Thermal stability of microstructure, mechanical properties, formability parameters and crystallographic texture in an Al-7075 alloy processed by accumulative roll bonding

Abstract

Accumulative roll bonding (ARB) is a severe plastic deformation (SPD) technique that has been extensively used in a wide range of metals to improve their mechanical properties. In particular, ARB processed materials display an increase in both yield and ultimate tensile strength, since the SPD processing induces a remarkable grain refinement. In precipitation-hardened alloys, such as aluminum 7075, this leads to a synergistic effect which further enhances strength. Although the reported results are promising for high-strength applications, thermal stability of the microstructure after processing remains an open question. In this paper, we present an investigation of the thermal stability of the texture, microstructure, and mechanical properties of Al-7075 samples processed by ARB to an equivalent Von Mises strain of 240%. After processing, yield and tensile strength displayed improvements of 30% and 20% respectively over the T6 condition. Crystallographic texture was found to depart from the rotated cube component to Dillamore/Taylor and Goss components. Several annealing heat treatments ranging from 373 to 673 K (100–400 °C) were carried out and it was found that the improved mechanical properties are stable up to 423 K (150 °C). The texture was found to slowly revert to a rotated cube with increasing temperature. The results are discussed in terms of the combination of strength and formability as calculated by the Lankford parameter using the visco-plastic self-consistent code (VPSC).