Microstructure and mechanical properties of laser melting deposited GW103K Mg-RE alloy

Mg-10Gd-3Y-0.4Zr (wt%) (GW103K) Mg-RE based alloy was manufactured in Laser melting deposition (LMD) process and its microstructure and mechanical properties were studied in as-fabricated and T6-treated conditions. As-fabricated LMDed GW103K alloy consists of equiaxed grains about 19 pm in size and Mg3Gd, GdH2 particles. Under conventional solution and aging treatment parameters, grains of LMDed alloy coarsen significantly, from 19 to 158 pm. Plenty of GdH2 particles can be observed after solution treatment. Yield strength (YS), ultimate tensile strength (UTS) and elongation of as-fabricated and T6-treated LMDed GW103K alloy at room temperature are 118-232 MPa-13.9% and 191-298 MPa-8.9%, respectively. Compared with sand cast alloy, as-fabricated LMDed GW103K alloy has comparable YS (-5 MPa), much higher UTS (+51 MPa) and elongation (+12.1%). Unfortunately, after T6 treatment under conventional heat treatment parameters, YS and UTS were about 40 MPa lower than those of sand cast alloy, with relatively higher elongation (+5.8%). Reduction of Gd, Y content during LMD process, grain growth and formation of GdH2 particles during heat treatment are believed to be the main reasons of the reduced YS and UTS.