Microstructure and deformation in the spray deposited Zn–22% Al alloy

Microstructure and deformation in Zn–22% Al that was prepared by spray atomization and deposition were investigated. The results show that the as-deposited alloy exhibits a non-uniform microstructure composed of coarse and fine lamellar eutectoid domains, and that elongations to failure in tensile samples having such a microstructure are less than 100%. When the lamellar structure is transformed into a fine equiaxed grain structure that is free of porosity as a result of heat treatment and extrusion, the alloy exhibits the characteristics of superplastic flow including: the attainment of elongations to failure in excess of 1600%, the observation of a sigmoidal relationship between stress and strain rate, and the presence of a threshold stress for superplastic flow that is sensitive to the presence of impurities. Microstructure characterization of the samples after creep deformation reveals a limited dislocation activity that is manifested in the presence of dislocation-particle interaction in some of the grains. A comparison in creep behavior between Zn–22% Al and 7 vol.% SiCp–Zn–22% Al composite that, like the alloy, was prepared by spray atomization and deposition shows the presence of a strengthening effect. This effect is explained in terms of the details of a deformation mechanism for superplastic flow that is based on dislocation accommodated boundary sliding.