Effect of Grain Size on the Superplastic Behavior of a 7475 Aluminum Alloy

Specimens of a super plastic 7475 aluminum alloy with grain sizes ranging between 9 and 35 |xm were tensile tested at a strain rate of 1 × 10 ^{- 4}/s at 457 and 517 °C. At 517 °C, the ductility was found to decrease with an increase in grain size. At 457 °C, on the other hand, the ductility was found to increase initially and then decrease for grain sizes larger than 14 μm. The latter decrease in ductility is attributed to the lowered ability for grain- boundary sliding with decreasing grain- boundary area. In the as- received material (grain size of 9 μm), the observed low ductility is attributed to an inhomogeneous microstructure.