Microstructure and Tensile Properties of n-SiCp/Mg-9%Al Composites Prepared by Ultrasonic Assisted Hot Pressing of Powder

In this paper, the Mg-9%Al alloy reinforced by 5 wt.% SiC nanoparticles was fabricated by hot pressing of powder with ultrasonic vibration under a semi-solid state. The influence of hot-pressing temperature on the microstructure and mechanical properties of the n-SiCp/Mg-9%Al composite was investigated. The results indicated that the density of the composite was increased significantly and the agglomeration of SiC nanoparticles was evidently reduced with the increase in the hot-pressing temperature from 450 to 510 °C. Additionally, the elevated hot-pressing temperature resulted in remarkable grain refinement. However, as the hot-pressing temperature increased to 530 °C, the density decreased and the average grain size increased, which caused a decline in the mechanical properties. The study of the interface between the n-SiCp and the matrix in the nanocomposite suggested that n-SiCp bonded well with the matrix without interfacial activity. The ultimate tensile strength, yield strength and elongation to fracture of the nanocomposites were simultaneously enhanced compared with that of the Mg-9%Al alloy. This improvement could be attributed to obvious grain refinement and the Orowan strengthening mechanism.