SiCp/AlSi10Mg composites with simultaneously enhanced tensile strength and ductility fabricated by laser powder bed fusion additive manufacturing

Currently, SiCp/Al composites fabricated by laser powder bed fusion (LPBF) suffer from poor plasticity caused by their low density and a great deal of coarse needle-like brittle phases, which seriously limits their application in aerospace field. High scanning speed can shorten the reaction time between SiC and Al liquid due to the short existence time of molten pool, effectively suppressing the nucleation and growth of these needle-like brittle phases. Therefore, an LPBF with a high-speed scanning printing strategy was proposed to fabricate micro-SiCp/Al composites in this study. The effects of energy density (E) on the densification, microstructure and mechanical properties of the composites were studied systematically. The contradiction that the higher the density, the more and coarser needle-like phases produced was successfully resolved. The micro-SiCp/Al composites with simultaneously enhanced strength and ductility were achieved at a proper E of 47 J/mm3, whose tensile strength and elongation reached 356.7 ± 5.0 MPa and 11.6 ± 0.4%, respectively. Among them, the elongation is almost 4 times the maximum value reported in the literature, which is mainly attributed to the extremely high compactness without any visible defects, the moderate dissolution and uniform distribution of SiC particles, the refined grains, a few nano-sized Al4C3 and Al4SiC4, and the interfacial structure SiC–Al4SiC4–Al with high interfacial bonding strength. Because these factors greatly reduced the stress concentration inside the composites and made the stress evenly distributed during loading, thus improving the ductility. Especially these in-situ synthesized Al4C3 and Al4SiC4 can not only promote the transformation of α-Al columnar grains to cellular grains, but also hinder the bending and motion of dislocations, playing a role in grain refinement and dispersion strengthening. The fracture mode of the composites is ductile fracture. Our work provides theoretical guidance and technical support for fabricating SiCp/Al composites with simultaneously enhanced strength and ductility.