Superior creep behavior of n-SiCp/Mg–9%Al composites fabricated by ultrasonic-assisted semi-solid hot pressing of powder

Abstract

The n-SiCp/Mg–9%Al composites reinforced with 7.5 wt% SiC nanoparticles were fabricated by semi-solid powder hot pressing technique-assisted with ultrasonic, which show finer grains and a more uniform microstructure compared to Mg–9%Al alloys. The steady-creep rates of the nanocomposite were approximately 12 times lower than those of the Mg–9%Al matrix alloy at 200 °C under an applied stress of 70 MPa due to the strengthening effect of the nano-sized SiCp. The creep resistance of the nanocomposite was investigated at temperatures between 175 and 225 °C under an applied stress in the range of 70–90 MPa. The creep stress exponents were 5.86–7.95, implying that the dominant creep mechanisms in the nanocomposite are dislocation climb and particle strengthening-controlled creep. The activation energies obtained for creep were in the range of 102–146 kJ/mol, which are higher than those for boundary diffusion and are believed to be associated with self-diffusion and the diffusion of Al atoms in the Mg matrix.