A study of the galvanic corrosion behavior of Inconel 718 after electron beam welding

In this paper, the galvanic corrosion behavior of as-received, solution-annealed and precipitation-hardened Inconel 718 sheets after electron beam welding was studied in 3.5 wt% NaCl solution at 30 °C. An easy and reliable specimen-preparation method of a weld for electrochemical testing is proposed. Microstructures of the welds were investigated with an optical microscope and a transmission electron microscope integrated with an energy-dispersive X-ray spectrometer for chemical composition analysis. Experimental results show that galvanic corrosion could take place in an Inconel 718 weld when it is freely corroded or anodically polarized in 3.5 wt% NaCl solution. Furthermore, differences in corrosion potential between the fusion zone, heat-affected zone and base metal in an Inconel 718 weld is the key factor for galvanic corrosion. Due to a relatively active corrosion potential and a very small exposed area compared to those of the adjacent heat-affected zone and base metal, severe attack of the fusion zone could be observed in the as-received and solution-annealed welds when they were anodically polarized at 2.0 V for a few seconds. However, galvanic corrosion of solution-annealed weld can be prevented through post precipitation heat treatment, which resulted in only a small difference in corrosion potentials between the fusion zone, heat-affected zone and base metal.