Asymmetric cold rolling of AA7075 alloy: The evolution of microstructure, crystallographic texture, and mechanical properties

Abstract

In the present work, for the first time, the effect of asymmetric rolling at room temperature on the microstructural evolution, texture, hardness, tensile properties, and fracture surface of AA7075 alloy was investigated. It was found that the width of grains significantly decreased to 2.6 μm by 60 % asymmetric rolling. Also, shear bands in the RD-ND (rolling direction – normal direction) plane of AA7075 after 40 % and 60 % asymmetric rolling were evident. In addition, the size of iron-rich intermetallic particles was reduced with increasing thickness reduction. Microstructure and texture revealed that new grains through continuous dynamic recrystallization (CDRX) are created after 40 % and 60 % strain. On the one hand, after applying only 10 % thickness reduction, average hardness demonstrated 75 % enhancement. On the other hand, maximum yield (611 MPa) and ultimate tensile (644 MPa) strengths achieved in the 60 % deformed sample, demonstrating 287 % and 73 % improvement compared to the initial sample. These results were due to strain hardening, dynamic/static precipitation, and Fe-rich particle fragmentation. The Portevin-Le Chatelier (PLC) effect is reduced with increasing the strain. Interestingly, the 40 % deformed sample revealed the serrated flow. For this reason, the 40 % rolled sample has a lower total elongation (4.4 %) than the 60 % deformed sample (11.1 %). The tensile strength of the 40 % deformed sample (575 MPa) was lower than the 10 % and 20 % rolled samples (581 and 594 MPa, respectively). This result was owing to the occurrence of softening mechanisms, strengthening the Goss {110}⟨001⟩ component, and weakening the Copper {112}⟨111⟩ orientation after 40 % asymmetric rolling. By increasing the thickness reduction up to 40 %, the number of dimples decreased. However, the fracture surface of the 60 % deformed sample showed a noticeable amount of small dimples.