A heat-resistant and dimensionally stable Al-Mg-Si alloy and its preparation method

Abstract

The application discloses an Al-Mg-Si alloy with good heat resistance and size stability, and the alloy is composed of the following components in percentage by mass: Mg 0.6-1.2%, Mn 0.3-0.5%, Si 0.5-0.9%, Cu 0.1-0.15%, Cr 0.15-0.2%, Zn 0.1-0.2%, Ti 0.10-0.15%, Sc 0.05-0.25%, Hf 0.05-0.25%, Bi 0.6-1.5%, and the balance of Al and inevitable impurity elements. The Al-Mg-Si alloy of some examples of the application can avoid the increase of electron scattering caused by the solid solution of Si and Fe elements in the matrix by adjusting the content of Mg and Si elements, and is beneficial to the improvement of the heat conduction performance of the alloy; the alloy contains Sc and Hf rare earth elements, so that the heat conduction performance and heat resistance of the alloy are improved; a small amount of Bi element is further added, so that the expansion of the alloy at a higher temperature is reduced, and the size stability of the alloy is improved; and the alloy is subjected to a stabilization treatment, so that the microstructure of the alloy is effectively stabilized, and the macroscopic residual stress of the hot extruded profile is obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy materials technology, specifically to an Al-Mg-Si alloy with good heat resistance and dimensional stability, and its preparation method. Background Technology

[0002] Energy shortages and environmental crises have spurred global innovation in automotive technology, driving the rapid development of new energy technologies, particularly electric vehicles. The core components of new energy vehicles are the motor, battery, and electronic control system, with the motor playing a crucial role in converting electrical energy into mechanical energy to propel the vehicle. Breakthroughs in motor technology are constraining the development of the next generation of new energy vehicles. The operation of motors in new energy vehicles generates a significant amount of heat, requiring motor materials with high thermal conductivity. Furthermore, to reduce vehicle weight and energy consumption, motor materials must also be lightweight and easily processed.

[0003] Aluminum alloys, with their low density, high specific strength, ease of processing, and good thermal conductivity, are ideal materials for motor housings and end caps. However, with the increasing mileage and maximum speed of new energy vehicles, the heat generated during motor operation is increasing. Conventional aluminum alloy motor housings are cast from Al-Si alloys, with a thermal conductivity not exceeding 120 W / (m·K), poor heat resistance, and low mechanical properties, making them prone to dimensional changes during long-term service, affecting the fit and sealing of motor components. Therefore, there is an urgent need for a motor material with high heat resistance and good dimensional stability.

[0004] Al-Mg-Si alloys are typical heat-treatable aluminum alloys, possessing advantages such as light weight, high heat dissipation, corrosion resistance, and adaptability to various processing methods. They are widely used in the automotive, architectural decoration, and electronic components industries. Al-Mg-Si alloys exhibit excellent processing properties and can be used to manufacture motor housings through hot extrusion. Al-Mg-Si alloy motor housings prepared by extrusion molding are lightweight, low-cost, energy-saving, environmentally friendly, and highly efficient, offering broad market prospects. However, extruded Al-Mg-Si alloy motor housings often have significant residual stress, which can easily lead to dimensional changes due to stress release during operation. Furthermore, due to the large coefficient of linear expansion of aluminum, temperature rise during the operation of high-speed aluminum motors can also easily cause dimensional changes and performance degradation. Therefore, controlling the microstructure of Al-Mg-Si alloys to maximize heat resistance is crucial to effectively ensure the stability of the alloy's dimensional and mechanical properties.

[0005] Dimensional stability is related to residual stress and microstructure. The presence of residual stress can induce plastic deformation in the alloy, affecting the precision of the parts. Reducing residual stress in the motor housing can be achieved through high-temperature heat treatment, but this results in a decrease in mechanical properties; therefore, a special stabilization process is required. Furthermore, the addition of appropriate alloying elements can precipitate a second phase that resists coarsening. This second phase can strengthen the alloy matrix and improve the alloy's heat resistance. Therefore, it is necessary to adjust the alloy composition and add microalloying elements to control the precipitated phases in the alloy to obtain an aluminum alloy motor housing with good heat resistance, high dimensional stability, and excellent mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one deficiency of the prior art and provide an Al-Mg-Si alloy with good heat resistance and dimensional stability, and a method for preparing the same.

[0007] The technical solution adopted in this invention is:

[0008] In a first aspect, the present invention provides an Al-Mg-Si alloy with good heat resistance and dimensional stability, wherein the alloy composition, by mass percentage, is: Mg 0.6-1.2%, Mn 0.3-0.5%, Si 0.5-0.9%, Cu 0.1-0.15%, Cr 0.15-0.2%, Zn 0.1-0.2%, Ti 0.10-0.15%, Sc 0.05-0.25%, Hf 0.05-0.25%, Bi 0.6-1.5%, with the balance being Al and unavoidable impurity elements.

[0009] In some instances, the Mg / Si mass ratio is 1.3 to 1.4.

[0010] In some instances, the sum of the masses of Sc and Hf is 0.2% to 0.4% by mass percentage.

[0011] In some instances, the mass ratio of Sc to Hf is 1:0.9 to 1:1.1.

[0012] In some instances, the mass ratio of Sc to Hf is 1.

[0013] In some instances, the content of the unavoidable impurity elements is ≤0.1% by mass percentage.

[0014] Secondly, the method for preparing the Al-Mg-Si alloy provided in the first aspect of this invention includes the following steps:

[0015] 1) Weigh the raw materials of each element according to the proportion, clean them thoroughly, and preheat and dry them;

[0016] 2) Melting and casting: Melt the preheated raw material in step 1) at 750-760℃. After melting, remove the slag and stir evenly. Then refine it at 730-740℃ in an oxygen-free environment. After removing the slag, let it stand for 20-30 minutes and cast it to obtain the alloy ingot.

[0017] 3) Heat the alloy ingot obtained in step 2) to 480-500℃, hold for 40-60 minutes, extrude and heat treat to obtain the profile;

[0018] 4) The profile obtained in step 3) is pre-expanded by 2-8%, and then subjected to cyclic stabilization treatment 3-5 times to obtain the Al-Mg-Si alloy.

[0019] In some instances, the stabilization treatment involves treating the pre-expanded profile at 155–170°C for 2–3 hours and then with liquid nitrogen for 20–35 minutes.

[0020] In some instances, the heat treatment in step 3) is as follows: heating to 520–540°C and holding for 1–1.5 hours, cooling at 70–90°C, and then holding at 300–350°C for 6–8 hours.

[0021] Thirdly, the application of the Al-Mg-Si alloy provided in the first aspect of this invention in the preparation of motor housings.

[0022] The beneficial effects of this invention are:

[0023] In some examples of the Al-Mg-Si alloys of this invention, by adjusting the content of Mg and Si elements and controlling the Mg / Si mass ratio to 1.3–1.4, a slight excess of Si is achieved, while Mg promotes the aging precipitation of the Mg₂Si phase. The lattice distortion caused by alloying elements dissolving in the matrix can lead to electron scattering, but precipitation in the form of the Mg₂Si phase helps to reduce electron scattering and improve the thermal conductivity of the alloy. Furthermore, with the Mg / Si mass ratio controlled within the range of 1.3–1.4, the alloy has only a trace excess of Si. This trace excess Si can form a phase with the impurity element Fe and dispersed in the aluminum matrix, avoiding the increased electron scattering caused by Si and Fe elements dissolving in the matrix, thus improving the thermal conductivity of the alloy.

[0024] Some examples of the Al-Mg-Si alloys of this invention contain Sc and Hf rare earth elements, with a total mass ratio of 0.2% to 0.4%, and Sc and Hf are in equal amounts. The addition of equiproportional Sc and Hf elements can, on the one hand, refine the grain size, reduce the segregation of alloying elements, reduce the scattering of electrons by alloying elements, and increase the mean free path of electrons, thereby improving the thermal conductivity of the alloy. On the other hand, during subsequent heat treatment, the alloy will precipitate coherently dispersed nano-Al3(Sc,Hf) phases. These nano-Al3(Sc,Hf) phases have a low coarsening rate and a significant strengthening effect, continuing to strengthen the alloy even when the motor housing temperature rises, thus improving the alloy's heat resistance. Furthermore, the nano-Al3(Sc,Hf) phases can hinder grain boundary migration, pin dislocations, and stabilize the alloy microstructure, thereby significantly improving the dimensional stability of the alloy.

[0025] In some examples of the Al-Mg-Si alloys of this invention, a small amount of Bi element is added, which can reduce the expansion of the alloy at higher temperatures and improve the dimensional stability of the alloy. Bi is a low-melting-point metallic element with a melting point of 271°C and a negative coefficient of volume shrinkage, indicating that Bi will shrink in volume as the temperature rises. After microalloying Bi element, Bi is mainly distributed as a pure Bi phase at the grain boundaries. When the alloy temperature rises, the Bi phase at the grain boundaries undergoes volume shrinkage. This special property offsets part of the volume expansion of Al grains at high temperatures, thereby promoting the dimensional stability of the alloy. At the same time, since Bi has low solid solubility in Al and hardly changes significantly with temperature, the Bi phase at the grain boundaries is very stable during the alloy temperature rise process and will not dissolve into the matrix, which can stabilize the mechanical properties of the alloy.

[0026] In some examples of the Al-Mg-Si alloys of this invention, a stabilization treatment was employed, which effectively stabilized the alloy microstructure and significantly reduced the macroscopic residual stress in the hot-extruded profiles. During the stabilization treatment, the precipitation of the second phase and the movement of dislocations occur simultaneously. During liquid nitrogen cryogenic treatment, atomic clusters are "frozen," while during heating and holding, atoms diffuse rapidly, causing larger atomic clusters to decompose into more numerous and smaller clusters. Ultimately, the alloy matrix contains a relatively fine and dispersed β′-Mg2Si phase. The reduced size and dispersed distribution of the precipitated phase are beneficial to improving the mechanical properties of the alloy. In addition, this special stabilization treatment generates thermal mismatch stress, which can promote the formation of stable dislocation cell structures through dislocation entanglement. It can also superimpose with residual stress to induce plastic deformation and release residual stress, thereby increasing the dimensional stability of the alloy.

[0027] The Al-Mg-Si alloys of some examples of this invention have a yield strength of 275–291 MPa, a tensile strength of 326–368 MPa at room temperature, a thermal conductivity of not less than 188 W / (m·K), and a dimensional change of less than 2.1‰ after 100℃ / 80h. This alloy exhibits excellent heat resistance while also possessing good mechanical properties and dimensional stability, making it suitable for use as a high-performance precision motor housing. Attached Figure Description

[0028] Figure 1 This is a scanning electron microscope image of the Al-Mg-Si alloy prepared in Example 3.

[0029] Figure 2 This is a physical image of the Al-Mg-Si alloy profile prepared in Example 3. Detailed Implementation

[0030] The following disclosure provides many different implementations or examples for different ways of implementing the present invention.

[0031] Based on the mass percentage of elements, the alloy chemical composition in each embodiment is as follows: Mg 0.6–1.2%, Mn 0.3–0.5%, Si 0.5–0.9%, Cu 0.1–0.15%, Cr 0.15–0.2%, Zn 0.1–0.2%, Ti 0.10–0.15%, Sc 0.05–0.25%, Hf 0.05–0.25%, Bi 0.6–1.5%, with unavoidable impurity elements ≤0.1%, and the balance being Al.

[0032] The raw materials selected are industrial pure Al, Mg, Zn ingots and pure Bi particles, as well as Al-10Mn, Al-20Si, Al-50Cu, Al-5Cr, Al-5Ti, Al-2Sc and Al-5Hf master alloys.

[0033] Unless otherwise specified, all instruments, equipment and raw materials involved in the following embodiments and comparative examples can be obtained from legitimate commercial channels.

[0034] Unless otherwise specified, the experimental and testing methods used in the following examples and comparative examples are conventional experimental and testing methods in the prior art. Specifically, the room temperature tensile test was performed according to GB / T228.1-2010, the thermal conductivity test according to GB / T10294-2008, and the dimensional stability test according to GB / T41739-2022. In all the following examples, the impurity content does not exceed 0.1 wt%.

[0035] Example 1

[0036] S1) According to the weight percentage of the constituent elements, take Mg: 0.8%, Mn: 0.35%, Si: 0.6%, Cu: 0.1%, Cr: 0.15%, Zn: 0.1%, Ti: 0.10%, Sc: 0.15%, Hf: 0.15%, Bi: 0.75%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0037] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 750°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 735°C. After slag removal, the material is allowed to stand for 20 minutes and then semi-continuously cast to obtain an alloy ingot.

[0038] S3) Extrusion molding: The prepared alloy ingot is heated to 495℃ and held for 50 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 28 mm and an extrusion ratio of 46.

[0039] S4) Heat treatment: Heat the hot-extruded profile to 530℃ and hold for 1 hour, then water cool at 80℃ and hold at 315℃ for 6.5 hours;

[0040] S5) Stabilization treatment: After pre-expansion of 4%, stabilization treatment is carried out at 170℃ for 2 h and liquid nitrogen for 20 min, with 3 cycles.

[0041] Example 2

[0042] S1) According to the weight percentage of the constituent elements, take Mg: 0.95%, Mn: 0.3%, Si: 0.7%, Cu: 0.1%, Cr: 0.15%, Zn: 0.15%, Ti: 0.10%, Sc: 0.2%, Hf: 0.2%, Bi: 1%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0043] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 755℃. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 730℃. After slag removal, the material is allowed to stand for 25 minutes and then semi-continuously cast to obtain an alloy ingot.

[0044] S3) Extrusion molding: The prepared alloy ingot is heated to 480℃ and held for 60 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 30 mm and an extrusion ratio of 45.

[0045] S4) Heat treatment: Heat the hot-extruded profile to 520℃ and hold for 1.5h, then water cool at 90℃ and hold at 300℃ for 8h.

[0046] S5) Stabilization treatment: After pre-expansion of 6%, stabilization treatment is carried out at 155℃ for 3 hours and liquid nitrogen for 35 minutes, with 5 cycles.

[0047] Example 3

[0048] S1) According to the weight percentage of the constituent elements, take Mg: 1.2%, Mn: 0.4%, Si: 0.9%, Cu: 0.15%, Cr: 0.18%, Zn: 0.1%, Ti: 0.10%, Sc: 0.15%, Hf: 0.15%, Bi: 1.5%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0049] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 760°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 740°C. After slag removal, the material is allowed to stand for 20 minutes and then semi-continuously cast to obtain an alloy ingot.

[0050] S3) Extrusion molding: The prepared alloy ingot is heated to 500℃ and held for 40 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 28 mm and an extrusion ratio of 48.

[0051] S4) Heat treatment: Heat the hot-extruded profile to 540℃ and hold for 1 hour, then cool it with water at 70℃ and hold it at 350℃ for 6 hours.

[0052] S5) Stabilization treatment: After pre-expansion by 2%, stabilization treatment is carried out at 160℃ for 2.5h and liquid nitrogen for 25min, with a cycle of 4 times.

[0053] Example 4

[0054] S1) According to the weight percentage of the constituent elements, take Mg: 0.9%, Mn: 0.35%, Si: 0.65%, Cu: 0.1%, Cr: 0.15%, Zn: 0.1%, Ti: 0.15%, Sc: 0.25%, Hf: 0.25%, Bi: 0.6%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0055] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 755℃. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas at 735℃. After slag removal, the mixture is allowed to stand for 30 minutes, and then semi-continuous casting is used to obtain alloy ingots.

[0056] S3) Extrusion molding: The prepared alloy ingot is heated to 495℃ and held for 50 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 30 mm and an extrusion ratio of 50.

[0057] S4) Heat treatment: Heat the hot-extruded profile to 535℃ and hold for 1 hour, then cool it with water at 85℃ and hold it at 330℃ for 7 hours.

[0058] S5) Stabilization treatment: After pre-expansion of 8%, stabilization treatment is carried out at 170℃ for 2 hours and liquid nitrogen for 30 minutes, with 3 cycles.

[0059] Example 5

[0060] S1) According to the weight percentage of the constituent elements, take Mg: 0.75%, Mn: 0.4%, Si: 0.55%, Cu: 0.1%, Cr: 0.2%, Zn: 0.15%, Ti: 0.15%, Sc: 0.1%, Hf: 0.1%, Bi: 1.2%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0061] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 750°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 735°C. After slag removal, the material is allowed to stand for 25 minutes and then semi-continuously cast to obtain an alloy ingot.

[0062] S3) Extrusion molding: The prepared alloy ingot is heated to 490℃ and held for 55 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 29 mm and an extrusion ratio of 52.

[0063] S4) Heat treatment: Heat the hot-extruded profile to 525℃ and hold for 1 hour, then water cool at 75℃ and hold at 310℃ for 7.5 hours.

[0064] S5) Stabilization treatment: After pre-expansion of 5%, stabilization treatment is carried out at 165℃ for 2.5h and liquid nitrogen for 25min, with a cycle of 4 times.

[0065] Comparative Example 1

[0066] S1) According to the weight percentage of the constituent elements, take Mg: 1.2%, Mn: 0.35%, Si: 0.6%, Cu: 0.1%, Cr: 0.15%, Zn: 0.15%, Ti: 0.15%, and the balance is Al; first clean the raw materials and place them in a drying oven for preheating;

[0067] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 750°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 735°C. After slag removal, the material is allowed to stand for 25 minutes and then semi-continuously cast to obtain an alloy ingot.

[0068] S3) Extrusion molding: The prepared alloy ingot is heated to 495℃ and held for 50 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 28 mm and an extrusion ratio of 46.

[0069] S4) Heat treatment: Heat the hot-extruded profile to 530℃ and hold for 1 hour, then cool it with water at 80℃ and hold it at 315℃ for 6 hours.

[0070] S5) Stabilization treatment: After pre-expansion of 6%, stabilization treatment is carried out at 155℃ for 3 hours and liquid nitrogen for 35 minutes, with 5 cycles.

[0071] Comparative Example 2

[0072] S1) According to the weight percentage of the constituent elements, take Mg: 0.67%, Mn: 0.35%, Si: 0.5%, Cu: 0.15%, Cr: 0.2%, Zn: 0.2%, Ti: 0.1%, Sc: 0.2%, Hf: 0.1%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0073] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 755℃. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 740℃. After slag removal, the material is allowed to stand for 20 minutes and then semi-continuously cast to obtain an alloy ingot.

[0074] S3) Extrusion molding: The prepared alloy ingot is heated to 485℃ and held for 55 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 30 mm and an extrusion ratio of 48.

[0075] S4) Heat treatment: Heat the hot-extruded profile to 520℃ and hold for 1.5h, then water cool at 90℃ and hold at 300℃ for 8h.

[0076] S5) Stabilization treatment: After pre-expansion by 2%, stabilization treatment is carried out at 160℃ for 2.5h and liquid nitrogen for 25min, with a cycle of 4 times.

[0077] Comparative Example 3

[0078] S1) According to the weight percentage of the constituent elements, take Mg: 0.85%, Mn: 0.3%, Si: 0.62%, Cu: 0.15%, Cr: 0.15%, Zn: 0.2%, Ti: 0.15%, Sc: 0.2%, Hf: 0.2%, Bi: 0.6%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0079] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 760°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 730°C. After slag removal, the material is allowed to stand for 30 minutes and then semi-continuously cast to obtain an alloy ingot.

[0080] S3) Extrusion molding: The prepared alloy ingot is heated to 500℃ and held for 40 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 29 mm and an extrusion ratio of 52.

[0081] S4) Heat treatment: Heat the hot-extruded profile to 540℃ and hold for 1 hour, then cool it with water at 70℃ and hold it at 350℃ for 6 hours.

[0082] S5) Stabilization treatment: After pre-expansion of 4%, stabilization treatment is carried out at 170℃ for 2 h and liquid nitrogen for 20 min, with 3 cycles.

[0083] Comparative Example 4

[0084] S1) According to the weight percentage of the constituent elements, take Mg: 1.1%, Mn: 0.45%, Si: 0.8%, Cu: 0.12%, Cr: 0.18%, Zn: 0.16%, Ti: 0.12%, Sc: 0.15%, Hf: 0.15%, Bi: 1%, with the balance being Al; first clean the raw materials and place them in a drying oven for preheating;

[0085] S2) The preheated raw material is placed in a graphite crucible in a melting furnace and melted at a melting temperature of 750°C. After the melting is completed, the slag is removed and the mixture is stirred evenly. Dry high-purity argon gas is used to refine and degas the material at 735°C. After slag removal, the material is allowed to stand for 25 minutes and then semi-continuously cast to obtain an alloy ingot.

[0086] S3) Extrusion molding: The prepared alloy ingot is heated to 490℃ and held for 45 min; a profile with an outer diameter of 170 mm is hot extruded using a hot extrusion bar with a diameter of 30 mm and an extrusion ratio of 45.

[0087] S4) Heat treatment: The hot-extruded profile is heated to 525℃ and held for 1 hour, then water-cooled at 80℃ and held at 325℃ for 7 hours; then it undergoes aging heat treatment, which involves heating to 170℃ and holding for 10 hours.

[0088] Room temperature tensile tests, thermal conductivity tests, and dimensional stability tests were conducted on the Al-Mg-Si alloys prepared in Examples 1-5 and Comparative Examples 1-4 according to GB / T 228.1-2010, GB / T10294-2008, and GB / T41739-2022 standards. The performance test results are shown in Table 1 below.

[0089] Table 1

[0090]

[0091] As shown in Table 1, the room-temperature mechanical properties, thermal conductivity, and dimensional stability of the Al-Mg-Si alloys prepared in Examples 1-5 are significantly improved compared to the comparative examples. Controlling the Mg / Si ratio within the range of 1.3-1.4 promotes the precipitation of the Mg2Si phase and reduces the influence of impurity elements on electron scattering, thereby improving the thermal conductivity and mechanical properties of the alloy.

[0092] The addition of equal proportions of Sc and Hf elements to the alloy resulted in the precipitation of fine, coherent Al3(Sc,Hf) phases, which hindered dislocation movement and grain boundary migration, leading to high strength and dimensional stability of the alloy even at higher temperatures. Furthermore, the added Bi element has a negative volume shrinkage coefficient and exhibits the unique property of thermal expansion and contraction, offsetting some of the volume expansion of Al grains at higher temperatures and contributing to the dimensional stability of the alloy.

[0093] In the other examples and comparative examples, the Al-Mg-Si alloys prepared underwent stabilization treatment compared to Comparative Example 4, which promoted the dispersed precipitation of fine Mg2Si phases, adjusted the dislocation configuration, significantly reduced the residual stress of the extruded profiles, and thus enhanced the dimensional stability of the alloy.

[0094] Figure 1 These are scanning electron microscope (SEM) images of the Al-Mg-Si alloy prepared in Example 3. From... Figure 1 As can be seen, recrystallization has occurred in the alloy's microstructure, and the recrystallized grains are uniformly distributed in size, with no abnormal grain growth. Fine-grained Bi phases are clearly distributed at the grain boundaries, while there are no obvious coarse secondary phases within the grains. These Bi phases undergo volume shrinkage when the alloy is heated, thereby compensating for the volume expansion of the grains and improving the dimensional stability of the alloy.

[0095] Figure 2 This is a photograph of the Al-Mg-Si alloy profile prepared in Example 3. From... Figure 2As can be seen, the Al-Mg-Si alloy motor housing obtained by the above preparation method has a complete shape, without obvious bending or collapse, and has good surface quality. The microstructure of the Al-Mg-Si alloy motor housing contains Bi phase to compensate for volume expansion and heat-resistant nano-Al3(Sc,Hf) phase. After cyclic stabilization treatment, the macroscopic residual stress is significantly reduced, and it has good heat resistance and dimensional stability.

[0096] 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. An Al-Mg-Si alloy with good dimensional stability at high temperature, characterized in that the alloy comprises, in mass percentage: Mg 0.6-1.2%, Mn 0.3-0.5%, Si 0.5-0.9%, Cu 0.1-0.15%, Cr 0.15-0.2%, Zn 0.1-0.2%, Ti 0.10-0.15%, Sc 0.05-0.25%, Hf 0.05-0.25%, Bi 0.6-1.5%, the balance being Al and unavoidable impurities, the mass ratio of Mg / Si being 1.3-1.4, the mass sum of Sc and Hf being 0.2-0.4%, and the mass ratio of Sc and Hf being 1:0.9-1. 1.1, a preparation method comprising the following steps: 1) proportionally weighing raw materials of each element, cleaning and preheating and drying; 2) smelting and casting: melting the preheated raw materials of step 1) at 750-760 ℃, after completion, removing slag and stirring uniformly, then refining at 730-740 ℃ in an oxygen-free environment, after removing slag, standing for 20-30 min, and casting to obtain an alloy ingot; 3) heating the alloy ingot obtained in step 2) to 480-500 ℃, holding for 40-60 min, extruding and forming, and then heat treating to obtain a profile, the heat treatment being: heating to 520-540 ℃, holding for 1-1.5 h, cooling at 70-90 ℃, and then holding at 300-350 ℃ for 6-8 h; 4) pre-expanding the profile obtained in step 3) by 2-8%, and then performing cyclic stabilization treatment for 3-5 times to obtain the Al-Mg-Si alloy, the stabilization treatment being: treating the pre-expanded profile at 155-170 ℃ / 2-3 h and liquid nitrogen / 20-35 min.

2. The Al-Mg-Si alloy according to claim 1, characterized in that The mass ratio of Sc and Hf is 1.

3. The Al-Mg-Si alloy according to claim 1, characterized in that The content of the inevitable impurity elements is ≤0.1% in mass percentage.

4. Use of the Al-Mg-Si alloy according to any one of claims 1-3 in the preparation of a motor shell.

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