High-strength Mg-Al-Si magnesium alloy and preparation method

Abstract

The invention discloses a high-strength Mg-Al-Si magnesium alloy and a preparation method, and belongs to the technical field of materials. The high-toughness heat-resistant magnesium alloy is prepared from the following components in percentage by weight: 8 to 9 percent of Al, 2 to 3 percent of Si, 0 to 1 percent of Zn, 0 to 0.5 percent of Mn, 0 to 0.3 percent of Ce and the balance of Mg and inevitable impurities. The preparation method comprises the following steps: rapidly solidifying a first alloy melt containing Al and Si to form a rapidly solidified strip, and carrying out cold pressing on the strip to form an Al-Si intermediate alloy ingot; according to the composition proportion of a target alloy, a magnesium ingot, an Al-Si intermediate alloy ingot, a zinc ingot, an Mg-Mn intermediate alloy and an Mg-Ce intermediate alloy are subjected to burdening and melting, and a magnesium alloy melt is obtained; then, the material is rapidly solidified to form a rapidly-solidified strip, and then the rapidly-solidified strip is crushed into alloy powder; performing hot pressing to obtain a billet; and the billet is subjected to multi-pass hot extrusion, and the final magnesium alloy bar is obtained. Through integrated innovation of component design and a preparation process, the alloy structure is remarkably refined while cost control is realized, so that the room-temperature and high-temperature mechanical properties of the magnesium alloy are comprehensively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and particularly relates to a high-strength Mg-Al-Si magnesium alloy and a preparation method thereof BACKGROUND With the in-depth development of industrialization in China, the demand for metal materials continues to grow, and the problems of energy consumption and environmental protection brought by it are increasingly prominent. Under this background, the lightweight and high-strengthening of materials has become one of the key ways to realize energy saving and green development. Magnesium alloy has become the lightest metal structural material in practical application due to its low density, good electromagnetic shielding performance, good damping and shock attenuation performance, easy cutting processing and rich resource reserves, etc. It is known as the green structural material of the 21st century and has broad application prospects in the fields of aerospace, transportation tools and electronic devices.

[0002] According to the existing patent and literature research, the current developed high-strength heat-resistant magnesium alloy mainly focuses on the following two technical routes: one is the alloy system containing medium and heavy rare earth elements (such as patents CN118581371A, CN115927939A, CN116949331A, CN117026042A, CN116121575A, CN115161528A, CN114836664A, etc.), which usually needs to be combined with homogenization treatment, plastic deformation (such as patents CN117778844A, CN113755730A, CN117286379A, etc.) and complex solid solution-aging process (CN117845114A, CN117385245A, CN116516225A, etc.) to control the microstructure and properties. Although this method can realize high strength and heat resistance, the addition of rare earth elements significantly increases the cost of raw materials, and the multi-step heat treatment and deformation process leads to a long production process and low efficiency, which restricts its large-scale application in the automotive and other civil industrial fields.

[0003] The second is to use alkaline earth elements to replace rare earth alloy systems, such as Mg-Al-Ca, Mg-Al-Sr and Mg-Al-Si systems, etc. However, these systems still have obvious limitations: Mg-Al-Ca system is easy to form coarse Mg2Ca and Al2Ca phase, which damages the room temperature mechanical properties, and higher Ca content increases the difficulty of smelting and pouring; Mg-Al-Sr system such as AJ52, AJ62, etc. has high requirement for smelting temperature, poor die casting process, and the strength of gravity casting alloy is only about 150 MPa, and the elongation is about 6%, and the comprehensive performance is insufficient; Mg-Al-Si system has coarse Chinese character-shaped Mg2Si phase in the structure, which seriously deteriorates the mechanical properties, and how to optimize the morphology, size and distribution of Mg2Si phase is still the research focus (such as patents CN 110468294A, CN200610095200, CN201910899941, CN117144216A, CN112853184A, CN110468294A, CN114346368A, CN101781720A, etc.).

[0004] In summary, the existing high-strength magnesium alloy generally has the defects of high cost, harsh forming process requirement, unsatisfactory room temperature performance, poor high temperature performance, etc., which greatly limits its more extensive application and promotion. Therefore, to provide a magnesium alloy with low cost, high strength, good plasticity and excellent heat resistance and a preparation method thereof, which has the characteristics of simple composition, good process adaptability and balanced comprehensive mechanical properties, to solve the problems of dependence on expensive rare earth, complex process and difficult to balance room temperature and high temperature performance in the prior art, has become a technical problem to be solved by the technical personnel in the field. SUMMARY

[0005] One of the purposes of the present application is to provide a high-strength Mg-Al-Si magnesium alloy, which overcomes the shortcomings of the casting method of the Mg-Al-Si magnesium alloy in the prior art, eliminates the coarse Chinese character-shaped Mg2Si phase in the alloy structure, and improves the morphology, distribution and size of the Mg2Si phase.

[0006] The second purpose of the present application is to provide a preparation method of the high-strength Mg-Al-Si magnesium alloy.

[0007] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: The first aspect of the present application discloses a high-strength Mg-Al-Si magnesium alloy, which is composed of the following components by mass percentage: 8-9wt.% Al, 2-3wt.% Si, 0-1wt.% Zn, 0-0.5wt.% Mn and 0-0.3wt.% Ce, and the balance is Mg and unavoidable impurities.

[0008] In some embodiments of the present application, the impurity content is <1wt.%.

[0009] In some embodiments of the present application, the average size of the α-Mg matrix grains in the high-ductility heat-resistant magnesium alloy is less than 2 μm.

[0010] The second aspect of the present application discloses a preparation method of the high-ductility Mg-Al-Si magnesium alloy, which comprises the following steps: S1. Preparing an intermediate alloy ingot: rapidly solidifying a first alloy melt containing components Al and Si to form a rapidly solidified strip, and cold-pressing the strip into an Al-Si intermediate alloy ingot; S2. Compounding and melting: compounding magnesium ingots, the Al-Si intermediate alloy ingot, zinc ingots, Mg-Mn and Mg-Ce intermediate alloys according to the compounding ratio of the target alloy, and sequentially melting the compounds under a protective atmosphere after preheating to obtain a uniform magnesium alloy melt; S3. Powdering: rapidly solidifying the magnesium alloy melt to form a rapidly solidified strip, and crushing the strip into alloy powder; S4. Forming and densifying: hot-pressing the alloy powder to obtain an ingot; S5. Plastic working: multi-pass hot-extruding the ingot to obtain a final magnesium alloy rod.

[0011] In some embodiments of the present application, in step S1, the first alloy melt is an Al-25%Si alloy, and the melting and rapid solidification are both performed under a CO2 protective atmosphere; Preferably, the rapid solidification operation in step S1 is specifically that the Al-25%Si alloy melt is sprayed through a small hole at the bottom of a crucible onto a rapidly rotating cooling roller under the action of gas back pressure for solidification, and the thickness of the rapidly solidified strip is 10-60 μm; more preferably 30 μm. Preferably, the Al-25%Si alloy is heated to 800-820 ℃, more preferably 810 ℃, after melting, and then sprayed onto a rapidly rotating cooling roller under the action of gas back pressure for solidification.

[0012] In some embodiments of the present application, in step S2, after melting the magnesium ingots, CO2-SF6 mixed gas is introduced for protection, the temperature is adjusted to 720-740 ℃, the preheated Al-Si intermediate alloy ingot, zinc ingot, Mg-Mn and Mg-Ce intermediate alloy are put in, and the mixture is fully melted to obtain a uniform magnesium alloy melt. Preferably, the volume content of SF6 in the CO2-SF6 mixed gas is not more than 2%.

[0013] In some embodiments of the present application, the rapid solidification operation in step S3 is: the magnesium alloy melt is sprayed through a small hole at the bottom of a crucible to a rapidly rotating cooling roller under the action of gas back pressure for solidification, and the thickness of the rapidly solidified strip is 10-60 μm; more preferably 30 μm. Preferably, the magnesium alloy melt is rapidly solidified after being kept at 770-790 ℃. Preferably, the rapidly solidified strip is broken into particles of 500-700 μm; more preferably 600 μm.

[0014] In some embodiments of the present application, in step S4, the pressure of the hot pressing is 280-320 MPa, the mold preheating temperature is 230-270 ℃, and the pressure holding time is 2-4 min.

[0015] In some embodiments of the present application, in step S5, the hot extrusion is two-pass extrusion, the first-pass extrusion ratio is 2.5-3.5, the second-pass extrusion ratio is 22-28, and the extrusion temperature is 340-360 ℃.

[0016] In some embodiments of the present application, in step S5, the hot extrusion is two-pass extrusion, the first-pass extrusion ratio is 3, the second-pass extrusion ratio is 25, and the extrusion temperature is 350 ℃.

[0017] The Mg-Al-Si alloy of the present application realizes the optimization of microstructure and the improvement of performance through material design and process innovation without relying on high-priced rare earth elements. The present application uses Al-Si rapidly solidified intermediate alloy as an additive of Al and Si elements to replace the traditional Al-25%Si ingot, pure Al or high-melting-point (1414 ℃) pure Si; not only fundamentally solves the process problem of difficult smelting of high-melting-point pure Si, but also significantly refines the microstructure of the intermediate alloy through the rapid solidification process, greatly reduces or even eliminates the primary silicon phase therein, and the Si element is mainly converted into a dendritic Al-Si eutectic silicon form (the dissolution temperature thereof corresponds to the Al-Si binary eutectic point 580 ℃), which is easier to dissolve in subsequent smelting. Based on the above material properties, the smelting of the magnesium alloy can be carried out at a relatively low temperature of less than 780 ℃. This not only reduces energy consumption and cost, but more importantly, effectively inhibits the severe oxidation and evaporation of the magnesium alloy at high temperature, and reduces the element burnout.

[0018] In terms of microstructure formation, the introduction of Al-Si intermediate alloy brings significant improvement: (1) dissolution and phase change: more Al-Si eutectic can melt into the magnesium matrix liquid, thereby promoting the formation of more Mg2Si strengthening phase. (2) organizational inheritance and refinement: benefiting from the inheritance effect of rapid solidification structure, after dissolution, coarse Chinese characters or bone-shaped primary silicon phase does not reappear, but polygonal blocky Mg2Si phase with small size and uniform distribution is formed. (3) Strengthening phase characteristics: Mg2Si phase has high melting point (1085℃), high hardness (460HV), high elastic modulus and low thermal expansion coefficient (7.5×10 -6 K -1 ) and other characteristics, which can effectively strengthen the matrix and improve the room temperature and high temperature mechanical properties and friction and wear properties of the alloy.

[0019] In addition, alloying elements Al and Zn have high solid solubility in the magnesium matrix, can play a solid solution strengthening effect, and have a refining effect on the grain. Research shows that the synergistic addition of the two can improve the strength while improving the plasticity of the alloy.

[0020] In summary, by using Al-Si rapid solidification intermediate alloy and corresponding low-temperature smelting process, the effective control of alloy organization is realized, and dispersed distribution of fine blocky Mg2Si strengthening phase and refined grains are obtained, thereby comprehensively improving the mechanical and physical properties of the magnesium alloy.

[0021] Compared with the prior art, the present application has the following beneficial effects: The present application has the advantages of scientific design, ingenious concept, integrated innovation of component design and preparation process, cost control, significantly refined alloy organization, comprehensive improvement of room temperature and high temperature mechanical properties of magnesium alloy, and provision of an effective technical approach for developing high-performance and low-cost magnesium alloy.

[0022] By optimizing the alloy composition, Al and Si are used as the second and third main additive elements, the use of expensive rare earth elements is greatly reduced or avoided, the performance is ensured, the raw material cost is effectively reduced, and good economic efficiency is achieved.

[0023] The present application uses Al-Si strip ingot to prepare Mg-Al-Si alloy, and adds a small amount of Zn to synergistically act with Al, thereby effectively improving the strength and plasticity of the alloy.

[0024] The present application uses rapid solidification process combined with subsequent deformation processing, which has high operability, stable process flow, can realize large-scale continuous industrialization, and has good engineering application prospect.

[0025] By the synergistic effect of the composition and the rapid solidification process, ultra-fine grains and fine and dispersed second phase (Mg2Si, β-Mg17 Al 12 ), greatly shorten the interphase distance, and increase the solid solubility of Al and Si in α-Mg, thereby realizing significant fine-grain strengthening and solid solution strengthening effects. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a metallographic structure diagram of an extruded rod of the alloy of Example 1 of the present application; Figure 2 is a tensile stress-strain curve diagram of the alloy of Example 1 of the present application at 150°C and 200°C; Figure 3 is a metallographic structure diagram of an ingot of Comparative Example 2 of the present application; Figure 4 is a metallographic structure diagram of an as-cast extruded rod of Comparative Example 2 of the present application; Figure 5 is a room temperature tensile and compressive stress-strain curve diagram of Comparative Example 2 and Example 1 of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of the present application. Unless otherwise specified, various raw materials, reagents, instruments and equipment and the like used in the present application can be purchased from the market or can be prepared by existing methods.

[0028] The high-strength Mg-Al-Si magnesium alloy provided by the present application is composed of the following components in mass percentage: 8-9wt.% Al, 2-3wt.% Si, 0-1wt.% Zn, 0-0.5wt.% Mn and 0-0.3wt.% Ce, with the balance being Mg and unavoidable impurities; the impurity content is <1wt.%.

[0029] In the high-strength and high-toughness heat-resistant magnesium alloy, the average size of the α-Mg matrix grains is less than 2μm.

[0030] Meanwhile, the present application also provides a preparation method of the high-strength Mg-Al-Si magnesium alloy, which comprises the following steps: S1. preparing an intermediate alloy ingot The first alloy melt containing components Al and Si is rapidly solidified to form a rapidly solidified strip, and the strip is cold-pressed into an Al-Si intermediate alloy ingot; The first alloy melt is Al-25%Si alloy, and the melting and rapid solidification are both carried out under CO2 protective atmosphere. The rapid solidification operation in step S1 is specifically as follows: the Al-25%Si alloy melt is heated to 800-820 ℃, more preferably 810 ℃, and then sprayed to a rapidly rotating cooling roller through a small hole at the bottom of a crucible under the action of gas back pressure for solidification, and the thickness of the rapid solidification ribbon is 10-60 μm, more preferably 30 μm. S2. batching and melting According to the component proportion of the target alloy, magnesium ingots, Al-Si intermediate alloy ingots, zinc ingots, Mg-Mn and Mg-Ce intermediate alloys are batched, and after preheating, they are sequentially melted under protective atmosphere to obtain a uniform magnesium alloy melt. In some embodiments of the present application, after the magnesium ingots are melted in step S2, CO2-SF6 mixed gas protection is carried out, the temperature is adjusted to 720-740 ℃, the preheated Al-Si intermediate alloy ingots, zinc ingots, Mg-Mn and Mg-Ce intermediate alloys are put in, and the magnesium alloy melt is obtained after sufficient melting. The volume content of SF6 in the CO2-SF6 mixed gas is not more than 2%.

[0031] S3. powdering The magnesium alloy melt is kept at 770-790 ℃, and then sprayed to a rapidly rotating cooling roller through a small hole at the bottom of a crucible under the action of gas back pressure for solidification to form a rapid solidification ribbon, and the ribbon is broken into alloy powder with a particle size of 500-700 μm, more preferably 600 μm.

[0032] The thickness of the rapid solidification ribbon is 10-60 μm, more preferably 30 μm. S4. forming and densification The alloy powder is hot-pressed at 280-320 MPa to obtain an ingot; the mold preheating temperature is 230-270 ℃, and the pressure holding time is 2-4 min.

[0033] S5. plastic working The ingot is subjected to multi-pass hot extrusion to obtain a final magnesium alloy rod.

[0034] In some embodiments of the present application, the hot extrusion is two-pass extrusion, the first-pass extrusion ratio is 2.5-3.5, the second-pass extrusion ratio is 22-28, and the extrusion temperature is 340-360 ℃.

[0035] Preferably, the first-pass extrusion ratio is 3, the second-pass extrusion ratio is 25, and the extrusion temperature is 350 ℃.

[0036] Example 1 This embodiment discloses a method for preparing high-strength Mg-Al-Si magnesium alloy (Mg-9Al-3Si) of the present application. The mass composition of the high-strength magnesium alloy in this embodiment is as follows: 9wt.% Al, 3wt.% Si, 1wt.% Zn, 0.5wt.% Mn, 0.3wt.% Ce, 86wt.% Mg, and the balance being inevitable impurities.

[0037] The preparation method is specifically as follows: S1. Preparation of intermediate alloy ingot First, the Al-25%Si ingot is placed into a crucible preheated to 780°C. After the alloy is melted, it is heated to 810°C and kept for 10 minutes. Then, the molten aluminum-silicon alloy solution is sprayed onto a rapidly rotating cooling roller through a small hole at the bottom of the crucible by gas back pressure, and a 30 μm thick Al-25%Si rapidly solidified strip is formed by rapid solidification. The rapidly solidified strip is cold-pressed into an Al-25%Si strip ingot using a press and a mold.

[0038] S2. Proportioning and melting According to the composition and proportion of the target alloy, the magnesium ingot, the Al-25%Si strip ingot, the zinc ingot, the Mg-Mn and Mg-Ce intermediate alloy are proportioned. First, the above raw materials are preheated to about 200°C in a drying oven; then pure Mg is placed in a crucible and melted. After complete melting, CO2-1vol.% SF6 mixed gas is introduced for protection, and the temperature is raised to 730°C. Then, pure Zn, Al-25%Si strip ingot, Mg-Mn and Mg-Ce intermediate alloy are added in turn, and after keeping for 15 minutes, the alloy liquid is stirred for 5 minutes to uniformly mix the components.

[0039] S3. Powdering After stirring, the surface dross is removed after standing for 15 minutes. The alloy liquid is transferred to a crucible preheated to 780°C and CO2 gas protection is introduced, and kept for 10 minutes. After the alloy liquid temperature is uniformly reached 780°C, it is sprayed onto the surface of a rapidly rotating cooling roller through a small hole at the bottom of the crucible under the action of gas back pressure. The cooling roller is in a CO2 protective atmosphere throughout the process, and the alloy is rapidly solidified to form a rapidly solidified strip about 30 μm thick. Finally, the strip is cut into a powder with a particle size of about 600 μm.

[0040] S4. Forming and densification The alloy powder prepared in step S3 is loaded into a cylindrical mold preheated to about 250°C, and kept for 5 minutes. Then, it is hot-pressed into a green body under a pressure of 300 MPa for 3 minutes.

[0041] S5. Plastic working Subsequently, the green body was subjected to two heat extrusion processes: the first extrusion ratio was 3, and the second extrusion ratio was 25, and the extrusion temperature was 350°C. The green body was kept for 5 minutes before extrusion (if the size of the blank increases, the holding time is correspondingly extended), and finally extruded into a rod.

[0042] The specific detection method of room temperature performance can refer to the national standard GB / T 16865-2013 Deformed aluminum, magnesium and its alloy products Tensile test sample and method; the high temperature tensile property test can refer to the national standard GB / T 228.2-2015 Metallic materials - Tensile test - Part 2: Method of test at elevated temperature. The mechanical properties of the rapidly quenched extruded alloy rod of the embodiment are as follows: the room temperature yield strength is 343 MPa, the tensile strength is 403 MPa, the elongation after fracture is 12%, and the tensile-compressive ratio is 1.017; the high temperature tensile yield strength decreases with the increase of temperature, and is 199 MPa at 150°C and 110 MPa at 200°C.

[0043] The metallographic structure morphology of the rapidly quenched extruded alloy rod of the embodiment is shown in FIG. 2. Figure 1 As can be seen from the figure, the rod structure is composed of ultra-fine grain matrix and dispersed distribution of fine second phase. Figure 1

[0044] The tensile stress-strain curves of the rapidly quenched extruded alloy rod of the embodiment at 150°C and 200°C are shown in FIG. 3. Figure 2 As can be seen from the figure, the yield strength and tensile strength of the rapidly quenched extruded alloy rod of the embodiment gradually decrease with the increase of temperature when stretched at high temperature of 150°C and 200°C, while the plastic deformation capacity increases, the elongation at break increases, and the typical metal material high temperature softening and plasticity increase behavior is shown, which shows that the material still maintains certain structural stability and deformation capacity at high temperature. Figure 2

[0045] Comparative Example 1 A Mg-2Al-1Si (AS21X) heat-resistant magnesium alloy, the alloy composition is 2.2wt.% of Al, 1.0wt.% of Si, and 0.2wt.% of Mn, and the balance is Mg and inevitable impurities, and the impurity content is less than 1wt%.

[0046] ​​The ingot was obtained by a conventional die casting process as follows: the Mg alloy melt was poured into the die chamber, and the pouring temperature was controlled at 680-700 °C. The mold was preheated to 180-250 °C, and the working temperature was maintained at 200-300 °C. Two-stage injection was used: slow injection (0.1-0.3 m / s) to smoothly push the melt into the ingate, and then high-speed fast injection (2-5 m / s) to fill the cavity with the melt in tens of milliseconds. High pressure of 40-80 MPa was applied immediately at the end of filling to increase the pressure and compensate for shrinkage. After holding for 3-10 seconds, the casting was ejected after cooling in the cavity for 20-40 seconds. The tensile yield strength, tensile strength, elongation and tensile-compressive ratio at room temperature were 120 MPa, 220 MPa, 13% and 1, respectively. The tensile yield strength, tensile strength and elongation of the AS21 die casting of the present comparative example at 150 °C were 87 MPa, 120 MPa and 27%, respectively.

[0047] Comparative Example 2 The present comparative example discloses a Mg-Al-Si high-strength magnesium alloy, which has the same alloy composition as Example 1 but different preparation method. The mass composition of the magnesium alloy of the present comparative example is: 9wt.% Al, 3wt.% Si, 1wt.% Zn, 0.5wt.% Mn, 0.3wt.% Ce, 86wt.% Mg, and the balance is inevitable impurities.

[0048] The preparation method is as follows: First, pure Mg, pure Zn, Al-25% Si ingot, Mg-Mn and Mg-Ce intermediate alloy were preheated to about 200 °C in a drying oven; then, the pure Mg was placed in a crucible and melted, and CO2-1vol.% SF6 mixed gas was introduced for protection, and the temperature was raised to 730 °C. Then, the pure Zn, Al-25% Si ingot, Mg-Mn and Mg-Ce intermediate alloy were added, and after holding for 15 min, stirring was performed to ensure that the alloy liquid was fully mixed. After stirring for 15 min, the slag was removed, and then the alloy ingot with the target composition was obtained by pouring into a metal mold preheated to 240 °C.

[0049] Subsequently, the alloy ingot was cut into a green body using a wire cutting machine, and then placed into an extrusion die preheated to 350 °C (extrusion ratio 25), and held for 5 min (the holding time was appropriately extended as the ingot size increased), and the target alloy was extruded.

[0050] After the alloy ingot was extruded into a rod, the tensile yield strength was 245 MPa, the tensile strength was 305 MPa, the elongation after fracture was 3%, and the tensile-compressive ratio was 0.905.

[0051] The metallographic morphology of the alloy ingot of the present comparative example is shown in FIG. 2; and the metallographic morphology of the as-cast extruded rod is shown in FIG. 3. Figure 3 Figure 4 The metallographic morphology of the alloy ingot of the present comparative example is shown in FIG. 2; and the metallographic morphology of the as-cast extruded rod is shown in FIG. 3.​Figure 3 and Figure 4 The microstructure of Mg-9Al-3Si alloy ingots and as-cast extrusion bars is shown. Figure 3 In the as-cast Mg-9Al-3Si ingot, the microstructure consists of an α-Mg matrix, a Mg2Si phase, and (α-Mg + β-Mg) phases. 17 Al 12 The Mg₂Si phase has a eutectic composition, with the α-Mg matrix having a grain size of approximately 80 μm and the Mg₂Si phase having a grain size between 30 μm and 60 μm, with almost all Mg₂Si precipitating along grain boundaries. Mg₂Si, as the high-temperature stable phase, exhibits the highest hardness, while the α-Mg matrix is ​​the softest. Figure 3 Compared to Mg-9Al-3Si ingots, Figure 4 The α-Mg matrix grains underwent dynamic recrystallization during extrusion at 350℃, reducing the α-Mg grain size from approximately 80 μm to [missing value]. Figure 3 (a) less than 20 μm.

[0052] Experimental Example 1 This test example compares the alloy of Example 1 of the present invention with the alloys of Comparative Example 1 and Comparative Example 2.

[0053] 1. The phase size, phase content, and phase distribution of Mg-9Al-3Si extruded rods prepared by different processes in Comparative Example 1 and Comparative Example 2 were compared; the results are shown in Table 1.

[0054] Table 1. Phase size, phase content, and phase distribution of Mg-9Al-3Si extruded bars.

[0055] 2. The mechanical properties of the alloys in Example 1, Comparative Example 1 and Comparative Example 2 were compared, and the results are shown in Table 2.

[0056] Table 2 Comparison of room temperature mechanical properties of alloys from Example 1 and Comparative Examples 1 and 2

[0057] 3. The tensile mechanical properties of the alloys in Example 1, Comparative Example 1 and Comparative Example 2 at different temperatures were compared, and the results are shown in Table 3.

[0058] Table 3 Comparison of tensile mechanical properties of alloys in Example 1 and Comparative Examples 1 and 2 at different temperatures

[0059] The tensile and compressive stress-strain curves of Mg-9Al-3Si extruded bars prepared by different processes in Example 1 and Comparative Example 2 are attached. Figure 5 As shown.

[0060] As can be seen from Table 1, compared with the as-cast alloy of Comparative Example 2, the α-Mg, Mg2Si and β-Mg 17 Al 12 The size of the phase is significantly reduced, the interlattice spacing is shortened, and the solid solubility of Al and Si in α-Mg is significantly improved, indicating that the rapid solidification treatment effectively refines the microstructure and enhances the solid solution strengthening effect.

[0061] As can be seen from Table 2, the room temperature mechanical properties of the rapidly quenched state of Example 1 are optimal: both the yield strength and the tensile strength are significantly higher than those of Comparative Examples 1 and 2, while the elongation remains at a high level, and the tensile-compressive ratio is close to 1, showing good tensile-compressive symmetry. Although the strength of Comparative Example 2 is improved, the elongation is low.

[0062] As can be seen from Table 3, at high temperature, Example 1 still performs excellently: at 150°C, the yield strength and tensile strength are much higher than those of Comparative Example 1; at 200°C, the yield strength, tensile strength and elongation of Example 1 all remain at a good level, indicating that the rapidly quenched material has more optimal high-temperature mechanical properties.

[0063] In combination Figure 5 According to the analysis of the curves, the tensile and compressive strengths of the as-cast extruded rod of Comparative Example 2 at room temperature are both significantly lower than those of the rapidly solidified state of Example 1, and its plasticity is poor and the elongation at break is low, which reflects the performance limitations brought by the traditional casting process due to coarse grains and uneven structure; while the rapid solidification process significantly improves the comprehensive mechanical properties of the material by refining the grains and improving the uniformity of the structure.

[0064] In summary, through composition optimization and rapid solidification process, the magnesium alloy of the present application has ultra-fine grains and a second phase structure with fine and dispersed distribution, thereby significantly improving its room temperature and high temperature strength, while maintaining good plasticity and tensile-compressive symmetry, and the comprehensive mechanical properties are fully optimized.

[0065] Finally, it should be noted that the above examples are only the preferred embodiments of the present application for illustrating the technical solutions of the present application, but not limiting them, and of course, they are not limiting the patent scope of the present application. Any modification or polishing without substantial meaning made within the main design idea and spirit of the present application, which still solves the same technical problems as the present application, should be included in the protection scope of the present application; in addition, the technical solutions of the present application are directly or indirectly applied to other related technical fields, which are also included in the patent protection scope of the present application.

Claims

1. A high strength Mg-Al-Si magnesium alloy, characterized in that, consists of the following components in mass percentage: 8-9 wt.% Al, 2-3 wt.% Si, 0-1 wt.% Zn, 0-0.5 wt.% Mn and 0-0.3 wt.% Ce, the balance being Mg and inevitable impurities.

2. The high-strength Mg-Al-Si magnesium alloy according to claim 1, characterized in that The impurity content is <1 wt.%.

3. The high-strength Mg-Al-Si magnesium alloy according to claim 1 or 2, characterized in that, The average size of the α-Mg matrix grains in the high-strength and high-toughness heat-resistant magnesium alloy is less than 2 μm.

4. The method according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: S1. Preparing an intermediate alloy ingot: rapidly solidifying a first alloy melt containing components Al and Si to form a rapidly solidified strip, and cold-pressing the strip into an Al-Si intermediate alloy ingot; S2. Compounding and melting: compounding magnesium ingots, Al-Si intermediate alloy ingots, zinc ingots, Mg-Mn and Mg-Ce intermediate alloys according to the component proportions of the target alloy, melting them in sequence under a protective atmosphere after preheating to obtain a uniform magnesium alloy melt; S3. Powdering: rapidly solidifying the magnesium alloy melt to form a rapidly solidified strip, and crushing the strip into alloy powder; S4. Forming and densifying: hot-pressing the alloy powder to obtain an ingot; S5. Plastic working: hot-extruding the ingot in multiple passes to obtain a final magnesium alloy rod.

5. The method of claim 4, wherein the high-strength Mg-Al-Si magnesium alloy is prepared by the following steps of: In step S1, the first alloy melt is an Al-25%Si alloy, and the melting and rapid solidification are both performed under a CO2 protective atmosphere; ​ Preferably, the rapid solidification operation in step S1 is specifically as follows: the Al-25%Si alloy melt is sprayed through a small hole at the bottom of a crucible onto a rapidly rotating cooling roller under the action of gas back pressure for solidification, and the thickness of the rapidly solidified strip is 10-60 μm; more preferably 30 μm; Preferably, the Al-25%Si alloy is heated to 800-820 ℃, more preferably 810 ℃, after melting, and then sprayed onto a rapidly rotating cooling roller under the action of gas back pressure for solidification.

6. The method for preparing a high-strength Mg-Al-Si magnesium alloy according to claim 4, characterized in that, In step S2, after the magnesium ingots are melted, CO2-SF6 mixed gas is introduced for protection, the temperature is adjusted to 720-740 ℃, the preheated Al-Si intermediate alloy ingots, zinc ingots, Mg-Mn and Mg-Ce intermediate alloys are put in, and the magnesium alloy melt is obtained after sufficient melting. Preferably, the volume content of SF6 in the CO2-SF6 mixed gas is not more than 5%.

7. The method for preparing a high-strength Mg-Al-Si magnesium alloy according to claim 4, characterized in that, In step S3, the rapid solidification operation is as follows: the magnesium alloy melt is sprayed through a small hole at the bottom of a crucible onto a rapidly rotating cooling roller under the action of gas back pressure for solidification, and the thickness of the rapidly solidified strip is 10-60 μm; more preferably 30 μm; Preferably, the magnesium alloy melt is rapidly solidified after being kept at 770-790 ℃; Preferably, the rapidly solidified strip is crushed into particles with a size of 500-700 μm; more preferably 600 μm.

8. The method for preparing a high-strength Mg-Al-Si magnesium alloy according to claim 4, characterized in that, In step S4, the hot-pressing pressure is 280-320 MPa, the mold preheating temperature is 230-270 ℃, and the pressure holding time is 2-4 min.

9. The method for preparing a high-strength Mg-Al-Si magnesium alloy according to claim 3, characterized in that, In step S5, the hot-extrusion is two-pass extrusion, the first-pass extrusion ratio is 2.5-3.5, the second-pass extrusion ratio is 22-28, and the extrusion temperature is 340-360 ℃.

10. The method of claim 9, wherein the high-strength Mg-Al-Si magnesium alloy is prepared by the steps of: preparing a Mg-Al-Si magnesium alloy by mixing Mg, Al, and Si; and performing a heat treatment on the Mg-Al-Si magnesium alloy. In step S5, the hot extrusion is a two-pass extrusion, with the first pass having an extrusion ratio of 3 and the second pass having an extrusion ratio of 25, and the extrusion temperature being 350°C.

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