Improved corrosion resistance of friction stir welded magnesium alloy with micro-arc oxidation/electroless plating duplex coating

The bare FSW joint was immersed in a NaCl solution with 3.5 wt% content for 0.5 h at room temperature, and the coated FSW joint was immersed in a NaCl solution for 6 h; the corrosion resistance was analyzed by observing the macro and micro-morphology of the corrosion surfaces. The electrochemical measurements were performed using a Gamry 3000 instruments. The sample was selected as the working electrode and the Pt foil was served as the counter electrode. A saturated calomel electrode (SCE) was used as the reference electrode. The sample reached the potential steady-state after being immersed in a NaCl solution for about 30 min. Electrochemical impedance spectroscopy (EIS) was applied at open circuit potential. The amplitude of the AC potential disturbance was 10 mV, and the frequency of the AC signals ranged from 100 kHz to 0.01 Hz. The EIS measurements for the duplex coatings were performed for passing immersion time of 0.5 h and 26 h. At least five samples were used to ensure the repeatability of the data. The polarization curve from the cathodic to anodic potential was determined at a scanning rate of 1 mV s 1. It should be noted that after polishing, the exposed area of the thermo-mechanically affected zone (TMAZ) was too small for electrochemical measurements. Therefore, no electrochemical measurement was obtained in the TMAZ.