Superplastic behaviour during compression of as-cast Al–Cu eutectic alloy

Abstract

This work investigates the superplastic behaviour of as-cast Al-Cu eutectic alloy. Compression tests were carried out at different strain rates and it is shown by measurements of the strain-rate-sensitivity index that the material becomes superplastic after about 25% engineering strain. Metallographic examinations of the deformed samples show that this superplasticity is achieved by the transformation of the initial lamellar structure to an equiaxed one. The same behaviour is observed during tensile tests with, however, a high degree of heterogeneity of the deformation. Similarly, during the compression tests, the specimen does not deform homogeneously, but through the development of shear bands with an equiaxed structure, which gradually extend over the whole volume of the sample. By deforming the specimens at different strain rates, it is shown that the homogeneity of deformation increases with increasing strain rate. The effect of a predeformation at high velocity under non-superplastic conditions on the resulting structure and superplastic behaviour at lower velocity was then investigated.