Microstructure, solidification behavior and mechanical properties of Al-Si-Mg-Ti/TiC fabricated by selective laser melting

Ball-milled Ti/TiC composite particles (TiC nanoparticles assembled on Ti microparticles) were designed, prepared, and mixed with Al-Si-Mg powder to fabricate an Al-Si-Mg-Ti alloy with TiC nanoparticles (Al-Si-Mg-Ti/TiC) by selective laser melting (SLM). Microstructure features, solidification behavior, and mechanical properties were investigated, and the relationship among them was established. The SLM-manufactured Al-Si-Mg-Ti/TiC material exhibited fine equiaxed-shaped alpha(Al) grains with nanoscale Si4Ti5 phases and Mg segregation along the grain boundaries. This structure benefited from heterogeneous nucleation as well as the grain growth restriction capabilities of TiC nanoparticles on alpha(Al), fast diffusion of Ti in the superheated Al liquid, and high chemical activity of Ti to Si during solidification. Furthermore, Ti enrichment in some local areas of the high-temperature pool and the consequently intense Marangoni convection improved the wettability between TiC nanoparticles and liquid Al without the interfacial reaction. Consequently, the SLM-manufactured Al-Si-Mg-Ti/TiC showed a high ultimate tensile strength of up to 562 +/- 7 MPa and an elongation of up to 8.8 % +/- 1.3 % before fracture. These increased mechanical properties are attributed to the combined effect of grain refinement and Orowan and load-bearing strengthening mechanisms.