Lower corrosion current density denotes a lower rate of corrosion. According to the results of figure and table 3, the base metal has the lowest value of corrosion current density and corrosion rate and therefore is more resistant to corrosion than other cases. Interestingly, friction stir processing has significantly decreased the corrosion resistance of the processed samples. This degrading behavior of friction stir processing towards corrosion was also mentioned in the works of and . This behavior might be due to the numerous dislocations in the stress-induced stir zone, which causes lattice deformations. The solution would permeate these localized flaws, causing the protective layer to break down and produce localized corrosion.