Melt pool Geometry and Microstructure Characterization in Additively Manufactured WE43 Alloy

Abstract: Mg-RE based alloys have exhibited promising properties in application for biodegradable implants. This work provides a systematic study on the characterization of melt pool geometry and profile for one such alloy, WE43. Using single track scans produced at various process parameters, this study aims to establish a PBF-LB processing window for the material. The laser single tracks were processed using an EOS M100 PBF-LB machine. Optical microscopy was used to conduct measurements of the melt pool depths and widths, for a set of melt pools with exposure parameters varying from 80 – 130 W in laser power at two different corresponding scanning speeds, 800 mm/s and 1100 mm/s. It was found that at an energy density of ~85 J/mm3, a keyholing behaviour is observed where the melt pool protrudes deep into the preceding layer, causing excessive remelting in the surrounding heat affected zone. The microstructure consisted of fine α-Mg (hcp) grains with globular intermetallic precipitates and Y, Zr oxides, with the tracks showing two distinct microstructure regimes consisting of cellular and equiaxed dendritic grains respectively. The equiaxed dendrites contained a RE-rich centre, which aided in their formation by acting as a nucleating agent. The influence of these microstructural features in the mechanical and corrosion properties of the final material is also discussed.   Keywords: Additive Manufacturing, WE43, Single track study, Powder Bed Fusion – Laser Beam