Investigating Electrochemical Behavior of the Nugget Zone in Dissimilar Friction Stir Lap Welded of Copper- Brass Joints

In this study, the weld nugget zone (WNZ) electrochemical behavior in copperbrass plates, welded using friction stir lap welding, in 0.015 M borate-buffered(Borax) (pH 9.3) and 1 M NaCl (pH 7.2) solutions are investigated. Therefore, dissimilar copper/ brass plates welded with welding conditions of welding speed of 25 mm/min and rotation speed of 710 rpm. Features of specimen welded nugget zone under open circuit potential; potentiodynamic polarizations are compered and then the morphology of the products corrosion formed in polarization experiment are analyzed using SEM. Electrochemical impedance spectroscopy (EIS) is used for the characterization of surface films formed on the welded specimens during 3600s immersion at Eocp in the two test solutions. Results showed that the welding process reduced the welded NZ corrosion resistance and offered lower corrosion resistance than copper and higher corrosion resistance than brass in 1 M NaCl (pH 7.2) solution. On the other hand, polarization plots showed that welding process results in current densities decreases from 0.512 for copper and 0.711 for brass to 0.213 µAcm−2 for the WNZ and significant shifts toward positive for corrosion potential in Borax solution. Indeed, the welded NZ corrosion rate in Borax solution was less than that in 1 M NaCl. The oxide film formed on the welded joints of NZ surface was more porous in borate buffer solution than in the NaCl solution. The hardness of welded joints was higher than copper and brass, and the highest hardness observed in the welded specimen nugget zone with low heat input during the welding process, because the grain refined most meaningfully in the welded joints NZ during welding process.