Effect of TiC content on the Al-15Si alloy processed by selective laser melting: Microstructure and mechanical properties

Selective laser melting (SLM) has been regarded as one of the most effective powder-based additive manufacturing (AM) methods for metal parts. The present study systematically investigated the influence of adding TiC content on the microstructural evolution and mechanical property of SLM hypereutectic Al-15Si alloy. Due to the high cooling rate during the SLM process, an ultrafine eutectic microstructure was observed in the form of spherical sub-micro-sized network eutectic Si embedded in the Al matrix, resulting in high tensile properties (398 MPa, 2.6%) and micro-hardness (154 Hv) for Al-15Si alloy. The solubility of Si atom in the Al matrix was calculated to be 9.37 at%. With increasing the TiC content from 1.0, 2.5 to 10 wt%, the solubility decreased rapidly and the network eutectic microstructure became coarser, precipitating out some small Si particles finally. That was because the TiC addition changed the thermodynamics of the melt pool, especially changed the undercooling degree in the SLM process. Attributing to the effect of eutectic microstructural evolution and the particle reinforcement, the micro-hardness was down firstly (146 Hv) and then up (177 Hv). Inversely, the tensile property firstly rose (578 MPa 7.86%) then descended (313 MPa, 2.24%). This study indicated that the microstructure and mechanical properties of SLM Al-15Si alloy can be tailored by suitable addition of TiC content.