AI-Zn-Mg合金の超塑性変形におけるボイドの形成

抄録

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.