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For a series of matrix aluminum alloys, an estimation of the thickness of the grain-boundary liquid phase under the optimum conditions of the manifestation of high-temperature superplasticity has been performed. It has been established that the contribution of grain-boundary sliding to the total deformation under these conditions is determining. It has been shown that the greater values of the thickness of the grain-boundary liquid phase correspond to greater values of the parameter m of the strain-rate sensitivity of the flow stress. The obtained dependences of the thickness of the grain-boundary liquid phase on m indicate that with increasing amount of the liquid phase the grain-boundary sliding progressively acquires features of viscous flow.

The morphology of fiber structures has been studied and the kinetics of their formation and growth at high homological temperatures upon superplastic deformation of the AMg6 and 1420 aluminum-based alloys containing viscous liquid-phase inclusions at the intercrystalline boundaries has been proposed. It has been found that, according to their morphology, the fiber formations can be divided into two types, namely, thin smooth cylindrical fibers and fibers whose specific feature is the presence of one or several droplike formations on their surface. The surface of fibers and grain edges to which the fibers are connected is strongly oxidized; the atomic concentration of magnesium in various regions of fibers and grains is different and is higher than that in the specimen as a whole. It was shown that the fibers were formed upon pore and crack opening as a result of viscous flow of solid-liquid material which is present at the intercrystalline boundaries.