Aging kinetics of 14H-LPSO precipitates in Mg-Zn-Y alloy

Abstract

Alloys with long-period stacking ordered structures (LPSO) have good properties and are highly regarded. Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method, and the aging heat treatment was performed at different temperatures and times. The microstructure and phase constitutions of the alloy were observed by means of optical microscopy and scanning electron microscopy methods. Results show the microstructure of as-cast Mg95.5Zn1.5Y3 mainly consists of α-Mg, W phases and LPSO phases. During the aging treatment, fine lamellar-shaped 14H-LPSO phase is formed at the grain boundaries and precipitates from the supersaturated magnesium matrix, and the volume fraction increases as the aging time increases. By controlling the aging time, Mg-Zn-Y alloys with different volume fractions of 14H-LPSO phase were prepared. The aging kinetics equation of the 14H-LPSO phase is summarized, that is f = 1−exp(−0.2705 t0.6368). The phase transformation mechanism of 14H-LPSO in Mg95.5Zn1.5Y3 alloy can be described as the change of dislocation energy.