Abstract
A study of cavitation during superplastic tensile straining of an Al-Zn-Mg alloy has been made using density measurements and metallographic examinations. The main results obtained are as follows:
(1) Both void nucleation and growth processes were associated with grain boundary sliding, and nucleation probably occured at boundaries or triple junctions involving second phase particles such as ZrAl3.
(2) The increase in void volume with the elongation was characterized by three different stages. The exponent of the void volume ratio with deformation time was 1.14–1.20 in stage I and 0.48–0.54 in stage II, respectively.
(3) The final fracture in this alloy occured by void interlinkage across the specimen, which was accelerated by a process of internal necking between the cavities. The maximum fracture elongation was achieved at the highest temperature, 520°C, because the strain-rate sensitivity m and the cavity spacing increased with increasing temperature and, therefore, the rate of internal necking was reduced.
