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

摘要

The n-SiCp/Mg-9%Al composites reinforced with 7.5wt% 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 degrees C under an applied stress of 70MPa due to the strengthening effect of the nano-sized SiCp. The creep resistance of the nanocomposite was investigated at temperatures between 175 and 225 degrees C under an applied stress in the range of 70-90MPa. 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 102-146kJ/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.