Effect of warm accumulative roll bonding on the evolution of microstructure, texture and creep properties in the 7075 aluminium alloy

The commercial 7075 Al alloy was severely deformed at 300°C by a 3:1 thickness reduction per pass accumulative roll bonding (ARB) process up to 5 passes. Examinations by transmission electron microscopy and electron backscatter diffraction revealed that the alloy microstructure was finer and more misoriented with increasing the number of ARB passes. The 5-passes sample exhibited a mean cell/(sub)grain diameter of 355nm and a mean boundary misorientation angle of 33°. The texture of the processed alloy was characterized by a Β-fibre, whose intensity increased with increasing the number of ARB passes. This intensification process is enhanced by the cutting and stacking steps promoting the formation of the Dillamore orientation. Uniaxial tensile tests conducted at 300°C and at an initial strain rate of 10 ^-2s ^-1 revealed that the processed alloy exhibited superplasticity, which was very sensitive to the stability of its microstructure at the testing temperature. An elongation to failure of 202% was registered for the 4-passes sample. Therefore, the present ARB process would allow short forming times at much lower temperatures than conventional.