Microstructure characteristics and its formation mechanism of selective laser melting SiC reinforced Al-based composites

SiC ceramic reinforced Al-based composites were successfully synthetized by selective laser melting (SLM) of 8.5 vol % SiC/AlSi10 Mg powder mixtures. The mechanism of microstructure evolution in an individual molten pool of the SLM processing was investigated. Three characteristic zones were well distinguished, including center and boundary areas of the molten pool as well as the heat-affected zone. The results revealed that the microstructure changing from columnar dendrite growth to cellular growth along the building direction could be attributed to the change of G/R (G is temperature gradient and R is solidification velocity). Phase identification of the SLM-fabricated parts was performed by X-Ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) analysis, further demonstrating the in-situ formed phases in the molten pool. Al4SiC4 crystals were formed in situ around the partially melted SiC ceramic particles. The nanoindentation tests conducted on different areas of the SLM-fabricated Al-based composites exhibited the high nanohardness (2.27 GPa and 2.15 GPa) and the elastic modulus (78.94 GPa and 75.46 GPa) in the center and boundary of molten pool, respectively, which were much higher than the reported value of conventional materials.