The mechanical properties of the superplastic AI- 33 Pct Cu eutectic alloy

Abstract

Experiments were conducted to determine the mechanical properties of the superplastic Al-33 Pct Cu eutectic alloy at temperatures from 673 to 723 K. Specimens were tested in a well-annealed condition and there was no evidence for grain growth even at the lowest experimental strain rate of 6.7 × 1(10^-7 s^-1. It is shown that the stress-strain curves rapidly attain a steady-state value at strain rates below '10^-4 s^-1, and there is a sigmoidal relationship between stress and strain rate which may be obtained using several different testing procedures. The maximum elongation to failure recorded in these experiments was 1475 Pct at an initial strain rate of 1.3 × 10^-5 s^-1. The true activation energy for plastic flow is 175 ±11 kJ mol^-1 in the superplastic region II, but it increases to 299 ± 18 kJ mol^-1 at low strain rates in region I. The exponent of the inverse grain size is 2.1 ±0.3 in region II. These results show that, when the grains size is stable, there is a genuine region I in the Al-33 Pct Cu alloy at initial strain rates below ~10^-5 s^-1.