Effect of linear energy density on the microstructure and properties of a Mg-Gd-Y-Zn-Zr alloy prepared by laser directed energy deposition

In this study, a Mg-7Gd-3Y-1Zn-0.4Zr (GWZ731K, wt.%) alloy was prepared via laser directed energy deposition (LDED). The effects of linear energy density (LED), and substrate preheating on the formed microstructure during LDED process of the GWZ731K alloy were systematically investigated. These effects were analyzed across different dimensions, specifically 0D (laser energy input and thermal influence), 1D (single-track samples), 2D (single-layer samples and wall-shaped samples) and 3D (block samples). Results demonstrate that LED is the suitable factor affecting the morphology of the molten pool. The lack-of-fusion defects with lower LED cannot be eliminated. Due to the special thermal process during the LDED, there will be a transition area at the bottom of the GWZ731K alloy. Preheating the substrate can reduce the area of this area and thus improve the forming quality. Meanwhile,the γ´ precipitates, especially, the LPSO structure appear during the LDED process, thereby improving the mechanical properties of the alloy. The UTS, YS and El. of the alloy are 283 ± 11 MPa, 180 ± 6 MPa and 5.7 ± 1.5% respectively.