Multi-scale control strategy to improve the strength and ductility of Mg-Gd-Y-Zr-Zn alloy prepared by the laser coaxial wire additive manufacturing

A high-strength GWZ831K alloy was achieved through laser coaxial wire additive manufacturing (LCWAM), and the microstructure and mechanical properties of the as-deposited and heat-treated states were systematically studied. The as-deposited sample exhibits a uniform microstructure with fine equiaxed grains, a small amount of eutectic phases and less microsegregation. Two typical microstructural morphologies can be actively obtained by improved solution treatment. One is the 18 R LPSO phases distributed along grain boundaries, and the other is the 14 H LPSO phases uniformly precipitated within grains. This leads to differences in aging behavior. The uniformly distributed 14 H LPSO phases within the grains effectively inhibit the growth of the β' phases during aging. The finer β' phases and higher number density improve the mechanical properties after aging. Additionally, the 14 H LPSO phases within the grains reduce the critical slip system (CRSS) for non-base slip system, promotes the initiation of pyramidal slip and thereby improving ductility. Ultimately, the LCWAM-GW831K alloy exhibits excellent ultimate tensile strength (UTS) and yield strength (YS) of 396 ± 7 MPa and 301 ± 2 MPa, respectively, with a good elongation (EL) of 7.7 ± 1.1 %. Compared to the as-deposited state, both strength and ductility are simultaneously enhanced. This study provides a new way for alloy design and microstructural regulation for high performance Mg alloy components prepared by the LCWAM process.