Temperature effect on the superplasticity of the 7475 Al alloy - An internal variable approach

Abstract

The recently proposed internal variable theory of structural superplasticity (SSP) has been applied to the deformation behavior of a fine-grained 7475 Al alloy at temperatures ranging from 430 to 516 degrees C. For this purpose, a series of load relaxation and tensile tests have been conducted at these temperatures. Flow curves obtained from load relaxation tests showed a noticeable concave region in the intermediate strain rate range suggesting the possible onset of grain boundary sliding (GBS) under the superplastic condition. Flow curves obtained at temperatures from 450 to 516 degrees C showed contributions from the grain boundary sliding (GBS) and the accommodating grain matrix deformation (GMD). The activation energies for GMD and GBS were obtained as 116.0 kJ/mol and 40.4 kJ/mol, respectively. A precipitate free zone (PFZ) was observed developing during the accommodation of GBS, and the ranges of temperature and strain rate within which PFZs appeared to form agree well with those of the concave regions in the flow curves.