Microstructural Evolution and Mechanical Response of Equal-Channel Angular Extrusion-Processed Al-40Zn-2Cu Alloy

Microstructural evolution, tensile properties, and impact toughness of an aluminum-zinc-copper (Al-40Zn-2Cu) alloy subjected to repetitive equal-channel angular extrusion (ECAE) up to four passes following either route A or route B(C) were investigated. The experimental results reveal that the ECAE eliminated as-cast dendritic microstructure along with casting defects such as microporosities almost completely. The ECAE-processed samples consisted of mostly elongated microconstituents via route A and equiaxed microconstituents via route BC. The high stresses imposed in ECAE lead to the fragmentation of the copper-rich theta phase into smaller particles with significant fragmentation occurring in the first pass and additional breaking in the subsequent passes in both routes. The ECAE processing simultaneously increased both the strength and ductility of the alloy as compared to the as-cast state, regardless of the processing route and number of passes. The deformation behavior of as-cast Al-40Zn-2Cu alloy has changed from brittle to ductile mode after ECAE due to the microstructural refinement, deformation-induced homogenization, and reduction of porosities. The limited impact toughness of as-cast alloy was significantly improved by multipass ECAE, especially in route A.