Superplastic deformation of duralumin LY12CZ under an electric field

The general superplastic deformation of many alloys had been studied exhaustively. Recently, the superplastic deformation of some alloys has been achieved by the application of an electric field to the process. Conrad and his colleagues have obtained the change of the flow stress and the strain-rate exponent during the superplastic deformation of 7475 Al alloy subjected to an external dc electric field. However, it is not clear how the electric field will affect the elongation and the growth of cavities quantitatively, and whether the type of cavities will change because of the existence of the external electric field. In this paper, the optimum process parameters for the super plastic deformation of duralumin LY12CZ, without any pre-treatment, subjected to an external dc electric field have been obtained, LY12CZ (corresponding to ASTM 2024) being used widely in the aeronautic-astronautic industry. Furthermore, the effect of the electric field on the superplasticity and the superplastic-deformation conditions has been investigated. The experimental results show that the application of the electric field: (i) decreases the flow stress by 10-25% and the degree of cavitation at the onset of the fracture by 11% approximately; (ii) reduces the rate of strain-hardening; and (iii) increases the strain-rate sensitivity exponent by 26-38%. It is important to note that: (iv) the elongation of the superplastic deformation of LY12CZ under the electric field increases by 14-45% as compared with that without the electric field; (v) the equivalent strain at the onset of the rapid growth of the cavities increases by 25% with the application of the electric field; and (vi) spherical cavities exist in the specimens after the tensile test when applying the electric field, as opposed to the V-type cavities for the general superplastic deformation of LY12CZ. From these investigations, the optimum process parameters for the superplastic deformation of LY12CZ under an electric field are as follows: the deformation temperature is 471°C and the initial strain rate is 0.333 × 10^-3 s^-1.