THE CHANGE IN THE FRACTAL DIMENSION OF THE SHAPE OF THE CAVITIES DURING THE SUPERPLASTIC DEFORMATION OF DURALUMIN LY12CZ

Cavities have been widely observed during the superplastic deformation of metals and alloys, the superplasticity of metals and alloys genera lly being sensitive to cavity formation. However, the shape of the cav ities is irregular during superplastic deformation, thus quantitative analysis of the shape of the cavities is one of the keys to the studyi ng of the superplastic deformation mechanism. In this paper, the quant itative effects of process parameters on the fractal dimension, D-f, o f the shape of cavities during the superplastic deformation of duralum in LY12CZ (approximately corresponding to ASTM 2024) with and without the application of an external electric field is studied. The experime ntal results show that: (i) the fractal dimension of the shape of cavi ties varies with the change of process parameters (deformation tempera ture, T, true strain, epsilon, initial strain rate, epsilon(0)), both with and without the application of an external electric field. (ii) t he fractal dimension of the shape of cavities also varies with the int ensity of the electric field, E, under otherwise identical conditions. The results in this paper show that the improvement of superplasticit y with the application of an external electric field is related to a l ower value of the fractal dimension in the quasi-stable flow stage of superplastic deformation.