Grain refining of Zn–22 wt.% Al superplastic alloy

Abstract

Abstract The superplastic deformation behaviour of two alloys of Zn–22 wt.% Al was studied in detail under identical conditions of grain size, temperature and initial strain rates. The second alloy has the same composition as the first alloy, but with the addition of 0.2 wt.% Al–5Ti–1B as a grain refiner. The two alloys were subjected to a special heat treatment process (solid solution heat treating, quenching and annealing) to obtain fine equi-axed grains. Thermomechanical treatment was carried out on the equi-axed structure that was obtained to produce extra-fine grains. Tensile tests at superplastic temperature revealed that extremely large superplasticity of this alloy can be obtained mainly with extra fine grains which has an affect, on the other hand, on the initial strain rate e , the grain size being decreased as the initial strain rate is increased. A greater superplastic elongation value can be obtained with higher strain rate and smaller grain size. Study of fracture surfaces of four specimens having maximum superplastic elongation revealed a granular fracture for this alloy.