Microstructural changes of the as-quenched Zn-22 mass% Al-2 mass% Cu alloy during cold rolling

A study of the microstructural changes of a Zn-22 mass%Al-2 mass%Cu alloy was conducted during rolling at room temperature. Cold rolling was pursued on the as-quenched and room temperature aged samples. A reduction in thickness of about 97.6% and a total elongation of 3510% were obtained in the former sample while a sudden crack was present in the later sample. The X-ray diffraction and TEM results showed that nanometric equiaxial grains of the α and η phases in a matrix of the β phase were present during the rolling process of the as-quenched sample. Aged sample showed the presence of micrometric equiaxial grains of the α and β phases. The formation of nanometric grains of the α and η phases seems to be occurred by a strain-induced phase transformation. These nanometric grains seem to be the responsible for the superplasticity observed at room temperature in this kind of alloys.