Microstructure and superplasticity of Al-Cu alloy melt spun ribbons

Abstract

Microstructural change and superplasticity of Al-Cu alloy melt spun ribbons were examined. Al-10mass%Cu ribbons had small α grains containing fine dispersed θ (Al2Cu) precipitates and the precipitates were effective in suppressing the grain growth during deformation at high temperatures. Al-33mass%Cu ribbons formed fine lamellar structure with small colonies as melt spun and fine equiaxed dual structure composed of α and θ phases was obtained during heating before tensile test. Tensile tests were performed at initial strain rates in the range of 1.7 × 10-4 to 1.7 × 10-1 s-1 and at various temperatures between 300 and 793 K. Superplasticity in both alloys occurred depending on the microstructure, temperature and strain rate. The peak in elongation-strain rate curves of Al-10mass%Cu ribbons appeared around a strain rate of 4 × 10-4 s-1 at 723 K, while the peak for Al-33mass%Cu ribbons was shifted to higher strain rate around 3 × 10-2 s-1 at 773 K. No significant change in equiaxed grains was observed during superplastic deformation of Al-33mass%Cu ribbons and the superplastic flow was mainly provided by the α/θ interfacial sliding accompanied by an accommodation process by diffusion of a large amount of vacancies and solute atoms. In Al-10mass%Cu ribbons, plastic flow was provided not only by grain boundary sliding but also by the motion and multiplication of dislocations in grains.