Optimum parameters and rate-controlling mechanisms for hot working of extruded Mg-3Sn-1Ca alloy

Abstract

The hot working behavior of extruded Mg–3Sn–1Ca alloy has been characterized by compression testing in the temperature range of 300–550 °C and strain rate range of 0.0003–10 s−1 with a view to evaluate the optimum processing parameters as well as the rate-controlling mechanisms. Processing maps, developed on the basis of the temperature and strain rate dependence of flow stress, exhibited two domains in which dynamic recrystallization occurs. Both these are in the temperature range 325–500 °C, with one in the lower strain rate range (0.0003–0.003 s−1) and the other in the higher strain rate range (1–10 s−1), the optimum temperature being 400 °C. Kinetic analysis in the above two domains yielded apparent activation energy values of 196 and 168 kJ/mole, respectively, which are higher than that for self-diffusion in pure magnesium suggesting that the large volume fraction of CaMgSn intermetallic particles in the matrix causes significant back stress. In the change-over strain rate range (0.003–0.3 s−1), unusual grain size changes have occurred which may render microstructural control difficult.