High-toughness die-casting magnesium alloy as well as preparation method and application thereof

Abstract

The invention relates to the technical field of magnesium alloy materials, in particular to a high-toughness die-casting magnesium alloy and a preparation method and application thereof. The high-toughness die-casting magnesium alloy provided by the invention comprises the following components in percentage by mass: 5%-7.5% of Al, 0.3%-0.65% of Mn, 0.6%-1.2% of RE, 0.2%-0.46% of V, 0.1%-0.48% of Sr, 0.1%-0.32% of Ti and the balance of Mg and inevitable impurity elements. Wherein RE comprises Ce and La, and the mass ratio of Ce to La is (2-2.5): 1. According to the high-toughness die-casting magnesium alloy, through the diversified synergistic effect of Ce and La mixed rare earth elements and V, Sr and Ti microalloy elements, the die-casting magnesium alloy with high strength, high plasticity, corrosion resistance and good casting fluidity is obtained, and the preparation cost is low.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy materials technology, and in particular to a high-strength and high-toughness die-cast magnesium alloy, its preparation method and application. Background Technology

[0002] Magnesium alloys possess advantages such as low density, high specific strength, good thermal and electrical conductivity, excellent damping and vibration reduction properties, electromagnetic shielding performance, and recyclability, making them a high-quality lightweight material. Die-cast magnesium alloys, in particular, exhibit excellent fluidity, enabling the production of die-cast parts with complex structures, thin walls, and higher surface quality, while also offering higher production efficiency. Therefore, die-cast magnesium alloys have broad application prospects in the automotive industry, accounting for over 80% of the magnesium alloys used in automobiles. Traditional die-cast magnesium alloys, primarily AZ91D and AM60B, have relatively low strength, plasticity, heat resistance, and corrosion resistance, limiting their use to low-load-bearing parts such as interior trim frames and dashboard frames, thus restricting their further expansion. With the trend towards lightweighting in automobiles, the application of die-cast magnesium alloys is expanding from interior parts to large-size, high-load-bearing critical parts such as body parts and chassis components, placing higher demands on the strength, plasticity, and casting fluidity of die-cast magnesium alloys. Therefore, developing a die-cast magnesium alloy with high strength, high plasticity, high fluidity, and low cost, and its preparation method, to meet the comprehensive performance requirements of die-cast magnesium alloys for integrated die-cast structural parts of automobiles, is of great significance for the further expansion of the application of die-cast magnesium alloys and the realization of automobile lightweighting.

[0003] Currently, the performance of die-cast magnesium alloys is improved through methods such as optimizing alloy composition and refining die-casting processes. Adding a single rare earth element can improve the mechanical properties of die-cast magnesium alloys, but the improvement is not significant. Furthermore, excessively high levels of rare earth elements can negatively impact the plasticity of magnesium alloys and increase production costs. The variety and abundance of rare earth elements lead to high alloy costs and present significant challenges in process control during actual die-casting production.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a high-strength and high-toughness die-cast magnesium alloy. Through the diversified synergistic effect of Ce and La mixed rare earth elements and V, Sr, and Ti microalloying elements, multiple dispersed second phases are precipitated, refining the microstructure characteristics such as α-Mg matrix grains and coarse dendritic structures. At the same time, it reduces micro-galvanic corrosion between the matrix and the second phase, ultimately obtaining a die-cast magnesium alloy with high strength, high plasticity, corrosion resistance, and good casting fluidity. This solves the problems of low strength and plasticity and insufficient casting fluidity of existing die-cast magnesium alloys, and meets the comprehensive performance requirements of high strength, high plasticity, and high fluidity for integrated die-cast structural parts in automobiles.

[0006] The second objective of this invention is to provide a method for preparing a high-strength and high-toughness die-cast magnesium alloy with low preparation cost.

[0007] A third objective of this invention is to provide the application of the high-strength and high-toughness die-cast magnesium alloy as described above, or the high-strength and high-toughness die-cast magnesium alloy prepared by the method described above, in integrated die-cast structural parts for automobiles.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a high-strength and high-toughness die-cast magnesium alloy, comprising the following components by weight percentage: Al 5%~7.5%, Mn 0.3%~0.65%, RE 0.6%~1.2%, V 0.2%~0.46%, Sr 0.1%~0.48%, Ti 0.1%~0.32%, with the balance being Mg and unavoidable impurity elements; RE includes Ce and La, with a mass ratio of Ce to La of (2~2.5):1.

[0009] Furthermore, the high-strength and high-toughness die-cast magnesium alloy comprises the following components by weight percentage: Al 5.5%~7%, Mn 0.3%~0.55%, Ce 0.4%~0.8%, La 0.2%~0.4%, V 0.25%~0.35%, Sr 0.15%~0.35%, Ti 0.1%~0.2%, with the balance being Mg and unavoidable impurity elements.

[0010] Furthermore, the unavoidable impurity elements include at least one of Fe, Ni, and Cu; And / or, in the high-strength and high-toughness die-cast magnesium alloy, the total content of the unavoidable impurity elements is ≤0.02wt%.

[0011] Furthermore, it includes at least one of the following features (1) to (5); (1) The yield strength of the high-strength and high-toughness die-cast magnesium alloy is 145~160MPa; (2) The tensile strength of the high-strength and high-toughness die-cast magnesium alloy is 260~280MPa; (3) The elongation after fracture of the high-strength and high-toughness die-cast magnesium alloy is 15%~19%; (4) The maximum bending angle of the high-strength and high-toughness die-cast magnesium alloy is 42°~48°; (5) The corrosion rate of the high-strength and tough die-cast magnesium alloy under neutral salt spray test conditions is 0.38~0.46 mm / a.

[0012] The present invention also provides a method for preparing the high-strength and high-toughness die-cast magnesium alloy as described above, comprising the following steps: The high-strength and tough die-cast magnesium alloy is obtained by sequentially melting, degassing, refining, slag removal, and die-casting of raw materials according to their elemental composition.

[0013] Furthermore, the preparation method of the high-strength and high-toughness die-cast magnesium alloy includes the following steps: S1. Magnesium ingots, aluminum ingots, Mg-Mn master alloy, Mg-30CeLa master alloy, Al-55V master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy are dried and pretreated in a heating furnace. S2. Under a protective atmosphere, the magnesium ingot is melted and heated to the first temperature. Then, aluminum ingot, Mg-30CeLa master alloy and Al-55V master alloy are added in sequence. After melting, the mixture is allowed to stand to obtain the first alloy melt. S3. Cool the first alloy melt to the second temperature, and then add Mg-Mn master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy in sequence. After melting, let it stand to obtain the second alloy melt. S4. The second alloy melt is subjected to degassing, refining, cooling and settling, slag removal and die casting in sequence to obtain the high strength and toughness die-cast magnesium alloy.

[0014] Furthermore, it includes at least one of the following features (1) to (5); (1) In step S1, the temperature of the drying pretreatment is 150~200℃ and the time is 10~20min; (2) In step S2, the protective atmosphere includes at least one of CO2, SF6 and N2; (3) In step S2, the temperature at which the magnesium ingot is melted is 660~680℃; (4) In step S2, the first temperature is 720~740℃; (5) In step S2, the settling time is 10~25min.

[0015] Furthermore, it includes at least one of the following features (1) to (3); (1) In step S3, the second temperature is 700~720℃; (2) In step S3, the settling time is 15~30min; (3) In step S4, the temperature of degassing and refining is 700~720℃.

[0016] Further, in step S4, the die-casting conditions are as follows: die-casting temperature is 680~700℃, mold temperature is 180~230℃, vacuum degree is 50~70mbar, injection speed is 2~6m / s, and pressure is 350~800bar.

[0017] The present invention also provides the application of the high-strength and high-toughness die-cast magnesium alloy as described above or the high-strength and high-toughness die-cast magnesium alloy prepared by the preparation method of the high-strength and high-toughness die-cast magnesium alloy as described above in integrated die-cast structural parts of automobiles.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The high-strength and high-toughness die-cast magnesium alloy of the present invention, by introducing a small amount of mixed rare earth elements Ce and La, preferentially precipitates a large amount of dispersed rod-shaped or needle-shaped Al during the solidification process. 11 The RE3 phase acts as a second-phase strengthening agent, and refines the precipitated α-Mg matrix grains, coarse dendritic structure, and β-Mg. 17 Al 12 The network-like second phase improves the strength and plasticity of die-cast magnesium alloys, while the pre-precipitated Al... 11 The RE3 phase suppressed high-potential β-Mg 17 Al 12 The formation of the second phase reduces micro-galvanic corrosion between the matrix and the second phase, improving the corrosion resistance of die-cast magnesium alloys. Simultaneously, rare earth elements effectively purify the melt, reduce high-temperature melt viscosity, and improve the casting fluidity of the alloy. Furthermore, the Ce and La mixed rare earth elements are low-cost rare earth byproducts, lowering the production cost of die-cast magnesium alloys.

[0019] (2) The high-strength and high-toughness die-cast magnesium alloy of the present invention, by adding trace amounts of microalloying elements such as V, Sr, and Ti, forms multiple second phases such as Al3V, Al4Sr, and Al3Ti in the die-cast magnesium alloy, which significantly improves the strength of the die-cast magnesium alloy. At the same time, the α-Mg matrix grains and dendritic structure are further refined, and β-Mg is distributed in a network on the grain boundaries. 17 Al 12 The phase fractures into blocky or granular shapes, which are evenly distributed in the matrix, improving the strength and plasticity of die-cast magnesium alloys.

[0020] (3) The high-strength and high-toughness die-cast magnesium alloy of the present invention, through the diversified synergistic effect of the composite addition of mixed rare earth elements and micro-alloying elements, has a yield strength of 145~160MPa, a tensile strength of 260~280MPa, an elongation after fracture of 15%~19%, a maximum bending angle of 42°~48°, a corrosion rate of 0.38~0.46mm / a under neutral salt spray test conditions, and a casting fluid length of 425~436mm. Compared with die-cast magnesium alloys such as AZ91D and AM60B, it has outstanding performance advantages and meets the comprehensive performance requirements of high strength, high plasticity and high fluidity of die-cast magnesium alloy for integrated die-cast structural parts of automobiles. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the preparation method of the high-strength and high-toughness die-cast magnesium alloy of the present invention; Figure 2 The stress-strain curves of the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 of the present invention are shown. Figure 3 The stress-strain curves of the die-cast magnesium alloys of Comparative Examples 1 to 5 of the present invention are shown. Figure 4 This is a flowability sample of the high-strength and tough die-cast magnesium alloy of Example 1 of the present invention; Figure 5 The fluidity sample of the die-cast magnesium alloy of Comparative Example 3 of the present invention; Figure 6 The microstructure of the high-strength and high-toughness die-cast magnesium alloy of Example 1 of the present invention; Figure 7 The image shows the microstructure of the die-cast magnesium alloy in Comparative Example 3 of this invention. Detailed Implementation

[0023] 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.

[0024] In some embodiments of the present invention, a high-strength and high-toughness die-cast magnesium alloy is provided, comprising the following components by mass percentage: Al 5%~7.5%, Mn 0.3%~0.65%, RE 0.6%~1.2%, V 0.2%~0.46%, Sr 0.1%~0.48%, Ti 0.1%~0.32%, with the balance being Mg and unavoidable impurity elements; RE includes Ce and La, with a mass ratio of Ce to La of (2~2.5):1.

[0025] The high-strength and high-toughness die-cast magnesium alloy of this invention, through the diversified synergistic effect of Ce and La mixed rare earth elements and V, Sr and Ti microalloying elements, precipitates multiple dispersed second phases, refines the microstructure characteristics such as α-Mg matrix grains and coarse dendritic structure, and at the same time reduces micro-galvanic corrosion between the matrix and the second phase, improves the casting fluidity of the alloy, and finally obtains a high-strength, high-plasticity, corrosion-resistant and high-fluidity die-cast magnesium alloy, solving the problems of low strength and plasticity and insufficient casting fluidity of existing die-cast magnesium alloys.

[0026] The high-strength and high-toughness die-cast magnesium alloy of the present invention, by introducing a small amount of mixed rare earth elements Ce and La, preferentially precipitates a large number of dispersed rod-shaped or needle-shaped Al atoms during solidification. 11 The RE3 phase acts as a second-phase strengthening agent, and refines the precipitated α-Mg matrix grains, coarse dendritic structure, and β-Mg. 17 Al 12 The network-like second phase improves the strength and plasticity of die-cast magnesium alloys, while the pre-precipitated Al... 11 The RE3 phase suppressed high-potential β-Mg 17 Al 12 The formation of the second phase reduces micro-galvanic corrosion between the matrix and the second phase, improving the corrosion resistance of die-cast magnesium alloys. Simultaneously, rare earth elements effectively purify the melt, reduce high-temperature melt viscosity, and improve the casting fluidity of the alloy. Furthermore, the Ce and La mixed rare earth elements are low-cost rare earth byproducts, lowering the production cost of die-cast magnesium alloys.

[0027] The high-strength and high-toughness die-cast magnesium alloy of the present invention, by adding trace amounts of microalloying elements such as V, Sr, and Ti, forms multiple second phases such as Al3V, Al4Sr, and Al3Ti in the die-cast magnesium alloy, significantly improving the strength of the die-cast magnesium alloy. At the same time, the α-Mg matrix grains and dendritic structure are further refined, and β-Mg is distributed in a network at the grain boundaries. 17 Al 12 The phase fractures into blocky or granular shapes, which are evenly distributed in the matrix, improving the strength and plasticity of die-cast magnesium alloys.

[0028] In different implementation methods, the mass percentages of each component in the high-strength and high-toughness die-cast magnesium alloy can be as follows: The mass percentage of Al can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, and any value between any two of these. The mass percentage of Mn can be 0.3%, 0.4%, 0.5%, 0.6%, 0.65%, or any value between any two of these. The mass percentage of RE can be 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, and any value between any two of these. The mass percentage of V can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.46%, or any value between any two of these. The mass percentage of Sr can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.48%, and any value between any two of these. The mass percentage of Ti can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.32%, and any value between any two of these. The mass ratio of Ce to La can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, or any value between any two of these ratios.

[0029] The mechanism of action of various microalloying elements and rare earth elements and their contents in the high-strength and high-toughness die-cast magnesium alloy of the present invention is as follows: Al is the main strengthening element in die-cast magnesium alloys. Al dissolves into the Mg matrix, which has a solid solution strengthening effect, and at the same time forms β-Mg with Mg. 17 Al 12The strengthening phase has a precipitation strengthening effect, significantly improving the strength of magnesium alloys, and can also improve the corrosion resistance and casting fluidity of magnesium alloys. When the Al content in magnesium alloys is low, the strength of magnesium alloys increases with increasing Al content. When the Al content is greater than 7.5 wt%, the increase in strength tends to plateau, but it will seriously reduce the plasticity of magnesium alloys. Therefore, the Al content in the high-strength and tough die-cast magnesium alloy of this invention is controlled at 5 wt% to 7.5 wt%.

[0030] Mn has a certain strengthening and purifying effect on die-cast magnesium alloys. Mn readily forms fine-grained Al8Mn5 phase with Al, which can act as a heterogeneous nucleation point to refine the grains and improve the strength of the magnesium alloy matrix. At the same time, Mn neutralizes impurities such as Fe and Ni, improving corrosion resistance and reducing the formation of brittle phases from high-melting-point impurities, thus preventing melt flow obstruction and improving casting fluidity. However, excessive Mn can easily form coarse Al-Mn phases, which can reduce the plasticity of the magnesium alloy. Therefore, the Mn content in the high-strength and high-toughness die-cast magnesium alloy of this invention is controlled at 0.3wt%~0.65wt%.

[0031] RE (a mixture of rare earth elements, Ce and La) preferentially forms high-melting-point Al with Al. 11 The RE3 phase, a high-temperature stable second phase, acts as a heterogeneous nucleation site, increasing the nucleation density of subsequent precipitates, refining the α-Mg matrix grains and coarse dendritic structure, while simultaneously inhibiting the formation of β-Mg at the grain boundaries. 17 Al 12 The reduced and refined phase content, after network fracture, results in a granular, dispersed distribution at the grain boundaries, significantly improving the strength and plasticity of magnesium alloys. Furthermore, with the addition of mixed rare earth elements such as Ce and La, low-potential Al phases preferentially form in the magnesium alloy. 11 RE3 phase, suppressing high-potential β-Mg 17 Al 12 The formation of the phase leads to the formation of α-Mg matrix and β-Mg 17 Al 12 The reduced number of microcouples between phases lowers the potential difference between the α-Mg matrix and the Al-RE phase, improving the corrosion resistance of magnesium alloys. The mixed rare earth elements Ce and La can also narrow the alloy solidification range, reduce melt oxidation, and improve melt purity, thereby reducing melt viscosity and improving casting fluidity. The mixed rare earth elements Ce and La are byproducts of Nd and Pr extraction from natural mixed rare earths, which not only reduces the preparation cost of rare earth magnesium alloys but also achieves efficient utilization of rare earth resources. Therefore, to obtain the best strengthening and toughening effect, the mixed rare earth content of Ce and La in the high-strength and tough die-cast magnesium alloy of this invention is controlled at 0.6wt%~1.2wt%.

[0032] V has a significant grain-refining effect on die-cast magnesium alloys. V forms a high-melting-point Al3V phase with Al. During alloy solidification, the high-melting-point Al3V phase forms and aggregates at the solid-liquid interface front before other phases, hindering the growth of α-Mg grains and thus refining the grains. At the same time, it inhibits β-Mg growth. 17 Al 12 The continuous network distribution of the phase gradually discretizes it, resulting in the formation of β-Mg. 17 Al 12 The phase will become finer. Therefore, the V content in the high-strength and high-toughness die-cast magnesium alloy of the present invention is controlled at 0.2wt%~0.46%.

[0033] Sr acts as a modifier in die-cast magnesium alloys, significantly improving the morphology, quantity, and distribution of the matrix and second phases. Adding trace amounts of Sr causes the coarse dendritic structure in the magnesium alloy to begin to break up, the α-Mg matrix grain size to decrease significantly, and simultaneously, β-Mg… 17 Al 12 Phase, Al 11 The RE3 phase changes from a network or needle-like shape to a small granular shape, resulting in a more uniform and refined microstructure. With increasing Sr content, a coarse network structure begins to appear in the second phase, adversely affecting the properties of the magnesium alloy. Therefore, in the high-strength and high-toughness die-cast magnesium alloy of this invention, the Sr content is controlled at 0.1wt%~0.48wt%.

[0034] Ti is a grain refiner in die-cast magnesium alloys. Adding trace amounts of Ti can further enhance the grain refinement effect on the microstructure of die-cast magnesium alloys, making the coarse dendritic structure more fragmented, and reducing β-Mg. 17 Al 12 Phase, Al 11 The RE3 phase transforms into a granular form and is uniformly distributed at the grain boundaries, improving the strength and ductility of the magnesium alloy. Furthermore, the addition of Ti forms a low-electrochemically active Al3Ti phase, while simultaneously suppressing β-Mg... 17 Al 12 The amount of Ti improves the corrosion resistance of magnesium alloys. With increasing Ti content, the grain size of die-cast magnesium alloys first decreases and then increases, while the strength and elongation correspondingly first increase and then decrease. Therefore, in the high-strength and high-toughness die-cast magnesium alloy of this invention, the Ti content is controlled at 0.1wt%~0.32wt%.

[0035] Based on the influence mechanism of microalloying elements and rare earth elements on the properties of die-cast magnesium alloys, the content of each component in die-cast magnesium alloys was further optimized.

[0036] In some preferred embodiments of the present invention, the following components are included by weight percentage: Al 5.5%~7%, Mn 0.3%~0.55%, Ce 0.4%~0.8%, La 0.2%~0.4%, V 0.25%~0.35%, Sr 0.15%~0.35%, Ti 0.1%~0.2%, with the balance being Mg and unavoidable impurity elements.

[0037] In some preferred embodiments of the present invention, the following components are included by weight percentage: Al 6%~6.5%, Mn 0.35%~0.45%, Ce 0.6%~0.7%, La 0.25%~0.35%, V 0.25%~0.3%, Sr 0.2%~0.3%, Ti 0.1%~0.2%, with the balance being Mg and unavoidable impurity elements.

[0038] In some embodiments of the present invention, unavoidable impurity elements include at least one of Fe, Ni and Cu.

[0039] In some embodiments of the present invention, the total content of unavoidable impurity elements in the high-strength and high-toughness die-cast magnesium alloy is ≤0.02wt%.

[0040] Fe, Ni, and Cu are harmful impurity elements in die-cast magnesium alloys. They combine with elements such as Al and Mg in the magnesium alloy to form intermetallic compounds such as Al3Fe and Mg2Ni, which are distributed on the grain boundaries of the matrix, deteriorating the strength and plasticity of the magnesium alloy, accelerating the electrochemical corrosion of the magnesium matrix, and severely reducing the mechanical properties and corrosion resistance of the magnesium alloy. Therefore, the total content of all impurity elements should be controlled to ≤0.02wt%.

[0041] In some embodiments of the present invention, the yield strength of the high-strength and high-toughness die-cast magnesium alloy is 145~160MPa; preferably 150~160MPa; the yield strength test standard is GB / T 228.1-2021.

[0042] In some embodiments of the present invention, the tensile strength of the high-strength and high-toughness die-cast magnesium alloy is 260~280MPa; preferably 265~280MPa; the tensile strength test standard is GB / T 228.1-2021.

[0043] In some embodiments of the present invention, the elongation after fracture of the high-strength and high-toughness die-cast magnesium alloy is 15%~19%; preferably 17%~19%; the standard for elongation after fracture testing is GB / T 228.1-2021.

[0044] In some embodiments of the present invention, the maximum bending angle of the high-strength and high-toughness die-cast magnesium alloy is 42°~48°; preferably 45°~48°; the maximum bending angle test standard is: VDA238-100.

[0045] In some embodiments of the present invention, the corrosion rate of the high-strength and high-toughness die-cast magnesium alloy under neutral salt spray test conditions is 0.38~0.46 mm / a; preferably 0.38~0.43 mm / a; the neutral salt spray test standard is GB / T 10125-2021.

[0046] In some embodiments of the present invention, the casting fluidity length of the high-strength and high-toughness die-cast magnesium alloy is 425~436mm; the casting fluidity test is conducted using a spiral flow ring sample, the pouring temperature is 690~700℃, and the mold temperature is 200~210℃.

[0047] In some embodiments of the present invention, a method for preparing the above-mentioned high-strength and high-toughness die-cast magnesium alloy is also provided, comprising the following steps: The raw materials, which are formulated according to their elemental composition, are sequentially melted, degassed, refined, slag removed, and die-cast to obtain a high-strength and tough die-cast magnesium alloy.

[0048] See Figure 1 In some embodiments of the present invention, the preparation method of high-strength and high-toughness die-cast magnesium alloy specifically includes the following steps: S1. Magnesium ingots, aluminum ingots, Mg-Mn master alloy, Mg-30CeLa master alloy, Al-55V master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy are dried and pretreated in a heating furnace. S2. Under a protective atmosphere, the magnesium ingot is melted and heated to the first temperature. Then, aluminum ingot, Mg-30CeLa master alloy and Al-55V master alloy are added in sequence. After melting, the mixture is allowed to stand to obtain the first alloy melt. S3. Cool the first alloy melt to the second temperature, and then add Mg-Mn master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy in sequence. After melting, let it stand to obtain the second alloy melt. S4. After the second alloy melt is subjected to degassing, refining, cooling and settling, slag removal and die casting in sequence, a high-strength and tough die-cast magnesium alloy is obtained.

[0049] In some embodiments of the present invention, in step S1, the temperature of the drying pretreatment is 150~200℃ and the time is 10~20min; the main purpose of the drying pretreatment is to remove the surface moisture of the raw material, avoid the explosion and oxidation of the high-temperature melt of magnesium alloy, and reduce the porosity defects generated during solidification.

[0050] In some embodiments of the present invention, in step S2, the protective atmosphere includes at least one of CO2, SF6 and N2; the single or mixed protective gas forms a denser protective film on the surface of the magnesium alloy melt, preventing magnesium from contacting oxygen, thereby reducing oxidation and burn-off during the magnesium alloy smelting process.

[0051] In some embodiments of the present invention, in step S2, the temperature at which the magnesium ingot is melted is 660~680°C, which ensures that the magnesium ingot is melted uniformly.

[0052] In some embodiments of the present invention, in step S2, the first temperature is 720~740℃; the melting points of aluminum ingots, Mg-30CeLa and Al-55V master alloys are relatively high, and the melting temperature needs to be appropriately increased to ensure complete melting.

[0053] In some embodiments of the present invention, in step S2, the settling time is 10-25 minutes.

[0054] In some embodiments of the present invention, in step S3, the second temperature is 700~720℃; the main purpose of adding Al-10Sr and Al-10Ti-1B master alloys is to form a large number of heterogeneous nucleation sites to refine the magnesium alloy structure. The melting temperature should not be too high, so it is necessary to control a lower melting temperature.

[0055] In some embodiments of the present invention, in step S3, the settling time is 15 to 30 minutes.

[0056] In some embodiments of the present invention, in step S4, the degassing and refining temperature is 700~720°C; in the degassing and refining stage of the second alloy melt, by introducing inert gas into the second alloy melt and stirring it evenly, the gas is allowed to fully contact the melt during the floating process, and fine oxide inclusions float to the surface of the melt, and are finally removed by slag removal, thereby achieving the purpose of purifying the melt.

[0057] In some embodiments of the present invention, in step S4, the die-casting conditions are as follows: die-casting temperature is 680~700℃, mold temperature is 180~230℃, vacuum degree is 50~70mbar, injection speed is 2~6m / s, and pressure is 350~800bar.

[0058] In some embodiments of the present invention, the application of the above-mentioned high-strength and high-toughness die-cast magnesium alloy or the high-strength and high-toughness die-cast magnesium alloy prepared by the above-mentioned high-strength and high-toughness die-cast magnesium alloy preparation method in integrated die-cast structural parts of automobiles is also provided.

[0059] The high-strength and high-toughness die-cast magnesium alloy of the present invention has excellent mechanical properties, corrosion resistance and casting fluidity, which are significantly better than existing commercial die-cast magnesium alloys such as AZ91D and AM60B. It can meet the comprehensive performance requirements of high strength, high plasticity and high fluidity of die-cast magnesium alloys for integrated die-cast structural parts of automobiles.

[0060] Example 1 The high-strength and high-toughness die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 6.2%, Mn 0.43%, Ce 0.68%, La 0.31%, V 0.28%, Sr 0.26%, Ti 0.15%, with the remainder being Mg and unavoidable impurity elements.

[0061] The method for preparing high-strength and high-toughness die-cast magnesium alloy provided in this embodiment includes the following steps: S1. Magnesium ingots, aluminum ingots, Mg-Mn master alloy, Mg-30CeLa master alloy, Al-55V master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy are dried in a heating furnace. The drying pretreatment temperature is 180℃ and the time is 15min. S2. Under the protective atmosphere of high-purity SF6 and N2 mixed gas in the melting furnace, the magnesium ingot is first completely melted at 680℃, then the temperature is raised to 730℃, and then aluminum ingot, Mg-30CeLa master alloy and Al-55V master alloy are added in sequence. After being fully melted, it is allowed to stand for 23 minutes to obtain the first alloy melt. S3. Cool the first alloy melt to 710℃, then add Mg-Mn master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy in sequence. After fully melting, let stand for 25 minutes to obtain the second alloy melt.

[0062] S4. The second alloy melt is uniformly stirred at 710℃ to complete the degassing and refining treatment. Then, it is subjected to cooling and settling, slag removal and die casting to obtain a high-strength and tough die-cast magnesium alloy. The die casting conditions are: die casting temperature of 700℃, mold temperature of 210℃, vacuum degree of 70mbar, injection speed of 4m / s, and pressure of 550bar.

[0063] Example 2 The high-strength and high-toughness die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 7.3%, Mn 0.6%, Ce 0.57%, La 0.23%, V 0.42%, Sr 0.45%, Ti 0.31%, with the remainder being Mg and unavoidable impurity elements.

[0064] The preparation method of the high-strength and high-toughness die-cast magnesium alloy provided in this embodiment is the same as that in Embodiment 1.

[0065] Example 3 The high-strength and high-toughness die-cast magnesium alloy provided in this embodiment comprises the following components by mass percentage: Al 5.2%, Mn 0.35%, Ce 0.49%, La 0.24%, V 0.21%, Sr 0.13%, Ti 0.11%, with the remainder being Mg and unavoidable impurity elements.

[0066] The preparation method of the high-strength and high-toughness die-cast magnesium alloy provided in this embodiment is the same as that in Embodiment 1.

[0067] Comparative Example 1 The die-cast magnesium alloy provided in this comparative example comprises the following components by weight percentage: Al 6%, Mn 0.43%, V 0.25%, Sr 0.24%, Ti 0.16%, with the remainder being Mg and unavoidable impurity elements.

[0068] The preparation method of the die-cast magnesium alloy provided in this comparative example is the same as that in Example 1, except that the Mg-30CeLa master alloy is not added.

[0069] Comparative Example 2 The die-cast magnesium alloy provided in this comparative example comprises the following components by weight percentage: Al 7.1%, Mn 0.51%, Ce 0.3%, La 0.3%, V 0.3%, Sr 0.25%, Ti 0.12%, with the remainder being Mg and unavoidable impurity elements.

[0070] The preparation method of the die-cast magnesium alloy provided in this comparative example is the same as that in Example 1, except that the mass ratio of Ce to La is 1:1.

[0071] Comparative Example 3 The die-cast magnesium alloy provided in this comparative example comprises the following components by weight percentage: Al 5.5%, Mn 0.45%, Ce 0.6%, La 0.27%, with the remainder being Mg and unavoidable impurity elements.

[0072] The preparation method of the die-cast magnesium alloy provided in this comparative example is the same as that in Example 1, except that intermediate alloys such as Al-55V, Al-10Sr and Al-10Ti-1B are not added.

[0073] Comparative Example 4 The die-cast magnesium alloy provided in this comparative example is die-cast magnesium alloy AZ91D; die-cast magnesium alloy AZ91D, by mass percentage, comprises the following components: Al 9.2%, Mn 0.31%, Zn 0.85%, with the remainder being Mg and unavoidable impurity elements.

[0074] The preparation method of the die-cast magnesium alloy (die-cast magnesium alloy AZ91D) provided in this comparative example is the same as that in Example 1, except that magnesium ingots, aluminum ingots, zinc ingots and Mg-Mn master alloys are used in the preparation process, and master alloys such as Mg-30CeLa, Al-55V, Al-10Sr and Al-10Ti-1B are not added.

[0075] Comparative Example 5 The die-cast magnesium alloy provided in this comparative example is die-cast magnesium alloy AM60B; die-cast magnesium alloy AM60B, by weight percentage, comprises the following components: Al 6.1%, Mn 0.45%, Zn 0.01%, with the remainder being Mg and unavoidable impurity elements.

[0076] The preparation method of the die-cast magnesium alloy (die-cast magnesium alloy AM60B) provided in this comparative example is the same as that in Example 1, except that magnesium ingots, aluminum ingots and Mg-Mn master alloys are used in the preparation process, and master alloys such as Mg-30CeLa, Al-55V, Al-10Sr and Al-10Ti-1B are not added.

[0077] Test case The chemical composition test results of the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 and the die-cast magnesium alloys of Comparative Examples 1-5 are shown in Table 1.

[0078] Table 1

[0079] To evaluate the mechanical properties and corrosion resistance of the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 and Comparative Examples 1-5, tensile tests were conducted according to GB / T 228.1-2021 to test the yield strength, tensile strength, and elongation after fracture of the die-cast magnesium alloys; VDA bending tests were conducted according to VDA238-100 to test the maximum bending angle of the die-cast magnesium alloys; and a 168-hour neutral salt spray corrosion test was conducted according to GB / T 10125-2021 to test the corrosion rate of the die-cast magnesium alloys. The results are recorded in Table 2. The stress-strain curves of the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 are shown below. Figure 2 As shown; the stress-strain curves of the die-cast magnesium alloys in Comparative Examples 1-5 are as follows. Figure 3 As shown.

[0080] Table 2

[0081] As shown in Table 2, the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 have a yield strength of 145-160 MPa, a tensile strength of 260-280 MPa, an elongation after fracture of 15%-19%, a maximum bending angle of 42°-48°, and a corrosion rate of 0.38-0.46 mm / a under neutral salt spray test conditions. Compared with the die-cast magnesium alloys of Comparative Examples 1-5, the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 have higher yield strength, tensile strength, and elongation after fracture, especially a significantly increased elongation after fracture, while also showing a significantly increased maximum bending angle and a significantly reduced corrosion rate. Therefore, in the high-strength and high-toughness die-cast magnesium alloy of the present invention, the addition of Ce and La mixed rare earth elements and V, Sr and Ti microalloying elements in proportion can strengthen the die-cast magnesium alloy matrix, synergistically refine the grain, dendritic structure and morphology of the second phase, and improve corrosion resistance. Ultimately, it achieves comprehensive performance of high strength, high plasticity and corrosion resistance, as well as low alloy preparation cost, meeting the performance requirements of peripheral connection and collision safety of integrated die-cast structural parts for automobiles.

[0082] In Comparative Example 1, no rare earth elements Ce and La were added. In Comparative Example 2, the ratio of rare earth elements Ce and La was 1:1. In Comparative Example 3, no refining elements V, Sr, and Ti were added for further microstructure modification. In Comparative Examples 4 and 5, the die-cast magnesium alloys AZ91D and AM60B were strengthened only by elements such as Al, Mn, and Zn, resulting in insufficient toughness and corrosion resistance of the die-cast magnesium alloys and low plasticity.

[0083] To evaluate the casting fluidity properties of the high-strength and high-toughness die-cast magnesium alloys of Examples 1-3 and Comparative Examples 1-5, casting fluidity tests were conducted using spiral flow ring samples under gravity casting conditions to test the casting fluidity of the die-cast magnesium alloys; the results are recorded in Table 3; the fluidity of the high-strength and high-toughness die-cast magnesium alloy of Example 1 is as follows: Figure 4 As shown; the fluidity of the die-cast magnesium alloy in Comparative Example 4 is as follows: Figure 5 As shown.

[0084] Table 3

[0085] As shown in Table 3, under the experimental conditions of metal mold and gravity casting, the casting flow length of the high-strength and high-toughness die-cast magnesium alloys in Examples 1-3 was 425-436 mm. Compared with the die-cast magnesium alloys of Comparative Examples 1-5, the high-strength and high-toughness die-cast magnesium alloys in Examples 1-3 exhibited higher casting fluidity. Therefore, the addition of a higher content of the low-melting-point element Al, as well as Ce, La, Mn, Sr, etc., to the high-strength and high-toughness die-cast magnesium alloys of the present invention has the effects of narrowing the solidification range, removing impurity elements, and purifying the high-temperature melt, which can effectively reduce the viscosity of the alloy melt, thereby improving the casting fluidity of the high-strength and high-toughness die-cast magnesium alloy and meeting the requirements of large-size, long-process die-casting molding of integrated automotive die-cast structural parts.

[0086] The microstructures of the high-strength and high-toughness die-cast magnesium alloy of Example 1 and the die-cast magnesium alloy of Comparative Example 3 were tested, and the results are as follows: Figure 6 and Figure 7 As shown; Figure 6 The microstructure of the high-strength and high-toughness die-cast magnesium alloy in Example 1; Figure 7 The microstructure of the die-cast magnesium alloy in Comparative Example 3 is shown.

[0087] from Figure 6 and Figure 7 It can be seen that the microstructure of the high-strength and high-toughness die-cast magnesium alloy in Example 1 is significantly refined, with equiaxed grains and no coarse dendritic structures. A large number of granular second phases are dispersed at grain boundaries and within the grains. These microstructural characteristics directly determine the high strength and plasticity of the die-cast magnesium alloy. In contrast, the die-cast magnesium alloy in Comparative Example 3 has coarse grains, large-sized dendritic or mixed-crystal structures, and a low content of precipitated strengthening phases that are distributed in elongated strips at the grain boundaries. This results in insufficient strengthening effect and microstructure refinement, leading to lower strength and plasticity in the die-cast magnesium alloy.

[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; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A high-strength and high-toughness die-cast magnesium alloy, characterized in that, By weight percentage, it includes the following components: Al 5%~7.5%, Mn 0.3%~0.65%, RE 0.6%~1.2%, V 0.2%~0.46%, Sr 0.1%~0.48%, Ti 0.1%~0.32%, with the balance being Mg and unavoidable impurity elements; RE includes Ce and La, with a mass ratio of Ce to La of (2~2.5):

1.

2. The high-strength and high-toughness die-cast magnesium alloy according to claim 1, characterized in that, By weight percentage, it includes the following components: Al 5.5%~7%, Mn 0.3%~0.55%, Ce 0.4%~0.8%, La 0.2%~0.4%, V 0.25%~0.35%, Sr 0.15%~0.35%, Ti 0.1%~0.2%, with the balance being Mg and unavoidable impurity elements.

3. The high-strength and high-toughness die-cast magnesium alloy according to claim 1, characterized in that, The unavoidable impurity elements include at least one of Fe, Ni and Cu; And / or, in the high-strength and high-toughness die-cast magnesium alloy, the total content of the unavoidable impurity elements is ≤0.02wt%.

4. The high-strength and high-toughness die-cast magnesium alloy according to claim 1, characterized in that, Includes at least one of the following features (1) to (5); (1) The yield strength of the high-strength and high-toughness die-cast magnesium alloy is 145~160MPa; (2) The tensile strength of the high-strength and high-toughness die-cast magnesium alloy is 260~280MPa; (3) The elongation after fracture of the high-strength and high-toughness die-cast magnesium alloy is 15%~19%; (4) The maximum bending angle of the high-strength and high-toughness die-cast magnesium alloy is 42°~48°; (5) The corrosion rate of the high-strength and tough die-cast magnesium alloy under neutral salt spray test conditions is 0.38~0.46 mm / a.

5. The method for preparing high-strength and high-toughness die-cast magnesium alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: The high-strength and tough die-cast magnesium alloy is obtained by sequentially melting, degassing, refining, slag removal, and die-casting of raw materials according to their elemental composition.

6. The method for preparing high-strength and high-toughness die-cast magnesium alloy according to claim 5, characterized in that, Includes the following steps: S1. Magnesium ingots, aluminum ingots, Mg-Mn master alloy, Mg-30CeLa master alloy, Al-55V master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy are dried and pretreated in a heating furnace. S2. Under a protective atmosphere, the magnesium ingot is melted and heated to the first temperature. Then, aluminum ingot, Mg-30CeLa master alloy and Al-55V master alloy are added in sequence. After melting, the mixture is allowed to stand to obtain the first alloy melt. S3. Cool the first alloy melt to the second temperature, and then add Mg-Mn master alloy, Al-10Sr master alloy and Al-10Ti-1B master alloy in sequence. After melting, let it stand to obtain the second alloy melt. S4. The second alloy melt is subjected to degassing, refining, cooling and settling, slag removal and die casting in sequence to obtain the high strength and toughness die-cast magnesium alloy.

7. The method for preparing high-strength and high-toughness die-cast magnesium alloy according to claim 6, characterized in that, Includes at least one of the following features (1) to (5); (1) In step S1, the temperature of the drying pretreatment is 150~200℃ and the time is 10~20min; (2) In step S2, the protective atmosphere includes at least one of CO2, SF6 and N2; (3) In step S2, the temperature at which the magnesium ingot is melted is 660~680℃; (4) In step S2, the first temperature is 720~740℃; (5) In step S2, the settling time is 10~25min.

8. The method for preparing high-strength and high-toughness die-cast magnesium alloy according to claim 6, characterized in that, Includes at least one of the following features (1) to (3); (1) In step S3, the second temperature is 700~720℃; (2) In step S3, the settling time is 15~30min; (3) In step S4, the temperature of degassing and refining is 700~720℃.

9. The method for preparing high-strength and high-toughness die-cast magnesium alloy according to claim 6, characterized in that, In step S4, the die casting conditions are as follows: die casting temperature is 680~700℃, mold temperature is 180~230℃, vacuum degree is 50~70mbar, injection speed is 2~6m / s, and pressure is 350~800bar.

10. The application of the high-strength and high-toughness die-cast magnesium alloy as described in any one of claims 1 to 4 or the high-strength and high-toughness die-cast magnesium alloy as described in any one of claims 5 to 9 in integrated die-cast structural parts for automobiles.

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