No abstract

The relation between strain and uniform elongation, and the effect of low-temperature annealing, were examined using an Al-Mg alloy (A5052) processed by accumulative roll bonding (ARB). Specimens were deformed by ARB for 1 to 7 cycles at room temperature, and then subjected to isochronal annealing for 30 min at temperatures ranging from 100 to 300 °C. Tensile properties, hardness, and grain boundary structure before and after annealing were investigated. The uniform elongation of ARB-processed specimens decreases with increasing ARB cycles. However, the elongation is improved by low-temperature annealing for specimens processed by ARB of 3 or more cycles. Higher strain in the ARB process results in higher uniform elongation after annealing, even though the specimens have the same value of 0.2% proof stress. This improvement of the uniform elongation by annealing is caused by annihilation of dislocations inside ultra-fine grains, which are developed by ARB of 3 or more cycles.

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.

No abstract