Effect of powder composition on WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion (L-PBF) of WE43 magnesium alloy has a promising application prospect in the fields of lightweight parts and biodegradable implants. Grain refinement in these components is expected for high strength and controlled biodegradation, however, grain structure of WE43 is sensitive to composition and processing. L-PBF WE43 exhibited significant diversity on the microstructure and properties with the fluctuation of powder composition, and the influencing mechanism remained unclear. In this study, L-PBF samples were fabricated with high formation quality using four different WE43 powders, in which the content of Nd and Zr were purposely adjusted. Their microstructure, tensile properties and corrosion resistance were characterized. L-PBF specimens composed of fine equiaxed grains were obtained from Mg-3.56Y-2.45Nd-1.14Gd-0.40Zr powder, achieving ultimate strength of 316 MPa and elongation of 15%. With the minor decrease of Nd and Zr content, which was still in the range of present standards of WE43, L-PBF specimens respectively exhibited abnormal grain growth and coarse columnar grains, leading to tremendous deterioration of mechanical properties and corrosion resistance. During the multiple layers of fusion and solidification, Zr promoted the columnar-to-equiaxed transition and generated finer grains, while Nd exerted pinning effect in the heat affected zone to keep the fine grains from abnormal grain growth. The results firstly demonstrate the significant influence of the minor change of alloying elements on the performance, and indicate that a stricter compositional standard of WE43 powder is necessary to achieve reliable properties for the L-PBF process.