The electrochemical machining of mild steel in NaBrO 3 solutions

Abstract

For a solution to be a good ECM electrolyte for a given metal, a uniform, potential-dependent, protective film must be formed on the metal surface; the transition from the passive to the transpassive states must occur over a narrow potential range on the polarization curve; and in the high current density regions, the film must be very thin, uniform and porous. If these conditions are not met, poor results will be obtained for the electrochemical machining of the given metal in the given solution. From polarization and film stripping studies, it was observed that these criteria were not met for mild steel in solutions of NaBrO 3. In agreement with the predictions, control of dimensions and geometry could not be achieved for the ECM of mild steel in 1·5M NaBrO 3 electrolyte in laboratory test rigs and the surface finish of the machined parts were badly pitted. These data support the contention that the electrochemical characteristics of the passivating film formed on the metal surface during the ECM of the metal in a given electrolyte play an essential role in determining the quality of the finished product.