The temperature dependence of superplasticity has been investigated in the range including the solidus temperature for a 7475 aluminum alloy. It is found that the superplastic elongation shows the maximum value in the vicinity of the solidus temperature at a comparatively low strain rate. Filaments are observed on the fracture surfaces of the broken specimens tested below the solidus temperature. Further, the thickness of a liquid phase during superplastic deformation is discussed from four aspects f flow stress, fracture surface, thermal analysis and composition analysis. The thickness of the liquid phase is estimated to be 10-60 nm for the superplastically-deformed specimen.
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