Die-cast magnesium alloy and preparation method and application thereof

Abstract

This invention relates to the field of metal casting, specifically to a die-cast magnesium alloy, its preparation method, and its applications. The die-cast magnesium alloy, by mass percentage, comprises the following components: Al 4.5wt%~5.5wt%, Mn 0.3wt%~0.6wt%, La 4.5wt%~5.5wt%, Zn 0.8wt%~1.2wt%, and Ti 0.01wt%~0.1wt%, with the balance being Mg and unavoidable impurities. The die-cast magnesium alloy exhibits synergistic effects through a specific ratio of Al, Mn, La, Zn, Ti, and Mg, possessing excellent tensile properties, corrosion resistance, and high-temperature creep resistance. Compared to traditional die-cast magnesium alloys such as AM50 and AZ91D, it possesses outstanding comprehensive performance advantages and can meet the comprehensive performance requirements of high-strength, heat-resistant components such as automotive gearbox housings and electric drive housings.

Description

Technical Field

[0001] This invention relates to the field of metal casting, and more specifically, to a die-cast magnesium alloy, its preparation method, and its application. Background Technology

[0002] Magnesium alloys are among the lightest metallic structural materials, possessing advantages such as low density, high specific strength, good damping properties, and ease of processing. They have broad application prospects in lightweighting fields such as aerospace, automotive, and electronics. The application of magnesium alloys in the automotive industry is steadily increasing year by year, with widespread use in key components such as gearbox housings, instrument panel brackets, and door panels. However, traditional die-cast magnesium alloys suffer from two major technological bottlenecks: poor corrosion resistance and insufficient high-temperature creep resistance, limiting their application under harsh operating conditions. Regarding corrosion resistance, magnesium has a low electrode potential, a loose and porous surface oxide film, and impurities such as Fe, Ni, and Cu easily form micro-galvanic corrosion cells, leading to pitting corrosion in humid and saline environments, thus shortening service life. Regarding high-temperature creep resistance, traditional die-cast magnesium alloys (such as AM50 and AZ91D) have β-Mg... 17 Al 12 The strengthening phase has a low melting point and is prone to softening above 120℃-130℃, making it unable to suppress grain boundary slip and dislocation movement. Meanwhile, automotive gearbox housings, electric drive housings, engine mounts and other components need to withstand loads at temperatures of 150℃-300℃ for extended periods. Creep deformation of traditional die-cast magnesium alloys can lead to structural failure. While existing technologies attempt to adjust elemental content or perform single-element modification, it is difficult to simultaneously achieve comprehensive properties such as high strength, corrosion resistance, and high-temperature creep resistance. For example, β-Mg mainly forms in the Mg-Al-Zn and Mg-Al-Mn systems. 17 Al 12 The reinforcing phase is prone to softening above 120℃, resulting in poor creep resistance and low corrosion resistance at high temperatures. The Chinese character-shaped Mg2Si phase in the Mg-Al-Si system cannot effectively hinder dislocation slip, making it difficult to significantly improve high-temperature creep resistance. Although the Al2Ca phase forms in Mg-Al-Ca alloys, improving creep resistance, these alloys are prone to hot cracking during die casting, reducing yield.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a die-cast magnesium alloy, its preparation method, and its applications, to solve the problem of poor corrosion resistance and high-temperature creep resistance of existing die-cast magnesium alloys. The corrosion-resistant and high-temperature creep-resistant die-cast magnesium alloy of this invention achieves excellent tensile properties, corrosion resistance, and high-temperature creep resistance through the optimal ratio of alloying elements such as Al, Mn, La, Zn, and Ti, as well as treatments such as high-speed melt shearing, high-pressure casting, and shot peening. Compared with traditional die-cast magnesium alloys such as AM50 and AZ91D, it possesses outstanding comprehensive performance advantages.

[0005] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A die-cast magnesium alloy, by mass percentage, comprises the following components: Al 4.5wt%~5.5wt%, Mn 0.3wt%~0.6wt%, La 4.5wt%~5.5wt%, Zn 0.8wt%~1.2wt%, and Ti 0.01wt%~0.1wt%, with the balance being Mg and unavoidable impurities.

[0006] The die-cast magnesium alloy exhibits synergistic effects through a specific ratio of Al, Mn, La, Zn, Ti, and Mg, combining excellent tensile properties, corrosion resistance, and high-temperature creep resistance. Compared with traditional die-cast magnesium alloys such as AM50 and AZ91D, it possesses outstanding comprehensive performance advantages and can meet the comprehensive performance requirements of high-strength and heat-resistant components such as automotive gearbox housings and electric drive housings.

[0007] A method for preparing the aforementioned die-cast magnesium alloy includes the following steps: (a) melting each raw material in a protective atmosphere according to a specified ratio to obtain a first alloy melt; (b) refining, settling, shearing, die-casting, and shot peening the first alloy melt.

[0008] The method for preparing the die-cast magnesium alloy involves shearing, die-casting, and shot peening of the molten alloy raw materials, which improves service performance. High-speed shearing between refining and die-casting further refines the grains, spheroidizes the primary phase, and homogenizes the composition, enhancing the alloy's strength and plasticity. Shot peening the die-cast casting introduces numerous dislocations and vacancies into the surface layer, serving as effective nucleation sites for precipitates and further promoting the formation of fine precipitates during creep, significantly improving creep resistance.

[0009] A vehicle component housing or support, primarily made of the aforementioned die-cast magnesium alloy.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The die-cast magnesium alloy provided by this invention is based on the Mg-Al alloy with excellent casting performance. By adding La, Zn, Mn and Ti, in terms of room temperature mechanical properties and high temperature creep resistance, La and Al preferentially form a high-melting-point second phase, which is dispersed in the grain boundaries and within the grains, pinning the grain boundaries and hindering dislocation movement, thereby improving room temperature mechanical properties and high temperature creep resistance. Mn can combine with Al to form an Al-Mn phase, increasing solidification nucleation sites, refining grains, and thus improving mechanical properties. In addition, the addition of Zn can promote the dynamic precipitation of fine precipitates during creep, hindering dislocation movement and effectively improving the creep resistance of the alloy. Ti can refine grains, increase strength, and at the same time refine the dynamic precipitates formed during creep, increasing creep resistance. In terms of corrosion resistance, due to the addition of La forming Al 11 Secondary phases such as La3 replace β-Mg, which has a high potential difference with α-Mg. 17 Al 12 In this phase, the potential difference decreases, the cathode activity weakens significantly, and the microgalvanic corrosion intensity decreases. Simultaneously, La, Zn, and Mn can form intermetallic compounds insoluble in the Mg matrix with impurity elements such as Fe, Ni, and Cu, reducing the enrichment of impurity elements in Mg and thus reducing the formation of cathode active sites, thereby improving corrosion resistance.

[0011] (2) The method for preparing die-cast magnesium alloy provided by the present invention involves shearing, die-casting, and shot peening of alloy raw materials of a certain composition, which can improve service performance. High-speed shearing between refining and die-casting can further refine grains, spheroidize primary phases, and homogenize composition, thereby improving alloy strength and plasticity. Shot peening of the die-cast casting can introduce a large number of defects such as dislocations and vacancies on the surface of the casting, which can serve as effective nucleation sites for precipitates, further promoting the generation of fine precipitates during creep and significantly improving creep resistance. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This is a comparison chart of the corrosion rates of the die-cast magnesium alloys prepared in Examples 1 and 2 of this invention and the magnesium alloys prepared in Comparative Examples 3-5.

[0014] Figure 2 The image shows a comparison of the steady-state creep strain of the die-cast magnesium alloys prepared in Examples 1 and 2 of this invention with that of the magnesium alloys prepared in Comparative Examples 3-5 over 100 hours.

[0015] Figure 3 The tensile stress-strain curves are those of the die-cast magnesium alloys prepared in Example 1 and Comparative Example 3 of this invention. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0017] One aspect of the present invention relates to a die-cast magnesium alloy comprising, by weight percentage: Al 4.5wt%~5.5wt%, Mn 0.3wt%~0.6wt%, La 4.5wt%~5.5wt%, Zn 0.8wt%~1.2wt%, and Ti 0.01wt%~0.1wt%, with the balance being Mg and unavoidable impurities.

[0018] In some specific implementations, by mass percentage, Al can be, for example, but not limited to, a point value or a range between any two of 4.5wt%, 4.7wt%, 4.9wt%, 5.1wt%, 5.3wt%, or 5.5wt%; Mn can be, for example, but not limited to, a point value or a range between any two of 0.3wt%, 0.4wt%, 0.5wt%, or 0.6wt%; La can be, for example, but not limited to, a point value or a range between any two of 4.5wt%, 4.7wt%, 4.9wt%, 5.1wt%, 5.3wt%, or 5.5wt%; Zn can be, for example, but not limited to, a point value or a range between any two of 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, or 1.2wt%; Ti For example, it can be a point value or a range of any one of 0.01wt%, 0.02wt%, 0.04wt%, 0.06wt%, 0.08wt%, or 0.1wt%, or any two of them.

[0019] The aforementioned die-cast magnesium alloy is based on a Mg-Al alloy with excellent casting properties. By adding La, Zn, Mn, and Ti, the alloy exhibits improved room-temperature mechanical properties and high-temperature creep resistance. La preferentially forms a high-melting-point second phase with Al, which is dispersed within and around grain boundaries, pinning grain boundaries and hindering dislocation movement, thus enhancing both room-temperature mechanical properties and high-temperature creep resistance. Mn can combine with Al to form an Al-Mn phase, increasing solidification nucleation sites, refining grains, and further improving mechanical properties. Furthermore, the addition of Zn promotes the dynamic precipitation of fine precipitates during creep, hindering dislocation movement and effectively improving the alloy's creep resistance. Ti refines grains, increases strength, and simultaneously refines the dynamically precipitated phases formed during creep, increasing creep resistance. Regarding corrosion resistance, the addition of La forms an Al phase... 11 Secondary phases such as La3 replace β-Mg, which has a high potential difference with α-Mg. 17 Al 12 In this phase, the potential difference decreases, the cathode activity weakens significantly, and the microgalvanic corrosion intensity decreases. Simultaneously, La, Zn, and Mn can form intermetallic compounds insoluble in the Mg matrix with impurity elements such as Fe, Ni, and Cu, reducing the enrichment of impurity elements in Mg and thus reducing the formation of cathode active sites, thereby improving corrosion resistance.

[0020] Al is one of the main strengthening elements in alloys. It can dissolve in the Mg matrix to form a limited solid solution, and β-Mg precipitates during solidification. 17 Al 12 Al significantly improves the strength and hardness of magnesium alloys. Simultaneously, the addition of Al can improve melt fluidity and narrow the solidification range, giving the alloy excellent casting properties. Excessive Al content (greater than 5.5%) will form a continuous network of β-Mg in the alloy. 17 Al 12 The presence of certain phases reduces the alloy's creep resistance, while excessively low Al content (less than 4.5%) reduces the alloy's casting properties.

[0021] The addition of La preferentially forms high-temperature stable Al with Al during solidification. 11 La3 phase, suppressing low-melting-point Mg 17 Al 12 Phase formation. Al 11 The La3 phase is dispersed throughout the grain boundaries and within the grains, effectively pinning the grain boundaries and hindering dislocation slip, thus improving room temperature tensile strength and high-temperature creep resistance. Furthermore, Al... 11 La3 is an equivalent second-phase substitute for β-Mg, which has a high potential difference with α-Mg. 17 Al 12 The potential difference decreased, the cathode activity weakened significantly, and the microcouple corrosion intensity decreased; Al 11The reduced potential difference between the La3 phase and the α-Mg matrix significantly decreases microgalvanic corrosion. Furthermore, the addition of expensive heavy rare earth elements such as Y, Nd, and Gd is avoided, reducing raw material production costs. Too low a La content (less than 4.5%) can lead to Al... 11 The La3 phase content is low, and it cannot effectively suppress Mg. 17 Al 12 The formation of this phase cannot effectively improve creep resistance. Excessive La content (greater than 5.5%) will lead to Al... 11 Excessive La3 phase content can fracture the matrix, reduce elongation, and increase the risk of sticking and hot cracking during the die casting process.

[0022] The addition of Zn can promote the dynamic precipitation of fine precipitates during high-temperature creep, hindering dislocation movement and effectively improving creep resistance. Simultaneously, Zn can form intermetallic compounds with impurity elements such as Fe, Ni, and Cu, reducing the impact of impurities on corrosion resistance. When the Zn content is below 0.8 wt%, fewer precipitates are formed during high-temperature creep, resulting in limited improvement in creep resistance; while when the Zn content is above 1.2 wt%, it increases the tendency for casting hot cracking.

[0023] Mn can form intermetallic compounds with impurity elements such as Fe, Ni, and Cu, reducing the enrichment of impurity elements in Mg and thus forming cathode active sites, thereby reducing corrosion caused by impurity elements. The Al-Mn preprecipitate phase increases solidification nucleation sites, refines grains, improves the tensile properties of the alloy, and enhances its resistance to grain boundary sliding at high temperatures. When the Mn content is below 0.3 wt%, it cannot fully combine with impurity elements to improve corrosion resistance; when the Mn content is above 0.6 wt%, coarse Mn-containing intermetallic compounds are formed, reducing mechanical properties.

[0024] Ti can refine grains, improve strength and plasticity, and refine the dynamic precipitates formed during creep, thus increasing creep resistance. However, if the Ti content is higher than 0.1 wt%, coarse Ti-containing second phases will be generated, reducing mechanical properties.

[0025] Mg serves as the Mg matrix for corrosion-resistant and high-temperature creep-resistant die-cast magnesium alloys.

[0026] Furthermore, the die-cast magnesium alloy has a yield strength of 174.2~183.3 MPa, a tensile strength of 280.3~292.7 MPa, and an elongation of 7.1%~9.3% at room temperature. The annual corrosion rate of the die-cast magnesium alloy in a 5% NaCl neutral salt spray test is 0.134~0.211 mm / a. The creep strain of the die-cast magnesium alloy after 100 h of creep at 150℃ and 50 MPa is 0.191%~0.197%.

[0027] Furthermore, the die-cast magnesium alloy comprises, by mass percentage, the following components: Al 4.8wt%~5.3wt%, Mn 0.4wt%~0.5wt%, La 4.8wt%~5.3wt%, Zn 0.9wt%~1.1wt%, and Ti 0.03wt%~0.08wt%, with the balance being Mg and unavoidable impurities.

[0028] Furthermore, the content of the impurities is ≤0.02%.

[0029] Another aspect of the present invention relates to a method for preparing the aforementioned die-cast magnesium alloy, comprising the following steps: (a) In a protective atmosphere, the raw materials are melted according to the proportions to obtain a first alloy melt; (b) The first alloy melt is refined, allowed to stand, sheared, die-cast, and shot-peened.

[0030] The method for preparing the die-cast magnesium alloy involves shearing, die-casting, and shot peening of alloy raw materials in a specific ratio, which improves service performance. High-speed shearing between refining and die-casting further refines the grains, spheroidizes the primary phase, and homogenizes the composition, enhancing the alloy's strength and plasticity. Shot peening the die-cast casting introduces numerous dislocations and vacancies into the surface layer, serving as effective nucleation sites for precipitates and further promoting the formation of fine precipitates during creep, significantly improving creep resistance.

[0031] Further, the melting process includes: performing a first melting process on pure Mg to obtain molten Mg; and performing a second melting process on the molten Mg, pure Al, Mg-Mn master alloy, pure Zn, Mg-La master alloy, and Al-Ti master alloy to obtain the first alloy melt.

[0032] Furthermore, the temperature of the first melting treatment is 680~720℃ (for example, it can be any one of 680℃, 690℃, 700℃, 710℃ or 720℃ or a range between any two), and the time is 1~2h (for example, it can be any one of 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h or a range between any two).

[0033] Furthermore, the temperature of the second melting treatment is 730~760℃ (for example, it can be any one of 730℃, 740℃, 750℃ or 760℃ or a range between any two), and the time is 1~2h (for example, it can be any one of 1h, 1.2h, 1.5h, 1.8h or 2h or a range between any two).

[0034] Furthermore, the protective atmosphere includes at least one of N2, CO2, or SF6. The conditions provided in this embodiment enable the alloy melt to have a uniform composition, minimal element loss, and few oxide inclusions. This invention does not impose any special limitations on the specific model or source of the smelting furnace; commercially available smelting furnaces well-known to those skilled in the art can be used.

[0035] Furthermore, the refining temperature is 720~740℃ (for example, it can be any value of 720℃, 725℃, 730℃, 735℃ or 740℃ or a range between any two), and the time is 20~40min (for example, it can be any value of 20min, 25min, 30min, 35min or 40min or a range between any two). Refining within this temperature range can effectively remove oxide inclusions, non-metallic inclusions, and dissolved hydrogen from the melt by utilizing the adsorption and dissolution effects of the refining agent, thereby reducing the gas content of the melt.

[0036] Furthermore, the refining process is carried out by adding a refining agent to the first alloy melt under stirring conditions.

[0037] Furthermore, the amount of the refining agent added is 0.5% to 1.0% of the melt weight, including but not limited to a point value or a range between any two of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. The refining agent is of a type conventional in the art and can be obtained through ordinary commercial channels.

[0038] Furthermore, the standing time is carried out at 720~740℃ for 20~40min, including but not limited to the point value of any one of 20min, 25min, 30min, 35min or 40min or the range between any two.

[0039] Furthermore, after the settling period and before the shearing process, a slag removal process is performed, which includes removing slag from the surface of the molten liquid using a slag removal tool. The specific operation is not particularly limited and can be determined based on the technical knowledge of those skilled in the art.

[0040] Furthermore, the shearing speed is 300~1000 r / min (e.g., any value or range between any two of 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, or 100 r / min), the time is 5~20 min (e.g., any value or range between any two of 5 min, 10 min, 15 min, or 20 min), and the temperature is 700~720℃ (e.g., any value or range between any two of 700℃, 705℃, 710℃, 715℃, or 720℃), which is equivalent to controlling the melt temperature to 700~720℃. High-speed melt shearing can further refine grains, spheroidize primary phases, optimize the solidification nucleation process, and improve and stabilize the strength and plasticity of magnesium alloys.

[0041] Furthermore, the conditions for the die-casting process include: an injection speed of 4~6 m / s (for example, it can be any one of 4 m / s, 5 m / s, or 6 m / s, or a range between any two), a pressure of 50~100 MPa (for example, it can be any one of 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, or 100 MPa, or a range between any two), a mold temperature of 210~230℃ (for example, it can be any one of 210℃, 215℃, 220℃, 225℃, or 230℃, or a range between any two), and a temperature of the alloy melt during the die-casting process of 700~720℃ (for example, it can be any one of 700℃, 705℃, 710℃, 715℃, or 720℃, or a range between any two).

[0042] Furthermore, the pressure of the die-casting process is 80~90MPa. The magnesium alloy obtained by die-casting according to the die-casting conditions in this embodiment, especially the preferred die-casting conditions, exhibits high density, good corrosion resistance, and excellent high-temperature creep resistance.

[0043] Furthermore, the shot peening pressure is 0.3~0.5 MPa (for example, it can be any point value or any range between 0.3 MPa, 0.4 MPa or 0.5 MPa, for ...

[0044] Furthermore, the shot peening medium used in the shot peening process has a particle size of 1.0~1.4mm, and the shot peening medium includes glass beads.

[0045] Shot peening can introduce a large number of defects such as dislocations and vacancies into the surface of castings, which serve as effective nucleation sites for precipitates, further promoting the generation of fine precipitates during creep and significantly improving creep resistance.

[0046] Another aspect of the invention relates to a vehicle component housing or support, primarily made of the aforementioned die-cast magnesium alloy.

[0047] Furthermore, the vehicle component housings include, but are not limited to: gearbox housings and / or electric drive housings.

[0048] Furthermore, the vehicle component support includes, but is not limited to, an engine mount.

[0049] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0050] Example 1 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 4.64%, Mn 0.58%, La 5.26%, Zn 1.02%, Ti 0.08%, impurity elements ≤0.02% and balance Mg.

[0051] The method for preparing die-cast magnesium alloy provided in this embodiment includes the following steps: (1) Prepare materials according to the formula composition; among them, Mg, Al, Zn are prepared in the form of pure magnesium blocks, pure aluminum blocks, and pure zinc blocks, Mn is prepared in Mg-5%Mn master alloy ingots (i.e., Mn content is 5wt%), La is prepared in Mg-30%La master alloy ingots (i.e., La content is 30wt%), and Ti is prepared in Al-10%Ti master alloy ingots (i.e., Ti content is 10wt%). (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment. The melting temperature is 700℃ and the time is 1.5h. Then, pure aluminum, pure zinc, Mg-5%Mn master alloy, Mg-30%La master alloy and Al-10%Ti master alloy are added and kept at 730℃ for 1h (second melting treatment). After melting, the molten metal is stirred evenly to obtain the first alloy melt. (3) At 730°C, add refining agent powder to the melt (first alloy melt) for refining and standing. The refining time is 30 min. Stirring and slag removal are carried out at the same time as adding refining agent. After standing for 30 min, the second alloy melt is obtained. (4) The melt (second alloy melt) is allowed to stand and cool down to 710°C, and then subjected to melt shearing treatment at a speed of 650r / min for 10min. (5) Die casting is performed at a pressure of 85.8 MPa, a mold temperature of 224°C, an injection speed of 6 m / s, and the temperature of the alloy melt during die casting is 710°C. (6) The die-cast sample was shot peened with glass pellets with a particle size of 1.2 mm as the shot peening medium, the shot peening pressure was 0.4 MPa, the distance was 200 mm, and the time was 3 min.

[0052] Example 2 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 4.51%, Mn 0.56%, La 5.16%, Zn 0.99%, Ti 0.1%, impurity elements ≤0.02% and balance Mg.

[0053] The preparation method is the same as in Example 1.

[0054] Example 3 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 5.12%, Mn 0.35%, La 4.95%, Zn 1.05%, Ti 0.05%, impurity elements ≤0.02% and balance Mg.

[0055] The preparation method is the same as in Example 1.

[0056] Example 4 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 5.03%, Mn 0.42%, La 5.01%, Zn 0.97%, Ti 0.09%, impurity elements ≤0.02% and balance Mg.

[0057] The preparation method is the same as in Example 1.

[0058] Example 5 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 5.18%, Mn 0.47%, La 4.62%, Zn 1.02%, Ti 0.08%, impurity elements ≤0.02% and balance Mg.

[0059] The preparation method is the same as in Example 1.

[0060] Example 6 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 4.5wt%, Mn 0.6wt%, La 4.5wt%, Zn 0.8wt%, Ti 0.01wt%, impurity elements ≤0.02% and balance Mg.

[0061] The method for preparing die-cast magnesium alloy provided in this embodiment includes the following steps: (1) Same as Example 1; (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment. The melting temperature is 720℃ and the time is 1h. Then, pure aluminum, pure zinc, Mg-5%Mn master alloy, Mg-30%La master alloy and Al-10%Ti master alloy are added and kept at 730℃ for 2h (second melting treatment). After melting, the metal liquid is stirred evenly to obtain the first alloy melt. (3) At 740°C, add refining agent powder to the melt (first alloy melt) for refining and settling. The refining time is 20 min. Stir and remove slag while adding refining agent. Settle for 30 min to obtain second alloy melt. (4) The melt (second alloy melt) is allowed to stand and cool down to 720°C, and then subjected to melt shearing treatment at a speed of 300r / min for 20min; (5) Die casting is performed at a pressure of 100MPa, a mold temperature of 230℃, an injection speed of 4m / s, and the temperature of the alloy melt during die casting is 720℃. (6) The die-cast sample was shot peened with glass pellets with a particle size of 1.4 mm as the shot peening medium, the shot peening pressure was 0.3 MPa, the distance was 150 mm, and the time was 2 min.

[0062] Example 7 The die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 5.5wt%, Mn 0.3wt%, La 5.5wt%, Zn 1.2wt%, Ti 0.1wt%, impurity elements ≤0.02% and balance Mg.

[0063] The method for preparing die-cast magnesium alloy provided in this embodiment includes the following steps: (1) Same as Example 1; (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment. The melting temperature is 680℃ and the time is 2h. Then, pure aluminum, pure zinc, Mg-5%Mn master alloy, Mg-30%La master alloy and Al-10%Ti master alloy are added and kept at 760℃ for 1h (second melting treatment). After melting, the metal liquid is stirred evenly to obtain the first alloy melt. (3) At 720°C, add refining agent powder to the melt (first alloy melt) for refining and settling. The refining time is 40 min. Stir and remove slag while adding refining agent. Settle for 30 min to obtain second alloy melt. (4) The melt (second alloy melt) is allowed to stand and cool down to 700℃, and then sheared at a speed of 1000r / min for 5min. (5) Die casting is performed at a pressure of 50 MPa, a mold temperature of 210°C, an injection speed of 6 m / s, and the temperature of the alloy melt during die casting is 700°C. (6) The die-cast sample was shot peened with glass pellets with a particle size of 1.0 mm as the shot peening medium, the shot peening pressure was 0.5 MPa, the distance was 300 mm, and the time was 4 min.

[0064] Comparative Example 1 The die-cast magnesium alloy in this comparative example comprises the following components by mass percentage: Al 6.28%, Mn 0.47%, La 4.70%, Zn 1.00%, Ti 0.1%, impurity elements ≤0.02% and balance Mg.

[0065] The preparation method is the same as in Example 1.

[0066] Comparative Example 2 The die-cast magnesium alloy in this comparative example comprises the following components by mass percentage: Al 6.41%, Mn 0.48%, La 3.62%, Zn 1.00%, Ti 0.08%, impurity elements ≤0.02% and balance Mg.

[0067] The preparation method is the same as in Example 1.

[0068] Comparative Example 3 The die-cast magnesium alloy in this comparative example comprises the following components by mass percentage: Al 5.08%, Mn 0.38%, impurity elements ≤0.02% and balance Mg.

[0069] The preparation method of this magnesium alloy includes the following steps: (1) Prepare materials according to the formula composition; among them, Mg and Al are prepared in the form of pure magnesium blocks and pure aluminum blocks, and Mn is prepared in the form of Mg-5%Mn intermediate alloy ingot (i.e., Mn content is 5wt%). (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment at a melting temperature of 700℃; then pure aluminum and Mg-5%Mn master alloy are added and kept at 730℃ for 1 hour (second melting treatment). After melting, the molten metal is stirred evenly to obtain the first alloy melt. (3) At 730°C, refining agent powder is added to the melt (first alloy melt) for refining, settling, and slag removal. After settling for 30 minutes, the second alloy melt is obtained. (4) After the melt (second alloy melt) reaches 720°C, die casting is carried out to obtain Mg-Al-Mn die-cast magnesium alloy; the die casting pressure is 87.6MPa, the mold temperature is 220°C, and the injection speed is 6m / s.

[0070] Comparative Example 4 The die-cast magnesium alloy in this comparative example comprises the following components by mass percentage: Al 9.21%, Zn 0.87%, impurity elements ≤0.02% and balance Mg.

[0071] The preparation method of this die-cast magnesium alloy includes the following steps: (1) Prepare materials according to the formula composition; among which, Mg, Al and Zn are prepared in the form of pure magnesium blocks, pure aluminum blocks and pure zinc blocks; (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment at a melting temperature of 700℃; then pure aluminum and pure zinc are added and kept at 730℃ for 1 hour (second melting treatment). After melting, the molten metal is stirred evenly to obtain the first alloy melt. (3) At 730°C, refining agent powder is added to the melt (first alloy melt) for refining, settling, and slag removal. After settling for 30 minutes, the second alloy melt is obtained. (4) After the melt (second alloy melt) reaches 720°C, die casting is carried out to obtain Mg-Al-Zn die-cast magnesium alloy; the die casting pressure is 85.5MPa, the mold temperature is 220°C, and the injection speed is 6m / s.

[0072] Comparative Example 5 The die-cast magnesium alloy in this comparative example comprises the following chemical components by mass percentage: Al 4.15%, RE (Ce, La mixed rare earth) 2.56%, impurity elements ≤0.02% and balance Mg.

[0073] The preparation method of the Mg-Al-RE die-cast magnesium alloy comprises the following steps: (1) Prepare materials according to the formula composition; among them, Mg and Al are prepared in the form of pure magnesium blocks and pure aluminum blocks, and RE is prepared in the form of Mg RE intermediate alloy ingots; (2) First, pure magnesium is placed in a melting furnace and CO2+SF6 protective gas is introduced for the first melting treatment. The melting temperature is 700℃. Then, pure aluminum and Mg RE intermediate alloy are added and kept at 730℃ for 1 hour (second melting treatment). After melting, the metal liquid is stirred evenly to obtain the first alloy melt. (3) At 730°C, refining agent powder is added to the melt (first alloy melt) for refining, settling, and slag removal. After settling for 30 minutes, the second alloy melt is obtained. (4) After the melt (second alloy melt) reaches 720°C, die casting is carried out to obtain Mg-Al-RE die-cast magnesium alloy; the die casting pressure is 88.3MPa, the mold temperature is 220°C, and the injection speed is 6m / s.

[0074] Comparative Example 6 The only difference between this comparative example and Example 1 is that Ti was not added.

[0075] Comparative Example 7 The only difference between this comparative example and Example 1 is that the Al content is 3%.

[0076] Comparative Example 8 The only difference between this comparative example and Example 1 is that the Zn content is 4%.

[0077] Comparative Example 9 The only difference between this comparative example and Example 1 is that step (6) in the preparation method is omitted, and shot peening is not performed.

[0078] Comparative Example 10 The only difference between this comparative example and Example 1 is that step (4) in the preparation method is omitted, and no shearing process is performed.

[0079] Comparative Example 11 The only difference between this comparative example and Example 1 is that the pressure of the die-casting process is 25 MPa.

[0080] Comparative Example 12 The only difference between this comparative example and Example 1 is that the shot peening pressure is 1.0 MPa.

[0081] Experimental Example Neutral salt spray tests were conducted on the die-cast magnesium alloys prepared in the examples and the comparative examples. The test methods, conditions, and sample preparation followed the national standard GB / T 10125. Referring to the mass loss obtained from GB / T 10125, and combining parameters such as material density, test time, and test surface area, the annual corrosion rate in mm / a was derived. The neutral salt spray test conditions were: test temperature 35℃, NaCl solution concentration 5%, and test time 168 h. A comparison of the annual neutral salt spray corrosion rates of the magnesium alloys prepared in Examples 1 and 2 and Comparative Examples 3-5 is provided. Figure 1 As shown in Table 1, the annual corrosion rate test results of the examples and comparative examples under neutral salt spray are presented in Table 1.

[0082] Table 1 Annual neutral salt spray corrosion rate of die-cast magnesium alloys prepared in the examples and comparative examples (the lower the value, the better the corrosion performance).

[0083] High-temperature creep tests were conducted on the corrosion-resistant and high-temperature creep-resistant die-cast magnesium alloys prepared in the examples and the die-cast magnesium alloys prepared in the comparative examples. Standard die-cast creep specimens were fabricated according to the mechanical industry standard (JB / T 5000.9), and the test method followed the national standard GB / T2039-2012. The high-temperature creep test conditions were: test temperature 150℃, applied load 50MPa, and test time 100h. A comparison of the 100h steady-state creep strain of the magnesium alloys prepared in Examples 1, 2, and Comparative Examples 3-5 is provided. Figure 2 As shown in Table 2, the 100-hour steady-state creep strain test results for the examples and comparative examples are presented.

[0084] Table 2. Steady-state creep strain of die-cast magnesium alloys prepared in the examples and comparative examples after 100 hours (the lower the value, the better the creep performance).

[0085] The corrosion-resistant and high-temperature creep-resistant die-cast magnesium alloys prepared in the examples and the die-cast magnesium alloys prepared in the comparative examples were subjected to room temperature tensile tests. The test methods were in accordance with the national standard GB / T228.1-2021 for room temperature tensile testing. Tensile test conditions: tensile rate 4.5 mm / min, gauge length 75 mm, cross-sectional area 37.5 mm². 2 The tensile stress-strain curves of the magnesium alloys prepared in Example 1 and Comparative Example 3 are shown below. Figure 3 As shown in Table 3, the room temperature tensile test results for the examples and comparative examples are shown in Table 3.

[0086] Table 3 Tensile test results of die-cast magnesium alloys prepared in the examples and comparative examples

[0087] From Tables 1-3 and Figures 1-3 It can be seen that the corrosion-resistant and high-temperature creep-resistant die-cast magnesium alloy prepared by this invention exhibits superior annual corrosion rate, 100-hour high-temperature creep strain, and room-temperature tensile properties compared to the comparative example. Therefore, the die-cast magnesium alloy provided by this invention can meet the comprehensive performance requirements of high strength, corrosion resistance, and high-temperature creep resistance, and requires no heat treatment, making it suitable for high-strength and heat-resistant components such as automotive gearbox housings and electric drive housings.

[0088] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A die-cast magnesium alloy, characterized in that, By mass percentage, it includes the following components: Al 4.5wt%~5.5wt%, Mn 0.3wt%~0.6wt%, La 4.5wt%~5.5wt%, Zn 0.8wt%~1.2wt%, and Ti 0.01wt%~0.1wt%, with the balance being Mg and unavoidable impurities.

2. The die-cast magnesium alloy according to claim 1, characterized in that, By mass percentage, it includes the following components: Al 4.8wt%~5.3wt%, Mn 0.4wt%~0.5wt%, La 4.8wt%~5.3wt%, Zn 0.9wt%~1.1wt%, and Ti 0.03wt%~0.08wt%, with the balance being Mg and unavoidable impurities.

3. The method for preparing die-cast magnesium alloy as described in claim 1 or 2, characterized in that, Includes the following steps: (a) In a protective atmosphere, the raw materials are melted according to the proportions to obtain a first alloy melt; (b) The first alloy melt is refined, allowed to stand, sheared, die-cast, and shot-peened.

4. The method for preparing die-cast magnesium alloy according to claim 3, characterized in that, The shearing process is performed at a speed of 300-1000 r / min for 5-20 min at a temperature of 700-720℃.

5. The method for preparing die-cast magnesium alloy according to claim 3, characterized in that, The conditions for the die casting process include: an injection speed of 4~6 m / s, a pressure of 50~100 MPa, a mold temperature of 210~230℃, and a melt temperature of 700~720℃ during the die casting process.

6. The method for preparing die-cast magnesium alloy according to claim 3, characterized in that, The shot peening process is performed at a pressure of 0.3~0.5MPa, a distance of 150~300mm, and a time of 2~4min. And / or, the particle size of the shot peening medium used in the shot peening treatment is 1.0~1.4mm.

7. The method for preparing die-cast magnesium alloy according to claim 3, characterized in that, The refining temperature is 720~740℃, and the time is 20~40min.

8. The method for preparing die-cast magnesium alloy according to claim 3, characterized in that, The melting process includes: performing a first melting process on pure Mg to obtain molten Mg; and performing a second melting process on the molten Mg, pure Al, Mg-Mn master alloy, pure Zn, Mg-La master alloy and Al-Ti master alloy to obtain the first alloy melt.

9. The method for preparing die-cast magnesium alloy according to claim 8, characterized in that, The temperature of the first melting treatment is 680~720℃, and the time is 1~2h; And / or, the temperature of the second melting treatment is 730~760℃, and the time is 1~2h.

10. A vehicle component housing or support, characterized in that, It is mainly made of the die-cast magnesium alloy as described in claim 1 or 2.

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