Microstructure, heat treatment and mechanical properties of TiB2/Al–7Si–Cu–Mg alloy fabricated by selective laser melting

Selective laser melting (SLM) of aluminium alloys is of research interest due to its potential benefits in fabricating complex components for aerospace and automotive industries. In order to improve the mechanical properties and demonstrate the credibility of selective laser melted (SLMed) Al alloys, the effects of post heat treatment on the microstructures and mechanical properties need to be studies. In the present work, the nano-TiB2 decorated Al–7Si–Cu–Mg samples were successfully fabricated using the SLM technique, and then post-treated by direct ageing and conventional T6 heat treatment. The as-built TiB2/Al–7Si–Cu–Mg sample exhibits fine equiaxed grain structures without preferred crystallographic texture due to the high cooling rate of SLM and the addition of nano-TiB2 particles. Nano-scale eutectic Si cells are present within the equiaxed grains. Inside the cells, there are dislocation tangles without precipitates. After direct ageing treatment, the grain and cell structures remain almost unchanged, and the new Al2Cu, Mg2Si, and Si phases are formed around the dislocations. While after T6 treatment, the fine grains grow up and the eutectic Si phases coarse leading to the broken of cell structures. Besides, the as-built TiB2/Al–7Si–Cu–Mg samples show high tensile strength and ductility (yield strength: 297.2 MPa, ultimate tensile strength: 474.6 MPa, elongation: 13.4%). During ageing, the yield strength is enhanced by ~35% due to precipitation hardening effect. While the broken of fine microstructure during T6 leads to the decrease of yield strength by ~16%. The microstructure development and preliminary strengthening mechanism were discussed. The effect of post-heat treatments can yield the SLMed TiB2/Al–7Si–Cu–Mg samples with appropriate mechanical properties, promoting a wide range of applications.