EFFECT OF GRAIN-SIZE ON THE SUPERPLASTIC BEHAVIOR OF A 7475-ALUMINUM-ALLOY

Specimens of a superplastic 7475 aluminum alloy with grain sizes rangi ng between 9 and 35 mu m were tensile tested at a strain rate of 1 x 1 0(-4)/s at 457 and 517 degrees C. At 517 degrees C, the ductility was found to decrease with an increase in grain size. At 457 degrees C, on the other hand, the ductility was found to increase initially and the n decrease for grain sizes larger than 14 mu m. The latter decrease in ductility is attributed to the lowered ability for grain-boundary sli ding with decreasing grain-boundary area. In the as-received material (grain size of 9 mu m), the observed low ductility is attributed to an inhomogeneous microstructure.