Magnesium alloy rolling method based on low-carbon steel female die sleeve

Abstract

The invention relates to a magnesium alloy rolling method based on a low-carbon steel female die sleeve, and belongs to the technical field of magnesium alloy rolling. Before rolling, a magnesium alloy plate is embedded into a low-carbon steel female die sleeve, in the heating process, the rolling direction and the transverse direction of the plate are restrained and limited through the thermal expansion coefficient, twice that of magnesium alloy, of low-carbon steel, so that the magnesium alloy is in a three-direction pressure stress state during rolling, and the limited rolling effect is achieved. Wherein the inner cavity of the low-carbon steel female die sleeve is designed into a rounded rectangle, so that the die sleeve can be prevented from being broken due to stress concentration. According to the method, the problems of high heating temperature and poor formability in the magnesium alloy rolling process are solved, the plasticity of the magnesium alloy is effectively exerted through the three-way pressure stress state, edge cracks cannot occur even if the magnesium alloy is rolled at the low temperature, the heating temperature is reduced from 350 DEG C to 200 DEG C, the forming capacity and surface quality of the magnesium alloy are effectively improved, and production energy consumption and cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy rolling technology, specifically a magnesium alloy rolling method based on a low-carbon steel die sleeve. Background Technology

[0002] Magnesium alloys are currently the lightest metallic structural materials used in engineering applications. They possess advantages such as high specific strength and specific stiffness, excellent electromagnetic shielding, and easy recyclability, making them widely used in aerospace, automotive, and electronics industries. Among the many magnesium alloy products, sheet metal has the highest application rate, covering various fields. Rolling is the main method for preparing magnesium alloy sheets in actual production, thus research on magnesium alloy rolling processes is of great significance.

[0003] However, due to the close-packed hexagonal structure of magnesium alloys, there are relatively few slip systems at room temperature, resulting in poor plastic deformation capacity. Rolling is typically required at medium to high temperatures (350-550℃), which limits the production of magnesium alloy sheets to some extent. On the one hand, as the heating temperature increases, the grains refined by rolling will recrystallize and coarsen again, weakening the dislocation strengthening and grain refinement strengthening effects of magnesium alloys, leading to a decrease in mechanical properties. On the other hand, excessively high temperatures are not conducive to controlling the shape and dimensions of magnesium alloy sheets, and easily cause severe oxidation of the sheet surface, damaging surface quality. Therefore, the development and application of magnesium alloy sheets are constrained, and the rolling forming and sheet quality are much worse than those of aluminum alloys.

[0004] Currently, magnesium alloy rolling requires heating both the workpiece and the rolls to ensure sufficient plasticity for deformation. The workpiece typically needs to be heated to 350-550℃, and the rolls to 150-200℃. This increases energy consumption, complicates equipment, and raises the production cost of magnesium alloy sheets. Against this backdrop, existing technology primarily addresses the significant temperature drop during magnesium alloy rolling by designing an aluminum cladding. This cladding encloses the magnesium alloy, which is then welded together before rolling to prevent edge cracking due to severe temperature drops. However, this technology still requires heating the workpiece to above 350℃ during the rolling process, resulting in high energy consumption. Furthermore, the welding of the cladding and workpiece adds to the production steps and complicates the process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a magnesium alloy rolling method based on a low-carbon steel die sleeve. During the heating process, this invention utilizes the fact that the thermal expansion coefficient of magnesium alloy is twice that of low-carbon steel to constrain the rolling direction and transverse direction of the sheet metal, placing the magnesium alloy under triaxial compressive stress during rolling. This is beneficial to the plasticity of the magnesium alloy, allowing it to be rolled at lower temperatures without edge cracking, effectively improving the formability of the magnesium alloy, and reducing energy consumption and cost in the magnesium alloy rolling process. This invention is designed to address the shortcomings of high heating temperatures and poor formability in magnesium alloy rolling.

[0006] This invention is achieved through the following technical solution: This invention designs a method for rolling magnesium alloys based on a low-carbon steel die sleeve, using conventional rolling methods. The method is characterized by performing the following steps before rolling:

[0007] Step 1: Prepare a low-carbon steel concave mold sleeve by setting an inner cavity of a suitable shape inside the low-carbon steel.

[0008] Step 2: Embed the magnesium alloy sheet into the inner cavity of the mold sleeve;

[0009] Step 3: Heat treatment is performed on the magnesium alloy sheet and mold sleeve.

[0010] The inner cavity of the low-carbon steel die sleeve is a rounded rectangle.

[0011] The magnesium alloy is a magnesium alloy of the AZ31, AZ80 or GWK series.

[0012] The magnesium alloy sheet and the low-carbon steel die sleeve are heated to 200°C and held for 40 minutes before rolling.

[0013] The rolling method involves rolling one pass and then heating and holding it in a furnace. The deformation amount for each pass is 5-10%, and the holding time is 10 minutes. After the last pass is rolled, water cooling is performed.

[0014] The present invention has the following beneficial effects:

[0015] (1) The method of the present invention utilizes the thermal expansion coefficient of magnesium alloy, which is twice that of low carbon steel, to make the plate and the die sleeve tightly bonded together after heating. During the rolling process, the material will be in a triaxial compressive stress state, and the deformation is mainly longitudinal elongation, while the transverse widening is restricted. This can effectively utilize the plasticity of magnesium alloy, so that it will not crack at the edge when rolled at a lower temperature, thus effectively improving its forming ability.

[0016] (2) The method of the present invention can effectively reduce the temperature required for rolling magnesium alloys (the heating temperature is reduced from 350°C to 200°C), which not only helps to strengthen the fine grains of magnesium alloys and improve the surface quality of rolled plates, but also effectively reduces production energy consumption and costs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a low-carbon steel die sleeve. In the diagram: 1 is the die sleeve, and 2 is the inner cavity.

[0018] Figure 2 This is a rendering of a magnesium alloy sheet rolled using the method of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to specific embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0020] Figure 1 This is a schematic diagram of the structure of a low-carbon steel die sleeve. This embodiment relates to a method for rolling magnesium alloy based on a low-carbon steel die sleeve, including the following steps: taking a low-carbon steel die sleeve 1 and a magnesium alloy sheet, and placing the magnesium alloy sheet in the inner cavity 2 of the die sleeve; the dimensions of the low-carbon steel die sleeve are 70×54×18mm (length×width×thickness); the magnesium alloy grade is AZ31B; the dimensions of the magnesium alloy sheet are 40×24×18mm (length×width×thickness); the inner cavity 2 of the die sleeve is a rounded rectangle, and its dimensions are the same as those of the magnesium alloy sheet.

[0021] The magnesium alloy sheet and the low carbon steel die sleeve 1 are placed in an electric resistance furnace and heated to 200℃ for 40 minutes.

[0022] Furthermore, since magnesium alloy has twice the coefficient of thermal expansion of low carbon steel, the magnesium alloy sheet and the low carbon steel die sleeve will be tightly bonded together.

[0023] After the magnesium alloy sheet is rolled once, it is put back into the furnace for heating and heat preservation. The deformation amount of each pass is 5-10%, the final rolled plate thickness is 5mm, the intermediate heat preservation time is 10min, and the last pass is water-cooled.

[0024] During the rolling process, it was found that the magnesium alloy sheet using a low-carbon steel die sleeve did not develop edge cracks due to low temperature and exhibited good surface quality, such as... Figure 2 As shown in the figure. Experiments showed that the tensile strength of the magnesium alloy sheet after using a low-carbon steel die sleeve reached 320 MPa, while also exhibiting good plasticity.

[0025] In summary, the method of the present invention can effectively utilize the plasticity of magnesium alloys under triaxial compressive stress, preventing edge cracking even when rolling at lower temperatures, thus effectively improving its forming ability and reducing energy consumption and costs.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A magnesium alloy rolling method based on a low carbon steel die sleeve, which is rolled using a conventional rolling method, characterized in that, Before rolling, the following steps are taken: Step 1: preparing a low-carbon steel die sleeve, and setting a suitable inner cavity in the low-carbon steel; Step 2: embedding a magnesium alloy plate into the inner cavity of the die sleeve; Step 3: heating the magnesium alloy plate and the die sleeve.

2. The magnesium alloy rolling method based on a low carbon steel female die sleeve according to claim 1, characterized by, The inner cavity of the low-carbon steel die sleeve is a round-cornered rectangle.

3. The magnesium alloy rolling method based on a low carbon steel die sleeve according to claim 1, characterized by, The magnesium alloy is of AZ31, AZ80 or GWK series.

4. The magnesium alloy rolling method based on a low carbon steel die sleeve according to claim 1, characterized by, The magnesium alloy plate and the low-carbon steel die sleeve are heated to 200℃ before rolling, and are kept for 40 minutes.

5. The magnesium alloy rolling method based on a low carbon steel die sleeve according to claim 1, characterized by, The rolling method is to put the rolled product into a furnace for heating and keeping after one-pass rolling, the deformation amount of each pass is 5-10%, the keeping time is 10 minutes, and the last-pass rolled product is water-cooled.

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