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 µm in size and Mg₃Gd, GdH₂ particles. Under conventional solution and aging treatment parameters, grains of LMDed alloy coarsen significantly, from 19 to 158 µm. 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.