Nano/ultrafine grained AA2024 alloy processed by accumulative roll bonding: A study of microstructure, deformation texture and mechanical properties

Abstract

In this study, the effect of accumulative roll bonding (ARB) process on the microstructure, deformation texture and mechanical properties of AA2024 strip was investigated. Microstructural observations were done by electron backscattering diffraction (EBSD) technique and scanning electron microscopy (SEM). Also, mechanical properties were performed by uniaxial tensile and microhardness tests. It was observed that accumulative roll bonding is a promising process for production of nano/ultrafine grained (NG/UFG) 2024 aluminum alloy after seventh ARB cycles, reaching grain sizes of smaller than 120 nm. The fraction of high angle grain boundaries and mean misorientation were represented increased by increasing the strain during the ARB process and reached to a saturated value of 64% and 25.37°, respectively. Deformation texture evolution demonstrated that the formation of nano shear bands at the final ARB cycle was facilitated by the formation of Brass {011}〈211〉 and Goss {011}〈100〉 components. By increasing the number of ARB cycles, the yield strength, tensile strength and microhardness of the ARB processed sample improved and reached to 345 MPa, 450 MPa and 141 HV after 7 cycles, respectively, which were 2.65, 2.40 and 2.23 times higher than obtained values for initial materials, i.e. 130 MPa, 188 MPa and 63.5 HV. After the tensile test, debonding can be observed especially in the interface formed in the last cycle. Observations revealed that the failure mode in the accumulatively roll bonded AA2024 strip was a shear ductile rupture with elongated shallow shear dimples.