7. Novel Aluminum Based Composites by Selective Laser Melting (SLM) Additive Manufacturing (AM): Tailored Formation of Multiple Reinforcing Phases and its Mechanisms

Selective laser melting (SLM) of the SiC/AlSi10Mg composites was performed to prepare the Al-based composites with the multiple reinforcing phases. The influence of the SLM processing parameters on the constitutional phases, microstructural features, and mechanical performance of the SLM-processed Al-based composites was studied. The reinforcing phases in the SLM-processed Al-based composites included the unmelted micron-sized SiC particles, the in situ formed micron-sized Al₄SiC₄ strips, and the in situ produced submicron Al₄SiC₄ particles. As the input “linear laser energy density” (LED) increased, the extent of the in situ reaction between the SiC particles and the Al matrix increased, resulting in a larger degree of formation of Al₄SiC₄ reinforcement. The densification rate of the SLM-processed Al-based composite parts increased as the applied LED increased. A sufficiently high density (~ 96 % theoretical density) was achieved for LED larger than 1000 J/m. Due to the generation of the multiple reinforcing phases, elevated mechanical properties were obtained for the SLM-processed Al-based composites, showing a high microhardness of 214 HV_0.1, a considerably low coefficient of friction (COF) of 0.39, and a reduced wear rate of 1.56 × 10⁻⁵mm³N⁻¹m⁻¹. At an excessive laser energy input, the grain size of the in situ formed Al₄SiC₄ reinforcing phase, both the strip- and particle-structured Al₄SiC₄, increased markedly. The significant grain coarsening and formation of the interfacial microscopic shrinkage porosity lowered the mechanical properties of the SLM-processed Al-based composites.