MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ULTRA-FINE GRAINED AZ31 ALLOY PROCESSED BY ECAP

Abstract

Commercial magnesium alloy AZ31 was processed by equal channel angular pressing preceded by hot extrusion (EX-ECAP). Microstructure evolution with strain due to ECAP was investigated by light and transmission electron microscopy. ECAP processing resulted in continuous grain fragmentation, significant grain refinement and the formation of dislocations. Dislocation structure changes in individual specimens after different number of ECAP passes were investigated by positron annihilation spectroscopy (PAS). Substantial increase of dislocation density occurred during the first two passes of ECAP and was followed by the decline manifesting the dynamic recovery at higher strains. The microstructure and defect structure evolution correlates well with mechanical properties as determined by a detail inspection of microhardness variations in individual ECAPed specimens.