High-yield-strength and high-elongation magnesium alloy sheet and preparation method thereof

Abstract

The invention discloses a magnesium alloy sheet with high yield strength and high elongation. The magnesium alloy sheet is prepared from the following elements in percentage by mass: 3.6%-4.4% of Zn, 0.4%-0.6% of Zr, 0.2%-0.5% of Ce and the balance of magnesium and inevitable impurities. The preparation method of the magnesium alloy sheet comprises the following steps: 1, carrying out homogenization treatment and hot extrusion deformation on a magnesium alloy cast ingot to obtain an extruded plate blank; 2, rolling the extruded plate blank to obtain a rolled thin plate; and thirdly, the rolled sheet is subjected to low-temperature short-time annealing treatment to obtain the magnesium alloy sheet. According to the method, the magnesium alloy cast ingot is subjected to homogenization treatment, extrusion, rolling and low-temperature short-time annealing treatment, the magnesium alloy sheet with high yield strength and high elongation is obtained through microalloying of rare earth elements in combination with optimized deformation and heat treatment processes, and the method is low in cost and has good industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the field of nonferrous metal material processing, and in particular relates to a high-yield strength and high-elongation magnesium alloy sheet and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium has excellent casting performance, chip performance and damping and shock absorption characteristics, which makes it of great value in reducing the weight of parts and achieving lightweight. In particular, magnesium alloy sheets have potential application value in 3C products, power battery housings, heat dissipation devices, etc. However, magnesium alloys face problems such as insufficient room temperature yield strength and poor elongation in actual applications. Optimization and innovation in both material composition and preparation and processing technology are the main means to prepare magnesium alloys with high yield strength and high elongation.

[0003] The tensile strength of pure magnesium is only 70MPa to 80MPa. The commercially available deformed magnesium alloy AZ31B, which is currently widely used, has a high room temperature tensile plasticity (12% to 21%), but its room temperature yield strength is low (150MPa to 200MPa), and is not suitable for use in fields with high requirements for material strength. Adding high content of rare earth elements such as Gd, Y, and Er to pure magnesium, after solid solution + aging process treatment, nano-precipitates dispersedly distributed inside the grains can be obtained. These precipitates can hinder the movement of dislocations during deformation, thereby greatly improving the room temperature strength of the material. The patent (authorization publication number CN109609825B) discloses a Mg-Gd-Er-Zn-Zr deformed magnesium alloy and its preparation method, wherein the rare earth element content exceeds 8%. On the basis of hot extrusion, pre-deformation and double-stage aging treatment processes are used to finally obtain a high-strength and high-plasticity magnesium alloy with a yield strength of more than 450MPa, a tensile strength of more than 480MPa, and an elongation of 8% to 15%.

[0004] In recent years, low alloy magnesium alloys have attracted more and more attention due to their low material cost. The patent (authorization publication number CN112899541B) discloses a Mg-Zn-Ca-Sn-Mn alloy, and uses hot extrusion, multi-pass controlled rolling, recrystallization treatment, and low temperature aging process to obtain a magnesium alloy with an average grain size of 2μm to 7μm. The yield strength of the magnesium alloy is ≥300MPa and the elongation is ≥15%. However, the invention involves many preparation process flows, especially after rolling deformation, recrystallization heat treatment and cold rolling aging or tensile pre-deformation aging treatment are required, which increases the preparation process of the plate to a certain extent. The patent (authorization publication number CN111304471B) discloses a method for preparing a low alloy high-strength magnesium alloy plate, and uses a low temperature upsetting deformation heat treatment method to prepare a Mg-Zn-Y alloy, and the yield strength reaches more than 400MPa, but the elongation is only less than 11.5%. The patent (authorization publication number CN103952613B) discloses a method for preparing a deformed magnesium alloy with a high yield strength ratio by hot extrusion process, wherein the yield strength exceeds 300 MPa, but the elongation thereof does not exceed 12.1%.

[0005] Therefore, based on traditional commercial alloys, developing low-cost high-yield strength and high-elongation magnesium alloy sheets and their preparation processes through micro-alloying of rare earth elements and optimizing deformation and heat treatment processes is a beneficial exploration to expand the application of magnesium alloys. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a magnesium alloy sheet with high yield strength and high elongation in view of the shortcomings of the above-mentioned prior art. The method obtains a magnesium alloy sheet with high yield strength and high elongation at low cost by microalloying rare earth elements and combining optimized deformation and heat treatment processes, thereby solving the problems of high cost, poor plasticity and insufficient strength of low-cost low-alloyed magnesium alloys in existing rare earth magnesium alloys.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a high yield strength and high elongation magnesium alloy sheet, characterized in that it is composed of the following elements in mass percentage: Zn 3.6% to 4.4%, Zr 0.4% to 0.6%, Ce 0.2% to 0.5%, and the balance is magnesium and inevitable impurities; the room temperature yield strength of the magnesium alloy sheet is 278MPa to 310MPa, and the elongation after fracture is 15% to 20%.

[0008] The above-mentioned high yield strength and high elongation magnesium alloy sheet is characterized in that it is composed of the following elements in percentage by mass: Zn 3.8% to 4.2%, Zr 0.5%, Ce 0.3% to 0.4%, and the remainder is magnesium and inevitable impurities.

[0009] At the same time, the present invention also discloses a method for preparing the above-mentioned high yield strength and high elongation magnesium alloy sheet, characterized in that the method comprises the following steps:

[0010] Step 1: homogenizing and hot extruding the magnesium alloy ingot to obtain an extruded slab;

[0011] Step 2: rolling the extruded slab obtained in step 1 to obtain a rolled sheet;

[0012] Step 3: Performing a low-temperature short-time annealing treatment on the rolled thin plate obtained in step 2 to obtain a magnesium alloy thin plate.

[0013] The above method is characterized in that the homogenization treatment in step 1 is: keeping the magnesium alloy ingot at 380°C to 430°C for 8h to 12h, and air cooling it to room temperature to obtain a homogenized ingot; the hot extrusion deformation is: extruding the homogenized ingot to obtain an extruded slab, and the extrusion temperature is 350°C to 400°C, the extrusion ratio is 20 to 35, and the extrusion speed is 0.1m / min to 5m / min.

[0014] The above method is characterized in that the number of rolling passes in step 2 is 4 to 6, the rolling insulation temperature is 390°C to 420°C, the insulation time between passes is 15 minutes, the total rolling reduction is 76% to 92%, and the single-pass reduction gradually decreases. The present invention adopts a higher rolling insulation temperature and a pass reduction that gradually decreases from large to small, thereby ensuring a smaller number of rolling passes while ensuring a larger total reduction, which is conducive to the smooth implementation of the thin plate preparation process.

[0015] The above method is characterized in that the thickness of the rolled thin plate in step 2 is 0.6 mm to 1.2 mm. The rolled thin plate of this thickness is suitable for 3C electronics, automotive power battery housing and other fields.

[0016] The above method is characterized in that the temperature of the low-temperature short-time annealing treatment in step 3 is 125°C to 175°C, the time is 18min to 30min, and after the annealing is completed, it is cooled to room temperature by air cooling. The present invention adopts a low-temperature short-time annealing treatment at a lower temperature and a shorter time for the rolled thin plate to reduce the impact on the grain size, thereby improving the elongation of the magnesium alloy thin plate without significantly reducing its strength, and has a small impact on the preparation cost of the material.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The magnesium alloy sheet of the present invention forms a refractory Mg-Zn-Ce phase by adding rare earth Ce elements. In the subsequent hot extrusion and rolling deformation process, the Mg-Zn-Ce phase is broken into fine particles, which promotes dynamic recrystallization and hinders the growth of recrystallized grains. The final average grain size is 3μm to 8μm, so that the magnesium alloy sheet has a good synergistic effect of strength and plasticity. At the same time, the rare earth Ce element promotes the non-basal slip of the magnesium alloy, weakens the basal texture strength, and improves the elongation and formability of the magnesium alloy sheet, thereby improving the plasticity of the magnesium alloy sheet.

[0019] 2. Only a trace amount of rare earth Ce element is added to the magnesium alloy sheet of the present invention, thus avoiding the addition of a large amount of rare earth precious metals and effectively reducing the cost of the titanium alloy sheet.

[0020] 3. The room temperature yield strength of the magnesium alloy sheet prepared by the present invention is 278MPa-310MPa, and the elongation after fracture is 15%-20%. It has both high yield strength and high elongation, and the preparation cost is low, and it has good industrial application prospects.

[0021] 4. The preparation method of the present invention has the characteristics of short flow and simple process, and is suitable for large-scale production.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a microstructure diagram of the magnesium alloy sheet prepared in Example 1 of the present invention.

[0024] Figure 2 The engineering stress-strain curves of the magnesium alloy sheets prepared in Examples 1 to 3 of the present invention and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0025] Example 1

[0026] The magnesium alloy sheet of this embodiment is composed of the following elements in percentage by mass: Zn 4.2%, Zr 0.5%, Ce 0.4%, and the remainder is magnesium and inevitable impurities, and the percentage by mass of the inevitable impurities is less than 0.05%.

[0027] The method for preparing the magnesium alloy sheet of this embodiment comprises the following steps:

[0028] Step 1, the magnesium alloy ingot is kept at 415° C. for 10 hours for homogenization treatment, air-cooled to room temperature to obtain a homogenized ingot, and then the homogenized ingot is extruded to obtain an extruded slab with a thickness of 5 mm, and the extrusion temperature is 380° C., the extrusion ratio is 32, and the extrusion speed is 0.5 m / min;

[0029] Step 2, the extruded slab obtained in step 1 is kept at 400°C for 30 minutes, and then rolled for 5 passes, wherein the holding temperature between passes is 400°C, the holding time between passes is 15 minutes, the rolling reductions of the single passes are 51.0% (2.55 mm), 31.1% (0.77 mm), 27.3% (0.46 mm), 23.0% (0.28 mm), and 14.8% (0.14 mm), respectively, and the total rolling reduction is 84%, to obtain a rolled sheet with a thickness of 0.8 mm;

[0030] Step 3: The rolled thin plate obtained in step 2 is subjected to a low-temperature short-time annealing treatment at 150° C. for 20 minutes, and after the annealing, it is cooled to room temperature by air cooling to obtain a magnesium alloy thin plate.

[0031] Figure 1 The microstructure of the magnesium alloy sheet prepared in this embodiment is shown in FIG. Figure 1 It can be seen that the structure of the magnesium alloy sheet is nearly equiaxed grains, and the grain size distribution is relatively uniform.

[0032] After testing, the average grain size of the magnesium alloy sheet prepared in this embodiment is 4.8 μm, the room temperature yield strength is 292.1 MPa, and the elongation after fracture is 20.3%. Figure 2 shown.

[0033] Example 2

[0034] The magnesium alloy sheet of this embodiment is composed of the following elements in percentage by mass: Zn 3.6%, Zr 0.4%, Ce 0.2%, and the remainder is magnesium and inevitable impurities, and the percentage by mass of the inevitable impurities is less than 0.05%.

[0035] The method for preparing the magnesium alloy sheet of this embodiment comprises the following steps:

[0036] Step 1, homogenizing the magnesium alloy ingot by keeping it at 380° C. for 8 hours, air cooling it to room temperature to obtain a homogenized ingot, and then extruding the homogenized ingot to obtain an extruded slab with a thickness of 5 mm, and the extrusion temperature is 350° C., the extrusion ratio is 20, and the extrusion speed is 5 m / min;

[0037] Step 2: The extruded slab obtained in step 1 is kept at 390° C. for 30 minutes, and then rolled in 4 passes, wherein the holding temperature between passes is 390° C., the holding time between passes is 15 minutes, and the total rolling reduction is 76%, to obtain a rolled sheet with a thickness of 1.2 mm;

[0038] Step 3: The rolled thin plate obtained in step 2 is subjected to a low-temperature short-time annealing treatment at 125° C. for 30 minutes, and after the annealing, it is cooled to room temperature by air cooling to obtain a magnesium alloy thin plate.

[0039] After testing, the average grain size of the magnesium alloy sheet prepared in this embodiment is 3.5 μm, the room temperature yield strength is 310.2 MPa, and the elongation after fracture is 15.4%. Figure 2 shown.

[0040] Example 3

[0041] The magnesium alloy sheet of this embodiment is composed of the following elements in percentage by mass: Zn 4.4%, Zr 0.6%, Ce 0.5%, and the remainder is magnesium and inevitable impurities, and the percentage by mass of the inevitable impurities is less than 0.05%.

[0042] The method for preparing the magnesium alloy sheet of this embodiment comprises the following steps:

[0043] Step 1, the magnesium alloy ingot is kept at 430° C. for 12 hours for homogenization treatment, air-cooled to room temperature to obtain a homogenized ingot, and then the homogenized ingot is extruded to obtain an extruded slab with a thickness of 5 mm, and the extrusion temperature is 400° C., the extrusion ratio is 35, and the extrusion speed is 0.1 m / min;

[0044] Step 2: The extruded slab obtained in step 1 is kept at 420° C. for 30 minutes, and then rolled for 6 passes, wherein the holding temperature between passes is 420° C., the holding time between passes is 15 minutes, and the total rolling reduction is 92%, to obtain a rolled sheet with a thickness of 0.6 mm;

[0045] Step 3: The rolled thin plate obtained in step 2 is subjected to a low-temperature short-time annealing treatment at 175° C. for 18 minutes, and after the annealing, it is cooled to room temperature by air cooling to obtain a magnesium alloy thin plate.

[0046] After testing, the average grain size of the magnesium alloy sheet prepared in this embodiment is 6.9 μm, the room temperature yield strength is 278.0 MPa, and the elongation after fracture is 17.4%. Figure 2 shown.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that step 3 is not performed, and the rolled thin plate obtained in step 2 is directly used as the magnesium alloy thin plate.

[0049] After testing, the average grain size of the magnesium alloy sheet prepared in this comparative example is 2.8 μm, the room temperature yield strength is 320.7 MPa, and the elongation after fracture is 13.0%. Figure 2 shown.

[0050] By comparing Example 1 of the present invention with Comparative Example 1, it can be seen that when the step 3 low-temperature short-time annealing treatment is not performed in Comparative Example 1, the average grain size of the prepared magnesium alloy sheet is relatively small, and the yield strength of the sheet is relatively high, but the elongation after fracture is only 13.0%; while after the low-temperature short-time annealing treatment in Example 1, the grain size grows slightly, but the elongation after fracture of the magnesium alloy sheet increases to 20.3%. It can be seen that the magnesium alloy sheet has a more excellent strength-plasticity synergistic effect at this time.

[0051] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A high yield strength and high elongation magnesium alloy sheet, characterized in that: The magnesium alloy sheet is composed of the following elements in mass percentage: 3.6% to 4.4% Zn, 0.4% to 0.6% Zr, 0.2% to 0.5% Ce, and the remainder is magnesium and inevitable impurities; the room temperature yield strength of the magnesium alloy sheet is 278MPa to 310MPa, and the elongation after fracture is 15% to 20%.

2. The high yield strength and high elongation magnesium alloy sheet according to claim 1, characterized in that: It is composed of the following elements in percentage by mass: Zn 3.8%-4.2%, Zr 0.5%, Ce 0.3%-0.4%, and the remainder is magnesium and inevitable impurities.

3. A method for preparing a high yield strength and high elongation magnesium alloy sheet as claimed in claim 1 or 2, characterized in that: The method comprises the following steps: Step 1: homogenizing and hot extruding the magnesium alloy ingot to obtain an extruded slab; Step 2: rolling the extruded slab obtained in step 1 to obtain a rolled sheet; Step 3: Performing a low-temperature short-time annealing treatment on the rolled thin plate obtained in step 2 to obtain a magnesium alloy thin plate.

4. The method according to claim 3, characterized in that The homogenization treatment in step one is: keeping the magnesium alloy ingot at 380°C to 430°C for 8h to 12h, and air cooling it to room temperature to obtain a homogenized ingot; the hot extrusion deformation is: extruding the homogenized ingot to obtain an extruded slab, and the extrusion temperature is 350°C to 400°C, the extrusion ratio is 20 to 35, and the extrusion speed is 0.1m / min to 5m / min.

5. The method according to claim 3, characterized in that: The rolling times in step 2 are 4 to 6 passes, the rolling insulation temperature is 390° C. to 420° C., the insulation time between passes is 15 minutes, the total rolling reduction is 76% to 92%, and the single-pass reduction gradually decreases.

6. The method according to claim 3, characterized in that The thickness of the rolled thin plate in step 2 is 0.6 mm to 1.2 mm.

7. The method according to claim 3, characterized in that The temperature of the low-temperature short-time annealing treatment in step 3 is 125° C. to 175° C., and the time is 18 min to 30 min. After the annealing is completed, it is cooled to room temperature by air cooling.

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