The relationship between (Mg,Zn)3RE phase and 14H-LPSO phase in Mg-Gd-Y-Zn-Zr alloys solidified at different cooling rates

Mg-10Gd-3Y-1.8Zn-0.5Zr (wt.%) (GWZ1032K) alloys are prepared by permanent mold casting at cooling rate of 5 K/s, or further prepared by melt spinning at cooling rate of 10(4) K/s, or by slow solidification at different cooling rates (0.5 K/s, 0.1 K/s, 0.01 K/s and 0.005 K/s). (Mg,Zn)(3)RE phase and 14H-LPSO structure in alloys under different conditions are measured by XRD and observed under electron microscope. It shows there is no LPSO structure in the alloy prepared by melt spinning at cooling rate of 10(4) K/s. In the alloy prepared by permanent mold casting at cooling rate of 5 K/s, fine lamellar 14H-LPSO structure appears in the matrix nearby grain boundaries. With the cooling rates slowing down from 0.5 K/s to 0.005 K/s, (Mg,Zn)(3)RE phase is gradually replaced by 14H-LPSO phase at grain boundaries, and lamellar 14H-LPSO structure also propagates in alpha-Mg matrix. Both (Mg,Zn)(3)RE phase and 14H-LPSO phase are present at grain boundaries in the alloys solidified at cooling rates of 0.5 K/s and 0.1 K/s. When the cooling rate is very slow (0.005 K/s), lamellar 14H-LPSO structure penetrates throughout the matrix grain. It suggests the cooling rate is an important factor for the formation of 14H-LPSO structure in as-cast GWZ1032K alloys. The orientation relationship between (Mg,Zn)(3)RE phase and 14H-LPSO phase is determined by the composite SAED patterns, which is expressed as (1 1 0)((mg,zn)3RE)//(0 01 4)(14H-LPSO phase), [(3) over bar3 2]((Mg,Zn)3RE)//[1 1 0](14H-LPSO phase) and [(1) over bar 1 2]((Mg. Zn)3RE)//[2 1 0](14H-LPSO phase). (c) 2010 Elsevier B.V. All rights reserved.