High-plasticity flame-retardant magnesium alloy and preparation method thereof

Abstract

The invention discloses a high-plasticity flame-retardant magnesium alloy and a preparation method thereof. The high-plasticity flame-retardant magnesium alloy comprises the following components in percentage by weight: 5-7% of A1, 2-4% of Ca, 0.5-1.5% of Zn, 0.2-0.5% of Mn and the balance of Mg and inevitable impurities. According to the invention, Al, Ca, Zn and Mn which are low in cost are added into magnesium, and the Mg-Al-Ca-Zn-Mn alloy is designed. The invention further discloses a preparation method of the high-plasticity flame-retardant magnesium alloy plate, extra shear stress is introduced by using an asymmetric extrusion die, and the strength of the alloy is maintained while the plasticity of the alloy is improved. Compared with a conventional Mg-Al-Ca alloy, the deformed alloy is higher in ignition point and more excellent in mechanical property, and can be used for preparing more magnesium alloy parts for transportation and aerospace.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy, and particularly relates to a high-plasticity flame-retardant magnesium alloy and a preparation method thereof. BACKGROUND

[0002] As a metal material with the smallest density, magnesium alloy has the advantages of specific strength and specific stiffness, and is one of the most promising structural materials at present, and is widely used in the fields of transportation and aerospace. However, when magnesium alloy is used as a part of a vehicle such as a car or a train, it is easy to be ignited in a fire, which limits the development of magnesium alloy in the transportation field. Therefore, there is an urgent need to develop a low-cost, high-strength and high-toughness, high ignition point, and excellent comprehensive performance deformation magnesium alloy.

[0003] The alloying and deformation process of magnesium alloy are the key research directions of the current magnesium alloy research. The ignition point of the alloy can be significantly improved by adding alloying elements, such as rare earth elements (Gd, Y, etc.) and alkaline earth elements (Ca, Be, etc.). For example, CN114934218A discloses a high-strength and high-plasticity flame-retardant magnesium alloy, which is composed of Al: 0.5-2.0%, Ca: 0.5-2.5%, Gd: 0.5-1.0%, Zr: 0.2-1.0%; impurity elements include Fe <0.005%, Cu <0.015%, Ni <0.002%; and the rest is Mg. The room temperature yield strength is 220 MPa, the tensile strength is 320 MPa, the plasticity is 12%, and the ignition point is 791℃. The Gd and Zr in it are both rare earth elements, which have a high cost and are difficult to meet mass production. The addition of Ca element can simultaneously improve the strength and ignition point of the alloy, especially the Mg-Al-Ca system deformation magnesium alloy, which has excellent strength and high ignition point characteristics. However, the increase of Ca content will form a hard and brittle phase, which will greatly improve the strength and ignition point of the alloy, but will also reduce the plasticity of the alloy.

[0004] Therefore, the application develops a high-plasticity flame-retardant magnesium alloy sheet based on the Mg-Al-Ca system alloy by using an asymmetric extrusion deformation process, which has important research significance for practical application. SUMMARY

[0005] In view of the technical problems existing in the prior art, the purpose of the application is to provide a high-plasticity flame-retardant magnesium alloy and a preparation method thereof, which comprehensively utilizes non-rare earth elements Al, Ca, Zn, and Mn for multi-component alloying, and adopts an asymmetric extrusion deformation method to additionally introduce severe shear stress, so as to refine the alloy grains, weaken the texture, and improve the mechanical properties of the alloy.

[0006] The technical scheme of the application is: A high plasticity flame-retardant magnesium alloy, which comprises, by weight percent, Al: 5-7 wt.%, Ca: 2-4 wt.%, Zn: 0.5-1.5 wt.%, Mn: 0.2-0.5 wt.%, and the balance being magnesium and unavoidable impurities.

[0007] Further, the high plasticity flame-retardant magnesium alloy, preferably, comprises, by weight percent, Al: 6.17 wt.%, Ca: 3.30 wt.%, Zn: 1.08 wt.%, Mn: 0.25 wt.%, and the balance being magnesium and unavoidable impurities.

[0008] Further, the high plasticity flame-retardant magnesium alloy, preferably, comprises, by weight percent, Al: 6.21 wt.%, Ca: 3.30 wt.%, Zn: 1.11 wt.%, Mn: 0.34 wt.%, and the balance being magnesium and unavoidable impurities.

[0009] A preparation method of the high plasticity flame-retardant magnesium alloy, comprising the following steps: Step one, taking pure magnesium ingot, pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy as raw materials, the raw materials are weighed according to the ratio, the surface oxide layer of the raw materials is polished and preheated, the preheating temperature is 200-250℃, and the preheating time is 10-20 minutes; Step two, the preheated pure magnesium ingot in step one is added into a stainless steel crucible, the stainless steel crucible containing the pure magnesium ingot is placed into an electric resistance furnace which has been heated to 740-750℃, and the pure magnesium ingot is completely melted under the protection of CO2 and SF6 mixed gas, then the preheated pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy in step one are added, after complete melting, the alloy melt is fully stirred and the surface dross is removed, and the alloy melt is obtained and kept; Step three, after the crucible and the alloy melt in step two are taken out, the crucible and the alloy melt are cooled to room temperature by using salt water, the alloy ingot is obtained, the surface layer containing oxide impurities of the alloy ingot is removed, and the alloy ingot is cut into an alloy ingot with a diameter of 75-80mm and a length of 40-50mm; Step four, the alloy ingot obtained in step three is subjected to primary solid solution treatment at 380-420℃ for 15-17h and secondary solid solution treatment at 490-520℃ for 47-50h, graphite powder is used to cover the alloy ingot during the solid solution treatment to prevent the surface of the alloy ingot from being excessively oxidized, and then the alloy ingot is quenched to room temperature by using hot water at 60-80℃; Step five, the alloy ingot after solution treatment in step four and the extrusion die are preheated and hot extruded to be a plate with a width of 55-57mm and a thickness of 4-6mm; the extrusion temperature is 330-380 DEG C, the extrusion speed is 5-10mm / s, and the extrusion ratio is 17:1-22:1.

[0010] Further, in the preparation method of the high plasticity and flame-retardant magnesium alloy, preferably, the content of Mg in the pure magnesium ingot is Mg≥99.98wt%, the content of Al in the pure aluminum block is Al≥99.98wt%, the content of Zn in the pure zinc block is Zn≥99.97wt%, the purity of Ca in the magnesium-calcium intermediate alloy is Ca: 20wt%-30wt%, and the purity of Mn in the magnesium-manganese intermediate alloy is Mn: 10wt%-15wt%.

[0011] Further, in the preparation method of the high plasticity and flame-retardant magnesium alloy, preferably, in the CO2 and SF6 mixed gas in step two, the volume ratio of SF6 is 0.1%-0.5%, and the rest is CO2.

[0012] Further, in the preparation method of the high plasticity and flame-retardant magnesium alloy, preferably, the stirring time in step two is 1-2min, and the holding time is 10-20min.

[0013] Further, in the preparation method of the high plasticity and flame-retardant magnesium alloy, preferably, in step five, the preheating temperature of the alloy ingot is 330-380 DEG C, and the preheating time is 20-30min; the preheating temperature of the extrusion die is 330-380 DEG C, and the preheating time is 1-2h.

[0014] The high plasticity and flame-retardant magnesium alloy is applied to a rail transit vehicle body material.

[0015] The advantages and beneficial effects of the present application are as follows: The present application comprehensively utilizes the addition of alkaline earth element Ca, other elements Al, Zn and Mn and the asymmetric extrusion deformation process to improve the structure and significantly improve the mechanical properties and flame-retardant properties of the magnesium alloy. 1. The present application limits the weight percentage of Ca to 2-4wt.%. The alloying of Ca element can effectively improve the strength and ignition point of the alloy, change the texture type of the magnesium alloy, and further improve the room temperature formability; however, the addition of a large amount of Ca element will form a coarse second phase, which further leads to poor plasticity of the alloy. 2. The present application adopts the asymmetric extrusion deformation process to obtain a deformed magnesium alloy plate. The asymmetric extrusion introduces additional shear stress, thereby refining the alloy grains and weakening the texture, which can simultaneously improve the strength and plasticity of the alloy.

[0016] 3、Compared with the prior art, the application does not contain rare earth elements, and the cost is reduced. The alloy material has good flame retardant performance, and meanwhile, the alloy has high comprehensive mechanical properties; specifically, the room temperature tensile strength is 259-290 MPa, the yield strength is 153-208 MPa, and the elongation is 15-19%. Meanwhile, the ignition point of the magnesium alloy is significantly improved to 1050 DEG C. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The EBSD diagram of the flame-retardant magnesium alloy described in the embodiment one of the application is shown, with a magnification of 1000; Figure 2 The SEM diagram of the flame-retardant magnesium alloy described in the embodiment one of the application is shown, with a magnification of 50; Figure 3 The EBSD diagram of the flame-retardant magnesium alloy described in the embodiment two of the application is shown, with a magnification of 1000. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0019] In the following embodiments, the Mg content in the pure magnesium ingot is Mg≥99.98wt%, the Al content in the pure aluminum block is Al≥99.98wt%, and the Zn content in the pure zinc block is Zn≥99.97wt%; the magnesium-calcium intermediate alloy and the magnesium-manganese intermediate alloy are all commercially available products, the purity of Ca in the magnesium-calcium intermediate alloy is Ca: 25wt%, and the purity of Mn in the magnesium-manganese intermediate alloy is Mn: 10wt%; the CO2 and SF6 are all commercially available products, and the volume ratio of CO2 to SF6 is 99.5:0.5. Embodiment 1

[0020] In this embodiment, a high-plasticity flame-retardant magnesium alloy includes, by weight percentage, Al: 6.17wt.%, Ca: 3.30wt.%, Zn: 1.08wt.%, Mn: 0.25wt.%, and the balance of magnesium Mg and unavoidable impurities. The preparation method includes the following steps: Step one, batching, grinding and preheating; taking pure magnesium ingot, pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy as raw materials, the raw materials are weighed according to the component ratio of the high-plasticity flame-retardant magnesium alloy described in this embodiment, the surface oxide layer of the raw materials is ground off and preheated, the preheating temperature is 250 DEG C, and the time is 20 minutes; Step two, the preheated pure magnesium ingot in step one is added into a stainless steel crucible, the stainless steel crucible with the pure magnesium ingot is put into an electric resistance furnace which has been heated to 740℃, and the pure magnesium ingot is completely melted under the protection of a mixed gas of CO2 and SF6, to obtain a pure magnesium melt; then the preheated pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy in step one are added, after complete melting, the alloy melt is fully stirred for 2 min and the surface scum of the melt is removed, to obtain an alloy melt and keep the alloy melt for 20 min; Step three, after the crucible and the alloy melt in step two are taken out, the crucible and the alloy melt are cooled to room temperature by using salt water, to obtain an ingot, a surface layer containing oxide impurities on the surface of the ingot is removed, and the ingot is cut into an alloy ingot with a diameter of 80 mm and a length of 40 mm; Step four, the alloy ingot obtained in step three is once solid solution treated at 400℃ for 16 h and twice solid solution treated at 515℃ for 48 h, graphite powder is used to cover the alloy ingot during the solid solution treatment, to prevent the surface of the alloy ingot from being excessively oxidized, and then the alloy ingot is quenched to room temperature by using hot water at 80℃; Step five, the alloy ingot after the solid solution treatment in step four is preheated at 340℃ for 30 min, an extrusion die is preheated at 340℃ for 1 h, and hot extrusion is performed, to extrude the alloy ingot into a plate with a width of 56 mm and a thickness of 5 mm; the extrusion temperature is 340℃, the extrusion speed is 10 mm / s, and the extrusion ratio is 18:1.

[0021] In this embodiment, a 5mm*5mm*5mm block is taken from the extruded plate for ignition point test, and an R4 hanging piece is taken for mechanical property test. Example 2

[0022] In this embodiment, a high-plasticity flame-retardant magnesium alloy includes, by weight percentage, Al: 6.21wt.%, Ca: 3.30wt.%, Zn: 1.11wt.%, Mn: 0.34wt.%, and the balance of magnesium Mg and unavoidable impurities. The preparation method includes the following steps: Step one, batching, grinding and preheating; pure magnesium ingot, pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy are used as raw materials, the raw materials are weighed according to the component proportion of the high-plasticity flame-retardant magnesium alloy described in this embodiment, the surface oxide layer of the raw materials is ground off and preheated, the preheating temperature is 250℃, and the preheating time is 20 minutes; Step two, the preheated pure magnesium ingot in step one is added into a stainless steel crucible, the stainless steel crucible with the pure magnesium ingot is put into an electric resistance furnace which has been heated to 740℃, and the pure magnesium ingot is completely melted under the protection of a mixed gas of CO2 and SF6, to obtain a pure magnesium melt; then the preheated pure aluminum block, pure zinc block, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy in step one are added, after complete melting, the alloy melt is fully stirred for 2 min and the surface scum of the melt is removed, to obtain an alloy melt and keep the alloy melt for 20 min; Step three, after the crucible and the alloy melt in step two are taken out, the crucible and the alloy melt are cooled to room temperature together by using salt water, a cast ingot is obtained, a surface layer containing oxide impurities on the surface of the cast ingot is removed, and the cast ingot is cut into an alloy cast ingot with a diameter of 80 mm and a length of 40 mm; Step four, the alloy cast ingot obtained in step three is once solid solution treated at 400℃ for 16h and twice solid solution treated at 515℃ for 48h, graphite powder is used to cover the alloy cast ingot during the solid solution treatment to prevent the surface of the alloy cast ingot from being excessively oxidized, and then the alloy cast ingot is quenched to room temperature by using hot water at 80℃; Step five, the alloy cast ingot after the solid solution treatment in step four is preheated at 360℃ for 30min, the extrusion die is preheated at 360℃ for 1h, hot extrusion is performed, and a plate with a width of 56mm and a thickness of 5mm is extruded; the extrusion temperature is 360℃, the extrusion speed is 10mm / s, and the extrusion ratio is 18:1.

[0023] In this embodiment, a 5mm*5mm*5mm block is taken from the extruded plate for ignition point test, and an R4 hanging piece is taken for mechanical property test.

[0024] Table 1: Performance test results of magnesium alloy in examples 1 and 2 As shown in Table 1, the low-cost high-plasticity flame-retardant magnesium alloy of the present application has a high ignition point of 1050℃, a maximum tensile strength of 290MPa at room temperature, a maximum yield strength of 208MPa, and a high plasticity with an elongation of 19%.

[0025] EBSD technology is used to analyze the plate extruded at 340℃ in example 1 and the plate extruded at 360℃ in example 2, and the results are shown in Figures (1) and (3). It can be seen that low-temperature extrusion refines the grains, improves the strength of the alloy through grain refinement strengthening, and simultaneously improves the plasticity of the plate.

[0026] As shown in Figure (2), the second phase of the extruded alloy is distributed in strips along the extrusion direction, a large number of spherical Al2Ca phases and a small number of blocky Al8Mn5 phases. A large number of thermally stable Al2Ca phases ensure the ignition point of the alloy.

[0027] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present application without departing from the purpose and scope of the technical solutions should be covered in the scope of the claims of the present application.

Claims

1. A high ductility, fire resistant magnesium alloy characterized in that, The components include A1: 5-7 wt.%, Ca: 2-4 wt.%, Zn: 0.5-1.5 wt.%, Mn: 0.2-0.5 wt.% by weight percentage, and the balance is magnesium Mg and inevitable impurities.

2. A high ductility, fire resistant magnesium alloy according to claim 1, characterized in that, The components include A1: 6.17 wt.%, Ca: 3.30 wt.%, Zn: 1.08 wt.%, Mn: 0.25 wt.% by weight percentage, and the balance is magnesium Mg and inevitable impurities.

3. The high ductility, fire resistant magnesium alloy of claim 1, wherein, The components include A1: 6.21 wt.%, Ca: 3.30 wt.%, Zn: 1.11 wt.%, Mn: 0.34 wt.% by weight percentage, and the balance is magnesium Mg and inevitable impurities.

4. A method of producing a high-ductility fire-retardant magnesium alloy as claimed in any one of claims 1 to 3, characterized by, The method comprises the following steps: Step one, taking pure magnesium ingot, pure aluminum block, pure zinc block, magnesium calcium intermediate alloy and magnesium manganese intermediate alloy as raw materials, the raw materials are weighed according to the proportion, the surface oxide layer of the raw materials is polished and preheated, the preheating temperature is 200-250 DEG C, and the preheating time is 10-20 minutes; Step two, the preheated pure magnesium ingot in step one is added to a stainless steel crucible, the stainless steel crucible containing the pure magnesium ingot is placed in an electric resistance furnace which has been heated to 740-750 DEG C, and is completely melted under the protection of CO2 and SF6 mixed gas, to obtain a pure magnesium melt; then the preheated pure aluminum block, pure zinc block, magnesium calcium intermediate alloy and magnesium manganese intermediate alloy in step one are added, after complete melting, the melt is fully stirred and the surface dross is removed, to obtain an alloy melt and keep warm; Step three, after the crucible and the alloy melt in step two are taken out, the crucible and the alloy melt are cooled to room temperature together by using salt water, to obtain an alloy ingot, the surface layer containing oxide impurities of the alloy ingot is removed, and the alloy ingot is cut into an alloy ingot with a diameter of 75-80 mm and a length of 40-50 mm; Step four, the alloy ingot obtained in step three is once solid solution treated at 380-420 DEG C for 15-17 h, and is twice solid solution treated at 490-520 DEG C for 47-50 h, graphite powder is used to cover the alloy ingot during the solid solution treatment, to prevent the surface of the alloy ingot from being excessively oxidized, and then the alloy ingot is quenched to room temperature by using hot water at 60-80 DEG C; Step five, the alloy ingot after the solid solution treatment in step four and an extrusion die are preheated and hot extruded, to be extruded into a plate with a width of 55-57 mm and a thickness of 4-6 mm; the extrusion temperature is 330-380 DEG C, the extrusion speed is 5-10 mm / s, and the extrusion ratio is 17:1-22:

1.

5. The method of producing a high-ductility fire-resistant magnesium alloy according to claim 4, characterized by, In the pure magnesium ingot in step one, the content of Mg is Mg≥99.98 wt%, the content of Al in the pure aluminum block is Al≥99.98 wt%, and the content of Zn in the pure zinc block is Zn≥99.97 wt%; the purity of Ca in the magnesium calcium intermediate alloy is Ca: 20 wt%-30 wt%, and the purity of Mn in the magnesium manganese intermediate alloy is Mn: 10 wt%-15 wt%.

6. The method of producing a high-ductility fire-resistant magnesium alloy according to claim 4, characterized by, In the CO2 and SF6 mixed gas in step two, the volume ratio of SF6 is 0.1%-0.5%, and the rest is CO2.

7. The method of producing a high-ductility fire-resistant magnesium alloy according to claim 4, characterized by, The stirring time in step two is 1-2 min; and the keeping warm time is 10-20 min.

8. The method of producing a high-ductility fire-resistant magnesium alloy according to claim 4, characterized by, In step five, the preheating temperature of the alloy ingot is 330-380℃, and the preheating time is 20-30min; the preheating temperature of the extrusion die is 330-380℃, and the preheating time is 1-2h.

9. Use of the high plasticity and flame-retardant magnesium alloy according to any one of claims 1-3 as a material for a rail transit vehicle body.

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