Abstract
The effects of strain-rate and drawing temperature on the drawing force and the mechanical properties of a superplastic Zn-Al alloy drawn under various conditions were investigated, compared with those of the annealed non-superplastic alloy of the same composition. The results obtained are as follows:
(1) The drawing force required for the superplastic Zn-Al alloy which was water quenched from 380°C after being heated for 1 hr (named the water quenched material) and the non-superplastic alloy of the same composition which was air cooled from 380°C after being heated for 1 hr (named the annealed material) decrease linearly with the rise in drawing temperature, and those values are minimum at eutectoid point 275°C. The drawing force increases with the strain-rate.
(2) Under the same condition, the drawing force for the water quenched material is always smaller than that for the annealed material.
(3) The maximum value of the drawing ratio for the water quenched material is larger than that for the annealed material. At too high a strain-rate, the blank prepared from the water quenched material breaks for lack of ductility (or of strength at temperatures higher than 200°C). At too low a strain-rate, it breaks from the lack of strength.
(4) The upper and lower limits of strain-rate for deep drawability become larger as the drawing temperature rises. They show the largest value at 200 and 250°C respectively and then decrease as the temperature rises. The range of strain-rate for deep drawability is most extensive at 150∼200°C and most narrow in the neighborhood of room temperature and 250°C.
(5) The compressive strength and hardness of the products drawn from the water quenched material increase with the rise in drawing temperature. The homogeneity of the products made of the water quenched material is higher than that of the products made of the annealed material.
(6) Strength of the products drawn from the water quenched material can be improved by annealing (air cooling from 380°C after being heated for 1 hr).
