Abstract
Fully annealed Al–Mg alloy (5083) bulk sheets were highly strained up to a true strain of 4.0 at 473 K by the novel Accumulative Roll-Bonding (ARB) process, and superplastic behavior of the ARBed sheets was investigated at elevated temperatures. Just before tensile tests, usual recrystallization structure whose mean grain size was 10 μm formed at 573 and 673 K, while the ultra-fine grains with a mean grain size of 280 nm formed homogeneously at 473 K. The electron diffraction study in TEM showed that the ultra-fine grains are polycrystals with large misorientations to each other. The ARBed sheets exhibited conventional superplasticity above 573 K, where the maximum elongation was 430% with a m-value (strain rate sensitivity) of 0.43 at 673 K at a strain rate of 1.7×10−3 s−1. Further, the ARBed sheets showed large elongation up to 220% and large m-value over 0.3 even at 473 K, which is nearly half of the melting point of this alloy, at 10−4 s−1 to 10−3 s−1. This large elongation at 473 K was concluded as low-temperature superplasticity caused by ultra-grain refining. The ARBed material kept ultra-fine grain size less than 1 μm even after low-temperature superplasticity at 473 K, so that the specimens largely deformed at 473 K still exhibited larger hardness than that of the fully recrystallized material.
