Magnesium (Mg) alloys are attractive due to their low density, high specific strength and good biocompability, but poor corrosion resistance continues to hinder their industrial use. Recent advances in additive manufacturing (AM) do pose new opportunities for increasing the use of such alloys, given the facility in fabricating complex geometries, directly tackling the poor formability of Mg alloys. However, the interplay of numerous processing parameters in AM makes it difficult to determine reliable process-microstructure relations. Establishing such relations is crucial in designing AM-fabricated Mg alloy components with improved corrosion resistance.

In this study, single track investigations were carried out for WE43 Mg alloy during laser-powder bed fusion (L-PBF). By eliminating the influence of hatch distance and scan strategy, an improved focus on the laser-material interactions could be performed. Melt pool microstructures were characterised for laser powers ranging from 80 to 130 W at a constant scan speed of 1100 mm/s. A thermo-fluid model was also developed to aid in prediction of metal flow and thermal distribution within the melt pools for the different laser powers.  

A transition from conduction to keyhole mode was identified with increasing laser power, which directly impacted melt pool microstructure in WE43. Specifically, conduction mode at 80 W promoted growth of a predominantly cellular microstructure, while keyhole mode at 130 W resulted in a high number of equiaxed dendrites. Numerous competitive growth fronts of non-uniform morphologies were also seen in the melt pool for 130 W. The numerical model was effective at attributing this to high recoil pressure and Marangoni convection consistent with keyhole mode melting. Moreover, the model determined differences in thermal gradients and solidification times along the melt pool for the operating modes, which helped establish an improved understanding of the relation between laser input and melt pool microstructure in WE43. This is a critical first step towards implementation of LPBF-fabricated WE43 Mg alloy components with unique microstructures and improved material properties.