Reduction of stray corrosion by using iron coating in NaNO3 solution during electrochemical machining

Abstract

Stray corrosion is a common phenomenon that occurs at the surface adjacent to the machining area during electrochemical machining (ECM). It can cause unwanted metal removal and has a substantial effect on the ECM precision. Standard through-mask ECM prevents stray corrosion with a locally insulated anode, which requires the insulating material to be positioned accurately and applied through a complex process, including resist application, exposure, developing, and stripping. This paper presents a new method for reducing stray current attack by using an iron coating on the surface of the anode workpiece in NaNO3 solution. The application of the iron coating to the whole initial surface of the workpiece does not require precision, and the process is simple and economical. Because the iron coating is passivated at low current densities and can be easily applied or removed, it can be used to reduce the stray current attack. The η-i curves of the nickel-based alloy, Inconel 718, show that its dissolution efficiency is higher at low current densities, indicating poor localization and severe stray corrosion during ECM. A simulation and an experimental study of ECM a convex on iron-coated and uncoated Inconel 718 workpieces were performed. The results showed that the iron coating on the surface of the workpiece significantly improves the machining accuracy. It reduces stray corrosion and the amount of stray removal on the non-machined top surface of the convex workpiece.