Effect of Interlayer Interval Time on the Microstructure and Mechanical Behavior of Additively Manufactured WE43 Mg Alloy

Additive manufacturing of magnesium (Mg) alloys has gained interest for the potential to fabricate complex geometries for extreme light-weighting or improved functionality. In this study, the effect of interlayer interval time and post-deposition processing (i.e., heat treatment and hot isostatic pressing (HIP)) on the microstructure and mechanical behavior of WE43 Mg specimens fabricated by laser powder directed energy deposition (LPDED) was investigated. Microstructure characterization was conducted using optical microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy. Mechanical behavior was evaluated using microhardness and uniaxial tensile testing. Post-processing resulted in improved yield strength, tensile strength, and ductility, which was attributed to a reduction in porosity and, to a lesser extent, the formation of second phase particles. The as-deposited specimens exhibited porosity below 3 pct and HIP treatment reduced porosity to below 0.1 pct. HIP specimens, processed with low interlayer interval time, exhibited the best combination of strength (~ 243 MPa tensile strength) and ductility (~ 9 pct elongation). Changes in interlayer interval time had limited impact on the grain size, hardness, or yield strength. However, increased interlayer interval time (~ 112 pct increase) caused a slight increase in gas porosity and dramatic reduction in tensile strength and ductility, which was attributed to the formation of lack-of-fusion defects in interlayer regions.