Damage evolution of Cu-inductors used for electromagnetic forming.

Electromagnetic forming (EMF) is a high-speed forming technology using the interactions of pulsed currents and magnetic fields to apply Lorentz forces to electrically conductive workpieces. The damage behavior of Cu-inductors used for EMF was investigated by electron microscopy, particularly electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDS). The process-specific electrical-thermo-mechanical load leads to plastic deformations on the inductor and melting and re-solidification of grain boundaries. Both weaken the inductor material. Cracks propagate at grain boundaries, where the thermo-mechanical load is concentrated, and become larger after each discharge. As a result, blowholes form, which cause failure of the inductor. Annealing and recrystallization processes as well as local melting at grain boundaries and formation of blowholes due to joule heating are probably the origin of the damage evolution during EMF. Understanding the correlations of these microstructural mechanisms will enable targeted heat treatment for wear-resistant inductors in the future.