The Influence Of Thermal Treatment On Mg-xZn Alloy And Semi-solid Water Quenching Microstructure

Because of the advantages of high specific strength, high stiffness and easy recovery, especially as the lightest structural metallic material, magnesium alloy has been widely used on the automotive, aerospace and other fields. This article study the effect of Mg-xZn content(x=3, 5, 7, 9wt.%) on the microstructure and mechanical properties of alloys. Analysis machines like optical microscope, scanning electron microscope, X-ray diffractrometry and mechanical property test instrument are used on the sample detection. The semi-solid microstructure of the alloys is prepared by the semi-solid isothermal-treatment method, non-dendritic microstructure evolution process and the effects of Zn content to the non-dendritic semi-solid microstructure were studied by Mg-Zn(x=3, 5, 7, 9wt.%)alloys. The microstructure evolution is studied through analyze the microstructure and properties which are different before heat-treatment and isothermal heat treatment process. The mechanism is discussed soon.Testing shows that the microstructures and mechanical properties of the Mg-xZn(x=3, 5, 7, 9wt.%) magnesium alloys have an obvious change with the increase of Zn content. The microstructure of the alloy is dendrite and Mg-xZn alloy is mainly composed of α-Mg and MgZn. The grain size of the alloy decreased with the increase of Zn content. The tensile strength and the hardness increase with the Zn content increase. When the content of Zn is 7%, the tensile strength gets the maximum value 210 Mpa and the hardness reaches the maximum value 54 HV. The elongation of the alloy decreased with the increase of Zn content. When the content of Zn is 3%, the elongation reaches the maximum value 15%.The fracture morphology of the alloy is less torn edges and more little dimple as the Zn content increase.Considering the comprehensive mechanical properties, we choose Mg-7Zn alloy undergoing homogenizing,solution and aging treatment. Heat treatment process to obtain the optimal homogenized at 335℃+96h, solutionized at 410℃ + 20 h, aging at 160℃, 98℃, 70℃(24h)+160℃. After the heat treatment its tensile strength has reached 313 MPa, hardness of 83.76 HV. Fracture analysis shows that, Mg-7Zn mainly solvability cleavage fracture.Analysis combined with the mechanical properties of Mg-xZn alloy. The alloy under semi-solid isothermal heat treatment then study the effects of different Zn content on semisolid nondendritic structure. The results shows that, Zn alloy can significantly refine the particle size. After studying the effects of time and temperature on the semisolid nondendritic structure, the results show that such as average particle size and the shape factor both determined by time, while the fraction of solid phase depend on temperature.The content of Zn has a large affect to the non-dendritic microstructure in the isothermal treatment process. Under the same heat treatment conditions, the higher the Zn element content, the experimental alloys non-dendritic microstructures are smaller and round. When the content of Zn is 7%, 30 min at 610 ℃, spherical particles with an average equivalent circle diameter is only 78.51μm, shape factor of 1.223.