Production of superplastic zinc–aluminium alloys

The production of superplastic properties in Zn–Al alloys involves control of casting, homogenization, quenching, transformation, and thermomechanical treatment to produce the required fine-grained equiaxed microstructure with a particular combination of superplastic and conventional properties. The optimum production route is determined mainly by the proportions of zinc and alumimum and the presence of other alloying elements, as they affect the shape and position of the TTT curve, the compositions of the phases, and their relative abundance. Results are presented which indicate the effect of processing variables and composition on the combination of superplastic with room-temperature tensile, and other conventional mechanical properties. While the majority of work concerns the production of sheet, the process routes for extruded rod and preforms will also be discussed. The impact of these on the use of superplastic-forming techniques for component manufacture will be indicated.