Inhomogeneous evolution of microstructure in AZ91 Mg-alloy during high temperature equal-channel angular pressing

The evolution of the microstructure in AZ91 Mg-alloy processed by equal-channel angular pressing (ECAP) at 543 K was investigated. The initial material was a supersaturated solid solution, therefore the severe plastic deformation and the precipitation occurred simultaneously. The precipitate morphology and the defect structure in the matrix were studied after 2 and 8 ECAP passes. As a result of ECAP, continuous precipitates formed instead of discontinuous ones usually observed at 543 K. After 2 passes of ECAP, both the size of precipitates and the solute atom concentration in the matrix showed a high level of inhomogeneity but after 8 passes the microstructure became more homogeneous. The precipitates coarsened with increasing the number of ECAP passes.