EFFECT OF FE ON DUCTILITY AND CAVITATION IN THE SUPERPLASTIC ZN-22 PCT AL EUTECTOID

In this investigation, the ductility and cavitation behavior of five g rades of the superplastic Zn-22 pet Al were studied under identical co nditions of grain size, temperature, and initial strain rate. These fi ve grades were prepared from high-purity Al and Zn using the same proc edure but different Fe impurity levels; grades A, B, C, D, and E conta in 1, 40, 120, 400, and 1460 ppm of Fe, respectively. A comparison bet ween the present results and those reported earlier for the creep beha vior of the five grades of Zn 22 pet Al demonstrates that while the pr esence of Fe has no noticeable effect on the steady-state creep rates during deformation in the superplastic region (where maximum ductility occurs), it has a pronounced effect;on the ductility and fracture beh avior of the alloy. The experimental data show that there is a signifi cant drop in the average elongation to fracture when Fe concentration exceeds 125 ppm, and that the ductility of grade E is approximately 50 pet of grade A for initial strain rates less than 10(-2) s(-1). In ad dition, the data reveal two important findings regarding cavitation be havior. First, neither the initial grain size nor the occurrence of gr ain growth has an effect on cavitation that is as significant as that arising from the presence of excessive impurities. Second, the presenc e of other impurities in addition to Fe in Zn-22 pet Al has the effect of enhancing cavitation. The effect of Fe, alone or in the presence o f other impurities, on ductility and cavitation in Zn 22 pet Al is exa mined in terms of phenomena associated with impurity segregation at bo undaries.