The Research On Die Casting Process, Microstructure And Properties Of ZA84 Magnesium Alloy

Die casting, characteristics of high production efficiency, good product quality and etc. is the most widely used method for the fabrication of components in automobiles. ZA84 magnesium alloy is a better composition of good mechanical properties among the Mg-Al-Zn ternary system, with its high-temperature mechanical properties superior to conventional AZ91 alloy, and it is desirable to find applications in the components of automobiles with the service temperature higher than 120℃. However, there has been few studies on die casting process and mechanical properties of ZA84 magnesium alloy up to now. Therefore, it is of great signifance to develop the optimized die casting process of ZA84 alloy and investigate the effects of alloying on its mechanical properties.the die casting process of ZA84 alloy was developed on a cold chamber die casting machine . The effects of injection velocity, injection pressure, pouring temperature and mold temperature on the surface quality, microstructure and mechanical properties of ZA84 die casting were investigated. According to the optimized die casting process, the effects of the content of Sn on the phase constitutions, microstructure, mechanical properties and thermal stability of ZA84 alloy were studied. The experimental results demonstrated that:①Die castings with fast injection possessed superior mechanical properties to those of slow injection with the other technical parameters unvaried. Die castings had finer microstructures and higher density with the injection pressure increasing, and thus the strength was greatly improved. As the pouring temperature increased, the density of die castings decreased, and the mechanical properties increased firstly then decreased. At the 120℃of the mold temperature, the density of ZA84 die casting increased, with the mold temperature increasing, tensile strength and hardness increased, but elongation increased firstly and then decreased.②Fast injection, injection pressure of 60MPa, pouring temperature of 690±10℃, and mold temperature of 170±10℃were the optimized die casting process parameters for the ZA84 magnesium alloy.③ZA84 alloy was composed ofα-Mg, Mg32(Al,Zn)49 and MgZn , while the alloy containing Sn was composed of four phases i.e.α-Mg, Mg32(Al,Zn)49, MgZn and Mg2Sn.④The addition of Sn played a role in prohibiting the formation of MgZn and accelerating the precipitation of Mg32(Al,Zn)49. The fine, dispersed Mg2Sn particles were distributed both at the grain boundary and in the grain, the amount of which...