The magnesium alloy AZ31B has a great potential for lightweight applications that do not require high strength. The superplastic forming method is already being used to form this alloy into complex lightweight components. However, in order to provide accurate predictions of the superplastic process of AZ31B, suitable constitutive models should be established. In this paper, the particle swarm optimization method is used to identify the parameters of a suitable constitutive model. High temperature bulge experiments are used to validate the model. Results indicate that the proposed power law model gives more accurate predictions for the lower strain rates.

Accurate constitutive material models are essential for the realistic simulation of metal forming processes. However, for superplastic forming, mostly the material models found in the literature are based on fitting of the simple power law equation. In this study, an AZ31B constitutive model that takes into account microstructural evolution is introduced. This model takes into account grain growth and cavity formation in addition to strain and strain rate hardening. The model parameters were calibrated using the results of high temperature bulge forming tests and microstructural analysis. The Taguchi optimization method was used in the fitting process. In order to verify the model, simulations of the superplastic forming of two different geometries were carried out, and the results were compared with those obtained experimentally. Results show that the proposed model can accurately predict the formed geometry and thickness distribution.