Comparison of superplastic behavior in two 5083 aluminum alloys

Superplastic elongation is generally controlled by both strain-rate sensitivity and particles causing cavitation. The superplastic tensile behavior of 5083 Al (nominally Al–4.6% Mg) alloys from two different sources has been examined. It is found that for nearly the same grain size, one of the alloys (alloy A) has a slightly lower strain-rate sensitivity m. This alloy also contains a significantly larger number of hard particles and inclusions. Because this alloy exhibits somewhat lower flow stress during constant strain-rate tests, a reduced tendency for cavity initiation was expected. However, the larger density of particles tends to increase cavitation by providing more nucleation sites. Then the lower m value leads to more rapid cavity growth and interlinkage. Thus, while the presence of fine grain size and high-angle grain boundaries are important for superplastic flow, this research shows that in similarly processed alloys small changes in m values and variations in alloy chemistry that generate cavity-causing particles can have a medium to large effect on superplastic elongation.