Method for preparing gradient isomerism AZ31 magnesium alloy rolled plate based on short-time high-frequency electromagnetic induction heating

Abstract

The invention discloses a method for preparing a gradient isomerism AZ31 magnesium alloy rolled plate based on short-time high-frequency electromagnetic induction heating. The method comprises the steps that firstly, an AZ31 magnesium alloy plate is polished, cleaned and aired, and the clean AZ31 magnesium alloy plate is obtained; secondly, the clean AZ31 magnesium alloy plate is subjected to multi-pass rolling, and an AZ31 magnesium alloy rolled plate is obtained; thirdly, the AZ31 magnesium alloy rolled plate is straightened, and a flat AZ31 magnesium alloy rolled plate is obtained; and fourthly, the flat AZ31 magnesium alloy rolled plate is subjected to short-time high-frequency electromagnetic induction heating, and the gradient isomerism AZ31 magnesium alloy rolled plate is obtained. According to the method, the AZ31 magnesium alloy rolled plate generates high-density induction current through the rolling and induction heating short-process technology, the AZ31 magnesium alloy rolled plate is heated at the top speed, the electromagnetic field is non-uniformly distributed in the AZ31 magnesium alloy rolled plate through the skin effect, a gradient heterogeneous structure is formed, the strength and plasticity of the AZ31 magnesium alloy rolled plate are synchronously improved, the technology is simple and easy to regulate and control, and the method is suitable for industrial production. The method is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of composite technology of metal plastic material processing and heat treatment, specifically relating to a method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating. Background Technology

[0002] Magnesium alloys, as the lightest structural materials, have been widely used in rail transportation and 3C industries due to their advantages such as low density, high specific strength, and high specific stiffness. However, due to their poor plasticity and low strength, the development and utilization technology of magnesium alloys is still far behind that of steel and aluminum alloys. Therefore, to expand the application of magnesium alloys, it is necessary to solve the problems of low strength and limited ductility. Among these methods, severe plastic deformation (SPD) (such as extrusion and rolling) is one of the means to improve the mechanical properties of magnesium alloys.

[0003] Rolling is the most economical and efficient method for producing magnesium alloy sheets through plastic forming, allowing for the flexible production of sheets of varying thicknesses and widths. The rolling process refines grains, improves microstructure, and significantly enhances the mechanical properties of the alloy. However, due to limitations in the preparation methods and cost, the current manufacturing process for magnesium alloy sheets (especially medium-thick and wide plates) requires multiple deformation and heat treatment passes, resulting in a cumbersome and extremely costly process that fails to meet the demands of industrial production. Therefore, further research and development of magnesium alloy sheet preparation and heat treatment technologies are necessary.

[0004] Induction heating is a special heat treatment process that utilizes the principles of electromagnetic induction and the skin effect of alternating current to generate a high-density induced current on the material surface, thereby heating it. Induction heating can achieve heating of different sizes and specifications according to requirements, different heating depths can be selected based on frequency, and precise localized heating can be achieved through coil coupling design. It also has advantages such as fast heating speed (only tens of seconds), energy saving, high production efficiency, no pollution, and easy automation. However, there has been no research on the combined application of induction heating technology in magnesium alloy rolled plates. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating. This method utilizes a short-process "rolling + induction heating" technique to generate a high-density induced current in the AZ31 magnesium alloy rolled plate for rapid heating. Furthermore, by leveraging the "skin effect," the electromagnetic field is unevenly distributed within the AZ31 magnesium alloy rolled plate, forming a gradient heterogeneous structure. This simultaneously improves the strength and plasticity of the AZ31 magnesium alloy rolled plate, solving the problem of the "strength-plasticity inversion" in magnesium alloys.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating, characterized in that the method includes the following steps: Step 1, Surface treatment: The AZ31 magnesium alloy plate is polished with 400# and 600# sandpaper in sequence, then cleaned with anhydrous ethanol, and then air-dried to obtain a clean AZ31 magnesium alloy plate. Step 2, Rolling: The clean AZ31 magnesium alloy plate obtained in Step 1 is rolled in multiple passes to obtain a straight AZ31 magnesium alloy rolled plate. Step 3: Short-time high-frequency electromagnetic induction heating: The AZ31 magnesium alloy rolled plate obtained in Step 2 is subjected to short-time high-frequency electromagnetic induction heating to obtain a gradient heterogeneous AZ31 magnesium alloy rolled plate.

[0007] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the thickness of the AZ31 magnesium alloy plate in step one is 20mm~50mm.

[0008] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the temperature of the multi-pass rolling in step two is 300℃~350℃, the rolling speed is 8m / min~12m / min, the reduction per pass is 8%~12%, the total reduction of the multi-pass rolling is 30%~50%, and the heat preservation time after the first pass rolling is 15min~25min, and the heat preservation time after the second pass rolling and subsequent passes rolling is 5min~15min.

[0009] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the thickness of the AZ31 magnesium alloy rolled plate in step two is 14mm~25mm.

[0010] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the frequency of the short-time high-frequency electromagnetic induction heating in step three is 300kHz~350kHz, the power is 5kW~15kW, the temperature is 100℃~200℃, and the distance between the heating coil used in the short-time high-frequency electromagnetic induction heating and the AZ31 magnesium alloy rolled plate is 0.2mm~0.6mm, and the duration of the entire short-time high-frequency electromagnetic induction heating process is 3s~5s.

[0011] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the short-time high-frequency electromagnetic induction heating in step three adopts single-sided heating, and the induction heating temperature refers to the surface temperature of the AZ31 magnesium alloy rolled plate away from the induction heating coil. Heating is stopped when the heating temperature reaches the set value. Since the heat treatment temperature of magnesium alloys is usually above 300℃ and the melting point is above 600℃, even a 10mm thick magnesium alloy rolled plate heats up very rapidly under high-frequency electromagnetic induction heating. This invention avoids the surface temperature of the magnesium alloy rolled plate reaching the melting point during the short-time high-frequency electromagnetic induction heating process by adopting single-sided heating, and at the same time avoids the high heat transfer rate being too fast, which weakens the skin effect brought about by the short-time high-frequency electromagnetic induction heating and is not conducive to the formation of gradient heterogeneous structure.

[0012] The above-mentioned method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating is characterized in that the short-time high-frequency electromagnetic induction heating in step three needs to be performed 5 to 7 times.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a rolling process combined with short-duration high-frequency electromagnetic induction heating. It utilizes the thermal and non-thermal effects generated by electromagnetic induction in the AZ31 magnesium alloy rolled sheet to improve its strength and plasticity. Specifically, the AZ31 magnesium alloy rolled sheet is rapidly heated by a high-density induced current, significantly reducing its dynamic recrystallization temperature. Due to the influence of the electron wind generated by the current, the crystal lattice undergoes severe distortion, the dislocation density distribution becomes more uniform, and the average grain size decreases, thereby improving the strength of the AZ31 magnesium alloy rolled sheet. Simultaneously, the electron wind also causes the lattice atoms to rearrange, increasing the interplanar spacing, reducing the elastic modulus, and decreasing the rheological stress, thus improving the plasticity of the AZ31 magnesium alloy rolled sheet.

[0014] 2. The "skin effect" of short-time high-frequency electromagnetic induction heating in this invention causes the electromagnetic field to be unevenly distributed in the AZ31 magnesium alloy rolled plate, thereby increasing the surface current of the AZ31 magnesium alloy rolled plate and weakening its internal current. This causes the temperature of the AZ31 magnesium alloy rolled plate to gradually decrease from the surface to the interior, and the corresponding grain size to gradually decrease. Generally, in metallic materials, reducing the grain size is beneficial to improving the material strength, while increasing the grain size is beneficial to providing the material plasticity. However, this invention, based on reducing the grain size through rolling, promotes the growth of surface grains through short-time high-frequency electromagnetic induction heating, so that the grain size in the AZ31 magnesium alloy rolled plate presents a gradient distribution, simultaneously improving the strength and plasticity of the AZ31 magnesium alloy rolled plate, and solving the problem of "strength-plasticity inversion" in magnesium alloys.

[0015] 3. Compared with traditional heat treatment, the short-time high-frequency electromagnetic induction heating of this invention is highly efficient, low-cost, and pollution-free. It is also easy to control the heating temperature and heating depth by adjusting parameters, thereby achieving local heating. This facilitates the microstructure and property control of AZ31 magnesium alloy rolled plates. The process is simple, efficient, and low-cost, making it suitable for industrial production.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 The images show the metallographic diagram, engineering stress-strain curve, and schematic diagram of the rolling + short-time high-frequency electromagnetic induction heating direction of the clean AZ31 magnesium alloy plate obtained in step one of Embodiment 1 of the present invention.

[0018] Figure 2 Metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two of Embodiment 1 of the present invention and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three.

[0019] Figure 3 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of Embodiment 1 of the present invention.

[0020] Figure 4 Metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two of Embodiment 2 of the present invention and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three.

[0021] Figure 5 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of Embodiment 2 of the present invention.

[0022] Figure 6 Metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two of embodiment 3 of the present invention and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three.

[0023] Figure 7 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two of embodiment 3 of the present invention and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three. Detailed Implementation

[0024] Example 1 This embodiment includes the following steps: Step 1, Surface treatment: The 20mm thick AZ31 magnesium alloy plate is polished with 400# and 600# sandpaper in sequence, then cleaned with anhydrous ethanol, and then air-dried for 1 hour to obtain a clean AZ31 magnesium alloy plate. Step 2, Rolling: The clean AZ31 magnesium alloy plate obtained in Step 1 is held at 300℃ for 30 minutes, and then rolled in multiple passes at a rolling speed of 8m / min, with a reduction of 8% per pass and a total reduction of 30%. The holding time after the first pass is 15 minutes, and the holding time after the second pass and subsequent passes is 5 minutes. This yields a 14mm thick, straight AZ31 magnesium alloy rolled plate. Step 3: Short-time high-frequency electromagnetic induction heating: The AZ31 magnesium alloy rolled plate obtained in Step 2 is subjected to short-time high-frequency electromagnetic induction heating at a frequency of 300kHz and a power of 5kW. The distance between the heating coil and the AZ31 magnesium alloy rolled plate is 0.2mm, and single-sided heating is used. The heating temperature refers to the temperature of the side of the AZ31 magnesium alloy rolled plate away from the induction heating coil. Heating is stopped when the heating temperature reaches 100℃. The entire short-time high-frequency electromagnetic induction heating process lasts for about 3s. The short-time high-frequency electromagnetic induction heating is repeated 5 times to obtain a gradient heterogeneous AZ31 magnesium alloy rolled plate.

[0025] Figure 1 The figures show the metallographic image, engineering stress-strain curve, and schematic diagram of the rolling + short-time high-frequency electromagnetic induction heating direction of the clean AZ31 magnesium alloy plate obtained in step one of this embodiment. As can be seen from the metallographic image in Figure (a), the average grain size of the AZ31 magnesium alloy without rolling and short-time high-frequency electromagnetic induction heating is relatively large. As can be seen from the engineering stress-strain curve in Figure (b), the strength of the clean AZ31 magnesium alloy plate (extruded plate) is relatively low, and the plasticity is about 10%. In Figure (c), ND, TD, and RD represent the directions perpendicular to the surface of the AZ31 magnesium alloy plate, the transverse direction, and the direction parallel to the surface of the AZ31 magnesium alloy plate and parallel to the rolling direction, respectively. I, II, and III represent the test sampling locations, where I represents the sampling location far from the heating location and III represents the sampling location close to the heating location.

[0026] Figure 2 The figures show the metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of this embodiment. As can be seen from the metallographic images of the AZ31 magnesium alloy rolled plate in Figures (a) to (b), the average grain size of the magnesium alloy decreases after rolling, and a small amount of twinned structure exists. As can be seen from the metallographic images of the gradient heterogeneous AZ31 magnesium alloy rolled plate in Figures (c) to (e), due to the "skin effect" of short-time high-frequency electromagnetic induction heating, the far end face of the AZ31 magnesium alloy rolled plate is subjected to high-density current, forming a high-density twinned structure.

[0027] Figure 3 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of this embodiment. Figure 3 It can be seen that, compared with the rolled AZ31 magnesium alloy plate, the tensile strength of the AZ31 magnesium alloy plate (Ⅰ, Ⅱ and Ⅲ) after short-time high-frequency electromagnetic induction heating remains basically unchanged, while the plasticity is significantly improved, and the elongation increases from 7.6% in the rolled state to 14.1%.

[0028] Example 2 This embodiment includes the following steps: Step 1, Surface treatment: The AZ31 magnesium alloy plate with a thickness of 33mm is polished with 400# and 600# sandpaper in sequence, then cleaned with anhydrous ethanol, and then air-dried for 1 hour to obtain a clean AZ31 magnesium alloy plate. Step 2, Rolling: The clean AZ31 magnesium alloy plate obtained in Step 1 is held at 320℃ for 30 minutes, and then rolled in multiple passes at a rolling speed of 10 m / min, with a reduction of 10% per pass and a total reduction of 40%. The holding time after the first pass is 20 minutes, and the holding time after the second pass and subsequent passes is 10 minutes each, to obtain a 20 mm thick, straight AZ31 magnesium alloy rolled plate. Step 3: Short-time high-frequency electromagnetic induction heating: The AZ31 magnesium alloy rolled plate obtained in Step 2 is subjected to short-time high-frequency electromagnetic induction heating at a frequency of 320kHz and a power of 10kW. The distance between the heating coil and the AZ31 magnesium alloy rolled plate is 0.4mm, and single-sided heating is used. The heating temperature refers to the temperature of the side of the AZ31 magnesium alloy rolled plate away from the induction heating coil. Heating is stopped when the heating temperature reaches 150℃. The entire short-time high-frequency electromagnetic induction heating process lasts about 3.8s. The short-time high-frequency electromagnetic induction heating is repeated 6 times to obtain a gradient heterogeneous AZ31 magnesium alloy rolled plate.

[0029] Figure 4The metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of this embodiment are shown in Figure (a). It can be seen from the metallographic image of the AZ31 magnesium alloy rolled plate that a mixed grain structure with different grain sizes appeared after rolling. This is because two deformation modes occurred during the rolling deformation process. One is large grains, which indicate that recrystallization has not occurred, and the other is fine chain-like recrystallized grains. Usually, this chain-like structure is caused by discontinuous dynamic recrystallization. Figure (b) shows the middle region of the AZ31 magnesium alloy rolled plate. The microstructure characteristics of this region are basically the same as those of the edge. From the metallographic images of the gradient heterogeneous AZ31 magnesium alloy rolled plates in Figures (c) to (e), it can be seen that according to their relative position to the coil, they are defined as region I (far from the coil end), region II (middle position), and region III (close to the coil end), respectively. The structures of different regions are different, thus forming a gradient heterogeneous structure.

[0030] Figure 5 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of this embodiment. Figure 5 It can be seen that, compared with the rolled AZ31 magnesium alloy plate, the tensile strength of the AZ31 magnesium alloy plate remains unchanged after short-time high-frequency electromagnetic induction heating, the yield strength decreases, and the plasticity is improved. The plasticity of different regions (I, II and III) shows a large difference. The gradient microstructure leads to a large difference in mechanical properties, mainly in plasticity.

[0031] Example 3 This embodiment includes the following steps: Step 1, Surface treatment: The 50mm thick AZ31 magnesium alloy plate is polished with 400# and 600# sandpaper in sequence, then cleaned with anhydrous ethanol, and then air-dried for 1 hour to obtain a clean AZ31 magnesium alloy plate. Step 2, Rolling: The clean AZ31 magnesium alloy plate obtained in Step 1 is held at 350℃ for 30 minutes, and then rolled in multiple passes at a rolling speed of 12m / min, with a reduction of 12% per pass and a total reduction of 50%. The holding time after the first pass is 25 minutes, and the holding time after the second pass and subsequent passes is 15 minutes each, to obtain a 25mm thick, straight AZ31 magnesium alloy rolled plate. Step 3: Short-time high-frequency electromagnetic induction heating: The AZ31 magnesium alloy rolled plate obtained in Step 2 is subjected to short-time high-frequency electromagnetic induction heating at a frequency of 350kHz and a power of 15kW. The distance between the heating coil and the AZ31 magnesium alloy rolled plate is 0.6mm, and single-sided heating is used. The heating temperature refers to the temperature of the side of the AZ31 magnesium alloy rolled plate away from the induction heating coil. Heating is stopped when the heating temperature reaches 200℃. The entire short-time high-frequency electromagnetic induction heating process lasts about 5s. The short-time high-frequency electromagnetic induction heating is repeated 7 times to obtain a gradient heterogeneous AZ31 magnesium alloy rolled plate.

[0032] Figure 6 The images show the metallographic images of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient isomorphic AZ31 magnesium alloy rolled plate obtained in step three of this embodiment. Figure 6 It can be seen that the AZ31 magnesium alloy rolled plate heated by short-time high-frequency electromagnetic induction exhibits a gradient structure of twin-grained-fine-coarse grains.

[0033] Figure 7 The figures show the engineering stress-strain curves of the AZ31 magnesium alloy rolled plate obtained in step two and the gradient heterogeneous AZ31 magnesium alloy rolled plate obtained in step three of this embodiment. Figure 7 It can be seen that, compared with the rolled AZ31 magnesium alloy plate, the tensile strength of the short-time high-frequency electromagnetic induction heating AZ31 magnesium alloy plate (Ⅰ, Ⅱ and Ⅲ) remains unchanged, while the plasticity is greatly improved.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating, characterized in that, The method includes the following steps: Step 1, Surface treatment: The AZ31 magnesium alloy plate is polished with 400# and 600# sandpaper in sequence, then cleaned with anhydrous ethanol, and then air-dried to obtain a clean AZ31 magnesium alloy plate. Step 2, Rolling: The clean AZ31 magnesium alloy plate obtained in Step 1 is rolled in multiple passes to obtain a straight AZ31 magnesium alloy rolled plate. Step 3: Short-time high-frequency electromagnetic induction heating: The AZ31 magnesium alloy rolled plate obtained in Step 2 is subjected to short-time high-frequency electromagnetic induction heating to obtain a gradient heterogeneous AZ31 magnesium alloy rolled plate.

2. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, The thickness of the AZ31 magnesium alloy plate mentioned in step one is 20mm~50mm.

3. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, In step two, the temperature of the multi-pass rolling is 300℃~350℃, the rolling speed is 8m / min~12m / min, the reduction per pass is 8%~12%, the total reduction of the multi-pass rolling is 30%~50%, and the heat preservation time after the first pass rolling is 15min~25min, and the heat preservation time after the second pass rolling and after the subsequent passes rolling is 5min~15min.

4. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, The thickness of the AZ31 magnesium alloy rolled plate mentioned in step two is 14mm~25mm.

5. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, The short-time high-frequency electromagnetic induction heating in step three has a frequency of 300kHz~350kHz, a power of 5kW~15kW, a temperature of 100℃~200℃, and the distance between the heating coil and the AZ31 magnesium alloy rolled plate is 0.2mm~0.6mm. The duration of the entire short-time high-frequency electromagnetic induction heating process is 3s~5s.

6. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, The short-time high-frequency electromagnetic induction heating described in step three uses single-sided heating. The induction heating temperature refers to the surface temperature of the AZ31 magnesium alloy rolled plate away from the induction heating coil. Heating is stopped when the heating temperature reaches the set value.

7. The method for preparing gradient heterogeneous AZ31 magnesium alloy rolled plates based on short-time high-frequency electromagnetic induction heating according to claim 1, characterized in that, The short-time high-frequency electromagnetic induction heating described in step three needs to be performed 5 to 7 times.

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