Effect of energy input on formability, microstructure and mechanical properties of selective laser melted AZ91D magnesium alloy

Selective laser melting (SLM) technology has been used to manufacture the AZ91D magnesium alloy. The relative density, microstructure, microhardness and tensile properties of the deposited AZ91D samples at different laser energy inputs were characterized. The results indicate that laser energy input plays a significant role in determining formation qualities of the SLMed samples. High density samples without obvious macro-defects can be obtained between 83 J/mm3 and 167 J/mm3. The SLMed AZ91D presents a unique layerwise feature in which the fully divorced eutectic β-Mg17Al12 distributing along the boundary of the equiaxed α-Mg matrix. The average size of α-Mg in overlapping regions is a little larger than that in the center of the scanning tracks due to the remelting process though the element distributions of Mg and Al are quite uniform. The microhardness of all samples shows directional independence. The microhardness and tensile strengths of the SLMed AZ91D at room temperature are superior to those of the die-cast AZ91D due to the combined effect of grain refinement and solid solution strengthening.