GRAIN ELONGATION AND ANISOTROPIC GRAIN-GROWTH DURING SUPERPLASTIC DEFORMATION IN AN AL-MG-MN-CU ALLOY

Evolution of grain morphology in a fine grained Al-Mg-Mn-Cu alloy duri ng uniaxial superplastic deformation is studied quantitatively. Grains undergo elongation, as well as dynamic grain growth along all directi ons, the separation and analysis of which is attempted here. Based on such analysis, the computed true grain growth rate along directions tr ansverse to the tensile axis are found to exceed that parallel to the tensile axis. Possible mechanisms for this new observation are suggest ed. A unique relationship between grain boundary sliding rate and dyna mic grain growth rate is found at different applied strain rates; this indicates that grain boundary sliding and grain boundary migration ra tes are inherently connected through the same mechanism. (C) 1997 Acta Metallurgica Inc.