Effect of SiC particles and the particulate size on the hot deformation and processing map of AZ91 magnesium matrix composites

Isothermal hot compression at the temperature range of 573-698 K and strain rates of 0.005-1.0 s−1 was used to investigate the flow behavior and processing characteristics of the nano-SiCp/AZ91 composites. Effects of the incorporated particles and their particulate size on the workability of the base alloy were then compared and discussed. Results show that compared with the monolithic AZ91 alloy, the incorporated nano-SiC particles effectively increase the flow stress of the composites by blocking the strain-induced dislocations, while effect of the micro-SiC particles varies due to the competition between pinning effect and particle stimulating nucleation (PSN) mechanism. Three domains of peak energy dissipation efficiency are identified in the processing map and the corresponding microstructures examined by EBSD indicate that continuous dynamic recrystallization (DRX) occurs during the compression. The instability characteristics at low temperature are severe mechanical twinning and micro-cracks, while that at high temperature is intergranular cracking. The incorporation of SiC particles enhances the high temperature (>655 K) workability of AZ91 by increasing the upper limit of the processing strain rate and enables low temperature processing by decreasing the lower limit of the temperature. However, the added particles impose a side effect by enlarging the instability domain of the base alloy to a lower strain rate and even higher temperature.