Microstructure and mechanical properties of Al matrix composite reinforced with micro/nano-sized yttrium oxyfluoride

Abstract

Aluminum matrix composites (AMCs) are widely studied because of their low density, high strength, and castability. Since the high strength and low cost of oxide, it is considered to be a suitable kind of reinforcements for AMCs. However, due to the poor wettability between Al melt and oxide, AMCs reinforced with oxides is usually difficult to be prepared by casting method. Al melt wets better with fluoride than with oxide, but the strength of fluorides is lower than oxides. Oxyfluoride may be a feasible choice for reinforcing AMCs with both good wettability and enough strength. In this study, nano-yttrium oxyfluoride (YOF)-reinforced AMCs were fabricated by employing molten-salt-assisted stirring casting for the first time. The microstructures and mechanical properties of the resulting AMCs with various contents of YOF were investigated in detail. The results indicated that YOF significantly improved the mechanical properties of the Al matrix. The morphology and distribution of the Y-rich phase evolved with an increase in the YOF content, and the formation of casting defects was promoted, these affected the strengthening effect of AMCs. The Al–0.06 vol% YOF composite exhibited optimal mechanical properties while maintaining favorable ductility. Its microhardness, yield strength, and ultimate tensile strength were 20%, 65.6%, and 62.8% higher than those of pure Al, respectively. Therefore, nano-YOF can act as a favorable reinforcement material for AMCs. Refining the coarse Y-rich particles in the composite with high YOF content, minimizing segregation and eliminating casting defects could further improve the mechanical properties of the Al–YOF composites, which can be investigated in future works.