Deformation behavior and microstructure evolution of pure Cu subjected to electromagnetic bulging

In this paper, pure Cu sheet with thickness of 1 mm was electromagnetically budged to form a conical shape workpiece. The deformation behavior and the microstructural evolution of the Cu sheet under electromagnetic bulging were systematically studied using strain analysis, optical microscopy (OM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It is found that the strain distribution in the workpiece is quite un-uniform from the bottom to the top due to the inhomogeneous electromagnetic pressure generated by the spiral coil. The characterization of microstructure reveals that the bulge deformation of the Cu sheet is governed by dislocation multiple slip and cross slip, which cause finally the formation of cell structures. However, the size and the boundary width of cells are closely related to the plastic strain, i.e., the cell size and boundary width decrease with increasing strain. In addition, low misorientation angle of cells inside the grains increases with increasing strain. This structural evolution is discussed on the basis of the low energy dislocation structures (LEDS) theory.