Microstructure and superplasticity of Al-Cu alloy melt spun ribbons

Microstructural change and superplasticity of Al-Cu alloy melt spun ribbons were examined. Al-10mass%Cu ribbons had small alpha grains containing fine dispersed theta (Al2Cu) precipitates and the precipitates were effective in suppressing the grain growth during deformation at high temperatures. Al-33mass%Cu ribbons formed ne lamellar structure with small colonies as melt spun and fine equiaxed dual structure composed of alpha and theta phases was obtained during heating before tensile test. Tensile tests were performed at initial strain rates in the range of 1.7 x 10(-4) to 1.7 x 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 x 10(-4) s(-1) at 723 K, while the peak for Al-33mass%Cu ribbons was shifted to higher strain rate around 3 x 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 alpha/theta 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.