3D forming space and abnormal lamellar microstructures in a Mg-10Gd-Zr alloy fabricated by laser powder bed fusion

Mg-10Gd-Zr (G10K, wt. %) is a commonly used high-performance magnesium-rare earth alloy that has demonstrated good suitability for additive manufacturing processes. However, the formability and microstructures need to be further explored for its engineering application. This study presents a systematic and in-depth investigation of the defects, microstructural characteristics, and mechanical properties of G10K alloy fabricated by laser powder bed fusion (LPBF) as a function of processing parameters. A 3D forming space for LPBF-G10K alloy is constructed by adopting laser beam diameter as the third variant other than laser power and scanning speed. With a laser beam diameter of 120 µm, the fluctuation of the melt pool is minimized, leading to the suppression of gas porosities and balling defects, and thus the expansion of forming zone of the alloy as compared to laser beam diameters of 100 or 140 µm. LPBF-G10K alloy under the optimal processing parameter consists of a heterogeneous microstructure of coarse and fine grains. The formation of abnormal lamellar structures in the coarse grains at the middle of melt pools is attributed to the planar growth along laser scanning direction. The lamellar coarse grains provide strength in the alloy due to texture-strengthening effect, while plastic deformation is primarily accommodated by equiaxed grains. These findings are instrumental for application and future modification of the LPBF-G10K alloy.