Magnesium alloy with excellent extrusion processing performance and strong plastic properties and its preparation method

Abstract

Magnesium alloy with excellent extrusion processing performance and strong plastic properties and its preparation method. The alloy is a Mg-Cu based alloy, and the mass percentages of its components are as follows: Cu: 0.2 - 1.8%, Mn: 0.25 - 0.7%, Ca: 0.1 - 0.7%, and the rest are magnesium, additive elements and inevitable impurities. The additive elements are one or more combinations of Zn and Al, and the addition amounts are as percentages: Zn: 0 - 1.2%, Al: 0 - 2.0%. The preparation method includes: melting, casting, heat treatment and extrusion processing. The highest extrusion speed of the alloy of the present invention is up to 80 m / min. At the same time, the extruded product has fine grains and a large number of fine strengthening phases, and has good mechanical properties; wires with a diameter of 1.2 mm can be extruded. The alloy of the present invention has simple composition, excellent extrusion processing forming performance and mechanical properties, and can be used in fields such as high-quality lightweight structural parts.

Description

Technical Field

[0001] The present invention relates to the field of metal materials and processing thereof, and in particular to a preparation technology of a magnesium alloy with excellent extrusion processing performance and strong plasticity. Background Art

[0002] As the lightest metal structural material, magnesium alloy has a series of advantages such as high specific strength and specific stiffness, excellent thermal conductivity and electrical conductivity, good electromagnetic shielding performance, and recyclability. It is known as the "green structural material of the 21st century". In recent years, with the rapid development of new energy vehicles, high-speed railways, airplanes and other means of transportation, as well as the development of lightweight technology for tooling materials in the construction field, the application of magnesium alloys in the above fields has attracted more and more attention. However, compared with aluminum alloys, magnesium alloys have poor mechanical properties and plastic processing properties, which limits their wide application. Compared with cast magnesium alloys, deformed magnesium alloys can obtain better mechanical properties such as higher strength and better ductility than the cast state through deformation processing, thereby meeting the needs of more structural parts.

[0003] Among them, extrusion processing can make the material withstand a large amount of deformation in a single forming process, and the extruded products are of various varieties and specifications, and can obtain plates, bars, profiles with complex cross-sections and pipes. At the same time, extrusion deformation processing is also an effective processing method for refining the microstructure of the material, and can also eliminate defects such as pores, looseness and shrinkage in the ingot, improve the performance of the extruded product, and improve the strength and plasticity of the material. However, compared with aluminum alloy extrusion processing, the production cost of magnesium alloy extrusion is high. The cost of producing magnesium alloy profiles of the same specifications is even 3 times higher than that of aluminum alloy, which seriously limits its industrial mass production and wide commercial application. This is mainly due to the low extrusion speed of magnesium alloys. For example, the extrusion outlet speed of the typical commercial magnesium alloy AZ31 is 10-20m / min, which is 1 / 5-1 / 2 of the typical aluminum alloy, and its recrystallized grains are easy to grow under high-speed extrusion conditions, and the mechanical properties are poor. The extrusion speed of commercial magnesium alloys AZ61, AZ80 and ZK60 alloys with higher strength is only 1 / 10 of that of typical aluminum alloys. Therefore, reducing the production cost of magnesium alloy extrusions by increasing the extrusion speed is particularly important for promoting the application of deformed magnesium alloys and expanding the market.

[0004] In the prior art, patent CN101418404 discloses a deformed magnesium alloy for high-speed extrusion, the composition of which is calculated by mass percentage: Al 5-7%, Zn 2-3%, Mn 7-9%, Li 3-4%, Zr 1-3%, and the rest is magnesium and inevitable impurities. The extrusion speed of the magnesium alloy can reach 20m / min, the tensile strength is 248-275MPa, the yield strength is 142-178MPa, the elongation is 18-23.8%, the Mn content in the alloy reaches 7-9%, the total content of the added elements in the alloy is as high as 26% and contains more precious elements (Li 3-4%, Zr 1-3%), which indirectly increases the difficulty of smelting and the production cost of the alloy, and the mechanical properties of the final obtained material are still low. The patent (publication number CN104032195A) discloses a high-performance thermally conductive magnesium alloy that can be efficiently extruded at low cost and a preparation method thereof, wherein the chemical composition weight percentage is: 0.1-0.8wt% Al, 0.1-0.6wt% Ca, 0.1-0.6wt% Mn, 0.05-0.4wt% La, and the rest is Mg. The patent can be produced by a fast extrusion process with a maximum outlet speed of not less than 20m / min. The yield strength of the extruded material is about 180MPa, the mechanical properties are insufficient, and the extruded material contains a certain amount of precious rare earth element La. Patent CN114540683A discloses a microalloyed corrosion-resistant low-cost magnesium alloy and its preparation method. The magnesium alloy composition mass percentage is: aluminum: 0.55-1.2%, manganese: 0.5-0.65%, zinc: 0-0.4%, calcium: 0.01-0.03%, and the rest is magnesium, additive elements and inevitable impurities; the additive element is one of samarium and lanthanum or a combination of the two, and the addition amount is calculated by mass percentage: samarium: 0.01-0.2%, lanthanum: 0.01-0.2%. The corresponding alloy can be extruded at an extrusion ratio of 20-150:1 and an extrusion speed of 20-70m / min. However, the mechanical properties of the alloy are low, with an average yield strength of 215MPa and an elongation of 10.9%. And it is necessary to perform solid solution and aging heat treatment after extrusion processing; in order to obtain an alloy with better performance, rare earth elements such as Sm and La need to be added to the alloy, and the processing cost and material cost are high.

[0005] In view of the problems of insufficient high-speed extrusion processing performance of most deformed magnesium alloys in the prior art, low mechanical properties of extruded materials, or excessively high raw material costs, how to reduce costs and simplify production processes to obtain high-strength and plastic low-alloy magnesium alloys is a technical problem that needs to be solved urgently. Therefore, it is of great economic and social significance to invent a new type of low-cost, high-performance magnesium alloy with low alloy content, no rare earth and other precious alloy elements added, and high-speed extrusion. Summary of the invention

[0006] In view of the deficiencies in the prior art that most wrought magnesium alloys are difficult to be extruded at high speeds, or the extrusion speeds and mechanical properties of the small amount of magnesium alloys that can be extruded at high speeds are still generally not high or the cost is relatively high, the present invention provides a magnesium alloy with excellent extrusion processability and high strength and plasticity, as well as a preparation method therefor.

[0007] The present invention relates to a magnesium alloy with excellent extrusion processability and high strength and plasticity, as well as a preparation method therefor. For the magnesium alloy with excellent extrusion processability and high strength and plasticity, the mass percentages of its chemical components are as follows: Cu: 0.2-1.8%, Mn: 0.25-0.7%, Ca: 0.1-0.7%, and the balance is magnesium, added elements and inevitable impurities. The added elements are one or more combinations of Zn and Al, and the addition amounts are as percentages: Zn: 0-1.2%, Al: 0-2.0%.

[0008] The preparation method of the magnesium alloy with excellent extrusion processability and high strength and plasticity according to the present invention includes the following steps:

[0009] Step (1) Melting: Under the protection of a protective gas or a covering agent, pure magnesium is added and heated to melt at 680-760°C; then Mg-Ca master alloy, Mg-Cu master alloy, and Mg-Mn master alloy are sequentially added and continuously heated to melt at 680-780°C; subsequently, one or any combination of pure Al and pure Zn is added, and stirred evenly at a temperature of 680-780°C. After refining, degassing, and slag removal, it is allowed to stand for 10-100 minutes to obtain an alloy melt.

[0010] Step (2) Casting: The uniformly melted magnesium alloy melt is cast by means of sand casting, permanent mold casting, or semi-continuous casting to obtain an as-cast alloy ingot.

[0011] Step (3) Heat treatment: The alloy ingot obtained in step (2) is heat-treated in a heat treatment furnace at a heat treatment temperature of 160-450°C for a time of 0.5-20 hours, and then cooled to room temperature by air cooling or water cooling.

[0012] Step (4) Extrusion processing: The heat-treated blank is cut into corresponding specifications and the surface oxide scale is removed, and then heated to the extrusion temperature and placed in a deformation die for hot extrusion processing. The extrusion deformation speed is 0.1-80 m / min, the extrusion ratio is 5-100, the extrusion temperature is 180-480°C, and the hot-deformed blank is directly cooled to room temperature to obtain the high-strength and high-plasticity magnesium alloy material.

[0013] 1) The present invention adopts the design idea of a small amount of multiple elements. Through the optimization of alloy elements, the mutual weakening between different elements is avoided, and they work together synergistically while avoiding the excessive growth of the second phase, which weakens the plasticity of the alloy.

[0014] 2) Compared with the prior art, a new type of magnesium alloy with excellent extrusion processability and strength-plasticity performance has been developed in the Mg-Cu based alloy. This alloy has excellent extrusion processability. The maximum extrusion speed of the magnesium alloy extruded material can reach 80 m / min.

[0015] 3) The grains of the extruded profiles prepared by the present invention are fine and uniform, and the average grain size can reach 2-30 μm. Coupled with the synergistic strengthening effect of the uniformly distributed micro-nano dual-scale second phases, the final extruded material can have good strength-plasticity performance. Its yield strength can reach up to over 320 MPa, and at the same time, the elongation rate reaches over 15%. While for the currently commercially available magnesium alloy AZ31 that can be extruded at high speed, when extruded at the same speed, the yield strength and tensile strength of the processed alloy are only 165 MPa and 246 MPa respectively.

[0016] 4) The magnesium alloy of the present invention can be extruded into wire materials with a minimum diameter of 1.2 mm. The obtained extruded materials have a smooth surface and no surface cracks, and can be widely used in the manufacture of magnesium alloy wire materials, showing great attraction in the fields of additive manufacturing and the preparation of fine parts.

[0017] 5) The heat treatment processes before and after extrusion are simple, require low temperatures and short times. And heat treatment is not required after extrusion. Good mechanical properties can be obtained in the as-extruded state, simplifying the production process, reducing energy consumption and production costs, and at the same time improving the processing efficiency.

[0018] 6) The preparation process of the magnesium alloy billet of the present invention is simple. The master alloy is easy to prepare and can be easily melted into the magnesium melt. Existing melting and extrusion equipment can be used for preparation without additional improvement, and the requirements for equipment are low.

[0019] 7) This magnesium alloy material does not contain rare earth elements and other precious metal elements. The cost of the alloying elements of the magnesium alloy extruded material of the present invention is low, and the extrusion speed is high, greatly reducing the material cost of the extruded material, which is of great significance for promoting the application of wrought magnesium alloys in the fields of aerospace, automobiles, high-speed rails, 3C products, etc. Description of the Drawings

[0020] Figure 1 are the physical pictures of the extruded rods of Examples 5, 6, 7 and the 1.2 mm wire of Example 10 of the present invention. Figure 2 is the as-extruded microstructure morphology parallel to the extrusion direction of Example 4. Figure 3 is the as-extruded microstructure parallel to the extrusion direction of Example 5. Figure 4 is the as-extruded microstructure parallel to the extrusion direction of Example 6. Figure 5 is the as-extruded microstructure parallel to the extrusion direction of Example 8. Figure 6 is the TEM photo of the as-extruded microstructure of Example 8. Figure 7It is the typical tensile curve of Example 5. Figure 8 It is the typical tensile curve of Example 6. Figure 9 It is the typical tensile curve of Example 7. Embodiment

[0021] The present invention relates to a magnesium alloy with excellent extrusion processing performance and high strength and plasticity, and a preparation method thereof. The magnesium alloy with excellent extrusion processing performance and high strength and plasticity has the following chemical composition by mass percentage: Cu: 0.2 - 1.8%, Mn: 0.25 - 0.7%, Ca: 0.1 - 0.7%, and the balance is magnesium, added elements and inevitable impurities. The added elements are one or more combinations of Zn and Al, and the addition amounts are as follows by percentage: Zn: 0 - 1.2%, Al: 0 - 2.0%.

[0022] The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to the present invention includes the following steps:

[0023] Step (1) Melting: Under the protection of a protective gas or a fluxing agent, pure magnesium is added and heated to melt at 680 - 760°C; then Mg-Ca master alloy, Mg-Cu master alloy, and Mg-Mn master alloy are sequentially added and heated to melt at 680 - 780°C; subsequently, one or any combination of pure Al and pure Zn is added, and the mixture is stirred evenly at 680 - 780°C. After refining to remove gas and skimming, it is allowed to stand for 10 - 100 min to obtain an alloy melt.

[0024] Step (2) Casting: The uniformly melted magnesium alloy melt is cast by means of sand casting, permanent mold casting, or semi-continuous casting to obtain a as-cast alloy ingot.

[0025] Step (3) Heat treatment: The alloy ingot obtained in step (2) is heat-treated in a heat treatment furnace. The heat treatment temperature is 160 - 450°C, and the time is 0.5 - 20 hours, and then it is cooled to room temperature by air cooling or water cooling.

[0026] Step (4) Extrusion processing: The heat-treated blank is cut into corresponding specifications and the surface oxide scale is removed, and then it is heated to the extrusion temperature and put into a deformation die for hot extrusion processing. The extrusion deformation speed is 0.1 - 80 m / min, the extrusion ratio is 5 - 100, the extrusion temperature is 180 - 480°C, and the hot-deformed blank is directly cooled to room temperature to obtain the high-strength and high-plasticity magnesium alloy material.

[0027] For the above-mentioned preparation method, the protective gas in step (1) is a mixed gas of Ar + SF6, a mixed gas of SF6 + CO2, or a mixed gas of Ar + SF6 + CO2.

[0028] For the preparation method described above, the covering agent in step (1) can be RJ-5 or RJ-2.

[0029] For the preparation method described above, the Mg-Ca master alloy in step (1) is a Mg-20Ca master alloy, the Mg-Mn master alloy is a Mg-5Mn master alloy, and the Mg-Cu master alloy is Mg-30Cu.

[0030] For the preparation method described above, the stirring in step (2) is mechanical stirring, argon gas blowing stirring, electromagnetic stirring or a combination thereof.

[0031] For the preparation method described above, the refining in step (2) can be refining by adding a refining agent, refining by blowing argon gas or a combination thereof.

[0032] The magnesium alloy of the present invention belongs to a new Mg-Cu series alloy with excellent extrusion processing performance. First, the trace alloying elements in the alloy interact with each other and with magnesium. These elements are added in a multi-element and trace composite manner, and a large number of fine second-phase particles containing Cu, Mn, and Ca with high thermal stability can be formed in-situ, which can avoid the reduction of alloy plasticity caused by excessive growth of the second phase. At the same time, these second-phase particles with high thermal stability at the micro-nano double scale can promote the nucleation of dynamic recrystallization during extrusion and inhibit the growth of recrystallized grains. Secondly, in addition to the micron-sized second phase, a large number of nano-sized second phases containing Cu, Mn, and Ca will also be formed in the matrix during the processing and preparation process, and a large number of solute segregation clusters will be formed at the grain boundaries. These nano-precipitates and the solute clusters segregated at the grain boundaries can also inhibit the growth of recrystallized grains, so as to obtain a fine grain structure under high-speed extrusion conditions. In addition, a small amount of alloying elements such as Cu and Mn dissolved in the matrix can also improve the extrusion deformation ability of the alloy, thus endowing the alloy with good extrudability. Finally, fine recrystallized grains, a sufficient number of micro-nano double-scale second phases, and solute clusters segregated at the interface can be obtained in the alloy after extrusion processing, which can act synergistically to significantly improve the strength and toughness of the alloy.

[0033] The technical solutions of the present invention will be described in detail through specific embodiments below. The following embodiments are all implemented on the premise of the technical solutions of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments. Example

[0034] It is designed to select Mg-0.5Cu-0.5Mn-0.12Ca (wt%), and prepare a magnesium alloy according to the composition ratio. The preparation method includes the following steps:

[0035] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the magnesium ingots preheated to 150 °C into the crucible of the melting furnace for heating, and introduce a mixed gas of Ar:SF6 = 100:1 (flow ratio) for protection against combustion. Raise the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, successively add Mg-20Ca master alloy (actual detected Ca content is 19.92 wt%), Mg-30Cu master alloy (actual detected Cu content is 30.12 wt%), and Mg-5Mn master alloy (actual detected Mn content is 5.1 wt%) preheated to about 150 °C, and raise the furnace temperature to 760 °C for holding until the master alloys are fully melted. Mechanically stir for 2 minutes to make the melt uniform, then adjust the furnace temperature to 720 °C, blow in argon for refining and degassing treatment, skim off the surface scum, and hold for 20 minutes to obtain the alloy melt;

[0036] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0037] (3) Heat treatment: Keep the cut as-cast alloy ingot at 200 °C for 4 h, and then perform water quenching treatment;

[0038] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale, then set the extrusion process parameters: blank temperature 300 °C, extrusion cylinder temperature 300 °C, die temperature 300 °C, extrusion speed 35 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 300 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0039] The second-phase composition of the obtained extruded alloy is Mg2Cu and α-Mn, and its mechanical properties are shown in Example 1 in Table 1.

[0040] Table 1 Mechanical properties of the alloy

[0041] Example

[0042] Designed to select Mg-0.5Cu-0.5Mn-0.5Zn-0.15Ca (wt%), formulate it into a magnesium alloy according to the composition ratio, and the preparation method includes the following steps:

[0043] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the magnesium ingots preheated to 150 °C into the crucible of the melting furnace and heat them. Add Solvent No. 5 to prevent combustion. Raise the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, successively add Mg-20Ca master alloy (actual detected Ca content is 19.92 wt%), Mg-30Cu master alloy (actual detected Cu content is 30.12 wt%), Mg-5Mn master alloy (actual detected Mn content is 5.1 wt%) and Zn blocks (99.95 wt %) preheated to about 150 °C, and raise the furnace temperature to 760 °C. Keep it warm until the raw materials are fully melted. Mechanically stir for 3 minutes to make the melt uniform, then adjust the furnace temperature to 720 °C, blow in argon for refining and degassing treatment, skim off the surface scum, keep it warm and stand for 20 minutes to obtain the alloy melt;

[0044] (2) Then, under the protection of a mixed gas of CO2:SF6 = 100:1 (flow ratio), use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0045] (3) Heat treatment: For the cut as-cast alloy ingots, first keep them at 300 °C for 5 h and then perform water quenching treatment;

[0046] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale. Then set the extrusion process parameters: blank temperature 300 °C, extrusion cylinder temperature 300 °C, die temperature 300 °C, extrusion speed 35 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 300 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a bar with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0047] The second phase composition of the obtained extruded alloy is Mg2Cu, MgZnCu, α-Mn, and its mechanical properties are shown in Example 2 in Table 1. Example

[0048] Design and select Mg-0.5Cu-0.5Mn-0.4Ca (wt%), proportion and prepare the magnesium alloy according to the composition ratio. The preparation method includes the following steps:

[0049] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the magnesium ingots preheated to 150 °C into the crucible of the melting furnace and heat them. Add Solvent No. 5 to prevent combustion. Increase the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, successively add Mg-20Ca master alloy (the actual detected Ca content is 19.92 wt%), Mg-30Cu master alloy (the actual detected Cu content is 30.12 wt%), and Mg-5Mn master alloy (the actual detected Mn content is 5.1 wt%) preheated to about 150 °C, and raise the furnace temperature to 760 °C. Keep it warm until the raw materials are fully melted. Mechanically stir for 2 minutes to make the melt uniform, then adjust the furnace temperature to 720 °C, blow in argon for refining and degassing treatment, skim off the surface scum, keep it warm and stand for 20 minutes to obtain the alloy melt;

[0050] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0051] (6) Heat treatment: For the cut as-cast alloy ingots, first keep them at 300 °C for 4 h, and then perform water quenching treatment;

[0052] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale. Then set the extrusion process parameters: blank temperature 310 °C, extrusion cylinder temperature 310 °C, die temperature 310 °C, extrusion speed 35 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0053] The second phase composition of the obtained extruded alloy is Mg2Cu, Mg2Ca, and α-Mn, and its mechanical properties are shown in Example 3 in Table 1. Example

[0054] Design and select Mg-0.3Cu-0.4Mn-0.8Al-0.13Ca (wt%), formulate it into a magnesium alloy according to the composition ratio, and the preparation method includes the following steps:

[0055] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the pure Mg (99.95 wt%) ingots preheated to 150 °C into the crucible of the melting furnace for heating, and introduce a mixed gas of Ar:CO2:SF6 = 40:59:1 (flow ratio) for protection against combustion. Raise the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, successively add Mg-20Ca master alloy (actual detected Ca content is 19.92 wt%) preheated to about 150 °C, Mg-30Cu master alloy (actual detected Cu content is 30.12 wt%), and Mg-5Mn master alloy (actual detected Mn content is 5.1 wt%), pure Al (99.95 wt%) ingots, and raise the furnace temperature to 760 °C. Keep it warm. After all the raw materials are melted, mechanically stir for 2 minutes to make the melt uniform. Then adjust the furnace temperature to 720 °C, add RJ-1 solvent for refining and degassing treatment, skim off the surface scum, keep it warm and stand for 20 minutes for standing treatment to obtain an alloy melt;

[0056] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0057] (3) Heat treatment: Keep the cut as-cast alloy ingots at 200 °C for 10 h, and then perform water quenching treatment;

[0058] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale. Then set the extrusion process parameters: blank temperature 300 °C, extrusion cylinder temperature 300 °C, die temperature 300 °C, extrusion speed 40 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 300 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0059] The second-phase composition of the obtained extruded alloy is MgAlCu, Al-Mn, α-Mn, and its mechanical properties are shown in Example 4 in Table 1. Example

[0060] Designed to select Mg-0.4Cu-0.4Mn-0.4Ca-0.5Zn (wt%), and formulate it into a magnesium alloy according to the composition ratio. The preparation method includes the following steps:

[0061] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the pure Mg (99.95 wt%) ingots preheated to 150 °C into the crucible of the melting furnace and heat them, and introduce a mixed gas of CO2:SF6 = 100:1 (flow ratio) for protection against combustion; increase the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, successively add Mg-20Ca master alloy (the actual detected Ca content is 19.92 wt%) preheated to about 150 °C, Mg-30Cu master alloy (the actual detected Cu content is 30.12 wt%), Mg-5Mn master alloy (the actual detected Mn content is 5.1 wt%), and pure Zn (99.95 wt%) ingots, and raise the furnace temperature to 760 °C and hold for heat preservation until the master alloys are fully melted; after all the raw materials are melted, stir for 2 minutes to make the melt homogeneous, then adjust the furnace temperature to 720 °C, add RJ-1 solvent for refining and degassing treatment, skim off the surface scum, hold for 20 minutes for static treatment to obtain the alloy melt;

[0062] (2) Casting: Use permanent mold casting to prepare cylindrical as-cast magnesium alloy billets with a diameter of 60 mm;

[0063] (3) Heat treatment: Keep the cut as-cast alloy ingots at 200 °C for 2 h, and then perform water quenching treatment;

[0064] (4) Extrusion processing: Cut the heat-treated billets into corresponding specifications and remove the surface oxide scale, and then set the extrusion process parameters: billet temperature 300 °C, extrusion cylinder temperature 300 °C, die temperature 300 °C, extrusion speed 35 m / min, extrusion ratio 36. Heat the deformed billets for 30 minutes to reach the required extrusion temperature of 300 °C, put them into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain bars with a diameter of 10 mm. The extruded materials are air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation as described.

[0065] The second-phase composition of the obtained extruded alloy is MgZnCu, α-Mn, Mg2Ca, and its mechanical properties are shown in Example 5 in Table 1. Example

[0066] Design and select Mg-0.4Cu-0.4Mn-0.4Ca-0.5Zn (wt%), formulate it into a magnesium alloy according to the composition ratio, and the preparation method steps (1) and (2) are the same as those in Example 5;

[0067] (3) Heat treatment: Keep the cut as-cast alloy ingots at 200 °C for 1 h, and then perform water quenching treatment;

[0068] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale. Then set the extrusion process parameters: blank temperature 310 °C, extrusion cylinder temperature 310 °C, die temperature 310 °C, extrusion speed 50 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and carry out extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0069] The second-phase composition of the obtained extruded alloy is MgZnCu, α-Mn, Mg2Ca, and its mechanical properties are shown in Example 6 in Table 1. Example

[0070] Design and select Mg-0.4Cu-0.4Mn-0.4Ca-0.5Zn (wt%), proportion and mix it into a magnesium alloy according to the composition ratio. The preparation method steps (1) and (2) are the same as those in Example 5;

[0071] (3) Heat treatment: Keep the cut as-cast alloy ingot at 200 °C for 0.6 h, and then perform water quenching treatment;

[0072] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale. Then set the extrusion process parameters: blank temperature 310 °C, extrusion cylinder temperature 310 °C, die temperature 310 °C, extrusion speed 80 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and carry out extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0073] The second-phase composition of the obtained extruded alloy is MgZnCu, α-Mn, Mg2Ca, and its mechanical properties are shown in Example 7 in Table 1. Example

[0074] Design and select Mg-1.3Cu-0.4Mn-0.4Ca-0.4Zn (wt%), proportion and mix it into a magnesium alloy according to the composition ratio. The preparation method includes the following steps:

[0075] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the pure Mg (99.95 wt%) ingot preheated to 150 °C into the crucible of the melting furnace and heat it, and introduce a mixed gas of CO2:SF6 = 100:1 (flow ratio) for protection against combustion; heat the furnace temperature to 750 °C at a heating rate of 10 °C / min. After the magnesium ingot is completely melted, sequentially add the Mg-20Ca master alloy (the actual detected Ca content is 19.92 wt%) preheated to about 150 °C, the Mg-30Cu master alloy (the actual detected Cu content is 30.12 wt%), the Mg-5Mn master alloy (the actual detected Mn content is 5.1 wt%), and the pure Zn (99.95 wt%) ingot, and raise the furnace temperature to 760 °C and keep it warm until the master alloy is fully melted; stir for 2 minutes after all the raw materials are melted to make the melt uniform, then adjust the furnace temperature to 720 °C, blow in argon for refining and degassing treatment, skim off the surface scum, and keep it still for 20 minutes for standing treatment to obtain the alloy melt;

[0076] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0077] (3) Heat treatment: Keep the cut as-cast alloy ingot at 200 °C for 1 h, and then perform water quenching treatment;

[0078] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale, and then set the extrusion process parameters: blank temperature 310 °C, extrusion cylinder temperature 310 °C, die temperature 310 °C, extrusion speed 25 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0079] The second-phase composition of the obtained extruded alloy is Mg2Cu, MgZnCu, α-Mn, Mg2Ca, and its mechanical properties are shown in Example 8 in Table 1. Example

[0080] Design and select Mg-0.8Cu-0.4Mn-0.2Ca-1.2Al (wt%), formulate it into a magnesium alloy according to the composition ratio, and the preparation method includes the following steps:

[0081] (1) Melting: Clean the melting furnace and heat it to 450 °C. Put the pure Mg (99.95 wt%) ingots preheated to 150 °C into the crucible of the melting furnace and heat them, and introduce a mixed gas of CO2:SF6 = 100:1 (flow ratio) for protection against combustion; heat the furnace temperature to 750 °C at a heating rate of 10 °C / min. After all the magnesium ingots are melted, sequentially add the Mg-20Ca master alloy (the actual detected Ca content is 19.92 wt%) preheated to about 150 °C, the Mg-30Cu master alloy (the actual detected Cu content is 30.12 wt%), the Mg-5Mn master alloy (the actual detected Mn content is 5.1 wt%), pure Zn (99.95 wt%) ingots, and pure Al (99.95 wt%) ingots, and raise the furnace temperature to 760 °C, hold the temperature until the master alloy is fully melted; after all the raw materials are melted, stir for 2 minutes to make the melt uniform, then adjust the furnace temperature to 720 °C, blow in argon for refining and degassing treatment, skim off the surface scum, hold the temperature and stand for 20 minutes for standing treatment to obtain an alloy melt;

[0082] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 60 mm;

[0083] (3) Heat treatment: Keep the cut as-cast alloy ingot at 200 °C for 1 h, and then perform water quenching treatment;

[0084] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale, and then set the extrusion process parameters: blank temperature 310 °C, extrusion cylinder temperature 310 °C, die temperature 310 °C, extrusion speed 25 m / min, extrusion ratio 36. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and perform extrusion processing according to the above parameters to obtain a bar with a diameter of 10 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation.

[0085] The second-phase composition of the obtained extruded alloy is MgAlCu, Mg2Cu, α-Mn, Mg2Ca, and its mechanical properties are shown in Example 9 in Table 1. Example

[0086] Design and select Mg-0.4Cu-0.4Mn-0.4Ca-0.5Zn (wt%), proportion and prepare it into a magnesium alloy according to the composition ratio. The preparation method in step (1) is the same as that in Example 5;

[0087] (2) Casting: Use permanent mold casting to prepare a cylindrical as-cast magnesium alloy blank with a diameter of 36 mm; (3) Heat treatment: Keep the cut as-cast alloy ingot at 400 °C for 5 h, and then perform water quenching treatment;

[0088] (4) Extrusion processing: Cut the heat-treated blank into corresponding specifications and remove the surface oxide scale, and then set the extrusion process parameters: blank temperature 350 °C, extrusion cylinder temperature 350 °C, die temperature 350 °C, extrusion speed 80 m / min, extrusion ratio 100, 10 holes per die. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 310 °C, put it into the extrusion cylinder and carry out extrusion processing according to the above parameters to obtain a rod with a diameter of 1.2 mm. The extruded material is air-cooled to obtain the Mg-Cu-based magnesium alloy with high-speed extrusion deformation as described above.

[0089] The second-phase composition of the obtained extruded alloy is MgZnCu, α-Mn, and Mg2Ca.

[0090] Select the currently commercial magnesium alloy AZ31. The alloy ingot is subjected to homogenization treatment at 400 °C for 24 h, peeled, and subjected to extrusion processing. The extrusion speed is 20 m / min, the extrusion ratio is 36, and the extrusion temperature is 360 °C. Heat the deformed blank for 30 minutes to reach the required extrusion temperature of 360 °C, put it into the extrusion cylinder and carry out extrusion processing according to the above parameters to obtain a rod with a diameter of 10 mm. The extruded material is air-cooled to obtain the AZ31 alloy of the comparative example. The second-phase group of the obtained extruded alloy has only a small amount of α-Mn phase, and its mechanical properties are shown in Comparative Example 1 in Table 1.

[0091] The following combines the experimental result data and conducts a comparative analysis from three aspects: the appearance quality, microstructure, and mechanical properties of the materials obtained after extrusion processing.

[0092] 1 Appearance quality of the extruded alloy

[0093] The magnesium alloy rods and wires prepared by high-speed extrusion in the present invention both have a smooth appearance. For example, Figure 1 are the macroscopic physical diagrams of the extrusion rods of Example 5 (extrusion speed 35 m / min), Example 6 (extrusion speed 50 m / min), Example 7 (extrusion speed 80 m / min) of the present invention and the 1.2 mm wire of Example 10 (extrusion speed 25 m / min), indicating that the highest extrusion speed of the alloy in the present invention can reach 80 m / min, and a magnesium alloy wire with a diameter of 1.2 mm can be successfully extruded. It can be seen that the magnesium alloy of the present invention has excellent extrusion processing performance.

[0094] 2 Microstructure

[0095] Under the condition of high-speed extrusion, almost complete dynamic recrystallization has basically occurred in the alloys of the present invention. The morphological features of the extrusion microstructure of the alloy of Example 4 prepared at an extrusion speed of 40 m / min parallel to the extrusion direction are respectively as Figure 2As shown, its average grain size is about 26 microns; the extruded microstructure parallel to the extrusion direction of the alloy of Example 5 prepared at an extrusion speed of 35 m / min is respectively as Figure 3 shown, and its microstructure exhibits a bimodal structure, consisting of grains of about 20 microns and fine grains of about 7 microns. Further increasing the extrusion speed to 50 m / min, the extruded microstructure parallel to the extrusion direction of the alloy of Example 6 with the same composition as that of Example 5 is respectively as Figure 4 shown, presenting a relatively uniform grain structure, and the average grain size is about 20 microns. The extruded microstructure parallel to the extrusion direction of the alloy of Example 8 prepared at an extrusion speed of 25 m / min is respectively as Figure 5 shown, and its microstructure also exhibits a bimodal structure, consisting of grains of about 20 microns and fine grains of about 8 microns. It shows that the alloy in the present invention can still have a fine recrystallized microstructure at an extrusion speed as high as 50 m / min, and the grain size is between 7 - 26 microns. As Figure 6 is the TEM photograph of the extruded microstructure of Example 8, it can be found that there are a large number of fine precipitates with various morphologies in the alloy; from Figure 5 the microstructure, it can also be found that micron-scale second phases can be constructed and dispersed in the matrix; in addition, there are a large number of solute segregation structures at the grain boundaries of these magnesium alloys prepared by high-speed extrusion containing Cu. This shows that the inhibition of the growth of recrystallized grains in the alloy of the present invention is related to the multi-scale multi-element micro-nano dual-scale thermally stable second phases, trace solute elements dissolved in the matrix, and solute segregation clusters at the grain boundaries.

[0096] 3 Mechanical properties

[0097] As shown in Table 1, the alloy of the present invention has good mechanical properties. Under the extrusion condition of 20 m / min, the average yield strength, tensile strength and elongation of the comparative alloy AZ31 are 154.8 MPa, 243.6 MPa and 17.4% respectively, while under higher extrusion speed conditions, the alloy of the present invention shows more excellent strength. The typical tensile curves of Example 5, Example 6 and Example 7 in the present invention are as Figure 7 , Figure 8 and Figure 9 shown, among which the average yield strength of Example 5 can reach 304.6 MPa, and at the same time it also has an elongation of about 20%, showing good strength-ductility matching. The good strength-ductility matching of the alloy of the present invention is closely related to the fine grains in the alloy, the large number of micro-nano dual-sized second phases, the solute segregation structure at the grain boundaries and the strengthening effect of the solute elements.

[0098] The raw materials and equipment used in the above examples are all obtained through well-known channels, and the operating processes used are within the grasp of those skilled in the art of the present technology.

Claims

1. A preparation method of a magnesium alloy with excellent extrusion processing performance and high strength and plasticity. The chemical composition of the magnesium alloy by mass percentage is as follows: Cu: 0.2 - 1.8%, Mn: 0.25 - 0.7%, Ca: 0.1 - 0.7%, and the rest is magnesium, additive elements and inevitable impurities. The additive elements are one or more combinations of Zn and Al, and the addition amount by percentage is: Zn: 0 - 1.2%, Al: 0 - 2.0%; It is characterized in that, The steps include: Step (1) Melting: Under the protection of protective gas or flux, pure magnesium is added and heated to melt at 680 - 760°C; then Mg-Ca master alloy, Mg-Cu master alloy, and Mg-Mn master alloy are added in sequence and continuously heated to melt at 680 - 780°C; subsequently, one or any combination of pure Al and pure Zn is added, stirred evenly at 680 - 780°C, refined to remove gas and slag removed, and then left standing for 10 - 100 min to obtain an alloy melt; Step (2) Casting: The uniformly melted magnesium alloy melt is cast by means of sand casting, permanent mold casting, or semi-continuous casting to obtain as-cast alloy ingots; Step (3) Heat treatment: The alloy ingots obtained in Step (2) are heat-treated in a heat treatment furnace, the heat treatment temperature is 160 - 450°C, the time is 0.5 - 20 hours, and then cooled to room temperature by air cooling or water cooling; Step (4) Extrusion processing: The billet after heat treatment is cut into corresponding specifications and the surface oxide scale is removed, then heated to the extrusion temperature and put into a deformation die for hot extrusion processing, the extrusion deformation speed is 0.1 - 80 m / min, the extrusion ratio is 5 - 100, the extrusion temperature is 180 - 480°C, and the billet after hot deformation is directly cooled to room temperature to obtain the magnesium alloy with excellent extrusion processing performance and high strength and plasticity.

2. The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to claim 1, wherein: The protective gas in Step (1) is: a mixed gas of Ar + SF6, a mixed gas of SF6 + CO2, or a mixed gas of Ar + SF6 + CO2.

3. The preparation method of the magnesium alloy with excellent extrusion processing performance and high plastic forming performance according to claim 1, characterized in that: The flux in Step (1) is RJ-5 or RJ-2.

4. The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to claim 1, characterized in that: The Mg-Ca master alloy in Step (1) is Mg-20Ca master alloy, the Mg-Mn master alloy is Mg-5Mn master alloy, and the Mg-Cu master alloy is Mg-30Cu.

5. The preparation method of the magnesium alloy with excellent extrusion processing performance and high plastic forming performance according to claim 1, characterized in that: The stirring in Step (2) is mechanical stirring, argon blowing stirring, electromagnetic stirring, or a combination thereof.

6. The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to claim 1, characterized in that: The refining in Step (2) is adding a refining agent for refining, blowing argon for refining, or a combination thereof.

7. The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to claim 1, characterized in that: The heat treatment in Step (3) is single-stage heat treatment or two-stage heat treatment. Among them, single-stage heat treatment is to hold at a certain constant temperature between 160 - 410°C for 0.5 - 20 hours and then cool, and two-stage heat treatment is to first perform heat treatment at a certain constant temperature between 160 - 380°C for 2 - 15 hours, and then raise the temperature to a certain temperature between 400 - 450°C for 1 - 5 hours of high-temperature heat treatment.

8. The preparation method of the magnesium alloy with excellent extrusion processing performance and high strength and plasticity according to claim 1, characterized in that: The die in Step (4) is a die for forming sheets, or rods, or tubes, or wires, or profiles.

9. The preparation method of the magnesium alloy with excellent extrusion processing performance and strong plastic properties according to claim 1, characterized in that: The cooling after the deformation processing in Step (4) is natural cooling in air, forced cooling by spraying water mist, or forced cooling by blowing air flow.

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