Electrochemical Corrosion Behaviour of Electron Beam Welded Copper and SS304 Dissimilar Metal Joints in NaCl-Saturated Solution

Abstract

Electron beam welding is used for high precision welds mainly in aerospace industries. It is a type of fusion welding process in which a high beam of electrons hits the metals, produce heat and melts the base metals and then solidifies to form a weldment which is generally stronger than the individual base metals. This paper presents the corrosion testing of Electron beam welded pure copper and stainless steel 304 weldment. Tafel polarization technique is used to find the electrochemical corrosion behaviour of electron beam welded copper and SS304 dissimilar metal joints in NaCl saturated solution. The experiment was carried out using a CHI electrochemical workstation with a three-electrode setup where the welded specimen act as the working electrode. Tafel plots were generated to analyze the corrosion characteristics. An active-passive transition is found that indicates the formation of a protective oxide layer. The corrosion potential (E_corr) and corrosion current density (I_corr) of the weldments proves that the weldment has superior corrosion resistance when compared with the base metals. A significant increase in oxygen content and decrease in Fe, Cr, Ni and Cu concentrations are noted in the energy dispersive X-ray analysis (EDX) which indicates the metal degradation due to electrochemical reactions. Small corrosion pits are observed during the microstructural analysis proves the presence of pitting corrosion. However, the low I_corr values of the weldment is very low when compared with pure copper and SS304 which shows the enhanced corrosion resistance in the weldment due to microstructural refinement and alloying effects in the fusion zone. These findings prove that Cu-SS304 dissimilar weld using EBW is suitable for aerospace applications.