Microstructural evolution and mechanical properties of Mg-8.1Gd-2.6Y-0.7Zn-0.5Zr alloy by multi-layer wire arc additive manufacturing

Abstract

Wire arc additive manufacturing (WAAM) of Mg-RE (rare-earth)-Zn alloys is important for meeting the requirements of lightweight large-scale components with high manufacturing flexibility. The Mg-8.1Gd-2.6Y-0.7Zn-0.5Zr (GWZ831K, wt.%) alloys were fabricated through the use of WAAM technology, and the microstructure evolution along the building direction and corresponding mechanical properties were then studied. The as-built sample in this paper was composed of finely equiaxed ɑ-Mg grains, eutectic (Mg, Zn)3(Gd, Y) phase, cubic phase, and γʹ precipitates. Furthermore, due to the in-suit heat treatments that were induced by the multiple thermal cycles, more γʹ precipitates were observed in the middle region. The microstructures at different heights were characterized by alternatively distributed fine equiaxed grains (melt pool boundaries, MPB) and coarse equiaxed grains (melt pools, MP). The mechanical properties of the as-built component were found to exhibit yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of 159 ± 1.0 MPa, 237 ± 4.0 MPa, and 6.7 ± 0.4 % in the building direction (BD) and 163 ± 5.1 MPa, 242 ± 8.7 MPa, and 7.0 ± 0.7 % in the traveling direction (TD). This demonstrates that the WAAM-processed GWZ831K alloy has good isotropy.