抄録
Superplasticity in Zn–Al eutectoid alloy has been studied for different processing histories. The processing treatments used in preparing the initial material are (1) mechanical working at room temperature by swaging of the cast material, (2) quenching after solution treatment at 375°C, (3) annealing at 250°C after treatment (2), and (4) furnace cooling after solution treatment at 375°C. Superplastic behavior at 250°C is observed in specimens with treatments (1) to (3). In the swaged specimens, the strain rate sensitivity index m is observed to increase with a greater amount of reduction in area. The behavior of a specimen swaged by 68% reduction in area is identical to that of quenched material. These observations indicate that a fine equiaxed structure, irrespective of how this structure is brought about by different treatments, leads to a superplastic behavior. Partial metastability of the structure is not essential to observe superplasticity. The material is also found to be superplastic above the eutectoid temperature, the time of holding at the test temperature before the start of the test being an important factor. Only short holding times seem to favor superplastic behavior.
