High-toughness extrusion casting magnesium alloy and preparation method thereof

Abstract

The invention discloses a high-toughness squeeze casting magnesium alloy and a preparation method thereof, the high-toughness squeeze casting magnesium alloy contains an Mg17Al12 strengthening phase, an MgZn strengthening phase and an Al 11RE3 strengthening phase, and RE is La, Ce or Nd; the alloy also contains an Al < 2 > Gd phase, an A < 12 > Y phase and / or an Al < 2 > Sm phase; the alloy is prepared from the following components in percentage by mass: 4.0 wt.% to 6.0 wt.% of aluminum, 1.0 wt.% to 3.0 wt.% of zinc, 4.0 wt.% to 6.0 wt.% of a first rare earth component, 1.5 wt.% to 3.0 wt.% of a second rare earth component, 0.3 wt.% to 0.5 wt.% of manganese, 0.2 wt.% to 0.5 wt.% of zirconium and the balance of magnesium and inevitable impurities, the mass percentage of the impurities is less than or equal to 0.3 wt.%; the preparation method of the high-toughness extrusion casting magnesium alloy comprises the following steps: preheating raw materials; smelting an alloy; extrusion casting; and heat treatment. According to the invention, the magnesium alloy is prepared by optimizing alloy components, a smelting process and a solid solution and aging heat treatment method, so that the prepared magnesium alloy has relatively high strength and plasticity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-ferrous materials and its processing technology. Specifically, it is a high strength and toughness extrusion casting magnesium alloy and its preparation method. BACKGROUND

[0002] Magnesium alloy is one of the most widely used light structural materials at present. Compared with commonly used structural materials such as steel and aluminum alloy, magnesium alloy has the advantages of low density, high specific strength and high specific stiffness, and has broad application prospects in the fields of transportation, aerospace, 3C products, etc. The performance of magnesium alloy materials is not balanced at present. The representative AE series magnesium alloy has good plasticity, but the strength of the alloy is not high. GWK series magnesium alloy is a kind of magnesium alloy that can be heat treated to strengthen. By using appropriate heat treatment process to treat GWK series magnesium alloy, strengthening phases such as columnar precipitated phase β' and basal plane precipitated phase γ" can be precipitated in the alloy, which makes the magnesium alloy exhibit high strength and toughness. However, the content of heavy rare earth elements in GWK series magnesium alloy is high, the alloy is expensive, and the plasticity is poor. Although people try to improve the strength and plasticity of magnesium alloy at the same time by alloying and large plastic deformation, the effect is often not satisfactory. Moreover, with the increasing demand for realizing the "double carbon" target, the development of high strength and toughness magnesium alloy materials with high strength and plasticity, and the realization of their lightweight application in the field of transportation, can effectively achieve the purpose of energy saving and emission reduction, and promote the realization of the "double carbon" target.

[0003] At present, AE series magnesium alloy has relatively balanced strength and plasticity, but its strengthening phase Al 11 RE3 basically exists in the form of large size needle or strip in the alloy, and its morphology size and distribution need to be further improved. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide a high strength and toughness extrusion casting magnesium alloy and its preparation method. By optimizing the alloy composition, making full use of the synergistic effect between alloy elements, optimizing the smelting process and carrying out appropriate solid solution treatment and aging heat treatment, an extrusion casting magnesium alloy with high strength and good plasticity is prepared.

[0005] To solve the above technical problems, the present application provides the following technical scheme:

[0006] A high strength and toughness extrusion casting magnesium alloy contains Mg 17 Al 12 strengthening phase, MgZn strengthening phase and Al 11 RE3 strengthening phase, RE is La, Ce or Nd; and further contains Al2Gd phase, Al2Y phase and / or Al2Sm phase.

[0007] The high-toughness extrusion-cast magnesium alloy is composed of the following components in mass percentage: 4.0-6.0 wt.% of aluminum, 1.0-3.0 wt.% of zinc, 4.0-6.0 wt.% of a first rare earth component, 1.5-3.0 wt.% of a second rare earth component, 0.3-0.5 wt.% of manganese, 0.2-0.5 wt.% of zirconium, and the balance of magnesium and inevitable impurities, with the mass percentage of the impurities being less than or equal to 0.3 wt.%.

[0008] The first rare earth component is at least one of lanthanum, cerium and neodymium, and the second rare earth component is at least one of gadolinium, yttrium and samarium.

[0009] When the components of the elements in the alloy are within the ranges, the elements can effectively form a synergistic effect, and by adding appropriate melting processes, solid solution treatment and aging heat treatment methods, the microstructure of the alloy can be optimized to obtain an extrusion-cast magnesium alloy with high strength and good plasticity.

[0010] The high-toughness extrusion-cast magnesium alloy is composed of the following components in mass percentage: 4.0-6.0 wt.% of aluminum, 1.0-3.0 wt.% of zinc, 4.0-6.0 wt.% of a first rare earth component, 1.5-3.0 wt.% of a second rare earth component, 0.3-0.5 wt.% of manganese, 0.2-0.5 wt.% of zirconium, and the balance of magnesium and inevitable impurities, with the mass percentage of the impurities being less than or equal to 0.3 wt.%.

[0011] Step (1), preheating of raw materials: the pure magnesium ingot, pure aluminum ingot, magnesium-zinc intermediate alloy, magnesium-manganese intermediate alloy, magnesium-zirconium intermediate alloy and magnesium-rare earth intermediate alloy as raw materials are heated to a preheating temperature and kept at the temperature;

[0012] Step (2), alloy melting: in a protective atmosphere, the preheated raw materials are added to a melting equipment and melted, and then refined to obtain a magnesium alloy melt;

[0013] Step (3), extrusion casting: the magnesium alloy melt obtained in step (2) is subjected to extrusion casting to obtain a magnesium alloy casting;

[0014] Step (4), heat treatment: the magnesium alloy casting obtained in step (3) is subjected to solid solution treatment and aging treatment, and then air-cooled to room temperature after the aging treatment is completed.

[0015] Smelting includes melting and refining processes. During the preparation of this magnesium alloy, the melting order and temperature of each raw material should not be altered. Since pure aluminum ingots, magnesium-zinc master alloys, and magnesium-manganese master alloys have relatively low melting points, they are melted first at lower temperatures. Magnesium rare earth master alloys, however, have relatively high melting points and require higher temperatures to melt. Furthermore, if rare earth master alloys remain in the melt for too long after melting, gravity segregation will occur, resulting in uneven distribution of rare earth elements in the alloy, directly affecting the alloy's microstructure and properties. Therefore, the melting order of magnesium rare earth master alloys should be as late as possible. Although magnesium-zirconium master alloys also have low melting points and could theoretically be added in the first stage of melting, Zr mainly plays a grain-refining role, and Zr tends to precipitate easily when present in the melt for a long time, weakening the grain-refining effect. Therefore, magnesium-zirconium master alloys are added in the final stage of melting and melted at a temperature lower than that of magnesium rare earth master alloys. By adding zinc to magnesium-zinc master alloys, manganese to magnesium-manganese master alloys, zirconium to magnesium-zirconium master alloys, and rare earth elements to magnesium-rare earth master alloys, and by combining specific melting sequences and melting temperatures, it is possible to fully melt all components, ensure uniform distribution of each element in the alloy, minimize the difference in element content at any location in the melt, and prevent a decrease in the grain-refining effect of Zr on the alloy.

[0016] During smelting, rapid heating may affect the uniformity of alloy composition, leading to severe oxidation on the melt surface, increasing the content of oxides and other inclusions, affecting the purity and mechanical properties of the alloy, and may also cause porosity in the alloy.

[0017] In squeeze casting, if the casting temperature is too low, the fluidity of the alloy melt is poor, which is not conducive to filling the mold and can easily lead to incomplete filling. If the casting temperature is too high, the melt can easily spray out from the mold parting surface or the gap between the hammer and the gate, and the melt is prone to oxidation, increasing defects such as oxide inclusions. At the same time, the excessively high melt temperature also increases the melting cost. Excessive holding pressure in squeeze casting increases costs and places higher demands on the mold, requiring a greater pressure-bearing capacity. At the same time, excessive pressure can easily cause molten metal to spray out from the gap. If the holding pressure is too low, the forced feeding effect during the alloy solidification process is weakened, which can easily lead to casting defects such as shrinkage cavities and porosity, thereby reducing the alloy's performance. Excessively long holding time has little effect on the alloy's microstructure and properties, but too short a holding time may cause the solution in the core of the casting to not solidify completely, affecting the feeding effect during solidification, easily leading to casting defects and reducing the alloy's performance.

[0018] Excessive solution time leads to grain growth, which is detrimental to improving the alloy's mechanical properties. Insufficient solution time results in incomplete decomposition of compounds in the alloy, failing to achieve a satisfactory solution effect. Excessively high solution temperature easily causes overheating and also leads to grain growth, which is detrimental to improving the alloy's mechanical properties. Insufficient solution temperature results in a poorer solution effect, requiring an extended solution time. Insufficient aging time will not reach the peak aging state, and the alloy's mechanical properties will not be at their maximum. Excessively long aging time will cause the precipitated phase to grow larger, which is detrimental to improving the alloy's mechanical properties. Insufficient aging temperature requires a longer time to achieve a good aging effect. Insufficient aging temperature will reduce the alloy's mechanical properties. This invention, by adjusting the solution treatment temperature to 480–500℃, the solution treatment holding time to 2–8h, the aging treatment temperature to 170–200℃, and the aging treatment holding time to 2–30h, enables zirconium, manganese, aluminum, zinc, the first rare earth component, and the second rare earth component to fully exert their synergistic effect. This allows each strengthening element to exist in the magnesium alloy as a fine-grained strengthening phase as much as possible, thereby significantly improving the strength and plasticity of extruded cast magnesium alloys.

[0019] The technical solution of the present invention achieves the following beneficial technical effects:

[0020] 1. The high-strength and high-toughness extrusion casting method for preparing magnesium alloys provided in this invention optimizes the alloy composition, the order of raw material addition during smelting, and the temperature during raw material melting. This results in a melt with uniform alloy element distribution, which facilitates sufficient contact between rare earth elements, magnesium, aluminum, and zinc to form a uniformly distributed strengthening phase and prevents the weakening of grain refinement caused by zirconium precipitation. Furthermore, an extrusion casting method is adopted to obtain castings with smaller grain sizes. The solution temperature, aging temperature, and holding time of the resulting magnesium alloy castings are further optimized to ensure suitable element solubility under specific heat treatment temperature and time conditions, preventing significant grain size increase during heat treatment. This results in a magnesium alloy with fine grains and a dense structure, exhibiting both high strength and good plasticity. Compared to existing technologies, the magnesium alloy material of this invention exhibits excellent strength and plasticity even after direct solution and aging treatment in the as-cast state. This material achieves high mechanical properties without requiring deformation treatments (such as homogenization and forging). Specifically, its tensile strength can reach 200MPa–221MPa, its yield strength is 305MPa–330MPa, and its elongation is 10.9%–15.8%. This performance level shows significant advantages compared to conventional as-cast alloys or as-cast alloys that have undergone solution aging treatment, and can meet the demand for high-performance magnesium alloys in the automotive lightweighting field.

[0021] 2. The magnesium alloy provided by this invention contains added Al, which can significantly improve the casting performance of the alloy. Under the preparation process of this invention, Al can form Mg with Mg. 17 Al 12 The strengthening phase, and by strictly controlling the Al content within a specific range, can prevent the formation of excessively large Mg phases. 17 Al 12 Furthermore, in the magnesium alloy prepared using the method of this invention, Zn can form a MgZn strengthening phase with Mg, which also strengthens the magnesium alloy. The solid solubility of Zn in Mg changes significantly with temperature; this invention further improves the mechanical properties of the alloy by adjusting the process parameters of solution treatment and aging treatment. Since Zr has a grain-refining effect on the alloy, it can improve the strength and plasticity of the alloy by reducing the grain size. In this invention, the Zr-containing intermediate alloy is melted last during the alloy smelting process, preventing Zr precipitation in the melt and fully utilizing the grain-refining effect of Zr.

[0022] 3. In the magnesium alloy prepared by the method of the present invention, La, Ce and Nd react with Al to form Al2O3. 11 RE3 compounds are reinforcing phases; Gd, Y, and Sm react with Al to form Al2Gd, Al2Y, and Al2Sm compounds, which in turn react with Al. 11 RE3 exhibits crystallographic matching relationships, which can optimize Al. 11 The morphology and size distribution of RE3 were improved, and the mechanical properties of the alloy were optimized. On one hand, when the total addition of La, Ce, and Nd was 4.0 wt.% to 6.0 wt.%, and the total addition of Gd, Y, and Sm was 1 / 2 to 1 / 3 of the total addition of La, Ce, and Nd, under the preparation method of this invention, the Al2Gd, Al2Y, and Al2Sm compounds (collectively referred to as Al2RE compounds) in the alloy reacted with Al... 11 With a suitable ratio of RE3, Al2RE compounds can effectively alter Al. 11RE3 does not rupture the alloy matrix, and the Al2Gd, Al2Y, and Al2Sm compounds are relatively small in size (if the addition of Gd, Y, and Sm is excessive, the size of the Al2Gd, Al2Y, and Al2Sm compounds will also be too large). On the other hand, the solid solubility of Gd, Y, and Sm in Mg changes significantly with temperature, making it possible to further improve the mechanical properties of the alloy by optimizing heat treatment parameters. Ultimately, under the premise of appropriate addition of Gd, Y, and Sm elements, this invention prevents excessive growth of precipitates by precisely controlling the solution treatment temperature to 480–500℃ and the holding time to 2–8 h, and the aging treatment temperature to 170–200℃ and the holding time to 2–30 h. Furthermore, the addition of Mn accelerates the aging hardening process (allowing the alloy to reach its highest mechanical properties in a shorter time), further reducing the problem of increased precipitate grain size caused by long-term aging treatment. Based on this, Zr refines the alloy grains, and Mg... 17 Al 12 MgZn, Al2RE and Al 11 The RE3 atoms are tightly bonded together to form a stable crystal structure, resulting in a smaller grain size, improved microstructure uniformity, and further enhanced alloy density. Ultimately, a suitable alloy composition and preparation method result in a magnesium alloy with both high strength and ductility.

[0023] 4. The high-strength, high-toughness extrusion-cast magnesium alloy proposed in this invention features a carefully selected alloying element composition. This reduces the content of expensive heavy rare earth elements while increasing the content of inexpensive light rare earth elements. Furthermore, under the rare earth element addition amounts and proportions provided by this invention, the alloying elements in the magnesium alloy exhibit synergistic effects, and the compounds of each element also exhibit significant modifying effects. Additionally, the solid solubility of each rare earth element is suitable under the preparation method provided by this invention, further enhancing the mechanical properties of the alloy. The strategy of composite addition of light and heavy rare earth elements also significantly reduces the manufacturing cost of the alloy compared to traditional GWK-based magnesium alloys, providing economic feasibility for the large-scale application of magnesium alloy materials.

[0024] 5. This invention optimizes the content of alloying elements, fully utilizes the synergistic effects between them, optimizes the microstructure of the alloy, and performs solution aging heat treatment to fully leverage the heat treatment strengthening effect of the alloying elements, ultimately producing a squeeze-cast magnesium alloy with both high strength and good plasticity. Squeeze-cast magnesium alloy castings cool faster than those produced by metal mold and sand casting, resulting in smaller grain sizes. Simultaneously, squeeze-cast magnesium alloy castings have fewer internal defects such as porosity, shrinkage cavities, and porosity compared to die casting and gravity casting. Therefore, the mechanical properties of the alloy can be further improved through heat treatment. Compared to existing technologies, the magnesium alloy preparation process of this invention is simpler; the magnesium alloy of this invention directly achieves excellent mechanical properties through solution aging treatment in the as-cast state. This optimization not only reduces preparation costs but also improves production efficiency. Attached Figure Description

[0025] Figure 1 Microstructure photograph of the high-strength and high-toughness extruded cast magnesium alloy obtained in Example 14 of this invention. Detailed Implementation

[0026] Example 1

[0027] In this embodiment, the mass percentages of each component in the high-strength and high-toughness extruded cast magnesium alloy are as follows: 4 wt.% Al, 1 wt.% Zn, 0.3 wt.% Mn, 0.2 wt.% Zr, 4 wt.% La and 1.5 wt.% Gd, with the total amount of impurities less than or equal to 0.3 wt.% and the balance being Mg.

[0028] The preparation method of high-strength and high-toughness extrusion-cast magnesium alloy in this embodiment includes the following steps:

[0029] (1) Raw material preheating: Pure magnesium ingots, pure aluminum ingots, magnesium-zinc master alloy, magnesium-manganese master alloy, magnesium-zirconium master alloy, magnesium-lanthanum master alloy and magnesium-gadolinium master alloy are preheated at 150°C for 2 hours (in Examples 2 to 20 and Comparative Examples 1 to 4, the addition of each element is the same as in Example 1, that is: except for magnesium and aluminum, the other elements are added in the form of magnesium master alloy).

[0030] (2) Melting: This is carried out in a crucible resistance furnace. The inner wall of the crucible is uniformly coated with a coating, dried, and then a mixture of SF6 and CO2 (the volume ratio of SF6 to CO2 in the mixture is 1:6) is continuously introduced into the crucible. The raw material is melted in the protective atmosphere formed by this mixture. When melting the raw material, the preheated pure magnesium ingot is first heated to 700°C along with the resistance furnace at a heating rate of 10°C / min to melt the pure magnesium ingot. After the pure magnesium ingot is melted, it is then added sequentially or simultaneously at 680-700°C. Pure aluminum ingots, magnesium-zinc master alloys, and magnesium-manganese master alloys are added and held at the temperature until they are completely melted to obtain a first mixture. Then, the temperature is raised to 720-750°C, and a preheated magnesium rare earth master alloy is added to the first mixture for melting. After the magnesium rare earth master alloy has completely melted, a second mixture is obtained. Heating is stopped, and the second mixture is cooled to 680-700°C. A preheated magnesium-zirconium master alloy is added to the second mixture, and the mixture is stirred with a stainless steel rod to obtain a melt to be refined.

[0031] (3) Refining: The melt to be refined is heated to 720-740°C at a heating rate of 10°C / min, and then 1wt.% to 4wt.% of the total mass of the raw materials are added to refine the melt. The refining agent is composed of a mixture of sodium chloride and calcium chloride, and the mass ratio of sodium chloride to calcium chloride is 1:1. After refining, the melt is allowed to stand at 710-720°C for 10 minutes, and then cooled to 690°C to remove the slag, thus obtaining the magnesium alloy melt.

[0032] (4) Extrusion casting: Magnesium alloy melt is extruded at 690℃. The extrusion casting process parameters are: extrusion pressure 30MPa, holding time 50s, mold preheating temperature 200℃. Magnesium alloy casting is obtained after extrusion casting.

[0033] (5) Heat treatment: The magnesium alloy casting obtained in step (4) is kept at 480°C for 2 hours for solution treatment. After the solution treatment, it is air-cooled to room temperature at a rate of 40°C / min. Then the solution-treated casting is kept at 170°C for 25 hours for aging treatment. After the aging treatment, the magnesium alloy casting is air-cooled to room temperature at a rate of 40°C / min.

[0034] The room temperature mechanical properties of the magnesium alloy prepared in Example 1 are shown in Table 1.

[0035] Examples 2 to 20

[0036] The mass percentages of some components in the high-strength and high-toughness extruded cast magnesium alloys of Examples 2 to 20 are shown in Table 2. The total amount of impurities is less than or equal to 0.3 wt.%, and the balance is Mg.

[0037] The preparation methods of the high-strength and high-toughness extrusion-cast magnesium alloys in Examples 2 to 20 are the same as those in Example 1. The differences in specific process parameters are shown in Table 3.

[0038] The room temperature mechanical properties test results of the high strength and toughness extruded cast magnesium alloys of Examples 2 to 20 are shown in Table 1.

[0039] Comparative Example 1

[0040] The mass percentages of some components in the high-strength and high-toughness extruded cast magnesium alloy of this comparative example are shown in Table 2. The total amount of impurities is less than or equal to 0.3 wt.%, and the balance is Mg.

[0041] The preparation method of the high-strength and high-toughness extrusion-cast magnesium alloy in this comparative example includes the following steps:

[0042] (1) Raw material preheating: The method of raw material preheating is the same as in Example 1. For the differences in specific process parameters, please refer to Table 3.

[0043] (2) Melting: The main difference between the melting method and Example 1 is that after the pure magnesium ingot is melted, pure aluminum ingot and magnesium-manganese intermediate alloy are added sequentially or simultaneously at 680-700°C, and the mixture is kept at the temperature until the pure aluminum ingot and magnesium-manganese intermediate alloy are completely melted to obtain the first mixture; the rest of the operation is the same as in Example 1.

[0044] (3) Refining: The refining method is the same as in Example 1.

[0045] (4) Squeeze casting: The squeeze casting method is the same as in Example 1. The difference in specific process parameters is shown in Table 3.

[0046] (5) Heat treatment: The heat treatment method is the same as in Example 1. The difference in specific process parameters is shown in Table 3.

[0047] The room temperature mechanical properties of the magnesium alloy prepared in Comparative Example 1 are shown in Table 1.

[0048] Comparative Example 2

[0049] The mass percentages of some components in the high-strength and high-toughness extruded cast magnesium alloy of this comparative example are shown in Table 2. The total amount of impurities is less than or equal to 0.3 wt.%, and the balance is Mg.

[0050] The preparation method of the high-strength and high-toughness extruded cast magnesium alloy in this comparative example is the same as that in Example 1. The differences in specific processing parameters are shown in Table 3.

[0051] The room temperature mechanical properties of the magnesium alloy prepared in Comparative Example 2 are shown in Table 1.

[0052] Comparative Example 3

[0053] The mass percentages of some components in the high-strength and high-toughness extruded cast magnesium alloy of this comparative example are shown in Table 2. The total amount of impurities is less than or equal to 0.3 wt.%, and the balance is Mg.

[0054] The preparation method of the high-strength and high-toughness extrusion-cast magnesium alloy in this comparative example includes the following steps:

[0055] (1) Raw material preheating: The method of raw material preheating is the same as in Example 1. For the differences in specific process parameters, please refer to Table 3.

[0056] (2) Melting: The main difference between the melting method and Example 1 is that after the pure magnesium ingot is melted, pure aluminum ingot and magnesium-manganese intermediate alloy are added sequentially or simultaneously at 680-700°C, and the mixture is kept at the temperature until the pure aluminum ingot and magnesium-manganese intermediate alloy are completely melted to obtain the first mixture; the rest of the operation is the same as in Example 1.

[0057] (3) Refining: The refining method is the same as in Example 1.

[0058] (4) Squeeze casting: The squeeze casting method is the same as in Example 1. The difference in specific process parameters is shown in Table 3.

[0059] (5) Heat treatment: The heat treatment method is the same as in Example 1. The difference in specific process parameters is shown in Table 3.

[0060] The room temperature mechanical properties of the magnesium alloy prepared in Comparative Example 3 are shown in Table 1.

[0061] Comparative Example 4

[0062] The mass percentages of some components in the high-strength and high-toughness extruded cast magnesium alloy of this comparative example are shown in Table 2. The total amount of impurities is less than or equal to 0.3 wt.%, and the balance is Mg.

[0063] The preparation method of the high-strength and high-toughness extruded cast magnesium alloy in this comparative example is the same as that in Example 1. The differences in specific processing parameters are shown in Table 3.

[0064] The room temperature mechanical properties of the magnesium alloy prepared in Comparative Example 4 are shown in Table 1.

[0065] Table 1. Results of room temperature mechanical properties test

[0066]

[0067] Table 2 shows the proportions of raw materials other than magnesium in each example or comparative example.

[0068]

[0069]

[0070] Table 3 Comparison of squeeze casting process parameters in each embodiment or comparative example

[0071]

[0072] Tables 2 and 3 compare the proportions of raw materials other than magnesium and the extrusion casting process parameters in each embodiment or comparative example. Some identical process parameters, such as the temperature during extrusion casting and the temperature during refining, are not shown in the tables. Combining Tables 1, 2, and 3, and comparing the embodiments and comparative examples, it can be seen that the composition of the magnesium alloy and the casting process parameters both affect the properties of the magnesium alloy.

[0073] The magnesium alloys provided in the above embodiments contain added Al, which significantly improves the casting performance of the alloys. Under the preparation process described in the above embodiments, Al can form Mg with Mg. 17 Al 12 The strengthening phase, and by strictly controlling the Al content within a specific range, can prevent the formation of excessively large Mg phases. 17 Al 12 Furthermore, in the magnesium alloy prepared using the methods described in the above embodiments, Zn can form a MgZn strengthening phase with Mg, which also strengthens the magnesium alloy. The solid solubility of Zn in Mg changes significantly with temperature. In the above embodiments, the mechanical properties of the alloy were further improved by adjusting the process parameters of solution treatment and aging treatment. Since Zr has a grain-refining effect on the alloy, it can improve the strength and plasticity of the alloy by reducing the grain size. In the above embodiments, during the alloy smelting process, the Zr-containing intermediate alloy was melted last to prevent Zr precipitation in the melt, thus fully utilizing the grain-refining effect of Zr.

[0074] In the magnesium alloy prepared by the method described in the above embodiments, La, Ce, and Nd react with Al to form Al2O3. 11 RE3 reinforced phase, Gd, Y and Sm react with Al to form Al2Gd, Al2Y and Al2Sm compounds respectively, and Al 11 RE3 exhibits crystallographic matching relationships, which can optimize Al. 11 The morphology and size distribution of RE3 were improved, and the mechanical properties of the alloy were optimized. On one hand, when the total addition of La, Ce, and Nd is 4.0 wt.% to 6.0 wt.%, and the total addition of Gd, Y, and Sm is 1 / 2 to 1 / 3 of the total addition of La, Ce, and Nd, under the preparation method described in the above examples, the Al2Gd, Al2Y, and Al2Sm compounds (collectively referred to as Al2RE compounds) in the alloy react with Al... 11 With a suitable ratio of RE3, Al2RE compounds can effectively alter Al. 11 RE3, and Al 11The morphology and size distribution of RE3 were fully optimized and improved without disrupting the alloy matrix, and the sizes of Al2Gd, Al2Y, and Al2Sm compounds were relatively small (if the addition of Gd, Y, and Sm is excessive, the sizes of Al2Gd, Al2Y, and Al2Sm compounds will also be too large). On the other hand, the solid solubility of Gd, Y, and Sm in Mg changes significantly with temperature, making it possible to further improve the mechanical properties of the alloy by optimizing heat treatment parameters. Ultimately, under the premise of appropriate addition of Gd, Y, and Sm elements, by precisely controlling the solution treatment temperature to 480–500℃ and the holding time to 2–8 h, and the aging treatment temperature to 170–200℃ and the holding time to 2–30 h, excessive growth of precipitates was prevented. Furthermore, the addition of Mn accelerated the aging hardening process (allowing the alloy to reach its highest mechanical properties in a shorter time), further reducing the problem of increased precipitate grain size caused by long-term aging treatment. Based on this, Zr refined the alloy grains, and Mg... 17 Al 12 MgZn, Al2RE and Al 11 The RE3 atoms are tightly bonded together to form a stable crystal structure, resulting in a smaller grain size, improved microstructure uniformity, and further enhanced alloy density. Ultimately, a suitable alloy composition and preparation method result in a magnesium alloy with both high strength and ductility.

[0075] As shown in Table 1, the alloys prepared in the above embodiments have high tensile strength and yield strength, and good elongation at break. With the addition of Gd, Y, or Sm elements, Al2Gd, Al2Y, or Al2Sm compounds will be formed in the alloy, respectively. These compounds can modify Al 11 RE3 compounds can further improve the mechanical properties of the alloy.

[0076] As shown in Table 1, the high-strength and high-toughness extruded cast magnesium alloy prepared in Example 14 has a good strength-plasticity match. Figure 1 This is a micrograph of the high-strength, high-toughness extruded cast magnesium alloy obtained in Example 14. Figure 1 It can be seen that the microstructure of the magnesium alloy prepared in Example 14 mainly consists of fine and dispersed needle-like and fine granular Al particles. 11 Composed of RE3 compounds, bulk Al2RE compounds, and a small amount of discontinuously distributed small-sized Mg. 17 Al 12 Compounds and MgZn compounds, which are beneficial for alloys to have both high strength and good plasticity.

[0077] Obviously, the above comparative examples are merely illustrative for clarity and not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A high-strength, high-toughness extrusion-cast magnesium alloy, characterized in that, Not only contains Mg 17 Al 12 Strengthening phase, MgZn strengthening phase and Al 11 RE3 strengthening phase, RE is La, Ce or Nd; also contains Al2Gd phase, Al2Y phase and / or Al2Sm phase.

2. The high-strength, high-toughness extruded cast magnesium alloy according to claim 1, characterized in that, The alloy is composed of the following components by mass percentage: 4.0 wt.% to 6.0 wt.% aluminum, 1.0 wt.% to 3.0 wt.% zinc, 4.0 wt.% to 6.0 wt.% first rare earth component, 1.5 wt.% to 3.0 wt.% second rare earth component, 0.3 wt.% to 0.5 wt.% manganese, 0.2 wt.% to 0.5 wt.% zirconium, with the balance being magnesium and unavoidable impurities; the impurities are less than or equal to 0.3 wt.% by mass. The first rare earth component is at least one of lanthanum, cerium and neodymium, and the second rare earth component is at least one of gadolinium, yttrium and samarium.

3. The high-strength, high-toughness extruded cast magnesium alloy according to claim 2, characterized in that, The first rare earth component is lanthanum and cerium, and the second rare earth component is gadolinium; the mass ratio of the first rare earth component to the second rare earth component is (2-3):

1.

4. The high-strength, high-toughness extruded cast magnesium alloy according to claim 3, characterized in that, The alloy is composed of the following components by mass percentage: 6.0 wt.% aluminum, 2.0 wt.% zinc, 3.0 wt.% lanthanum, 2.0 wt.% cerium, 2.0 wt.% gadolinium, 0.4 wt.% manganese, 0.5 wt.% zirconium, with the balance being magnesium and unavoidable impurities; the mass percentage of impurities is less than or equal to 0.3 wt.%.

5. A method for preparing high-strength and high-toughness extrusion-cast magnesium alloy, characterized in that, The high-strength, high-toughness extrusion-cast magnesium alloy, as described in any one of claims 1-4, is prepared according to the following steps: Step (1) Raw material preheating: Heat the pure magnesium ingot, pure aluminum ingot, magnesium-zinc master alloy, magnesium-manganese master alloy, magnesium-zirconium master alloy and magnesium rare earth master alloy as raw materials to the preheating temperature and keep them warm. Step (2), alloy melting: In a protective atmosphere, preheated raw materials are added to and melted in the melting equipment, and then refined to obtain magnesium alloy melt; Step (3), squeeze casting: The magnesium alloy melt obtained in step (2) is squeeze cast to obtain magnesium alloy castings; Step (4) Heat treatment: The magnesium alloy casting obtained in step (3) is subjected to solution treatment and aging treatment. After the aging treatment is completed, it is air-cooled to room temperature.

6. The method for preparing high-strength and high-toughness extrusion-cast magnesium alloy according to claim 5, characterized in that, Step (2) includes the following steps: Step (2-1): Heat the pure magnesium ingot together with the smelting equipment to melt the pure magnesium ingot. Then, at the first melting temperature, add pure aluminum ingot, magnesium-zinc master alloy and magnesium-manganese master alloy to the melted pure magnesium ingot in sequence or simultaneously, and keep it at the temperature until the pure aluminum ingot, magnesium-zinc master alloy and magnesium-manganese master alloy are completely melted to obtain the first mixture. Step (2-2): Heat the first mixture to the second melting temperature, add magnesium rare earth master alloy to the first mixture, and keep it heated until the magnesium rare earth master alloy is completely melted to obtain the second mixture; Step (2-3): Cool the second mixture to the third melting temperature, add magnesium-zirconium master alloy to the second mixture, keep it at the temperature and stir until the magnesium-zirconium master alloy melts to obtain the melt to be refined; Steps (2-4): Heat the melt to be refined to the refining temperature at a heating rate of 10℃ / min, add a refining agent composed of a mixture of sodium chloride and calcium chloride to the melt to be refined, and refine it. The mass ratio of sodium chloride to calcium chloride is: sodium chloride: calcium chloride = 1:

1. Then, let it stand and skim off the scum in sequence to obtain magnesium alloy melt.

7. The method for preparing high-strength and high-toughness extrusion-cast magnesium alloy according to claim 6, characterized in that, In step (1), the preheating temperature is 150-200℃ and the holding time is 1-2 hours; In step (2-1), the pure magnesium ingot is heated to 700℃ along with the smelting equipment, and the first melting temperature is 680~700℃; in step (2-2), the second melting temperature is 720~750℃; in step (2-3), the third melting temperature is 680~700℃. In steps (2-4), the amount of refining agent added is 1 wt.% to 4 wt.% of the total mass of the raw materials, and the refining temperature is 720 to 740℃. After refining, the mixture is first allowed to stand at 710 to 720℃ for 10 minutes, and then cooled to 680 to 700℃ to remove the scum.

8. The method for preparing high-strength and high-toughness extrusion-cast magnesium alloy according to claim 5, characterized in that, In step (3), the mold used for extrusion casting is preheated to 200-300℃, the temperature during extrusion casting is 680-700℃, the pressure during extrusion casting is 30-80 MPa, and the holding time is 30-50 s; In step (4), the solution treatment temperature is 480-500℃, the solution treatment holding time is 2-8h, and after the solution treatment, the magnesium alloy casting is air-cooled to room temperature at a cooling rate of 40℃ / min; the aging treatment temperature is 170-200℃, the aging treatment holding time is 2-30h, and after the aging treatment, the cooling rate of air-cooling to room temperature is 40℃ / min.

9. The method for preparing high-strength and high-toughness extrusion-cast magnesium alloy according to claim 8, characterized in that, In step (3), the mold used for extrusion casting is preheated to 300°C, the temperature during extrusion casting is 690°C, the pressure during extrusion casting is 80 MPa, and the holding time is 40 s. In step (4), the solution treatment temperature is 500℃ and the solution treatment holding time is 8h; the aging treatment temperature is 200℃ and the aging treatment holding time is 10h.

10. The method for preparing high-strength and high-toughness extrusion-cast magnesium alloy according to claim 5, characterized in that, In step (2), the protective atmosphere is a mixture of SF6 and CO2, with a volume ratio of SF6 to CO2 of 1:6.

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