High-ductility magnesium alloy and method for producing the same

Abstract

The application provides a high-toughness magnesium alloy large-deformation composite extrusion method and belongs to the field of magnesium alloy materials and deformation processing thereof.The existing extrusion mode is optimized, the cooperation relationship between a billet and a die cavity is realized by changing the shape and size of the extrusion billet, additional upsetting strain is introduced in the extrusion process, single-pass upsetting extrusion composite deformation is realized, the grain is refined, the mechanical properties are improved, and the temperature rise caused by the large deformation process is relieved by cooperating with the differential temperature extrusion mode to relieve the grain growth caused by the temperature rise in the large deformation process.The upsetting and extrusion composite deformation is realized in the single-pass extrusion process, the process flow is shortened, the die shape does not need to be changed, different structures and properties can be obtained by controlling the upsetting amount of the billet, and the short-flow high-freedom high-performance magnesium alloy preparation is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of magnesium alloy materials and their deformation processing, in particular to a high strength and toughness magnesium alloy large deformation composite extrusion method. BACKGROUND

[0002] Under the background of the continuous promotion of the "double carbon" goal and the urgent demand for weight reduction of major equipment, lightweight has become a prominent research direction in the field of metal structural materials. Magnesium alloys have a variety of excellent properties, such as low relative density, good strength and toughness. Effective weight reduction and good plasticity and toughness make magnesium alloys have broad application prospects in the fields of automobiles, electronic communications, aerospace, etc.

[0003] The high cost and scarcity of heavy rare earth elements (Gd, Ho, etc.) limit their large-scale use in industrial production. Among a series of rare earth-free magnesium alloys, Mg-Al-Sn-Ca alloy provides a low-cost way to develop new deformation magnesium alloys with high strength and plasticity. Mg-Al-based alloy is the most widely used magnesium alloy system, with good strength and ductility. The addition of Sn can reduce the stacking fault energy of magnesium and form a high-temperature melting point phase of Mg2Sn, which inhibits the growth of dynamic recrystallized grains and improves the plasticity of Mg-Al alloy. Ca is a rich and inexpensive element, and its atomic size is similar to that of rare earth elements. Adding Ca to magnesium alloys can reduce the stacking fault energy, form CaMgSn intermetallic compounds and randomize the texture, thereby improving the strength and plasticity of magnesium alloys.

[0004] Asymmetric extrusion technology makes full use of the characteristics of magnesium alloys that are prone to dynamic recrystallization. By introducing shear deformation, dynamic recrystallization is promoted, and the basal plane texture is weakened or tilted, which can improve the mechanical properties of magnesium alloys through single-pass extrusion. Invention patent CN112570480B discloses a method for realizing texture weakening of ATX magnesium alloy sheet by asymmetric extrusion, which better improves the forming performance of magnesium alloy extruded sheet.

[0005] By changing the shape of the billet to achieve upsetting-extrusion composite deformation, a large number of dislocations and twins can be formed in the extruded billet at the beginning of extrusion, generating a large number of nucleation sites to promote recrystallization and refine the grains. However, a large amount of deformation heat and friction heat is often generated during large deformation, which can cause the fine grains that have undergone recrystallization to grow at the later stage of extrusion, which is not conducive to mechanical properties. By controlling the temperature difference between the mold and the extruded billet, differential temperature extrusion can alleviate the temperature rise caused by large deformation. Invention patent CN115478199B discloses a high strength and toughness magnesium alloy deformation material and a preparation method thereof, which obtains a good balance of strength and plasticity by differential temperature extrusion. However, the total mass percentage of alloying elements in the magnesium alloy used in the said patent is more than 7%, and the extrusion speed is slow, which is not conducive to low-cost and efficient production.

[0006] Therefore, it is necessary to develop a short process high-efficiency preparation method of magnesium alloy which can be used in actual industrial production, and realize high strength and plasticity synergy in medium and low alloy content magnesium alloy. SUMMARY

[0007] The purpose of the present application is to provide a high strength and toughness magnesium alloy large deformation composite extrusion method, which optimizes the existing extrusion method, changes the shape and size of the extrusion billet, realizes the different matching relationship between the billet and the mold cavity, introduces additional upsetting strain in the extrusion process, realizes single pass upsetting extrusion composite deformation, refines the grain, improves the mechanical properties, and at the same time cooperates with the differential temperature extrusion method, relieves the grain growth caused by temperature rise in the large deformation process, and realizes the short process low cost efficient production of high strength and toughness magnesium alloy.

[0008] To achieve the above purpose, the present application provides the following technical scheme:

[0009] A high strength and toughness magnesium alloy large deformation composite extrusion method, comprising three steps of casting billet preparation, stepwise solid solution heat treatment, differential temperature asymmetric upsetting extrusion, and the specific operation is:

[0010] Step one: taking high-purity Mg ingot, high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy as raw materials, and according to the proportion of aluminum: 1.0-6.0wt%, tin: 0.2-1.2wt%, calcium: 0.1-0.6wt%, and the balance of magnesium, the above raw materials are weighed, then the above raw materials are alloy smelting, the obtained alloy melt is gravity cast into ingot, and then the cast ingot is removed, polished and prepared for the next step;

[0011] Step two: the obtained ingot in step one is placed in a heat treatment furnace, and the ingot is subjected to stepwise solid solution treatment, and immediately after the heat treatment program is finished, the ingot is water quenched to obtain better solid solution effect;

[0012] The step-by-step solid solution treatment is set as three stages, the first stage is heated from room temperature to 320-380 DEG C, and is kept at the corresponding temperature for 2-3 hours, the purpose of this stage is to prevent the ingot from cracking due to sudden heating; the second stage is heated from 320-380 DEG C to 420-430 DEG C, and is kept at the corresponding temperature for 2-4 hours, the purpose of this stage is to make the lower melting point intermetallic compound in the ingot remelt into the Mg matrix, improve the element segregation in the as-cast alloy, prevent the defects such as extrusion thermal cracks caused by segregation, and the alloy elements remelted can produce fine dynamic precipitates in the process of large deformation composite extrusion, which is beneficial to the improvement of mechanical properties; the third stage is heated from 420-430 DEG C to 470-490 DEG C, and is kept at the corresponding temperature for 2-3 hours, the purpose of this stage is to make the coarse and difficultly soluble phase melt as much as possible without growing, so as to prevent its adverse effect on the subsequent extrusion process and mechanical properties.

[0013] Step three: the heat treated blank obtained in step two is subjected to shape processing to obtain an extrusion blank, then the extrusion blank and the extrusion die are respectively coated with a lubricant and preheated, the extrusion blank is preheated at 380-400 DEG C for 20-60 minutes, and the extrusion die is preheated at 100-380 DEG C for 10-80 minutes; the extrusion die is selected as an asymmetric large shear extrusion die, the shape of the extrusion blank is selected as a circular truncated cone, a ladder-shaped or a rectangular cylindrical shape with a contour size smaller than the size of the extrusion cavity according to the shape of the extrusion die cavity and the requirement of different upsetting amount, so that the extrusion blank can realize synchronous upsetting deformation in the extrusion process; after preheating, the preheated extrusion blank is placed in the extrusion die cavity, the die temperature and the blank temperature are different to realize differential temperature asymmetric upsetting extrusion; then the extruded magnesium alloy is immediately water quenched to obtain an extruded magnesium alloy.

[0014] The high strength and toughness magnesium alloy prepared by the above method mainly comprises the following components in percentage by mass: aluminum:

[0015] 1.0-6.0wt%, tin: 0.2-1.2wt%, calcium: 0.1-0.6wt%, unavoidable impurity content ≤0.05%, and the balance is magnesium.

[0016] Preferably, the alloy melting process in step one is specifically as follows:

[0017] 1) melt high-purity Mg ingot, at the melting furnace temperature of 690-710 DEG C, the mixed protective gas with the volume fraction of 1% SF6 and 99% CO2 is introduced into the furnace body to reduce oxidation loss;

[0018] 2) after the Mg ingot is fully melted, high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy are sequentially added into the melt;

[0019] 3) After the alloy raw material is fully melted, the melt is sequentially subjected to stirring, argon blowing refining and slag removal operation, and the alloy melt is kept at 680-700 DEG C for 10 minutes to obtain the alloy melt.

[0020] Preferably, the mold for casting in step one is a sub-fast water-cooled copper mold, a Y-shaped iron mold or a cylindrical ingot iron mold.

[0021] Preferably, the heating process in step two has a heating rate of not more than 5 DEG C / min.

[0022] Preferably, in step two, a small amount of high-purity Ar gas is introduced into the heat treatment furnace during the stepwise solution treatment to protect the ingot from oxidation and burning loss.

[0023] Preferably, in step three, the specific operation of the outer shape processing mainly includes cutting the heat-treated blank using a wire electrical discharge machining device to obtain the required outer shape size, and polishing the cut blank with sandpaper to obtain an extrusion blank after removing the surface oxide layer.

[0024] Preferably, in step three, the die cavity of the asymmetric large shear extrusion die is rectangular or cylindrical, the extrusion ratio is 10-50, and the center line of the extrusion outlet to the length ratio of the two sides of the cavity is 1.1-4.

[0025] Preferably, in step three, the extrusion speed of the differential temperature asymmetric upsetting extrusion is 8-18 mm / s.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The present application realizes upsetting and extrusion composite deformation in a single pass extrusion process by designing the matching relationship of the extrusion blank with different shapes or sizes and the die cavity, shortens the process flow, promotes grain refinement during the large deformation upsetting extrusion process, and at the same time, without changing the shape of the die, different structures and properties can be obtained by controlling the upsetting amount of the blank, realizing short process and high degree of freedom high-performance magnesium alloy preparation.

[0028] (2) The present application realizes differential temperature extrusion by controlling the temperature difference between the extrusion die and the extrusion blank, so that the magnesium alloy extrusion blank can deform at a lower temperature, reducing the production cost, at the same time, relieving the temperature rise brought by large deformation process, preventing grain growth caused by excessive extrusion temperature, and being beneficial to stabilizing the mechanical properties of the product.

[0029] (3) The present application realizes high strength and high plasticity by using magnesium alloy with medium and low alloying element mass percentage, the total alloy mass fraction is not more than 6%, the mechanical properties reach the level of high alloy, breaking the strength and toughness barrier of magnesium alloy, and improving the strength and plasticity synergistically.

[0030] (4) The application proposes large deformation process coupled with differential temperature extrusion. The upsetting process before extrusion can activate the metal flow inside the blank to ensure the smoothness of the subsequent deformation process. The deformation heat and friction heat generated in the large deformation process can dynamically compensate the temperature difference between the blank and the die to maintain the extrusion temperature at a certain level. Under the comprehensive action, the conventional magnesium alloy, the difficult-to-deform rare earth magnesium alloy or part of the light alloy can realize large extrusion ratio high-speed extrusion at a lower extrusion temperature, and the application range is wider.

[0031] (5) The application can produce deformed magnesium alloy at a higher extrusion speed and obtain good mechanical properties. The extrusion exit speed can reach 20 m / min at the fastest, and high-efficiency production can be realized.

[0032] (6) The asymmetric extrusion die used in the application can introduce additional shear strain to randomize the grain orientation, which helps to improve the uniformity of the mechanical properties in each direction of the extruded magnesium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a schematic diagram of the trapezoidal extrusion blank shape and its placement method in the die;

[0034] Figure 2 It is a statistical diagram of the mechanical properties of the embodiment. DETAILED DESCRIPTION

[0035] The technical solutions in the application will be described clearly and completely below in combination with the drawings of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the application.

[0036] Example 1: Mg-3.8Al-1.1Sn-0.4Ca

[0037] A high-strength magnesium alloy large deformation composite extrusion method mainly includes three steps of casting blank preparation, stepwise solid solution heat treatment, differential temperature asymmetric upsetting extrusion. The specific operation is as follows:

[0038] (1) Casting blank preparation:

[0039] High-purity Mg ingot, high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy are used as raw materials, and the above raw materials are weighed according to the proportion of aluminum: 3.8wt%, tin: 1.1wt%, calcium: 0.4wt%, and the balance is magnesium, and alloy smelting is carried out;

[0040] The alloy smelting process comprises: melting high-purity Mg ingot, introducing mixed protective gas with a volume fraction of 1% SF6 and 99% CO2 into the furnace body at a smelting furnace temperature of 710 ℃ to reduce oxidation loss, after the Mg ingot is fully melted, high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy are sequentially added to the melt, after the alloy raw materials are fully melted, the melt is sequentially subjected to stirring, argon blowing refining and slag removal operation, after the alloy melt is kept at 690 ℃ for 10 minutes, it is poured into a sub-rapid water-cooled copper mold to obtain an ingot, the pouring riser is removed, and the oxide skin is polished for the next step of ladder solid solution heat treatment.

[0041] (2) Ladder solid solution heat treatment: the ingot obtained in the previous step is placed in a heat treatment furnace, and the ingot is subjected to ladder solid solution treatment, and the ladder solid solution treatment process can be set as three stages, the first stage is heated from room temperature to 375 ℃ and kept for 3 hours, the purpose of this stage is to prevent the ingot from cracking due to sudden heating; the second stage is heated from 375 ℃ to 430 ℃ and kept for 2 hours, the purpose of this stage is to make the lower melting point intermetallic compound in the ingot melt into the Mg matrix, improve the element segregation in the as-cast alloy, prevent the defects such as extrusion heat cracks caused by segregation, and the alloy elements melted in the process of large deformation composite extrusion can produce fine dynamic precipitates, which is beneficial to the improvement of mechanical properties; the third stage is heated from 430 ℃ to 490 ℃ and kept for 3 hours, the purpose of this stage is to make the coarse and difficult-to-dissolve phase melt as much as possible without growing, to prevent its adverse effects on the subsequent extrusion process and mechanical properties. The heating rate is not more than 5 ℃ / min, and a small amount of high-purity Ar gas is introduced into the heat treatment furnace to protect the ingot during the ladder solid solution treatment process to prevent oxidation loss. After the heat treatment program is finished, the ingot is immediately water quenched to obtain a better solid solution effect.

[0042] (3) Differential temperature asymmetric upsetting extrusion: using a wire cut electrical discharge machining device to cut the heat treated blank obtained in the previous step to obtain a ladder-shaped blank with an upper bottom width of 10 mm, a lower bottom width of 70 mm, a height of 45 mm, and a thickness of 10 mm. The cut blank is polished with sandpaper, and after removing the surface oxidation layer, a ladder-shaped extrusion blank is obtained. Graphite lubricant is applied to the surface of the extrusion blank and the surface of the asymmetric extrusion die cavity. The die cavity is rectangular, with a cavity size of 70 mm wide x 12 mm thick x 80 mm high. The extrusion ratio is 21, and the center line of the extrusion outlet to the length ratio of the two sides of the cavity is 1.5. The extrusion blank is placed in a heating furnace preheated to 400°C for 60 minutes. The die is preheated to 200°C with a heating jacket and kept for 20 minutes. The die temperature and the blank temperature are different to achieve differential temperature extrusion. After the extrusion blank and the extrusion die are preheated, the preheated extrusion blank is placed in the extrusion die, with the 70 mm lower bottom edge in contact with the bottom of the die cavity and the 10 mm upper bottom edge located on the shorter side of the die center line and side wall. Subsequently, positive extrusion is carried out at a speed of 16 mm / s. The extruded magnesium alloy is immediately water quenched to obtain an extruded magnesium alloy with a width of 20 mm and a thickness of 2 mm.

[0043] The main components of the magnesium alloy are: aluminum: 3.8wt%, tin: 1.1wt%, calcium: 0.4wt%, unavoidable impurities content ≤0.05%, and the balance is magnesium.

[0044] Example 2: Mg-2.0Al-0.8Sn-0.5Ca

[0045] A high strength and toughness magnesium alloy large deformation composite extrusion method mainly includes three steps of casting blank preparation, stepwise solid solution heat treatment, and differential temperature asymmetric upsetting extrusion. The specific operation is as follows:

[0046] (1) Casting blank preparation:

[0047] High-purity Mg ingot, high-purity Al block, high-purity Sn block, and Mg-20Ca intermediate alloy are used as raw materials. The above-mentioned raw materials are weighed according to the proportions of aluminum: 2.0wt%, tin: 0.8wt%, calcium: 0.5wt%, and the balance is magnesium, and alloy smelting is carried out;

[0048] The alloy smelting process comprises: melting high-purity Mg ingot, introducing mixed protective gas with a volume fraction of 1% SF6 and 99% CO2 into the furnace body at a smelting furnace temperature of 710 ℃ to reduce oxidation loss, and after the Mg ingot is fully melted, sequentially adding high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy into the melt, and after the alloy raw materials are fully melted, sequentially performing stirring, argon blowing refining and slag removal operations on the melt, and after the alloy melt is kept at 690 ℃ for 10 minutes, casting into a sub-rapid water-cooled copper mold to obtain an ingot, removing the casting riser, and polishing the oxide skin for the next step of ladder solid solution heat treatment.

[0049] (2) Ladder solid solution heat treatment: the ingot obtained in the previous step is placed in a heat treatment furnace, and the ingot is subjected to ladder solid solution treatment, and the ladder solid solution treatment process can be set as three stages, the first stage is heated from room temperature to 320 ℃ and kept for 2 hours, the purpose of this stage is to prevent the ingot from cracking due to sudden heating; the second stage is heated from 320 ℃ to 430 ℃ and kept for 2 hours, the purpose of this stage is to make the lower melting point intermetallic compound in the ingot melt into the Mg matrix, improve the element segregation in the as-cast alloy, prevent defects such as extrusion heat cracks caused by segregation, and the alloy elements melted in the process of large deformation composite extrusion can produce fine dynamic precipitates, which is beneficial to the improvement of mechanical properties; the third stage is heated from 430 ℃ to 490 ℃ and kept for 2 hours, the purpose of this stage is to make the coarse and difficult-to-dissolve phase melt as much as possible without growing, to prevent its adverse effects on the subsequent extrusion process and mechanical properties. The heating rate is not more than 5 ℃ / min, and a small amount of high-purity Ar gas is introduced into the heat treatment furnace to protect the ingot during the ladder solid solution treatment process to prevent oxidation loss. After the heat treatment program is completed, the ingot is immediately water quenched to obtain a good solid solution effect.

[0050] (3) Differential temperature asymmetric upsetting extrusion: using a wire cutting electrical discharge machining device to cut the heat treated billet obtained in the previous step to obtain a rectangular billet with a height of 50 mm, a width of 55 mm and a thickness of 12 mm, and polishing the cut billet with sandpaper to obtain a rectangular extrusion billet after removing the surface oxide layer. Apply graphite lubricant to the surface of the extrusion billet and the surface of the asymmetric extrusion die cavity, the die cavity is rectangular with a size of 70 mm wide x 12 mm thick x 80 mm high, the extrusion ratio is 21, and the center line of the extrusion outlet to the length ratio of the two sides of the cavity is 1.5. Place the extrusion billet in a heating furnace preheated to 400°C for 40 minutes, preheat the die to 220°C with a heating jacket and keep it for 20 minutes, the die temperature is different from the billet temperature to achieve differential temperature extrusion. After the extrusion billet and the extrusion die are preheated, place the preheated extrusion billet in the extrusion die, with the 55 mm wide side in contact with the bottom of the die cavity, the billet is located on the shorter side of the center line and the side wall of the die, then proceed with positive extrusion, the extrusion speed is 15 mm / s, and the extruded magnesium alloy is immediately water quenched to obtain an extruded magnesium alloy with a width of 20 mm and a thickness of 2 mm.

[0051] The main components of the magnesium alloy are: aluminum: 2.0wt%, tin: 0.8wt%, calcium: 0.5wt%, unavoidable impurity content ≤0.05%, and the balance is magnesium.

[0052] Example 3: Mg-2.2Al-0.8Sn-0.5Ca

[0053] A high strength and toughness magnesium alloy large deformation composite extrusion method mainly includes three steps of casting billet preparation, stepwise solid solution heat treatment, and differential temperature asymmetric upsetting extrusion, and the specific operation is as follows:

[0054] (1) Casting billet preparation:

[0055] High-purity Mg ingot, high-purity Al block, high-purity Sn block, and Mg-20Ca intermediate alloy are used as raw materials, and the above-mentioned raw materials are weighed according to the proportions of aluminum: 2.2wt%, tin: 0.8wt%, calcium: 0.5wt%, and the balance is magnesium, and alloy melting is carried out;

[0056] The alloy melting process includes: melting high-purity Mg ingot, at a melting furnace temperature of 710°C, introducing a mixed protective gas with a volume fraction of 1% SF6 and 99% CO2 into the furnace body to reduce oxidation loss, after the Mg ingot is fully melted, high-purity Al block, high-purity Sn block, and Mg-20Ca intermediate alloy are sequentially added to the melt, after the alloy raw materials are fully melted, the melt is sequentially subjected to stirring, argon blowing refining, and slag removal operation, the alloy melt is kept at 700°C for 10 minutes, and then cast into a sub-fast water-cooled copper mold to obtain an ingot, remove the pouring riser, and polish the oxide skin for the next step of stepwise solid solution heat treatment.

[0057] (2) Step solid solution heat treatment: the cast ingot obtained in the previous step is placed in a heat treatment furnace, and the cast ingot is subjected to step solid solution treatment. The step solid solution treatment process can be set as three stages. In the first stage, the temperature is increased from room temperature to 320°C, and the temperature is kept for 2 hours. The purpose of this stage is to prevent the cast ingot from cracking due to sudden heating. In the second stage, the temperature is increased from 320°C to 430°C, and the temperature is kept for 2 hours. The purpose of this stage is to make the lower melting point intermetallic compound in the cast ingot melt into the Mg matrix, improve the element segregation in the as-cast alloy, prevent defects such as extrusion thermal cracks caused by segregation, and the alloy elements melted can produce fine dynamic precipitates in the process of large deformation composite extrusion, which is beneficial to improve the mechanical properties. In the third stage, the temperature is increased from 430°C to 490°C, and the temperature is kept for 2 hours. The purpose of this stage is to make the coarse and insoluble phase melt as much as possible without growing, so as to prevent its adverse effects on the subsequent extrusion process and mechanical properties. The heating rate during the heating process is not more than 5°C / min, and a small amount of high-purity Ar gas is introduced into the heat treatment furnace during the step solid solution treatment process to protect the cast ingot from oxidation and burning. After the heat treatment program is completed, the cast ingot is immediately water quenched to obtain a better solid solution effect.

[0058] (3) Differential temperature asymmetric upsetting extrusion: the heat treated billet obtained in the previous step is cut using a wire cut electrical discharge machining device to obtain a rectangular billet with a height of 55 mm, a width of 50 mm and a thickness of 12 mm. The cut billet is polished with sandpaper to remove the surface oxidation layer to obtain a rectangular extrusion billet. Graphite lubricant is applied to the surface of the extrusion billet and the surface of the asymmetric extrusion die cavity. The die cavity is rectangular with dimensions of 70 mm wide x 12 mm thick x 80 mm high. The extrusion ratio is 21, and the center line of the extrusion outlet to the length ratio of the two sides of the cavity is 1.5. The extrusion billet is placed in a heating furnace preheated to 390°C for 40 minutes, and the die is preheated to 210°C for 20 minutes using a heating jacket. The die temperature and the billet temperature are different to achieve differential temperature extrusion. After the extrusion billet and the extrusion die are preheated, the preheated extrusion billet is placed in the extrusion die with the 50 mm wide side in contact with the bottom of the die cavity. The billet is located on the side with a shorter distance from the center line of the die to the side wall. Then, the positive extrusion is carried out at a speed of 15 mm / s. The extruded magnesium alloy is immediately water quenched to obtain an extruded magnesium alloy with a width of 20 mm and a thickness of 2 mm.

[0059] The main components of the magnesium alloy are as follows in terms of mass percentage: aluminum: 2.2wt%, tin: 0.8wt%, calcium: 0.5wt%, unavoidable impurity content ≤0.05%, and the balance is magnesium.

[0060] Comparative Example 1:

[0061] Title: Influence of Al Addition on the Microstructure and Mechanical Properties of Mg-Zn-Sn-Mn-Ca Alloys. Journal: Materials. Authors: Shujuan Yan, Caihong Hou, Angui Zhang, Fugang Qi. Page 14, Mg-6Sn-4Zn-1Mn-0.2Ca-2Al ingot was extruded at 350℃ with an extrusion ratio of 25 and an exit speed of 2m / min. The extruded Mg alloy was aged at 90℃ for 24h and 180℃ for 8h to obtain the best mechanical properties of tensile strength 350MPa and elongation 14%. The total alloying element mass percentage is 13.2%.

[0062] Comparative Example 2:

[0063] Title: Effect of extrusion speed on microstructure and mechanical properties of Mg-Al-Ca-Sn alloy. Journal: Materials Research Express. Authors: Maochao Zhang, Chao Yang, Zhenshuai Li, Shuai Bao, Peiran Ye, Yungui Chen. Page 7, Mg-2.5Al-2Ca-1Sn ingot was extruded at 260℃ with an extrusion ratio of 25 and an exit speed of 6mm / min. The best mechanical properties of tensile strength 302MPa and elongation 11.4% were obtained. The total alloying element mass percentage is 5.5%.

[0064] The mechanical properties of the high strength and ductility extruded magnesium alloys of Example 1-3 and the mechanical properties of Comparative Example 1 and Comparative Example 2 are shown in Table 1.

[0065] Table 1

[0066]

[0067] From Table 1, it can be seen that in Example 1, the total alloying element mass percentage is less than that of Comparative Example 1, and by only one pass of extrusion, the tensile strength and elongation are more excellent than those of Comparative Example 1 after extrusion and two-step aging heat treatment. In Example 2 and Example 3, the total alloying element mass percentage is less than that of Comparative Example 2, and by only one pass of extrusion, the elongation is much higher than that of Comparative Example 2, and there is also a great advantage in high strength and ductility.

Claims

1. A method of high-ductility magnesium alloy processing by large-strain compound extrusion, characterized in that, The method is specifically operated as follows: Step one: high-purity Mg ingot, high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy are used as raw materials, and the raw materials are weighed according to the ratio of aluminum: 1.0-6.0wt%, tin: 0.2-1.2wt%, calcium: 0.1-0.6wt%, and the balance is magnesium, then the above-mentioned raw materials are subjected to alloy smelting, the obtained alloy melt is subjected to gravity casting to form an ingot, and then the ingot is removed from the casting riser, and the oxide skin is polished for the next step; Step two: the ingot obtained in step one is placed in a heat treatment furnace, and the ingot is subjected to stepwise solid solution treatment, and immediately after the heat treatment process is completed, the ingot is subjected to water quenching; Among them, the stepwise solid solution treatment is set to three stages, the first stage is heated from room temperature to 320-380℃, and is kept at the corresponding temperature for 2-3 hours; the second stage is heated from 320-380℃ to 420-430℃, and is kept at the corresponding temperature for 2-4 hours; the third stage is heated from 420-430℃ to 470-490℃, and is kept at the corresponding temperature for 2-3 hours; Step three: the heat treated blank obtained in step two is subjected to external shape processing to obtain an extrusion blank, and then the extrusion blank and the extrusion die are respectively coated with a lubricant and preheated, the extrusion blank is preheated at 380-400℃ for 20-60 minutes, and the extrusion die is preheated at 100-220℃ for 10-80 minutes; the extrusion die is selected to be an asymmetric large shear extrusion die, and the shape of the extrusion blank is selected to be a circular truncated cone, a ladder-like shape, or a rectangle or a cylinder with a contour size smaller than the size of the extrusion cavity of the extrusion die, so that the extrusion blank can be deformed by upsetting simultaneously during the extrusion process; After preheating, the preheated extrusion blank is placed in the extrusion die cavity for positive extrusion to realize differential temperature asymmetric upsetting extrusion; then the extruded magnesium alloy is immediately water quenched to obtain an extruded magnesium alloy, i.e. a high-strength and high-toughness magnesium alloy; The specific operation of the external shape processing includes using an electric spark wire cutting equipment to cut the heat treated blank to obtain a required external size, using sandpaper to polish the cut blank, and removing the surface oxide layer to obtain an extrusion blank; The die cavity of the asymmetric large shear extrusion die is rectangular or cylindrical, the extrusion ratio is 10-50, and the ratio of the center line of the extrusion outlet to the length of the two sides of the cavity is 1.1-4.

2. The high-ductility magnesium alloy method of claim 1, wherein, The process of the alloy smelting in step one is as follows: 1) melt the high-purity Mg ingot, and introduce a mixed protective gas with a volume fraction of 1% SF6 and 99% CO2 into the furnace body at a smelting furnace temperature of 690-710℃ to reduce oxidation loss; 2) after the high-purity Mg ingot is fully melted, add high-purity Al block, high-purity Sn block and Mg-20Ca intermediate alloy into the melt in sequence; 3) after the alloy raw materials are fully melted, the melt is subjected to stirring, argon blowing and slag removal in sequence, and the alloy melt is obtained after being kept at 680-700℃ for 10 minutes.

3. The high tough magnesium alloy method of large deformation compound extrusion according to claim 1, characterized in that, The mold for casting in step one adopts a sub-fast water-cooled copper mold or a Y-shaped iron mold.

4. The high toughened magnesium alloy method of large deformation compound extrusion according to claim 1, characterized in that, The mold for casting in step one is a cylindrical ingot iron mold.

5. The high toughened magnesium alloy method of large deformation compound extrusion according to claim 1, characterized in that, The heating process in step two has a temperature rising rate of no more than 5℃ / min.

6. The high toughened magnesium alloy method of large deformation compound extrusion according to claim 1, characterized in that, The heat treatment furnace in step two is connected with high-purity argon to protect the ingot during the step-by-step solid solution treatment.

7. The high toughened magnesium alloy method of large deformation compound extrusion according to claim 1, characterized in that, The extrusion speed of the positive extrusion in step three is 8-18mm / s.

8. A high-strength and high-toughness magnesium alloy prepared by the method according to any one of claims 1-7.

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