Superplastic characteristics in a doubly-extruded ZK60/SiC/17p magnesium-based composite

A fine-grained (∼1.7m) magnesium-based composite, ZK60/SiC/17p, is shown to behave superplastically in a wide range of temperature. The influences of strain rate on the flow stress and elongation in the composite were characterized. It was found that the composite exhibited superplasticity (elongation > 300%) in a wide range of temperature (463 ∼ 773 K). In addition, the material showed a high strain rate sensitivity of 0.5 and an activation energy of 81 kJ/mol at high strain rates (∼0.1 s^-1) and at relatively high temperatures. Based upon these results, it was proposed that the dominant deformation mechanism is grain-boundary sliding accommodated by a grain-boundary diffusion process at high temperatures. Datum at a low temperature of 463 K (=0.5Tm), however, does not fall on the liner function of the Arrhenius plot for the high temperature region. This indicates that the deformation mechanism at low temperatures is provably different form that at high temperatures.