Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

This study was done to evaluate the nugget zone (NZ) corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding (FSLW) in a solution of 0.015 mol/L borax (pH 9.3). To this end, dissimilar copper/ brass plates were welded with two dissimilar heat inputs (low and high) during the welding procedure. The high and low heat inputs were conducted with 710 r/min, 16 mm/min and 450 r/min, 25 mm/min, respectively. Using open circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS) and Tafel polarization tests, the electrochemical behavior of the specimens in borate buffer solution was assessed. With the help of scanning electron microscope (SEM), the morphology of welded specimen surfaces was examined after immersion in the test solution. According to the results, the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input. The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals. Furthermore, an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.