The contributions of grain size, dislocation density and twinning to the strength of a magnesium alloy processed by ECAP

A ZK60 magnesium alloy was processed by equal-channel angular pressing (ECAP) for up to 8 passes at 473 K and the evolution of strength and microstructural parameters were determined using hardness testing and X-ray line profile analysis. The results show the subgrain size and twin boundary density increase between 1 and 2 passes and then decrease, the dislocation density continuously decreases up to 8 passes and the measured microhardness remains reasonably constant between 1 and 8 passes of ECAP. The results are interpreted using a model based on the additive effects of the dislocation density and an average size factor incorporating the effects of both the twin and the subgrain boundaries.