Microstructural changes in a Zn–Al eutectoid alloy modified with 2 wt.% Cu after superplastic deformation

Abstract

This work focuses on the characterization of microstructural changes in Zn–Al eutectoid alloy modified with 2wt.% Cu when it is superplastically deformed varying the strain rate and temperature. Microstructural characterization was carried out by SEM and AFM techniques and it was shown that increasing the superplastic strain leads to a change of an initial fine equiaxed grain microstructure (0.85μm), formed by a Zn rich (η) and Al rich (α) phases, toward a microstructure consisting on flow bands. These flow bands formed mainly by elongated grains of the η phase, tend to be aligned along the tensile direction. The flow bands formation is promoted by an increase in temperature or a decrease in strain rate during deformation process. The morphologies and dimensions of flow bands were found to strongly depend on the testing conditions. The largest and thinnest flow bands were observed at 10−3s−1 and 513K. Experimental results evidenced that the origin of these microstructural changes, where deformation capability and growth of Zn-rich phase is significant, was not associated with a micro-superplastic phenomenon. Rather, it is associated to a non-homogeneous plastic flow and possible changes in the controlling deformation mechanism of this alloy, where recrystallization assisted by a redistribution of elements by diffusion is significant.