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For conventional A356 aluminum alloy, the addition of rare earth elements is an effective way to modify its microstructures and improve its mechanical properties. The effect of rare earth Er on microstructures and properties of as-cast A356 aluminum alloy was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that rare earth element Er is a good modifier for A356 aluminum alloy, which is able to improve obviously the microstructure of as-cast alloy. The addition of Er refines the primary α-Al phase, decreases the secondary dendrite arm spacing and the dendrite arm diameter, and modifies the eutectic Si in as-cast structure simultaneously. When the amount of Er reaches 0.4% (mass fraction, the same below), the refinement effect is the most significant, secondary dendrite arm spacing decreases from 53.6μm to 17.5μm and the morphology of eutectic Si transforms from thick lath-shaped to short rod-like or round granular. Compared with A356 alloy, the tensile strength and elongation of A356 aluminum alloy with the addition of 0.4%Er increase by 15.1% and 29.8% respectively.

Abstract: Many experimental and theoretical studies indicated that the decrease of the size of the reinforcing particles can lead to substantial improvements in the mechanical performance of the composites. However, the investigations on the addition of the nano particles into conventional metal materials are still rare, especially the nano-TiC p into the Al–Cu alloys. In this study, the Ni coated nano-TiC p reinforced Al–Cu matrix composites were successfully fabricated by a casting route. It was found that the nano-TiC p was in the α-Al grains. The α-Al dendrites became finer and more developed. Moreover, the θ′ precipitates in the Al–Cu matrix were finer and uniformly distributed. The tensile strength and elongation of the composites increased simultaneously. After T6 heat treatment, compared with the unreinforced Al–Cu alloy, the tensile strength and elongation of the 0.8wt.% nano-sized TiC p /Al–Cu composite increased from 485MPa and 6.6% to 573MPa and 12.4%, respectively. [Copyright &y& Elsevier]