The Effect of Superplastic Deformation on Subsequent Service Properties of Fine Grained 7475 Al

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Abstract
Intergranular cavitation may be a limiting factor in the otherwise highly promising commercial exploitation of the recently developed superplastic forming process for the high strength aluminum alloy, 7475. A preliminary investigation has been carried out to quantify the effects of superplastic deformation on the major ambient temperature service properties. It is shown that the properties most degraded by the development of cavitation after large superplastic strains are those that depend on the local strain at tensile fracture. This affects, mainly, ductility and fatigue life. However, the effects are not generally significant below effective superplastic strains of about 0.8 to 0.9 (120–150 percent elongation) with the optimum forming conditions (T=516°C, ε˙=2×10−4 s−1). Furthermore, since the fine grain processing has an initial beneficial effect on the ductility-related properties, compared to conventionally processed sheet, most superplastically formed components would suffer very litle, if any, design penalties.

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