Tribological behavior of eutectic Al–12Si alloy manufactured by selective laser melting

Al–Si alloys have been extensively used to make complex-shaped components for automobile and aerospace applications. However, the Si coarse-flakes in conventionally casted alloys can initiate cracks and result in poor mechanical properties. Therefore, it is important to discover an ultra-fine grain structure that can provide desirable properties to fulfill the ever-growing application demands. The present study aims to manufacture a eutectic Al–12Si (wt.%) alloy by using an additive manufacturing process based on the selective laser melting (SLM) mechanism and compare the structure, tribological behavior, worn subsurface morphologies and mechanical properties with the conventionally casted eutectic Al–Si alloy. Structural analysis revealed that the SLMed Al–Si alloy has nanoscale spherical Si-phase in a supersaturated Al matrix, whereas that made by the traditional casting method is of microscale Si coarse-flakes. This structural refinement remarkably improves the mechanical properties to 80.8% hardness, 17.3% elastic modulus, more than twice of the tensile strength and creep behavior compared to the traditionally casted alloy. The tribological and subsurface structural evaluation confirms that the SLMed Al–Si alloy can significantly reduce the wear rate in both directions without any substantial worn subsurface damages. It is clear that the wear mechanism of the traditionally casted Al–Si alloy mainly involves the primary Si coarse-flakes crushing-delamination-pull out with severe subsurface damages. However, the nano-sized Si particles in the SLMed Al–Si alloy produce only inlays into the Al-matrix without significant subsurface damage. Thus, the refinement of the grain structure and nanoscale Si phase are the key factors for the improvement of the mechanical properties and tribological behavior of the SLMed Al–Si alloy.