High-plasticity Mg-Sn-Zn-Zr alloy and preparation method thereof

Abstract

The invention provides a high-plasticity Mg-Sn-Zn-Zr alloy and a preparation method thereof, and belongs to the technical field of magnesium alloy deformation processing. The preparation method of the high-plasticity Mg-Sn-Zn-Zr alloy, provided by the invention, comprises the following steps: directly carrying out positive extrusion deformation treatment on an as-cast alloy, and then carrying out differential-temperature equal-channel angular extrusion deformation treatment to obtain the high-plasticity Mg-Sn-Zn-Zr alloy, during the differential temperature equal channel angular pressing deformation treatment, the temperature of the alloy is 100-150 DEG C, and the temperature of the mold is 300-350 DEG C. According to the method, during differential-temperature equal-channel angular pressing deformation treatment, the alloy and the mold are both heated, so that after differential-temperature equal-channel angular pressing deformation treatment is carried out, a double-heterostructure in which coarse and fine crystal double-peak crystal grains and a second phase of a harmonic-like structure coexist is formed, and the alloy performance is remarkably improved; and the ductility of the high-plasticity Mg-Sn-Zn-Zr alloy is as high as 37.9%.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy deformation processing technology, specifically relating to a high-plasticity Mg-Sn-Zn-Zr alloy and its preparation method. Background Technology

[0002] Magnesium and magnesium alloys, as lightweight strategic materials, have broad application prospects in aerospace, automotive, 3C electronics, and biomedical fields due to their low density, high specific strength / specific stiffness, excellent vibration damping, excellent heat dissipation, and recyclability. However, magnesium has a close-packed hexagonal structure, resulting in fewer active slip systems at room temperature, leading to poor room-temperature plasticity and processing formability, which severely limits the widespread application of magnesium alloys.

[0003] Mg-Sn-Zn-Zr alloy (TZK alloy) is a magnesium alloy with high strength, high plasticity, good corrosion resistance, and low density, exhibiting significant advantages and broad application prospects. Temperature differential equal channel angular extrusion (DT-ECAP) technology is highly suitable for processing and preparing TZK alloys, significantly refining grains, optimizing microstructure, and improving mechanical and corrosion resistance.

[0004] Currently, the DT-ECAP process for TZK alloys typically involves heating the alloy sample above its recrystallization temperature while keeping the mold at room temperature. However, this process can lead to unstable deformation and even cracking. To address these issues, a new process has emerged that involves heating only the mold during DT-ECAP treatment, without heating the alloy sample. In existing technologies, after solution aging and positive extrusion deformation of the as-cast alloy, DT-ECAP treatment (heating only the mold, not the alloy sample) can increase the tensile yield strength of the TZK alloy to over 330 MPa. However, this negatively impacts the plasticity of the TZK alloy, reducing the elongation to below 20%. Furthermore, solution aging heat treatment is required before deformation, making the process complex. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high-plasticity Mg-Sn-Zn-Zr alloy. The preparation method provided by this invention has a simple process and produces a Mg-Sn-Zn-Zr alloy with high plasticity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a high-plasticity Mg-Sn-Zn-Zr alloy, comprising the following steps: directly subjecting a cast Mg-Sn-Zn-Zr alloy to positive extrusion deformation treatment to obtain a positive extrusion alloy; subjecting the positive extrusion alloy to differential temperature equal channel angular extrusion deformation treatment to obtain a high-plasticity Mg-Sn-Zn-Zr alloy; wherein during the differential temperature equal channel angular extrusion deformation treatment, the alloy temperature is 100-150℃ and the die temperature is 300-350℃.

[0008] Preferably, the positive extrusion deformation process includes: placing the cast Mg-Sn-Zn-Zr alloy into a positive extrusion mold and heating it together to the positive extrusion temperature, holding it at that temperature, and then performing positive extrusion to obtain the positive extruded alloy.

[0009] Preferably, the heating rate is 14-16°C / min, the positive extrusion temperature is 300-350°C, and the heat preservation time is 1-1.5h.

[0010] Preferably, the positive extrusion speed is 10-15 mm / s and the extrusion ratio is 11-12:1.

[0011] Preferably, before the differential temperature equal channel corner extrusion deformation treatment, the mold and the alloy are heated to the temperature of the differential temperature equal channel corner extrusion deformation treatment and held at that temperature; the heating rate of the mold is 18-22℃ / min and the holding time is 30-60min; the heating rate of the alloy is 14-16℃ / min and the holding time is 10-20min.

[0012] Preferably, the extrusion speed of the differential temperature equal channel corner extrusion deformation treatment is 6-10 mm / s.

[0013] Preferably, the deformation path of the differential temperature equal channel corner extrusion deformation treatment is path Bc, Ba, A or C.

[0014] Preferably, the number of passes for the differential temperature equal channel corner extrusion deformation treatment is 1 to 4; no annealing treatment is performed between each pass.

[0015] The present invention also provides a high-plasticity Mg-Sn-Zn-Zr alloy prepared by the preparation method described in the above technical solution.

[0016] Preferably, the composition of the high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0017] This invention provides a method for preparing a high-plasticity Mg-Sn-Zn-Zr alloy, comprising: directly subjecting a cast Mg-Sn-Zn-Zr alloy to positive extrusion deformation treatment to obtain a positive extrusion alloy; subjecting the positive extrusion alloy to differential temperature equal channel angular extrusion deformation treatment to obtain a high-plasticity Mg-Sn-Zn-Zr alloy; wherein during the differential temperature equal channel angular extrusion deformation treatment, the alloy temperature is 100-150℃ and the die temperature is 300-350℃. This invention directly subjects as-cast Mg-Sn-Zn-Zr alloys to positive extrusion deformation, inducing the formation of a banded structure of the second phase in the as-cast alloy. Subsequent differential temperature isochannel angular extrusion deformation further results in a heterogeneous structure where coarse and fine-grained bimodal grains coexist with a harmonic-like second phase. By controlling the die temperature to 300–350°C and the alloy temperature to 100–150°C during the differential temperature isochannel angular extrusion deformation, this heterogeneous structure is induced to enhance toughness and significantly improve the plasticity of the Mg-Sn-Zn-Zr alloy. Simultaneously, it eliminates the need for solution aging heat treatment before positive extrusion deformation, simplifying the process and improving the efficiency of magnesium alloy preparation. Experimental results show that after four passes of differential temperature isochannel angular extrusion deformation, the elongation of the obtained high-plasticity Mg-Sn-Zn-Zr alloy reaches 37.9%. Attached Figure Description

[0018] Figure 1 Stress-strain curves of the high-plasticity Mg-Sn-Zn-Zr alloys prepared in Examples 1-4;

[0019] Figure 2 The stress-strain curve of the Mg-Sn-Zn-Zr alloy prepared in Comparative Example 1 is shown.

[0020] Figure 3 Microstructure diagram of the high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 2;

[0021] Figure 4 Microstructure diagram of the high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 4;

[0022] Figure 5 The image shows the microstructure of the Mg-Sn-Zn-Zr alloy prepared in Comparative Example 1. Detailed Implementation

[0023] This invention provides a method for preparing a high-plasticity Mg-Sn-Zn-Zr alloy, comprising: directly subjecting a cast Mg-Sn-Zn-Zr alloy to positive extrusion deformation treatment to obtain a positive extrusion alloy; subjecting the positive extrusion alloy to differential temperature equal channel angular extrusion deformation treatment to obtain a high-plasticity Mg-Sn-Zn-Zr alloy; wherein during the differential temperature equal channel angular extrusion deformation treatment, the alloy temperature is 100-150℃ and the die temperature is 300-350℃.

[0024] This invention involves directly subjecting a cast Mg-Sn-Zn-Zr alloy to positive extrusion deformation to obtain a positive extrusion alloy.

[0025] As one embodiment of the present invention, the as-cast Mg-Sn-Zn-Zr alloy can be obtained by melting and casting metal raw materials.

[0026] This invention does not have special requirements regarding the type of metal raw material; any raw material well-known to those skilled in the art can be selected. In one embodiment of this invention, the metal raw material can be a pure metal or an intermediate alloy raw material. In an embodiment of this invention, the metal raw material is a high-purity magnesium ingot, a high-purity tin ingot, a high-purity zinc ingot, and a Sn-30Zr intermediate alloy ingot; the purity of the high-purity magnesium ingot, high-purity tin ingot, and high-purity zinc ingot is preferably 99.9%.

[0027] In one embodiment of the present invention, the melting temperature can be 740–770°C. In this embodiment, the melting specifically includes: heating the metal raw material to 770°C and holding it at that temperature for 10 minutes; then cooling it to 760°C and holding it until all the metal raw material melts; continuing to hold it at that temperature for 15 minutes; then removing surface slag and stirring the melt evenly; continuing to hold it at that temperature for 10 minutes; removing surface slag again and stirring the melt evenly; and finally cooling it to 740°C for casting.

[0028] In one embodiment of the present invention, the smelting and casting are preferably carried out under the protection of a mixed gas of CO2 and SF6; the volume ratio of CO2 to SF6 can be 99:1. This mixed gas protection ensures the purity of the melt.

[0029] In one embodiment of the present invention, after casting, the resulting product can be cooled to obtain an as-cast Mg-Sn-Zn-Zr alloy. In another embodiment of the present invention, the cooling method can be air cooling or water cooling. In this embodiment, the cooling method is water cooling.

[0030] In this invention, the as-cast Mg-Sn-Zn-Zr alloy is directly subjected to positive extrusion deformation. This invention eliminates the need for solution aging treatment prior to positive extrusion deformation, allowing the subsequent positive extrusion deformation to induce the formation of a banded structure in the second phase of the as-cast alloy.

[0031] In this invention, the positive extrusion deformation process preferably includes: placing the cast Mg-Sn-Zn-Zr alloy into a positive extrusion mold and heating it together to the positive extrusion temperature, holding it at that temperature, and then performing positive extrusion to obtain the positive extruded alloy.

[0032] In one embodiment of the present invention, before placing the as-cast Mg-Sn-Zn-Zr alloy into the forward extrusion die, it is preferable to coat various parts of the die cavity and the surface and sides of the as-cast Mg-Sn-Zn-Zr alloy with a lubricant. In an embodiment of the present invention, the lubricant is composed of high-purity graphite and machine oil.

[0033] In this invention, the heating rate is preferably 14-16°C / min, more preferably 14-15°C / min; the positive extrusion temperature is preferably 300-350°C, more preferably 310-330°C; and the holding time is preferably 1-1.5h, more preferably 1-1.2h. In an embodiment of this invention, the heating rate is 15°C / min, the positive extrusion temperature is 320°C, and the holding time is 1h.

[0034] In this invention, the forward extrusion speed is preferably 10–15 mm / s, more preferably 11–13 mm / s; the extrusion ratio is preferably 11–12:1, more preferably 11–11.5:1. In an embodiment of this invention, the forward extrusion speed is 12 mm / s, and the extrusion ratio is 11.1:1. By optimizing the forward extrusion speed and extrusion ratio within the above ranges, this invention can obtain a fine grain structure, thereby improving strength and toughness.

[0035] In one embodiment of the present invention, the product obtained after positive extrusion deformation can be cooled to obtain a positive extrusion alloy. In another embodiment of the present invention, the cooling method can be air cooling or water cooling. In this embodiment, the cooling method is air cooling.

[0036] After obtaining the positive extrusion alloy, the present invention performs differential temperature equal channel angular extrusion deformation treatment on the positive extrusion alloy to obtain a high plasticity Mg-Sn-Zn-Zr alloy.

[0037] In this invention, before the differential temperature equal channel corner extrusion deformation treatment, it is preferable to heat the mold and the alloy to the temperature for the differential temperature equal channel corner extrusion deformation treatment and then hold them at that temperature. As one embodiment of this invention, before heating the mold and the alloy, it is preferable to coat the surfaces of the mold and the alloy with a lubricant. In an embodiment of this invention, the lubricant is composed of high-purity graphite and machine oil.

[0038] In this invention, the heating rate of the mold is preferably 18–22 °C / min, and the holding time is preferably 30–60 min. In an embodiment of this invention, the heating rate of the mold is 20 °C / min, and the holding time is 60 min, 50 min, 40 min, or 30 min.

[0039] In this invention, the heating rate of the alloy is preferably 14-16°C / min, more preferably 15-16°C / min; the holding time is preferably 10-20 min. In an embodiment of this invention, the heating rate of the alloy is 15°C / min, and the holding time is 20 min, 15 min, or 10 min.

[0040] In this invention, during the differential temperature equal channel corner extrusion deformation process, the alloy temperature is 100–150°C, preferably 110–130°C, and more preferably 120–130°C; the die temperature is 300–350°C, preferably 310–330°C, and more preferably 320–330°C. In an embodiment of this invention, the alloy temperature is 120°C, and the die temperature is 320°C. During the differential temperature equal channel corner deformation process, because the alloy temperature is consistently below the alloy's recrystallization temperature, the recrystallization process is incomplete, easily leading to the formation of unrecrystallized coarse grains and resulting in a bimodal grain structure with a coarse-fine grain distribution.

[0041] In this invention, the extrusion speed of the differential temperature equal channel corner extrusion deformation treatment is preferably 6-10 mm / s, more preferably 7-9 mm / s. In an embodiment of this invention, the extrusion speed of the differential temperature equal channel corner extrusion deformation treatment is 8 mm / s.

[0042] In this invention, the deformation path of the differential temperature equal channel corner extrusion deformation treatment is preferably a path Bc, Ba, A or C, and more preferably a path Bc.

[0043] As one embodiment of the present invention, the channel intersection angle of the differential temperature equal channel corner extrusion deformation treatment can be 120°, and the outer angle can be 60°.

[0044] In one embodiment of the present invention, the product obtained after differential temperature channel corner extrusion deformation can be cooled. In another embodiment of the present invention, the cooling method can be air cooling or water cooling. In this embodiment of the present invention, the cooling method is water cooling.

[0045] In this invention, the number of passes in the differential temperature equal channel corner extrusion deformation treatment is preferably 1 to 4, more preferably 4. As one embodiment of this invention, annealing treatment may not be performed between each pass.

[0046] The preparation method provided by this invention can obtain a Mg-Sn-Zn-Zr alloy with a dual heterostructure in which coarse and fine bimodal grains and a second phase with a harmonic-like structure coexist, exhibiting high plasticity; and it eliminates the need for solution aging heat treatment, allowing direct temperature differential isothermal angular extrusion deformation of the positive extrusion alloy, making the process simple.

[0047] The present invention also provides a high-plasticity Mg-Sn-Zn-Zr alloy prepared by the preparation method described in the above technical solution.

[0048] In this invention, the preferred composition of the high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0049] The high-plasticity Mg-Sn-Zn-Zr alloy obtained by this invention has high plasticity and an elongation of up to 37.9%.

[0050] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0051] Example 1

[0052] The preparation method of high-plasticity Mg-Sn-Zn-Zr alloy is as follows:

[0053] Preparation of as-cast Mg-Sn-Zn-Zr alloy: The melting and casting process was carried out under the protection of a mixed gas of CO2 and SF6 (volume ratio 99:1). A stainless steel crucible was placed in a pit-type resistance furnace and heated to 300°C. High-purity magnesium ingots, high-purity tin blocks, high-purity zinc ingots, and Sn-30Zr master alloy ingots were added simultaneously. The metal raw materials were heated to 770°C and held for 10 minutes. Then, the temperature was lowered to 760°C and held until all the metal raw materials melted. The temperature was held for another 15 minutes. Then, the surface slag was removed with a slag skimmer and the melt was stirred evenly with a stainless steel stirring rod. The temperature was held for another 10 minutes. The surface slag was removed again and the melt was stirred evenly. Finally, the temperature was lowered to 740°C and the melt was poured into a stainless steel mold and cooled in clean water to obtain the as-cast Mg-Sn-Zn-Zr alloy.

[0054] Forward extrusion deformation treatment: The cast Mg-Sn-Zn-Zr alloy is placed in a forward extrusion die. A lubricant composed of high-purity graphite and machine oil is coated on all parts of the die cavity and the surface and sides of the cast Mg-Sn-Zn-Zr alloy. The cast Mg-Sn-Zn-Zr alloy is placed in the forward extrusion die and heated in a box-type heat treatment furnace at a rate of 15℃ / min to the forward extrusion temperature of 320℃ and held for 1 hour. Then the die is removed and forward extrusion deformation is performed at a forward extrusion speed of 12mm / s and an extrusion ratio of 11.1:1. After air cooling to room temperature, a disc-shaped forward extruded alloy with dimensions of h = 150~160mm and d = 12mm is obtained. It is then cut to obtain a disc-shaped forward extruded alloy with dimensions of h = 62mm and d = 12mm.

[0055] Differential temperature equal channel angular extrusion deformation treatment: The positive extrusion alloy is directly subjected to differential temperature equal channel angular extrusion deformation treatment. A lubricant composed of high-purity graphite and machine oil is coated on the mold and the alloy surface with dimensions of h=62mm and d=12mm. The mold is placed in a box-type heat treatment furnace and heated at a heating rate of 20℃ / min to a temperature of 320℃ for a holding time of 60min. At the same time, the alloy is placed in another box-type treatment furnace and heated at a heating rate of 15℃ / min to a temperature of 120℃ for a holding time of 20min. The alloy is then placed in the mold and subjected to the first pass of differential temperature equal channel angular extrusion deformation at a speed of 8mm / s, a deformation path of Bc, a channel intersection angle of 120°, and an outer angle of 60°. The alloy is then quenched in clean water to obtain a high-plasticity Mg-Sn-Zn-Zr alloy.

[0056] The composition of the obtained high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0057] Example 2

[0058] The high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 1 was subjected to a second pass of differential temperature equal channel angular extrusion deformation treatment according to the differential temperature equal channel angular extrusion deformation treatment method described in Example 1. The difference between the second pass and the first pass is that the holding time of the mold is replaced from 60 min to 50 min, the holding time of the alloy is replaced from 20 min to 15 min, and when the alloy is placed into the mold, the direction of the first pass alloy is rotated by 90° according to the Bc path.

[0059] The composition of the obtained high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0060] Example 3

[0061] The high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 2 was subjected to a third pass of differential temperature equal channel angular extrusion deformation treatment according to the differential temperature equal channel angular extrusion deformation treatment method described in Example 1. The difference between the third pass and the first pass is that the holding time of the mold is replaced from 60 min to 40 min, the holding time of the alloy is replaced from 20 min to 15 min, and when the alloy is placed into the mold, the direction of the second pass alloy is rotated by 90° according to the Bc path.

[0062] The composition of the obtained high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0063] Example 4

[0064] The high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 3 was subjected to a fourth pass of differential temperature equal channel angular extrusion deformation treatment according to the differential temperature equal channel angular extrusion deformation treatment method described in Example 1. The difference between the fourth pass and the first pass is that the holding time of the mold is replaced from 60 min to 30 min, the holding time of the alloy is replaced from 20 min to 10 min, and when the alloy is placed into the mold, the alloy direction of the third pass is rotated 90° according to the Bc path.

[0065] The composition of the obtained high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

[0066] Comparative Example 1

[0067] The phrase "heating the mold at a rate of 20°C / min, at a temperature of 320°C, and holding for 60 min, while simultaneously placing the alloy in another box-type furnace and heating it at a rate of 15°C / min, at a temperature of 120°C, and holding for 20 min" in the differential temperature channel corner extrusion deformation treatment of all passes in Example 4 is replaced with the phrase "heating the mold at a rate of 20°C / min, at a temperature of 320°C, and holding for 60 min" which only heats the mold and not the alloy.

[0068] The composition of the obtained Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, and the remainder is Mg.

[0069] Tensile tests were performed on the high-plasticity Mg-Sn-Zn-Zr alloys obtained in Examples 1-4 and the Mg-Sn-Zn-Zr alloy obtained in Comparative Example 1, with a strain rate of 5 × 10⁻⁶. -4 s -1 Three parallel specimens were prepared for each group of samples, and the average value was taken. The stress-strain curves of the high-plasticity Mg-Sn-Zn-Zr alloys obtained in Examples 1-4 are shown below. Figure 1 As shown, the stress-strain curve of the Mg-Sn-Zn-Zr alloy in Comparative Example 1 is as follows. Figure 2 As shown.

[0070] Figure 1 Tensile curves of the Mg-Sn-Zn-Zr alloys in Examples 1-4 are shown. Figure 1 It can be seen that, Figure 1 The high-plasticity Mg-Sn-Zn-Zr alloy of Example 1 has a tensile strength of 300 MPa and an elongation of 21.7%; the high-plasticity Mg-Sn-Zn-Zr alloy of Example 2 has a tensile strength of 312 MPa and an elongation of 24.4%; the high-plasticity Mg-Sn-Zn-Zr alloy of Example 3 has a tensile strength of 310 MPa and an elongation of 29.3%; and the high-plasticity Mg-Sn-Zn-Zr alloy of Example 4 has a tensile strength of 310 MPa and an elongation of 37.9%. Figure 1 It can be seen that as the number of passes in the differential temperature channel corner extrusion deformation treatment increases from 1 to 4, the tensile strength of the high-plasticity Mg-Sn-Zn-Zr alloy first increases and then decreases, with the maximum tensile strength when the number of passes is 2. The elongation of the high-plasticity Mg-Sn-Zn-Zr alloy gradually increases, with the maximum elongation and best plasticity when the number of passes is 4.

[0071] Figure 2 The tensile curves are for the Mg-Sn-Zn-Zr alloy of Comparative Example 1. From... Figure 2 As can be seen, the Mg-Sn-Zn-Zr alloy of Comparative Example 1 has an elongation of 36.5% and a tensile strength of 295 MPa. The overall mechanical properties of the alloy of Comparative Example 1 are worse than those of Example 4.

[0072] The microstructure of the high-plasticity Mg-Sn-Zn-Zr alloys obtained in Examples 2 and 4, and the Mg-Sn-Zn-Zr alloy obtained in Comparative Example 1, was observed using an optical microscope. The microstructure images of the high-plasticity Mg-Sn-Zn-Zr alloys obtained in Examples 2 and 4 are shown below. Figure 3 and Figure 4 As shown, the microstructure of the Mg-Sn-Zn-Zr alloy obtained in Comparative Example 1 is as follows. Figure 5 As shown.

[0073] Figure 3This is a microstructure diagram of the high-plasticity Mg-Sn-Zn-Zr alloy from Example 2. Figure 4 This is a microstructure diagram of the high-plasticity Mg-Sn-Zn-Zr alloy from Example 4. Figure 3 It can be seen that a significant "banded structure," i.e., a second-phase enrichment region, appears in the high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 2. Correspondingly, a second-phase depleted region also appears, and the two together constitute a harmonic-like heterogeneous distribution characteristic of the second phase. Simultaneously, in the "banded structure" region, the alloy grain size is fine, while in the second-phase depleted region, the grain size is relatively coarse, forming a coarse-fine grain bimodal heterogeneous structure. Figure 4 It can be seen that the second-phase heterogeneous distribution characteristics of the high-plasticity Mg-Sn-Zn-Zr alloy prepared in Example 4 are more obvious. The second-phase depleted region is surrounded by the second-phase enriched region, forming a harmonic structure composed of a depleted phase core and a rich phase shell. The volume fraction of this structure is significantly increased, and the grain size of the alloy also shows obvious coarse and fine grain bimodal heterogeneous structure characteristics.

[0074] Figure 5 The microstructure of the Mg-Sn-Zn-Zr alloy obtained in Comparative Example 1 is shown below. Figure 5 As can be seen, after the process in Comparative Example 1, no obvious harmonic structure features were formed in the alloy. Therefore, its heterogeneous effect contributes little to the alloy properties.

[0075] As can be seen from the above embodiments and comparative examples, the microstructure of the high-plasticity Mg-Sn-Zn-Zr alloy obtained by the preparation method of this application forms a dual heterogeneous structure in which coarse and fine bimodal grains and a harmonic-like second phase coexist. Moreover, when the tensile strength is between 300 and 312 MPa, the Mg-Sn-Zn-Zr alloy exhibits excellent plasticity and an elongation of up to 21.7% to 37.9%.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-plasticity Mg-Sn-Zn-Zr alloy, comprising the following steps: The as-cast Mg-Sn-Zn-Zr alloy is directly subjected to positive extrusion deformation treatment to obtain a positive extrusion alloy; The positive extrusion alloy was subjected to differential temperature equal channel angular extrusion deformation treatment to obtain a high plasticity Mg-Sn-Zn-Zr alloy. During the differential temperature equal channel corner extrusion deformation treatment, the alloy temperature is 100-150℃ and the mold temperature is 300-350℃.

2. The preparation method according to claim 1, characterized in that, The positive extrusion deformation process includes: placing the cast Mg-Sn-Zn-Zr alloy into a positive extrusion mold, heating it together to the positive extrusion temperature, holding it at that temperature, and then performing positive extrusion to obtain the positive extruded alloy.

3. The preparation method according to claim 2, characterized in that, The heating rate is 14-16℃ / min, the positive extrusion temperature is 300-350℃, and the heat preservation time is 1-1.5h.

4. The preparation method according to claim 2, characterized in that, The positive extrusion speed is 10-15 mm / s, and the extrusion ratio is 11-12:

1.

5. The preparation method according to claim 1, characterized in that, Before the differential temperature equal channel corner extrusion deformation treatment, the mold and the alloy are heated to the temperature of the differential temperature equal channel corner extrusion deformation treatment and held at that temperature. The heating rate of the mold is 18-22℃ / min and the holding time is 30-60min. The heating rate of the alloy is 14-16℃ / min and the holding time is 10-20min.

6. The preparation method according to claim 1, characterized in that, The extrusion speed of the differential temperature equal channel corner extrusion deformation treatment is 6-10 mm / s.

7. The preparation method according to claim 1, characterized in that, The deformation path of the differential temperature equal channel corner extrusion deformation treatment is path Bc, Ba, A or C.

8. The preparation method according to claim 1, characterized in that, The differential temperature equal channel corner extrusion deformation process has 1 to 4 passes; no annealing is performed between each pass.

9. The high-plasticity Mg-Sn-Zn-Zr alloy prepared by the preparation method according to any one of claims 1 to 8.

10. The high-plasticity Mg-Sn-Zn-Zr alloy according to claim 9, characterized in that, The composition of the high-plasticity Mg-Sn-Zn-Zr alloy is: Sn: 6.2wt%, Zn: 3.5wt%, Zr: 0.3wt%, with the remainder being Mg.

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