The deformation kinetics of a superplastic zinc-aluminum alloy.

Abstract

The deformation behavior of a commercial near eutectoid zinc-aluminum alloy was studied by subjecting standard tensile specimens to stress relaxation experiments at constant temperatures between 258 0K to 344 0K. To satisfy the constant strain condition of such experiments, the testing machine was controlled by a computer; for comparative purposes, other tests were conducted using the normal stress relaxation procedure. The results of the experiments were analysed using the theory of deformation kinetics. It was concluded that, for the temperature range covered in this investigation, the deformation mechanisms operate sequentially. The activation volumes associated with forward activation over the first barrier were measured to be 13 +/- 1 b3; for the forward activation over the second barrier, the activation volumes were found to be 38 +/- 14 b3, while those characteristic to the backward flow over the first barrier varied from 27 to 252 b3. It was not possible to obtain accurate measurements of the activation energies; consequently, no conclusion could be drawn as to the nature of the deformation mechanisms. The stress exponent, defined as ∂lntau/∂lntau, was also measured; the values found varied from 2.1 to 9.3.