Large strain behaviour of a superplastic copper alloy—I. Deformation

Effects of an Electric Current on the Superplastic Deformation Behavior of 3Y-TZP in an Oxygen-Lean Atmosphere

The aim of this paper is to investigate the mechanism of an electric current-assisted superplastic deformation on 3Y-TZP in an oxygen-lean atmosphere. The experiments were performed with different electric currents in the range of 0~5 A. The results show that the flow stress of 3Y-TZP during the deformation was significantly decreased by the combination of Joule heating and the applied current effect. The microstructures of the deformed specimens were all equiaxed grains without an obvious preferential grain growth. The stress exponent n = 2.05~2.61 suggested that the dominant deformation of 3Y-YZP with/without the electric current was grain boundary sliding at 1400 °C. The activation energy of the deformation which decreased from 465 kJ mol-1 to 315 kJ mol-1 by the electric current indicated that the lattice diffusion of Zr cation during the deformation was enhanced. And the deformation rate of 3Y-TZP with the electric current may be controlled by the grain boundary diffusion of Zr cation.

An Accurate Constitutive Model for AZ31B Magnesium Alloy during Superplastic Forming

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.

Finite Element Modeling of Superplastic Forming in the Presence of Back Pressure

It is established that some superplastic materials undergo significant cavitation during deformation. Cavitation not only limits the superplastic ductility of the material, but also reduces the service properties and the fatigue performance of the formed parts. Experimental results have shown that an effective method to eliminate cavitation is the application of hydrostatic pressure during deformation. In this work, finite element simulations are carried out to study the effects of hydrostatic pressure on damage evolution during SPF. The analysis is conducted for the superplastic copper based alloy Coronze-638 at 550 °C. The results clearly demonstrate the effectiveness of the superimposition of hydrostatic pressure in reducing the amount of cavities generated during SPF and improving the integrity of the formed part.