Nickel–copper alloys are commonly utilized for their corrosion resistance in electrochemical applications, marine engineering, and various other fields. The corrosion resistance of these metal combinations significantly improves with higher nickel substance. Therefore, in this study, the impact of a 10% HCl solution on Monel400 and AISI 1020 carbon steel welded joints, produced by Friction Stir Welding and Shielded Metal Arc Welding, was examined. The microstructures of the weld were analysed using both Scanning Electron Microscopy (SEM) and optical microscopy. Corrosion behavior was assessed through cyclic and potentiodynamic polarization tests, with specimens submerged in a 10% HCl solution for 30 days. The study revealed a dealloying phenomenon, specifically nickel leaching from Monel 400, referred to as denickelation. Results showed that corrosion rates of Monel400- 1020 Carbon steel joint with FSW, and SMAW welding using ENiCu-7 and ENiCrFe-3 electrodes were respectively 20. mpy 26 mpy and 30 mpy, the pitting potential was about 1600V in FSW specimen and 1500V in SMAW specimen.