Ultrafine-grained Al–Zn–Mg–Cu alloy processed via cross accumulative extrusion bonding and subsequent aging: Microstructure and mechanical properties

Abstract

Ultrafine-grained (UFG) materials produced by severe plastic deformation methods generally exhibit a higher strength, but a lower uniform ductility. In this paper, an UFG Al–Zn–Mg–Cu alloy was fabricated via cross accumulative extrusion bonding (CAEB) and subsequent aging to achieve high strength and moderate uniform elongation. The influences of CAEB and subsequent aging on microstructure and tensile properties of the alloy were investigated. After CAEB, TEM characterization revealed that the microstructure exhibited typically ED-elongated ultrafine grains (740 ± 20 nm). Post-CAEB aging led to the formation of many nano-sized particles with different morphologies. These particles precipitated in the grain interiors and at grain boundaries, among which the main strengthening phase was η′ phase. EBSD characterization showed that the fraction of high angle grain boundaries increased to 61.0% for the post-CAEB aged alloy. At the same time, microtexture was significantly weakened as the CAEB process was applied to the alloy. The main texture components were mainly composed of Cu and S as well as a small amount of Brass and Cube. In addition, the tensile test at room temperature demonstrated that the post-CAEB aged sample possessed a high ultimate tensile strength of 562 MPa while simultaneously maintaining a moderate uniform elongation of 21.5%.