Structural superplasticity of an Al alloy in low strain rate regime-An internal variable approach

Most of the conventional approaches for structural superplasticity have utilized the external variables such as total stress and strain. The effect of grain size and test temperature has not, however, been clarified quantitatively yet from these approaches. A quantitative analysis for structural superplasticity has recently been progressed considerably with the use of the internal variable concept. Nevertheless the precise role of grain size and test temperature on flow characteristics has not been elucidated especially in low strain rate region. Several fundamental characteristics, such as the validity of threshold stresses and the role of grain size, are yet to be resolved or still in controversy in the superplasticity community. In this study, a series of load relaxation and tensile tests has been conducted in the above regard to obtain the flow curves, which were consequently analyzed based on the internal variable theory for structural superplasticity, focusing especially on the low strain rate region.