Researches On Microstructures And Properties Of Mg-6Zn-1Mn Wrought Magnesium Alloy

Along with the development of the research and manufacture , the magnesium alloys are used in many fields, just as vehicle, electronic products and military industry. Magnesium alloys were divided into two kinds according to containing zirconium or not. Some literatures indicated that zirconium, which is a sort of grain refiners, can refine the casting structure of magnesium alloys. The magnesium alloys containing zirconium which fall short of 1% in gross have the good high-temperature behavior and room-temperature property. But due to high manufacture cost, they are just used in aviation, spaceflight and militray fields. The zirconium-free magnesium alloys are in common used for construction members. However, the problem of existing zirconium-free magnesium alloys is low strength, become a key factor of restricting the development and application of it. The way of alloying and grain refining can enhance the mechanical property and working qualities of zirconium-free magnesium alloys. The most challenging thing in the area is to exploit high strength zirconium-free magnesium alloys, which is of great importance to the application of the magnesium alloy in the future.In this paper, Mg-5.77Zn-1.25Mn (ZM61) has been studied by smelting, extrusion, heat treatment, mechanical tests and metallography analysis. Experimental results indicated that certain a mount of Zn can increase the tensile strength and yield strength. The alloy can be extruded at 310°C-330°C. The process of extrusion can significantly improve mechanical properties because of fine grain obtained via complete dynamic recrystallization. The effect to properties of heat treatment is complicated. The result can be resorted to the combination of strengthening brought by solid solution and aging, and deterioration by the course grains. For the solid solution strengthening and the later precipitation strengthening is good for properties, while the long time keeping of alloys under elevated temperature could reduce the properties as the grains would grow. The results show that solid solution and aging heat treatment will not improve the strength of ZM61, but amend plastic property. The solid solution and two-stage aging heat treatment can markedly improve the strength of ZM61. The optimized process is that the extruded alloys are first-stage aging at 90°C for 24h, second-stage aging at 180°C for 16h, after it is dissolved at 420°C for 2 hours in the needing of high strength and the typical properties areσ_b=366.8MPa,σ_0.2=340.5MPa,δ=6.3%. The alloys are aging at 180°C with 20 hours after it is dissolved at 400°C for 2 hours in the needing of high distortion capacity and the typical properties areσb=317.3MPa,σ0.2=249.1MPa,δ=14.9%, respectively.