SUPERPLASTICITY OF FINE-GRAINED 7475-AL-ALLOY AND A PROPOSED NEW DEFORMATION MECHANISM

A study has been made to investigate the superplastic deformation mech anisms of 7475 Al alloy in relation to the variation of grain size ran ging between 5.5 mu m and 13 mu m The strain-rate sensitivity (in) was increased with decreasing grain size in the superplastic deformation regime. Microstructural investigation after tension tests revealed tha t the dispersoid free zones were produced mostly at the grain boundari es normal to the tensile direction. A new model for describing the def ormation behavior of the 7475 Al alloy has been proposed based on the assumption that the grain boundary sliding was accommodated by both di ffusional Bow and slip. This new model well predicts many aspects of e xperimental results. (C) 1997 Acta Metallurgica Inc.