Low-cost low-alloy-content rare-earth-free high-strength heat-resistant magnesium alloy and preparation method thereof

Abstract

The invention provides a rare earth-free high-strength heat-resistant magnesium alloy with low cost and low alloy content and a preparation method thereof, the alloy comprises the following components in percentage by mass: 0.8-1.5% of Zn, 0.1-0.6% of Ca, 0.1-0.6% of Mn, 0-0.3% of Al, less than or equal to 3% of total alloy additive amount, less than or equal to 0.05% of inevitable impurities and the balance of Mg, and the preparation method mainly comprises the steps of smelting, casting, stepped solution treatment and differential temperature rapid extrusion. When the obtained high-strength heat-resistant magnesium alloy is used at the temperature higher than or equal to 200 DEG C, the tensile strength is higher than or equal to 245MPa, and the ductility is higher than or The adopted alloy elements are low in cost, the preparation process is simple, and the industrial application field of the high-strength heat-resistant magnesium alloy is further expanded on the basis of low cost and low alloy content.

Description

Technical Field

[0001] The present invention belongs to the field of metal material processing, and particularly relates to a low-cost, low-alloy-content rare-earth-free high-strength heat-resistant magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloys have the advantages of low density, high specific strength and specific stiffness, good damping and vibration reduction performance, good machinability, and easy recyclability, and are known as "green materials in the 21st century". At present, with the increasing demand for lightweight, the application demand for heat-resistant magnesium alloys is also gradually expanding. However, the existing magnesium alloys have poor heat resistance, and their mechanical properties will significantly decrease when the temperature exceeds 150 °C, which seriously restricts the further application of magnesium alloys in the engineering field.

[0003] To obtain magnesium alloys with high thermal stability, the existing research methods mainly improve the high-temperature mechanical properties of magnesium alloys by increasing the total content of alloying elements or adding precious metal elements such as rare-earth elements or adopting complex processes. For example: The article "Unveiling the mechanical response and deformation mechanism of extruded Mg-2.5Nd-0.5Zn-0.5Zr alloy sheet under high-temperature tensile" published by Wencong Zhang et al. in Journal of Alloys and Compounds, Volume 911, Page 164987 discloses that by adding rare-earth element Nd and precious metal element zirconium, etc., to introduce high-density thermally stable phases, the tensile strength of the extruded Mg-2.5Nd-0.5Zn-0.5Zr (wt.%) alloy is only 199 MPa at 200 °C. The article "Microstructures and mechanical properties of extruded Mg-8Gd-3Zn-0.4Zr alloys containing Zn" published by Meng Jian et al. in Materials Science and Engineering A, Volume 505, Pages 13-19 discloses that by adding 8% of rare-earth elements and elements such as precious metal element zirconium and long-term aging treatment, a large number of Mg 5 Gd, LSPO and other thermally stable phases are introduced in the extruded Mg-8Gd-3Zn-0.4Zr (wt%) alloy, and the tensile strength of this alloy is only 198 MPa at 200 °C.

[0004] Although existing methods can effectively improve the high-temperature mechanical properties of magnesium alloys, the large amount of alloying elements and rare earth elements added will not only significantly increase the price of raw materials and production costs, but also increase the resistance to thermomechanical deformation, and reduce extrusion / rolling formability and production efficiency. In addition, while existing technologies can improve room temperature mechanical properties, it is difficult to simultaneously improve high-temperature properties. Therefore, how to develop magnesium alloys with low alloy content, high strength and heat resistance, simultaneous improvement of room temperature and high temperature mechanical properties of alloys, good formability and suitable for industrial production under the conditions of reducing raw material costs, simplifying processes, achieving short processes and low energy consumption is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-cost, low-alloy content, rare earth-free, high-strength, heat-resistant magnesium alloy. The low-cost, low-alloy content, rare earth-free, high-strength, heat-resistant magnesium alloy is composed of Zn: 0.8-1.5%, Ca: 0.1-0.6%, Mn: 0.1-0.6%, Al: 0-0.3%, unavoidable impurities ≤ 0.05%, and the balance is Mg, calculated by mass percentage;

[0006] Its preparation method comprises the following steps:

[0007] (1) The ingredients are prepared according to the above mass percentages, and the CO 2 and SF 6 Under the protection of the mixed gas, pure magnesium is heated and melted at 650-710°C to obtain a melt, and the CO 2 and SF 6 The volume ratio of the molten metal is 90-99:10-1, slag is removed to remove impurities and oxide layer on the surface of the melt, and then preheated high-purity aluminum, high-purity zinc, magnesium calcium and magnesium manganese master alloy are added in sequence, and the temperature is kept for 10-20 minutes, and then stirring, argon blowing refining and slag removal and heat preservation are carried out for 10-20 minutes, and then gravity casting is used to obtain a magnesium alloy ingot;

[0008] (2) subjecting the magnesium alloy ingot obtained in step (1) to stepwise solution treatment and water quenching to obtain a magnesium alloy ingot after solution heat treatment;

[0009] The step-by-step solution treatment in step (2) is divided into two stages: the first stage: keeping at 250-400°C for 1-8 hours; the second stage: keeping at 400-480°C for 2-7 hours; the heating rate in each stage is less than 8°C / min;

[0010] (3) The magnesium alloy ingot obtained in step (2) is subjected to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy. The specific process of the differential temperature rapid extrusion is as follows: preheat at 300 - 450 °C for 30 - 90 min and then extrude at 150 - 250 °C, the extrusion speed is 18 - 30 m / min, and the extrusion ratio is 15:1 - 30:1;

[0011] The low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy has excellent high-temperature mechanical properties. The size of its fine grain region is ≤ 1.5 μm. When used at ≥ 200 °C, its tensile strength is ≥ 245 MPa and the elongation is ≥ 29%.

[0012] Furthermore, in step (1), the gravity casting: the mold is a water-cooled copper mold.

[0013] Furthermore, the stepwise solution treatment in step (2) is divided into two stages: the first stage: hold at 300 - 380 °C for 2 - 4 hours; the second stage: hold at 420 - 450 °C for 3 - 5 hours; the heating rate of each stage is ≤ 5 °C / min.

[0014] The present invention has the following characteristics compared with the prior art:

[0015] Compared with the prior art, the present invention omits the addition of rare-earth alloy elements and precious metal zirconium and other elements in the selection of alloy elements. The selected alloy elements are inexpensive. In addition, the content of rare earth or precious metals added in the prior art is relatively high, and the addition amount of the above elements with high costs generally exceeds 3%. However, the total alloy element content added in the present invention is lower than the addition amount of precious metal elements in the prior art, controlled at ≤ 3%. Compared with high-alloy-content magnesium alloys (such as commercial AZ91 alloy) or existing magnesium alloys containing high contents of rare earth or precious metal elements, the total alloy element addition content of the present invention is lower (mass fraction ≤ 3%) and the addition of rare earth or precious metal elements is omitted. Therefore, compared with the prior art, the present invention significantly reduces the production cost and breaks through the limitation of the development of high-strength and heat-resistant magnesium alloys on the high dependence on expensive elements in the past.

[0016] Therefore, the alloy element addition cost of the present invention is low and it is conducive to processing, suitable for industrial production; the present invention utilizes the interaction between alloy elements, through the coordinated regulation of element ratio, process and process parameters, so that high-density nanoclusters precipitate in the deformed structure, and at the same time, heat-stable phases and grain boundary segregation are formed, synchronously and greatly improving the room-temperature and high-temperature strength and plasticity of the low-alloy-content, rare-earth-free magnesium alloy. The specific advantages are as follows:

[0017] (1) Compared with the prior art, the present invention realizes stable and rapid extrusion, wherein the extrusion speed is much faster than the prior art, achieving a short process flow and being suitable for industrial production. At the same time, the frictional heat generated during the processing of the alloy is significantly reduced, which will enable the present invention to obtain a finer microstructure than the prior art. In addition, during deformation, it is easier to dynamically precipitate α-Mn, Al 8 Mn 5 and other thermally stable phases and form Zn-Ca-Al solute segregation at grain boundaries / subgrain boundaries / dislocations, delaying the dynamic recrystallization behavior during extrusion, so that the grain size of the low-alloy magnesium alloy is significantly refined, and the size of the fine grain region is ~0.8 - 1.5 μm;

[0018] (2) Compared with the prior art that only improves the high-temperature mechanical properties of the alloy through thermally stable second phases (such as (Mg,Al) 2 Ca, Al 8 Mn 5 , α-Mn, etc.), while forming thermally stable second phases, the present invention can also form nano-clusters with a number density of ~6×10 23 -2×10 24 m -3 , realizing the coexistence of various nano-clusters such as Ca-Ca, Al-Ca, Zn-Ca, Zn-Ca-Mn, (Mg,Al) 2 Ca, Al 8 Mn 5 , α-Mn and other nano-precipitates, and Zn-Ca-Al solute segregation. Under the multi-stage strengthening effect of nano-clusters, nano-precipitates, and solute segregation at grain boundaries / subgrain boundaries / dislocations, it strongly hinders grain growth, grain boundary movement, and dislocation movement at high temperatures, making grain boundary strengthening still have a great effect at high temperatures, greatly improving the high-temperature mechanical properties of the low-alloy magnesium alloy, breaking through the technical bottleneck that it is difficult to simultaneously improve the mechanical properties, formability, and processability of magnesium alloys at high temperatures, and it is difficult to simultaneously improve the strength and plasticity of alloys at room temperature and high temperatures in the prior art, and further expanding the industrial application range of magnesium alloys.

[0019] (3) Compared with the traditional high-temperature and long-time heat treatment, the present invention significantly reduces the heat treatment temperature, shortens the time and saves energy by reducing the addition amount of alloy elements and simplifying the process, effectively dissolving the coarse second phase while avoiding overburning. In addition, the extrusion speed of the present invention is much higher than that of the prior art, realizing short-process processing, avoiding the occurrence of thermal cracking due to fast extrusion in the prior art. Therefore, the process of the present invention is simple and does not require subsequent processing and heat treatment, shortening the alloy preparation process. The short-process, low-energy consumption and low-cost preparation of high-strength and heat-resistant magnesium alloys is achieved, breaking the technical bottleneck of the prior art that it is difficult to simultaneously improve the room temperature mechanical properties and high temperature mechanical properties of alloys, and can simultaneously achieve the simultaneous improvement of the room temperature and high temperature mechanical properties of the alloy, which is conducive to the industrial production of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a stress-strain curve of the Mg-0.8Zn-0.5Ca-0.2Mn-0.3Al alloy obtained in Example 2 when stretched at 200°C. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further explained and illustrated below in conjunction with specific embodiments:

[0022] Example 1

[0023] A low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy Mg-1.2Zn-0.3Ca-0.5Mn (by mass percentage: Zn: 1.2%, Ca: 0.3%, Mn: 0.5%, unavoidable impurities ≤ 0.05%, the balance is Mg), the preparation method of which comprises the following steps:

[0024] (1) The ingredients are prepared according to the above mass percentages, and the CO 2 and SF 6 Under the protection of the mixed gas, pure magnesium is heated and melted at 650°C to obtain a melt, and the CO 2 and SF 6 The volume ratio of the molten metal is 91-96:9-4, slag is removed to remove impurities and oxide layer on the surface of the melt, and then preheated high-purity zinc, magnesium calcium and magnesium manganese master alloy are added in sequence, and the temperature is kept for 10 minutes, and then stirring, argon blowing refining and slag removal and heat preservation are carried out for 15 minutes, and then gravity casting is used to obtain a magnesium alloy ingot;

[0025] (2) subjecting the magnesium alloy ingot obtained in step (1) to a stepwise solution treatment and water quenching to obtain a magnesium alloy ingot, wherein the stepwise solution treatment is carried out at 300° C. for 4 h and then at 420° C. for 5 h;

[0026] (3) The magnesium alloy ingot obtained in step (2) is subjected to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy. The specific process of the differential temperature rapid extrusion is as follows: The ingot is preheated at 450 °C for 60 min and then extruded at 250 °C. The extrusion speed is 20 m / min, and the extrusion ratio is 21:1.

[0027] The fine grain zone size of the low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy Mg-1.2Zn-0.3Ca-0.5Mn is 1.3 μm, and the number density of nano clusters is 7.3×10 23 m -3 , and it has excellent high-temperature mechanical properties at 220 °C. Among them, the tensile strength is 259 MPa, and the elongation is 33%.

[0028] Example 2

[0029] A low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy Mg-0.8Zn-0.5Ca-0.2Mn-0.3Al (by mass percentage: Zn: 0.8%, Ca: 0.5%, Mn: 0.2%, Al: 0.3%, inevitable impurities ≤ 0.05%, the balance is Mg), and its preparation method includes the following steps:

[0030] (1) Weigh the raw materials according to the above mass percentage. Under the protection of a mixed gas of CO 2 and SF 6 , pure magnesium is heated and melted at 680 °C to obtain a melt. The volume ratio of CO 2 and SF 6 is 94-98:6-2. Skim the impurities and oxide layer on the surface of the melt, and then successively add preheated high-purity aluminum, high-purity zinc, magnesium-calcium and magnesium-manganese master alloys. Keep warm for 15 min, then stir, refine with argon gas and remove the slag, and keep warm for 10 min. Then, a magnesium alloy ingot is obtained by gravity casting;

[0031] (2) The magnesium alloy ingot obtained in step (1) is subjected to stepwise solution treatment and water quenching to obtain a magnesium alloy ingot. The stepwise solution treatment is to keep warm at 350 °C for 2 h and then at 420 °C for 3 h

[0032] (3) The magnesium alloy ingot obtained in step (2) is subjected to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy. The specific process of the differential temperature rapid extrusion is as follows: The ingot is preheated at 350 °C for 60 min and then extruded at 180 °C. The extrusion speed is 30 m / min, and the extrusion ratio is 30:1;

[0033] The fine grain zone size of the low-cost, low-alloy-content, rare-earth-free high-strength heat-resistant magnesium alloy Mg-0.8Zn-0.5Ca-0.2Mn-0.3Al is 1.1 μm, and the nanocluster number density is 1.2×10 24 m -3 , and it has excellent high-temperature mechanical properties at 200 °C. Among them, the tensile strength is 245 MPa and the elongation is 43%.

[0034] Example 3

[0035] A low-cost, low-alloy-content, rare-earth-free high-strength heat-resistant magnesium alloy Mg-1.0Zn-0.6Ca-0.6Mn-0.1Al (by mass percentage: Zn: 1.0%, Ca: 0.6%, Mn: 0.6%, Al: 0.1%, unavoidable impurities ≤ 0.05%, the balance is Mg), and its preparation method includes the following steps:

[0036] (1) Weigh the raw materials according to the above mass percentage. Under the protection of a mixed gas of CO 2 and SF 6 , heat and melt pure magnesium at 710 °C to obtain a melt. The volume ratio of the CO 2 and SF 6 is 93-95:7-5. Skim the impurities and oxide layer on the surface of the melt, and then sequentially add preheated high-purity aluminum, high-purity zinc, magnesium-calcium, and magnesium-manganese master alloys. Keep warm for 15 min, then stir, refine with argon gas blowing, remove the slag, and keep warm for 10 min. Then, obtain a magnesium alloy ingot by gravity casting;

[0037] (2) Subject the magnesium alloy ingot obtained in step (1) to stepwise solution treatment and water quenching to obtain a magnesium alloy ingot. The stepwise solution treatment is to keep warm at 330 °C for 3 h and then at 450 °C for 3 h;

[0038] (3) Subject the magnesium alloy ingot obtained in step (2) to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free high-strength heat-resistant magnesium alloy. The specific process of the differential temperature rapid extrusion is: preheat the ingot at 400 °C for 60 min and then extrude at 150 °C. The extrusion speed is 18 m / min and the extrusion ratio is 15:1;

[0039] The fine grain zone size of the low-cost, low-alloy-content, rare-earth-free high-strength heat-resistant magnesium alloy Mg-1.0Zn-0.6Ca-0.6Mn-0.1Al is 1.5 μm, and the nanocluster number density is 6.3×10 23 m -3 , and it has excellent high-temperature mechanical properties at 200 °C. Among them, the tensile strength is 270 MPa and the elongation is 29%.

[0040] Example 4

[0041] Low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy Mg-1.5Zn-0.1Ca-0.1Mn-0.25Al (by mass percentage: Zn: 1.5%, Ca: 0.1%, Mn: 0.1%, Al: 0.25%, unavoidable impurities ≤ 0.05%, the balance is Mg), and its preparation method includes the following steps:

[0042] (1) Weigh materials according to the above mass percentages. Under the protection of a mixed gas of CO 2 and SF 6 , heat pure magnesium to melt at 690 °C to obtain a melt. The volume ratio of the CO 2 and SF 6 is 92-98:8-2. Skim the impurities and oxide layer on the surface of the melt, and then sequentially add preheated high-purity aluminum, high-purity zinc, magnesium-calcium, and magnesium-manganese master alloys. Keep warm for 15 min, then stir, refine with argon gas blowing, remove the slag, and keep warm for 10 min. Then, obtain a magnesium alloy ingot by gravity casting;

[0043] (2) Subject the magnesium alloy ingot obtained in step (1) to stepwise solution treatment and water quenching to obtain a magnesium alloy ingot. The stepwise solution treatment is to keep warm at 300 °C for 4 h and then at 450 °C for 2 h;

[0044] (3) Subject the magnesium alloy ingot obtained in step (2) to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy. The specific process of the differential temperature rapid extrusion is as follows: Preheat the ingot at 300 °C for 60 min and then extrude at 200 °C. The extrusion speed is 25 m / min, and the extrusion ratio is 25:1;

[0045] The grain size of the fine grain region of the low-cost, low-alloy-content, rare-earth-free, high-strength and heat-resistant magnesium alloy Mg-1.5Zn-0.1Ca-0.1Mn-0.25Al is 0.8 μm, and the number density of nano clusters is 1.7×10 24 m -3 . It has excellent high-temperature mechanical properties at 215 °C. Among them, the tensile strength is 260 MPa, and the elongation is 30%.

[0046] Comparative Example 1

[0047] The title of the paper is "Microstructures and Mechanical Properties of Extruded Mg-Ho-Zn Alloys with Different Ho / Zn Ratios", the name of the journal is "The Journal of Minerals", and the authors are Jiaan Liu, Jie Wang, Mengli Yang, Xiaoru Zhang, Chaojie Che, Dongwen Zhou, Yonghua Wang. It reports the extruded Mg-5.63Ho-2.24Zn (wt.%) alloy, with an extrusion ratio of 13:1, an extrusion speed of 3.9 m / min, an extrusion temperature of 370 °C, an average grain size of 13 μm, the best tensile strength of 170 MPa at 200 °C, and an elongation of 29%.

[0048] Comparative Example 2

[0049] The title of the paper is "Effect of Zr,Zn and Cu additions on elevated-temperature mechanical properties of as-extruded Mg-3Sn-1Ca alloy", the name of the journal is "Materialiin Tehnologije", and the authors are Jia Zheng, Yongzhi Yu, Fu, Li, Wenyi Hu. It reports the extruded Mg-3Sn-1Ca (wt.%) alloy, with an extrusion ratio of 19:1, an extrusion speed of 18 m / min, an extrusion temperature of 300 °C, an average grain size of 3.5 μm, the best tensile strength of 81 MPa at 200 °C, and an elongation of 27%.

[0050] Comparative Example 3

[0051] The title of the paper is "Effects of T5 treatment on microstructure and mechanical properties at elevated temperature of AZ80-Ag alloy", the name of the journal is Materials, and the authors are Zeng, Gang, Chuming Liu, Yonghao Gao, Shunong Jiang, Shilun Yu, and Zhiyong Chen. It reports a multi-pass rolling + long-time aging Mg-8.10Al-0.46Zn-0.18Mn-0.18Ag (wt.%) alloy with an average grain size of 40 μm, an optimal tensile strength of 180 MPa, and an elongation of 29% at 175 °C.

[0052] Compared with Comparative Examples 1-3, the present invention has the least addition content of elements, and omits the addition of precious metal elements such as Ho and Ag in the comparative examples. At a service temperature higher than that of the prior art, it obtains strength and plasticity superior to those of the prior art, achieving a significantly improved technical effect.

[0053] In summary, compared with the prior art, the present invention omits rare earth alloys or other precious metal elements in the selection of alloying elements, and the total content of the added alloying elements is low (≤3%). It has low cost, improves the extrusion speed to achieve short-process processing, significantly reduces the production cost and is conducive to processing, omits long-time aging, and is suitable for industrial production; by utilizing the interaction between alloying elements, through the coordinated regulation of element ratios, processes, and process parameters, the grain size of the microstructure of the low-alloy-content magnesium alloy is greatly refined, and the size of the fine-grained region is ~0.8 - 1.5 μm, and high-density Ca-Ca, Al-Ca, Zn-Ca, Zn-Ca-Mn, etc. nanoclusters (number density ~6×10 23 -2×10 24 m -3 ), (Mg,Al) 2 Ca, Al 8 Mn 5, heat-stable second phases such as α-Mn, the ternary co-segregation of Zn-Ca-Al at dislocations and grain boundaries, etc., ultimately enable the rare-earth-free low-alloy-content magnesium alloy obtained in the present invention to simultaneously improve the high-temperature mechanical properties, formability and machinability. At ≥200 °C, the tensile strength is ≥245 MPa and the elongation is ≥29%. In contrast, the present invention obtains higher strength and plasticity under the use temperature higher than or equivalent to that of the prior art such as the comparative example. Therefore, compared with the prior art, the present invention breaks through the limitations of the development of high-strength heat-resistant magnesium alloys highly dependent on expensive rare earths and precious metal elements in the past, as well as the technical bottleneck that it is difficult to simultaneously improve the strength and plasticity at room temperature and high temperature. In addition, compared with traditional magnesium alloys with high-temperature long-time heat treatment, slow extrusion, high rare-earth content or high alloy content, the present invention reduces the addition amount of alloying elements and simplifies the process, significantly reduces the heat treatment temperature, shortens the time and saves energy, and does not require subsequent processing and heat treatment, shortening the alloy preparation process. It realizes the short-process, low-energy consumption, low-cost preparation of high-strength heat-resistant magnesium alloys, and simultaneously improves the room-temperature and high-temperature strength and plasticity of the alloy, which is beneficial to the industrial production of magnesium alloys.

[0054] In addition, each embodiment of the present invention adopts different component ratios and process parameters, but the obtained properties are different. Under the condition of higher high-temperature thermal stability performance than the prior art, it can also make the properties obtained by each embodiment different and significantly higher than the technical effects obtained by the prior art. This shows that the excellent effect of the present invention is not determined by a certain component or process parameter, but is achieved through the synergistic regulation of components, ratios, processes and process parameters. And only within the scope protected by the claims of the present invention can the most excellent technical effects be achieved.

[0055] The above shows and describes the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0056] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Low-cost, low-alloy content, rare-earth-free, high-strength, heat-resistant magnesium alloy, characterized by: The low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy comprises, by mass percentage, 0.8-1.5% Zn, 0.1-0.6% Ca, 0.1-0.6% Mn, 0-0.3% Al, ≤0.05% unavoidable impurities, and the balance Mg; Its preparation method comprises the following steps: (1) The ingredients are prepared according to the above mass percentages, and pure magnesium is heated and melted at 650-710° C. under the protection of a mixed gas of CO2 and SF6 to obtain a melt, wherein the volume ratio of CO2 to SF6 is 90-99:10-1, and impurities and an oxide layer on the surface of the melt are removed by slag removal. Then, preheated high-purity aluminum, high-purity zinc, magnesium-calcium and magnesium-manganese master alloy are added in sequence, and the mixture is kept warm for 10-20 minutes. The mixture is then stirred, refined with argon gas, and the slag is removed and kept warm for 10-20 minutes. Then, a magnesium alloy ingot is obtained by gravity casting; (2) subjecting the magnesium alloy ingot obtained in step (1) to stepwise solution treatment and water quenching to obtain a magnesium alloy ingot after solution heat treatment; The step-by-step solution treatment in step (2) is divided into two stages: the first stage: keeping at 250-400°C for 1-8 hours; the second stage: keeping at 400-480°C for 2-7 hours; the heating rate in each stage is less than 8°C / min; (3) subjecting the magnesium alloy ingot obtained in step (2) to differential temperature rapid extrusion and water quenching to obtain a low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy, wherein the specific process of the differential temperature rapid extrusion is: preheating at 300-450° C. for 30-90 min, then extruding at 150-250° C., the extrusion speed is 18-30 m / min, and the extrusion ratio is 15:1-30:1; The low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy has excellent high-temperature mechanical properties, with a fine grain size of ≤1.5 μm, and a tensile strength of ≥245 MPa and an elongation of ≥29% when used at ≥200°C.

2. The low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy according to claim 1, characterized in that: Gravity casting described in step (1): the mold is a water-cooled copper mold.

3. The low-cost, low-alloy-content, rare-earth-free, high-strength, heat-resistant magnesium alloy according to claim 1, characterized in that: The step-by-step solution treatment in step (2) is divided into two stages: the first stage: keeping at 300-380°C for 2-4 hours; the second stage: keeping at 420-450°C for 3-5 hours; the heating rate in each stage is ≤5°C / min.

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