Simultaneous enhancements of strength and toughness in an Al-12Si alloy synthesized using selective laser melting

The effect of selective laser melting (SLM), an additive manufacturing technique employed to produce metallic components, on the mechanical properties of the Al-12Si alloy is investigated, with particular emphasis on understanding the effect of laser track direction on quasi-static tensile, fracture, fatigue crack growth, and unnotched fatigue properties. The effect of post-SLM heat treatment as well as the scanning strategy (linear vs. checker board hatch style) was examined and the results are compared with those obtained on specimens produced through the conventional casting route. The SLM alloys exhibit a mesostructure, in addition to the fine, supersaturated Al-rich cellular structure with Si particles along the boundaries. While the latter imparts high strength at the cost of ductility, the mesostructure, which arises due to the laser track hatching, causes the crack path to be tortuous, and in turn leads to substantial increase in fracture toughness. This imparts significant anisotropy to fracture while tensile properties are nearly-isotropic. The unnotched studies reveal that the tensile residual stresses, shrinkage porosity, and unmelted powder particles, can degrade the unnotched highest fatigue properties considerably and hence need be eliminated for high fatigue strength. The SLM process offers new avenues for material design that would exploit the micro- and meso-structures generated by the process for simultaneous enhancement in strength and toughness.