Effect of strain rate path on cavitation in superplastic aluminium alloy

The effect of a rapid pre-strain on the cavitation behaviour of commercially processed superplastic (SP) aluminium alloy 5083 sheet material deformed in uniaxial tension has been compared with that for deformation under constant strain rate conditions. It was observed for the two test conditions, that there was continuous nucleation of cavities. There were some differences in the distributions of cavity sizes for similar strains between the two testing conditions. However, these were not considered of significance because when the volume fraction of cavities was plotted against SP strain the two sets of data lay on, or close to, the same exponential curve. Metallographic examination showed that cavities were often associated with intermetallic particles. Analysis of the experimental data led to the conclusion that the growth of cavities was controlled primarily by plastic deformation, although diffusion may play a role in the early stages of growth. Overall, the levels of cavitation were lower than those often reported for other SP aluminium alloys. This is attributed to the low levels of iron and silicon impurities, and hence the absence of large constitutive particles considered to promote cavitation, and to the relatively low strains attainable in the alloy.