Electrochemical impedance measurements on Ni-P coated magnesium alloy, chromated magnesium alloy, and anodised aluminium alloys in aqueous salt solutions

Both electroless nickel coated and chromated surfaces of magnesium alloy AZ31 and hydrothermally sealed anodised surfaces of unallolyed aluminium Al-2S and aluminium alloy 6061 licit e he prepared and the corrosion behaviour of these surfaces in aqueous KCl and K2SO4 solutions has been studied using electrochemical impedance spectroscopy (EIS). The effect of the concentration of hypophosphite in the plating bath used for electroless plating on the Ni-P layers formed and their corrosion behaviour has also been studied. The EIS studies have shown that the diffusion of ionic species is less for yellow chromated surfaces of magnesium alloy than for black chromated ones. In the case of anodised aluminium surfaces, impedance values are much higher in KCl than in K2SO4 solutions. The effect of anodising time on pore resistance R-po and barrier capacitance C-b has also been studied. Data from EIS indicate that the pore resistance of aluminium alloys A1-2S and AA 6061 attains a saturation value after anodisation for similar to45 min.