m-δ Relationship and Structural Evolution during a Constant Strain-Rate Superplastic Deformation of an Aluminum Alloy

Abstract

ABSTRACTAt 515° C with a constant strain-rate of 6.7× 10−3 min−1,tensile specimen of LC4 aluminum alloy with an initial average grain size of 8.7μm exhibited good superplasticity. A fracture elongation of 4649% was obtained. Under such deformation conditions, the m-δrelationship belongs to the mL=mmax type , with a maximum m value of 0.78 at 94% strain. The m-δ relationship can be expressed as δI(%)= (CI ×0.0067(mI−0.5) −1) × 100. During superplastic deformation, three kinds of structural evolution take place, namely the formation of precipitate-free zones adjacent to grain boundaries due to diffusional creep, grain coarsening and cavity generation. The m-δ relationship of superplasticity of the alloy mentioned above can be explained on the basis of the structural evolution during superplastic deformation.