DEFORMATION CHARACTERISTICS OF AN AL-6CU-O.4ZR SUPERPLASTIC ALLOY

The results of a mechanical property and TEM microstructural investigation of a superplastic Al-Cu-Zr alloy are reported. The conventional 3 stage ln σvs ln ∈ curve is observed, but a high value of m is retained to low strain-rates and suggests that any operative creep yield stress is low. Marked mechanical property changes occur in the initial stages of deformation at the same time as dynamic recrystallization removes the initially directional microstructure of highly elongated grains. Following deformation at the higher strain-rates, Regions II and III, individual dislocations, dislocation networks, and low angle boundaries are observed. After deformation in Region I little evidence of any dislocation activity is seen. It is shown that two distinct recrystallization behaviors occur. In samples statically annealed for long periods recrystallization takes place in a discontinuous manner, high angle boundaries sweeping out from the ρ-particles, which act as nuclei. In the case of superplastically deformed samples the dynamic recrystallization is continuous in nature, and not related to the ρ-particles present. The current theories explaining the beneficial effects of ternary additions to Al-Zr alloys are examined in the light of the above observations. © 1979 The Metallurgical of Society of AIME.