THE EFFECTS OF TEMPERATURE AND STRAIN RATE ON EXTENDED DUCTILITY OF ALUMINUM

The torsional ductility of high purity aluminum was measured over a wide range of temperature and strain rate and several trends were observed. At each strain rate the ductility first increases with increasing temperature to a "peak ductility", beyond which it decreases. Dramatic ductilities, of over 90 in some cases, are observed in the vicinity of the peaks. The peak ductility appears to increase with increasing strain rate. Contrary to earlier investigations, the temperature at which the peak ductility is observed increases with increasing strain rate. At temperatures below the peak, as temperature rises, dynamic recovery mitigates internal stresses and may retard crack nucleation to produce improved ductility. Increased strain rate at a given temperature increases the internal stresses and the ductility decreases. At temperatures above the peak, diffusive void formation reduces the ductility. Consequently, increased strain rate raises the amount of torsional strain relative to the increase in cavity growth rate and the ductility increases.