Achieving strength-ductility synergy in Mg–Al alloy fabricated by CMT+P directed energy deposition through heat input regulation

Magnesium alloys are widely used in aerospace, biomedical, and transportation fields due to their low density, high specific strength, and good thermal conductivity. Wire arc-directed energy deposition (WA-DED) offers high deposition efficiency and low cost, making it a promising route for manufacturing large, high-strength Mg-Al alloy parts. In this study, the cold metal transfer plus pulsed (CMT+P) process was employed to fabricate AZ31 magnesium alloy thin-walled parts under five heat input conditions (160, 205, 240, 342, and 410 J/mm), denoted as S1-S5, respectively. By combining numerical simulation with various characterization methods, a systematic analysis of the microstructure and properties of this alloy was conducted. The sidewall microstructure consisted of equiaxed grains with a step-like distribution, and no significant crystallographic texture was observed under any heat input. Within this process range, as the heat input increased, grain size first increased then decreased, while porosity exhibited the opposite trend. By adjusting the deposition heat inputs, the S4 thin-walled part showed excellent strength and ductility. This study elucidated the mechanism by which heat input influences the mechanical properties through the regulation of the microstructure, providing a theoretical basis for the optimization of the WA-DED process of AZ31 magnesium alloy.