Improvement of Uniform Elongation by Low Temperature Annealing in Al-2.5%Mg Alloy Processed by Accumulative Roll Bonding

Abstract

Al-2.5%Mg alloy (A5052) sheets were processed by accumulative roll bonding (ARB) for 1 to 7 cycles (equivalent strains from 0.8 to 5.6) at room temperature. The sheets processed by ARB for 7 cycles were then annealed isochronally for 30 min at temperatures in the range from 100°C to 400°C. Interestingly, it was found that the specimen annealed at 200°C followed by 7 cycles of ARB had the same level of yield stress (about 320 MPa) but a larger uniform elongation than the specimen processed by 3 cycles of ARB. The improvement in uniform elongation by low-temperature annealing is discussed in terms of the mechanism that the evolution of dislocation substructures inside ultra-fine grains causes plastic instability at a very early stage of the tensile test. Hardening by annealing was also observed in the specimen annealed at 100°C followed by 7 cycles of ARB.