Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

Abstract

To investigate the effects of solution temperature and the decomposition of I-phase on the microstructure, phase composition and mechanical properties of as-cast Mg-6Zn-1.4Y-0.6Zr alloy, solution treatment at 440 ìC, 460 ìC and 480 ìC and further aging treatment were conducted on the alloy. The results indicate that the net-like intermetallic compounds (mainly I-phase) dissolve into the メ-Mg matrix gradually with the increase of solution temperature from 440 ìC to 480 ìC. Besides, the I-phase decomposes completely at 480 ìC, with the formation of fine W-phase (thermal stable phase) and Mg7Zn3 phase. In addition, a great number of fine and dispersive Mg-Zn binary phases precipitate in the メ-Mg matrix during the aging treatment. Due to the increase of solute atoms and the precipitation of strengthening phases, such as W-phase and Mg-Zn phases, the optimal strength is obtained after solution treatment at 460 ìC for 8 h and aged at 200 ìC for 16 h. The yield strength (YS), ultimate tensile strength (UTS) and elongation are 208 MPa, 257 MPa and 3.8%, respectively. Compared with the as-cast alloy, the increments of YS and UTS are 117% and 58%, respectively, while the decrement of elongation is 46%.

Keywords

• magnesium alloy; heat treatment; microstructure; mechanical properties