The effects of extrusion speed and temperature on the extrusion stress and the mechanical properties of the superplastic eutectoid Zn-Al alloy extruded under various conditions were investigated, and then compared with those of the annealed non-superplastic alloy of the same composition. The results obtained are as follows:
(1) Eutectoid Zn-Al alloy which was cast and then furnace cooled after heating at 380°C for 1 hr (named the annealed material) does not show superplasticity. But the alloy, water quenched from 380°C followed by tempering at 180°∼220°C, shows superplasticity, and the maximum value of strain-rate sensitivity exponent m was 0.55. The alloy was named the tempered material.
(2) Extrusion stress decreases with increase in extrusion temperature, and the value of the extrusion stress of the tempered material becomes minimum at eutectoid temperature 275°C. It then increases a little at 300°C.
(3) If the conditions of extrusion are indentical, the extrusion stress of the tempered material is always smaller than that of the annealed material. When extrusion temperature was at 250°C, the extrusion stress of the former was 25% of that of the latter.
(4) The tensile strength and the hardness of the extruded tempered material becomes larger as the extrusion speed increases and the temperature rises, but the reduction in area shows larger value as the extrusion speed increases and the temperature drops. A slight drop of tensile strength is found at eutectoid temperature 275°C.
(5) The tensile strength and the hardness of the extruded tempered material are smaller than those of the extruded annealed material, but the tensile strength and the hardness of the former which was followed by heat treatment (furnace cooled from 380°C) are remarkably improved and become superior to those of the latter.