alloy of some examples of the present application introduces nano Y2O3 particles in the refining process, which plays a key role in optimizing the melt behavior and solidification structure, thereby synergistically improving the surface quality. On the one hand, the uniformly dispersed nano particles effectively increase the viscous resistance of the melt, which can stabilize the flow front and suppress turbulence and air entrapment during high-speed filling of die casting, thereby directly reducing the flow line defects. On the other hand, these high-melting-point nano particles are pushed to the interdendritic region during solidification, and through the strong pinning effect on dendrites and grain boundaries, the skeleton strength of the dendritic network at the end of solidification is significantly enhanced. This strengthening effect effectively suppresses the tearing and flow of liquid film under thermal stress, thereby reducing the tendency of hot cracking and laying the foundation for high surface quality.

[0025] The preparation method of the high surface quality die casting aluminum alloy of some examples of the present application uses a "low speed - medium speed - high speed" three-stage injection curve, which essentially controls the thermal field and flow field during the melt filling process. The low speed of the initial stage ensures that the melt advances with a smooth laminar flow interface, avoiding turbulent air entrapment; the high speed of the final stage provides sufficient kinetic energy for the thin-walled region which cools quickly, preventing cold shut caused by premature solidification of the melt front. The high vacuum environment completely eliminates the hindrance of gas to the continuous advancement of the solid-liquid interface, ensuring seamless filling of the melt, thereby obtaining high surface quality without flow lines. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the macroscopic (left) and microscopic (right) photographs of flow lines of a common low-silicon die casting aluminum alloy (ADC6 alloy).

[0027] Figure 2 is the appearance photograph of the die casting thin-walled part of Example 1 before anodic oxidation.

[0028] Figure 3 is the photograph of the die casting thin-walled part of the conventional low-silicon alloy (ADC6 alloy) (left) and Example 1 (right) after anodic oxidation treatment.

[0029] Figure 4 is the Sc / Yb, Y element distribution organization photograph of the die casting aluminum alloy of Example 1, which shows the coherent / hemi-coherent precipitation of Sc / Yb, Y in the intracrystalline and grain boundary, forming a composite phase.

[0030] Figure 5 is the segregation of Eu, Bi and Sb in the grain boundary of the die casting aluminum alloy of Example 1, which plays a function of paste-shaped zone feeding.

[0031] Figure 6 is the photograph of the die casting aluminum alloy of Example 1, in which nano Y2O3 particles are dragged and the flow lines are reduced, and it can be seen that the nano Y2O3 particles are pushed to the interdendritic region, which has a dragging and pinning effect on the dendrite growth. DETAILED DESCRIPTION

[0032] The first aspect of the present application provides: A high surface quality die casting aluminum alloy for thin-walled parts, having a chemical composition consisting of: Si 0.05-0.5 %, Mg 0.1-0.8 %, Mn 0.8-3.2 %, Zn 0.05-0.5 %, Cu 0.01-0.25 %, Bi 0.3-0.5 %, Sb 0.1-0.3 %, Fe 0.1-0.6 %, Yb 0.03-0.15 %, Y 0.01-0.03 %, Sc 0.01-0.3 %, Zr 0.05-0.2 %, Eu 0.01-0.03 %, Sr 0.03-0.3 %, La 0.01-0.15 %, Ce 0.01-0.15 %, and the balance being Al and inevitable impurities.

[0033] In some examples, the content of each of the impurity elements is ≤0.05 %, and the total content of all the impurity elements is ≤0.1 %. By controlling the amount of impurities, The second aspect of the present application provides: The preparation method of the high surface quality die casting aluminum alloy according to the first aspect of the present application comprises the following steps: S1) Raw material preparation and melting: raw materials are prepared according to the alloy composition ratio, and the raw materials are melted, alloying is performed at 710-740 ℃, and an alloy melt is obtained; S2) Refining and degassing: the alloy melt is subjected to refining and degassing treatment at 710-740 ℃, and the hydrogen content of the melt is controlled to be ≤0.12 ml / 100g Al; S3) Die casting forming: the treated melt is transferred to a die casting machine for die casting, and a die casting part is obtained.

[0034] In some examples, in the step S2, 0.02-0.04 % of nano Y2O3 particles based on the total mass of the melt are added to the melt and uniformly dispersed by shearing. The introduction of nano Y2O3 particles during the refining process can optimize the melt behavior and solidification structure, thereby synergistically improving the surface quality. On the one hand, the uniformly dispersed nano particles effectively increase the viscous resistance of the melt, which can stabilize the flow front, suppress turbulence and air entrainment during high-speed filling of die casting, and directly reduce the flow mark defects. On the other hand, these high-melting-point nano particles are pushed to the interdendritic region during solidification, and through the strong pinning effect on dendrites and grain boundaries, the skeleton strength of the dendritic network at the end of solidification is significantly enhanced. This strengthening effect effectively suppresses the tearing and flow of liquid film under thermal stress, thereby reducing the tendency of hot cracking and laying the foundation for high surface quality.

[0035] In some examples, in the process of die casting, a three-stage velocity curve is used for injection: low-speed filling in the initial stage, the speed is 0.2-0.3 m / s; medium-speed filling in the middle stage, the speed is 0.6-0.8 m / s; high-speed filling in the final stage, the speed is 1.2-1.5 m / s. In this way, the thermal field and flow field during the filling process of the melt can be better controlled. The low speed in the initial stage ensures that the melt advances with a smooth laminar interface, avoiding turbulent air entrainment; the high speed in the final stage provides sufficient kinetic energy for the thin-walled region which cools rapidly, preventing cold shut caused by premature solidification of the melt front.

[0036] In some examples, in the process of die casting, the injection pressure is 80-120 MPa. In this way, die casting can be better achieved, and the specific pressure can be adjusted according to the size, wall thickness, etc. of the casting to obtain the best effect.

[0037] In some examples, in the process of die casting, the holding pressure is 60-80 MPa. In this way, it is beneficial to obtain a higher quality die casting, and the specific pressure can be adjusted according to the size, wall thickness, etc. of the casting to obtain the best effect.

[0038] In some examples, in the process of die casting, the vacuum degree of the mold cavity is reduced to 100-300 mbar by the mold vacuum system before and / or at the end of the melt filling. Vacuum is beneficial to reduce the filling resistance and is beneficial to the melt filling to obtain a higher quality die casting.

[0039] In some examples, the die casting is subjected to T5 or T6 heat treatment. By performing T5 or T6 heat treatment, the plasticity, hardness, etc. of the die casting can be further adjusted to meet the needs of different application scenarios.

[0040] In some examples, the T5 heat treatment system is: aging treatment at 180-220℃ for 4-10 hours; the T6 heat treatment system is: solid solution treatment at 510-520℃ for 2-3 hours, followed by water quenching or air cooling, and then aging treatment at 160-180℃ for 6-8 hours.

[0041] The above features can be arbitrarily combined without conflict.

[0042] The third aspect of the present application provides: A die-cast thin-walled part is prepared from the high-surface-quality die-cast aluminum alloy of the first aspect of the present application or prepared by the preparation method of the second aspect of the present application and is further subjected to anodic oxidation treatment.

[0043] In some examples, the wall thickness of the die-cast thin-walled part is not more than 2 mm.

[0044] In some examples, the wall thickness of the die-cast thin-walled part is 0.8-1.6 mm.

[0045] In some examples, the die-cast thin-walled part is an electronic product shell or skeleton structure.

[0046] In some examples, the electronic product includes, but is not limited to, a notebook computer, a tablet computer, and the like.

[0047] The high-surface-quality die-cast aluminum alloy and the preparation method thereof according to the present application will be described in detail below in combination with examples and comparative examples. These examples are only used to more clearly explain the present application and are not used to limit the scope of the present application. Unless otherwise specified, the reagents and instruments used in the present application can be obtained through commercial channels.

[0048] The alloy compositions of different examples are shown in Table 1.

[0049] Table 1, Alloy mass composition (wt.%) of different examples

[0050] Note: The values in the table are percentages, the balance is Al and unavoidable impurities, the individual content of impurity elements is ≤0.05 wt.%, and the total content is ≤0.1 wt.%.

[0051] Preparation of die-cast alloys of Examples 1-3 and Comparative Examples 1-8 For the convenience of comparison, the preparation methods of the die-cast alloys of Examples 1-3 and Comparative Examples 1-8 are as follows: Prepare pure Al ingot, pure Mg ingot, pure Zn ingot, and Al-Cu, Al-Mn, Al-Fe, Al-Ti, Al-Sc, Al-Yb, Al-Y, Al-Eu, and other intermediate alloys according to the weight percentage shown in Table 1.

[0052] The preparation method includes the following steps: Alloy melting: melt the pure Al ingot completely in a melting furnace at 720°C and keep it for 2 hours. Then add all the raw materials except the pure Mg ingot, keep it at 720°C for 40 minutes to fully melt and homogenize. Keep the melt temperature at 720°C, press the pure Mg ingot into the bottom of the melt, and keep it for 20 minutes to completely dissolve.

[0053] Refining and modification: add 0.3% of refining agent based on the total mass of the melt to the melt for degassing refining, for 15 minutes. Then, add 0.03% of nano Y2O3 powder based on the total mass of the melt, and disperse it for 3 minutes using a high-speed mechanical shearing device (speed 1200 rpm).

[0054] Die casting: The treated melt was transferred to the die casting machine cylinder and die casting was carried out under vacuum assistance. The key process parameters were: mold temperature 220°C, three-stage injection was used: low speed (0.3 m / s) filling of the runner and sprue in the first stage, medium speed (0.7 m / s) switching filling in the second stage, high speed (1.3 m / s) filling of the cavity and pressurization in the last stage, injection pressure 100 MPa, and the mold cavity vacuum degree was controlled at 150 mbar.

[0055] Heat treatment: The die casting was solution treated at 515°C for 2.5 hours, then water quenched, and then aged at 170°C for 7 hours (T6 state).

[0056] Anodizing: The aluminum alloy die casting after pretreatment of water washing, degreasing, and neutralization was placed in an acid solution for anodizing, and finally, sealing treatment was carried out.

[0057] Example 4: The composition was the same as in Example 1.

[0058] The preparation method included the following steps: Alloy melting: The same as in Example 1.

[0059] Refining: 0.3% of a refining agent based on the total mass of the melt was added to the melt for degassing refining, which lasted for 15 minutes (Note: no nano Y2O3 powder was added in this step).

[0060] Die casting: The treated melt was transferred to the die casting machine cylinder and die casting was carried out. The key process parameters were: mold temperature 210°C, three-stage injection was used (low speed 0.25 m / s in the first stage, medium speed 0.7 m / s in the second stage, and high speed 1.4 m / s in the last stage), injection pressure 110 MPa, and the mold cavity vacuum degree was controlled at 200 mbar.

[0061] Heat treatment: The same as in Example 1.

[0062] Example 5: The composition was the same as in Example 1.

[0063] The preparation method included the following steps: Alloy melting: The same as in Example 1.

[0064] Refining and modification: 0.3% of a refining agent based on the total mass of the melt was added to the melt for degassing refining, which lasted for 15 minutes. Then, 0.03% of nano Y2O3 powder based on the total mass of the melt was added, and high-speed mechanical shearing device was used for dispersion for 3 minutes.

[0065] Die casting: The process parameters were the same as in Example 4.

[0066] Heat treatment: The same as in Example 1.

[0067] Example 6: The ingredients are the same as in Example 1.

[0068] In the preparation method, the parameters of the die casting step are adjusted as follows: mold temperature 230℃, three-stage injection is used: initial stage low speed 0.28 m / s, middle stage medium speed 0.65 m / s, final stage high speed 1.45 m / s, injection pressure 85 MPa, and the cavity vacuum degree is controlled at 100 mbar. The other steps are the same as in Example 5.

[0069] Performance detection Mechanical properties: standard tensile specimens are processed and tested according to GB / T 228.1 to obtain tensile strength, yield strength and elongation.

[0070] Fluidity: the length of the melt to fill the spiral flow channel is measured according to the standard test method for die casting spiral fluidity mold.

[0071] Surface quality (flow lines): after the die casting parts are uniformly sandblasted, two experienced inspectors evaluate the flow line defect grade under standard light source (1st best, 5th worst).

[0072] Hot cracking tendency: the die casting is carried out using the actual production mold of the die casting thin-walled part, the number of cracked parts found by appearance or non-destructive testing of 50 products is counted, and the hot cracking occurrence rate (%) is calculated.

[0073] The performance detection results of the alloys of different examples are shown in Table 2.

[0074] Table 2, performance detection results of alloys of different examples

[0075] According to the performance detection results in Table 2, it can be seen that: 1) The compositions of Example 2 and Example 3 are within the protection scope of the claims of the present application, and the performance data show that under different composition ratios, the alloy can still maintain high strength and low flow line defect grade, which proves the effectiveness and reliability of the composition design of the present application in a wide range.

[0076] 2) Comparing Example 1 with Comparative Example 1 (without rare earth), it can be seen that after the absence of key rare earth elements such as Sc, Yb, Y, Eu, etc., the mechanical properties and fluidity of the alloy are greatly reduced, and the flow lines and hot cracking tendency are rapidly deteriorated. This fully proves the indispensability of the rare earth combination of the present application for solving the core defects of low-silicon aluminum alloy.

[0077] 3) Comparative Example 1 vs. Comparative Example 2 (Yb out of range): When Yb content exceeds the range of the present application, although the strength is acceptable, the flow grade and hot cracking tendency are significantly deteriorated, proving that the elements need to be in a specific ratio to achieve the best synergistic effect, rather than simply adding them.

[0078] 4) Comparative Example 1 vs. Comparative Example 3 (without Bi / Sb): After the absence of Bi / Sb combination, the alloy flowability is significantly reduced, proving that it has an important contribution to improving the melt filling ability.

[0079] 5) Comparative Example 1 vs. Example 4 (same composition, but without Y2O3): Under the same composition and basic process, the alloy without the addition of nano Y2O3 particles has significantly higher flow defects and hot cracking incidence than Example 1 and Example 5 after the addition, proving that the introduction of nano Y2O3 can synergistically optimize the melt behavior and solidification structure, and is an effective means to further improve the surface quality and hot cracking resistance.

[0080] 6) Comparative Example 1, Example 5 and Example 6: (same composition, adjusting the die casting process parameters within the scope of the claims) Using the alloy composition of the present application, under different die casting process parameters within the scope of the claims, excellent comprehensive performance and high surface quality can be obtained, proving that the preparation method of the present application has a wide process window and good reliability, rather than being limited to a single parameter combination.

[0081] 7) Comparative Example 1 vs. Comparative Example 4 (Sc out of range): When the Sc content (0.40%) significantly exceeds the upper limit of the present application (0.3%), the alloy plasticity (elongation) drops sharply to 3.5%, and the hot cracking incidence is as high as 35%. This shows that excessive Sc can form coarse and brittle Al3Sc phases, severely damaging the toughness and hot cracking resistance of the material.

[0082] 8) Comparative Example 1 vs. Comparative Example 5 (Y out of range): When the Y content (0.05%) exceeds the range of the present application (0.01-0.03%), it also leads to deterioration of toughness and flowability, and exacerbates the tendency of surface flow and hot cracking, proving that the addition of Y needs to be precisely controlled within a specific low range.

[0083] 9) Comparative Example 1 vs. Comparative Examples 6 and 7 (Eu insufficient or out of range): Eu element plays a key role in lubrication in the present application. Comparative Example 6 (Eu 0.001%, <0.01%) shows a decrease in feeding ability and deterioration of flowability; Comparative Example 7 (Eu 0.10%, >0.03%) leads to coarsening of the structure, and deterioration of plasticity and surface quality. This proves that there is a narrow optimal window for Eu content, and performance will decrease significantly if it exceeds this window.

[0084] 10) Comparative Example 1 vs. Comparative Example 8 (Si is out of limit): Although the flowability is increased and the strength is slightly improved when Si is increased to 0.6%, the plasticity is severely damaged and the flow mark defect level is sharply increased to 4.0. This strongly proves that even if the Si upper limit of the present application is slightly exceeded (0.5%), the core purpose of "high surface quality" will be completely violated, black spots will be easily generated after anodizing, and the flow mark problem will become very serious.

[0085] Figure 2 is the appearance photo of the die-casting thin-wall part of Example 1 before anodizing, and it can be seen that the surface quality of the thin-wall part is high and there is no flow mark.

[0086] Figure 3 is the photo of the die-casting thin-wall parts of the conventional low-silicon alloy (ADC6 alloy) (left) and Example 1 (right) after the same anodizing treatment. It can be seen that the surface of the die-casting thin-wall part of the present application is uniform and bright after anodizing treatment, while the surface of the ADC6 alloy is relatively dull after anodizing treatment, and there are visible flow marks and color differences in different parts.

[0087] Figure 4 is the Sc / Yb, Y element distribution organization photo of the die-casting aluminum alloy of Example 1, and it can be seen that Sc / Yb, Y is co-grained / half-co-grained precipitated in the grain and the grain boundary to form a composite phase.

[0088] Figure 5 is the Eu, Bi and Sb segregation in the grain boundary of the die-casting aluminum alloy of Example 1, which plays the function of paste-shaped zone feeding.

[0089] Figure 6 is the photo of the nanometer Y2O3 dragging the grains and reducing the flow marks in Example 1, and it can be seen that the nanometer Y2O3 particles are pushed to the interdendritic regions, which have a dragging and pinning effect on the dendrite growth.

[0090] The above is a further detailed description of the present application, which cannot be regarded as a limitation on the specific implementation of the present application. For ordinary skilled persons in the technical field to which the present application belongs, simple deductions or replacements without departing from the concept of the present application are within the protection scope of the present application.

Claims

1. A high surface quality die cast aluminium alloy for thin walled parts, characterized in that, The chemical composition is: Si 0.05-0.5 %, Mg 0.1-0.8 %, Mn 0.8-3.2 %, Zn 0.05-0.5 %, Cu 0.01-0.25 %, Bi 0.3-0.5 %, Sb 0.1-0.3 %, Fe 0.1-0.6 %, Yb 0.03-0.15 %, Y 0.01-0.03 %, Sc 0.01-0.3 %, Zr 0.05-0.2 %, Eu 0.01-0.03 %, Sr 0.03-0.3 %, La 0.01-0.15 %, Ce 0.01-0.15 %, and the balance of Al and inevitable impurities.

2. The high surface quality die cast aluminum alloy of claim 1, wherein, The single content of the impurity elements is ≤0.05 %, and the total content is ≤0.1 %.

3. A process for the production of the high surface quality die cast aluminium alloy according to claim 1 or 2, characterized in that, The method comprises the following steps: S1) raw material preparation and melting: preparing raw materials according to the alloy component ratio, and melting the raw materials to obtain an alloy melt by alloying at 710-740 ℃; S2) refining and degassing: refining and degassing the alloy melt at 710-740 ℃, and controlling the hydrogen content of the melt to be ≤0.12 ml / 100g Al; S3) die casting: transferring the treated melt to a die casting machine for die casting to obtain a die casting.

4. The production method according to claim 3, characterized by, In the step S2, 0.02-0.04 % of nano Y2O3 particles based on the total mass of the melt is added to the melt and uniformly dispersed by shearing.

5. The preparation method according to claim 3, characterized in that, At least one of the following conditions is met during the die casting process: A three-stage velocity curve is used for injection: low-speed filling in the initial stage at a speed of 0.2-0.3 m / s; medium-speed filling in the middle stage at a speed of 0.6-0.8 m / s; and high-speed filling in the final stage at a speed of 1.2-1.5 m / s; The injection pressure is 80-120 MPa; The holding pressure is 60-80 MPa; Before and / or at the end of melt filling, the vacuum degree of the mold cavity is reduced to 100-300 mbar by the mold vacuum system.

6. The method of any one of claims 3 to 5, wherein the method further comprises, The die casting is subjected to T5 or T6 heat treatment.

7. The preparation method according to claim 6, characterized in that, The T5 heat treatment system is: aging treatment at 180-220 ℃ for 4-10 hours; and the T6 heat treatment system is: solid solution treatment at 510-520 ℃ for 2-3 hours, followed by water quenching or air cooling, and then aging treatment at 160-180 ℃ for 6-8 hours.

8. A thin-walled die cast component, characterised in that, The die casting obtained by the high-surface-quality die casting aluminum alloy of claim 1 or 2, or prepared by the preparation method of any one of claims 3-7, is further subjected to anodic oxidation treatment.

9. The thin-walled die cast part according to claim 8, characterized in that The wall thickness is not more than 2 mm.

10. Thin-walled die cast part according to claim 8 or 9, characterized in that The die casting thin-walled part is an electronic product shell or skeleton structure.

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