SUPERPLASTIC DEFORMATION OF DURALUMIN LY12CZ UNDER AN ELECTRIC-FIELD

The general superplastic deformation of many alloys had been studied e xhaustively. 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 sensitivity exponent during the superplastic defo rmation of 7475 Al alloy subjected to an external dc electric field. H owever, it is not clear how the electric field will affect the elongat ion and the growth of cavities quantitatively, and whether the type of cavities will change because of the existence of the external electri c field. In this paper, the optimum process parameters for the super p lastic deformation of duralumin LY12CZ, without any pre-treatment, sub jected to an external dc electric field have been obtained, LY12CZ (co rresponding to ASTM 2024) being used widely in the aeronautic-astronau tic industry. Furthermore, the effect of the electric field on the sup erplasticity and the superplastic-deformation conditions has been inve stigated. The experimental results show that the application of the el ectric field: (i) decreases the flow stress by 10-25% and the degree o f cavitation at the onset of the fracture by 11% approximately; (ii) r educes the rate of strain-hardening; and (iii) increases the strain-ra te sensitivity exponent by 26-38%. It is important to note that: (iv) the elongation of the superplastic deformation of LY12CZ under the ele ctric field increases by 14-45% as compared with that without the elec tric 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 t ensile test when applying the electric field, as opposed to the V-type cavities for the general superplastic deformation of LY12CZ. From the se investigations, the optimum process parameters for the superplastic deformation of LY12CZ under an electric field are as follows: the def ormation temperature is 471-degrees-C and the initial strain rate is 0 .333 x 10(-3) s-1.