Research Of Mg-9Zn-xAl Magnesium Alloys And Semi-solid Microstructure

Magnesium alloys are widely used in the fields of automobiles, electronics and aerospace. However, the conventional magnesium alloys have poor high temperature mechanical properties, which greatly restrict their applications. Therefore, developing novel low-cost heat-resistance magnesium alloys has become a hot topic recently.Mg-Zn-Al system with the potential of developing high-performance heat-resistant magnesium alloys, high zinc low aluminum alloys could essentially eliminateβphase which with poor thermal stability. This article selected Mg-9Zn as the matrix alloy and researched the effect of Al content on the organization and properties of Mg-9Zn-xAl magnesium alloys which treated by T6 heat treatment, besides, the effect of Al content on semi-solid non-dendritic organization was researched. The main conclusions are given in the following.(1) The second phase of Mg-9Zn-xAl magnesium alloys changed from MgZn binary phase toτ(Mg32 (A1, Zn) 49) ternary phase with the increasing of x value from 2 to 6, and the number increased as well as size magnified. The mechanical properties of as-cast alloys took the tendency of increased at first and then decreased, the elongation and hardness were on the rise. After T6 heat treatment, the second phase of microstructure which was long block irregular transformed into Short round bar microstructure, mechanical properties had significantly increased than the properties of as-cast alloys, the elongation and micro-hardness varied complicatedly . By comparison, ZA94 alloy that solutionized at 350℃for 20h and aginged at 175℃for 16h had the best properties, tensile strength, elongation and micro-hardness were: 289Mpa, 4.5% and 118HV respectively.(2)In the process of Mg-9Zn-xAl magnesium alloy prepared for non-dendritic slurry by isothermal heat treatment, the minimum temperature of preparing semi-solid slurry reduced with the Al content increased and the regularity with the heating temperature and time turned better. The stage of spheroidized evolution for ZA92 was relatively short. The regularity of ZA96 was better than ZA92 and ZA94. At the heating temperature of 580℃holding for 20min, ZA96 obtained the roundest and smallest non-dendritic spherical particles, which calculated by the software that the average particle diameter was 46.03μm, shape factor was 1.12, and solid fraction was 40.2%.