The influence of copper additions on the superplastic forming behaviour of the ZnAl eutectoid

Abstract

Measurements of the flow stress ( σ f ) and strain-rate sensitivity ( m) over a wide range of strain rates (ε) and at temperatures between 20°C and 300°C have been made on a range of SP alloys, basically the ZnAl eutectoid, (78 Zn-22 Al) but with additions of copper up to 1·0%, see Table 1. These additions do not significantly affect σ f or m above about 150°C. Again, the peak in the m vs. ε curve is not displaced by these copper additions above about 150°C. The creep rate at room temperature decreases with increasing copper content and varies by a factor of about 140 between 0 and 1·0% copper. An empirical vacuum-forming test shows that copper at these concentrations has no effect on the vacuum-forming time at 250–260°C.