Abstract
Foil metallurgical processing has been performed to investigate the possibility of a grain size control method. In the present work, a stack of 7475 aluminium alloy foils, each 15 or 40 μm in thickness, was press bonded at a temperature of 573 K under heavy thickness reduction, followed by annealing at 773 K for 1.2 ks. The laminate grain size in the thickness direction was clearly decreased with increasing thickness reduction ratio of up to 15–10: 1 and was controlled to the attained foil thickness. In the laminate with an attained foil thickness of 10 or 18 μm, rectangular grains were aligned along the bonding interfaces to form a brickwork pattern. Grain size control and grain refinement could be achieved during foil metallurgical processing by the grain growth inhibition function of the oxide particles at the interfaces, which were ∼ 50–100 nm in thickness and 100–200 nm in length. The fine grained laminates showed an increase in proof stress with decrease in grain size at room temperature and an increase in the optimum strain rate for superplastic flow.
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