Effect of single roll drive cross rolling on the microstructure, crystallographic texture, and mechanical behavior of Al–Zn–Mg–Cu alloy

Abstract

In this work, the effect of single roll drive cross rolling on the microstructure, crystallographic texture, hardness, tensile properties, and fracture behavior of AA7075 aluminum alloy was investigated. It was found that with increasing the thickness reduction, the grain size reduced and the average width of grain for the 40% deformed sample decreased to 3.7 ± 0.4 µm. Due to the nature of the cross-rolling process, several X-type shear bands were observed after 40% deformation. The recrystallization texture is notably intensified to its highest value of 4.4 × R, after only 20% cold deformation due to the occurrence of continuous dynamic recrystallization (CDRX). The intensity of recrystallization texture sharply dropped to its lowest value of 2.7 × R. This was due to the rotation of Goss-orientated new grains in the 20% deformed sample toward copper orientation during 40% rolling. With increasing the thickness reduction, the overall texture intensity significantly reduced owing to the nature of the cross-rolling process in which the rolling direction rotates 90° after each 10% strain. Two texture transitions were observed along τ fiber: rolling (copper) texture to recrystallization (Goss) texture after 20% thickness reduction and recrystallization to the rolling texture after 40% deformation. The hardness and strength increased by increasing the thickness reduction, while the ductility decreased. After a 40% thickness reduction, yield strength significantly increased from 138.3 ± 4.4 MPa (for initial sample) to the highest value of 580.5 ± 11.5 MPa, demonstrating 320% increment, in the 0° direction. This increment for 45° and 90° direction was 265% and 337%, respectively. By 40% rolling, the value of in-plane anisotropy (IPA) remarkably decreased to its lowest value of 3.4% due to texture weakening. With increasing the rolling reduction to 20%, the severity of Portevin–Le Chatelier (PLC) increased in the flow curves due to the occurrence of CDRX and also strengthening of the rotated cube {001} < 110 > and E {111} < 110 > components. With increasing the rolling reduction, the size of cleavage facets and the severity of delamination increased, and the number and depth of dimples decreased.