Development Of High Strength Magnesium Alloy
Magnesium alloy is the lightest metal structure material currently used, with a density of 1.74 g / cm3, which is only equivalent to 2 / 3 of aluminum and 1 / 4 of steel. At the same time, magnesium alloy also has the advantages of high specific strength, high specific modulus, damping and vibration reduction, electromagnetic shielding, easy processing and recycling. At present, magnesium alloy has become an important material in national defense and military, aerospace, automobile, electronic communication and other industrial fields. For example, the use of magnesium alloy to manufacture automobile parts can not only reduce the quality of the automobile and reduce fuel consumption, but also help the automobile to reduce vibration, thus improving the comfort and safety of the automobile; In the field of national defense and military industry, reducing the structural quality means improving the range and accuracy of weapons, improving the maneuverability of aircraft, and reducing energy consumption. With the launch of large-scale engineering projects such as large aircraft, lunar orbiting, high-speed rail transit, and electric vehicles in China, there are bound to be greater expectations and higher requirements for magnesium alloys.
However, the absolute mechanical properties of magnesium alloys are still low. The development of high strength magnesium alloy is a hot research topic in material science.
1、 Using rare earth to improve the strength of magnesium alloy. Adding nd to the magnesium alloy can improve the high temperature strength of the alloy and make the casting structure compact. The results show that mg-4.4zn-1.2nd-0.35zr alloy has higher tensile strength at lower than 473k, while mg-4.4zn-2nd-0.35zr alloy shows higher tensile strength at higher than 523K. The addition of GD and y can obviously improve the strength of magnesium alloy. The friction stir process was introduced into Mg-10Gd-3Y-0.5Zr magnesium alloy casting, and significant grain refinement effect was obtained. Finally, 439mpa high-strength cast magnesium alloy was obtained. Mg-10gd-5.66y-0.65zr-1.6zn alloy was prepared by traditional casting extrusion, and the ultra-high strength magnesium alloy bar with tensile strength of 542mpa was obtained. Mg-12gd-1.9y-0.69zr alloy and mg-17gd-0.51zr alloy prepared by traditional hot rolling method have yield strength above 360 MPa and tensile strength above 400 MPa.
2、 The properties of magnesium alloy were improved by plastic deformation. The microstructure of traditional cast magnesium alloys is very coarse and the mechanical properties are poor. Due to the hexagonal structure and poor plastic deformation ability of magnesium alloy, the traditional single plastic deformation method is difficult to further improve its mechanical properties. In view of this difficulty, the large plastic deformation technology is used to exert its strong grain refinement effect, which can directly refine the internal structure of the material to sub micron or even nanometer level. The technology of large plastic deformation includes equal channel angular extrusion, cumulative rolling and so on. Mg-y-zn alloy prepared by large plastic deformation has comprehensive mechanical properties of tensile strength of 400MPa, yield strength of 340mpa and elongation of 20% at 250 ℃. The application of two or more traditional plastic deformation processes to magnesium alloys is another way to improve the plastic deformation ability and comprehensive mechanical properties of magnesium alloys. For example, a high-strength mg-14gd-0.5zr magnesium alloy sheet with a yield strength of 445mpa and a tensile strength of 482mpa was developed by combining extrusion, cold rolling and aging processes. A high-strength and heat-resistant Mg-Gd-Y alloy was developed by Central South University in combination with forging and rolling technology. The thick plate with thickness of 30-80 mm was prepared by multi-directional forging; Then, the thick plate is rolled into 2-10 mm thin plate by hot rolling, and the maximum total reduction is more than 90%; After rolling and aging treatment, the tensile strength of the alloy at room temperature is ≥ 475 MPa, the yield strength is ≥ 440mpa, and the elongation is ≥ 3%; Tensile strength ≥ 330 MPa and elongation ≥ 12% at 250 ℃. This preparation method expands the application range of magnesium alloys, especially can meet the application in aerospace industry.