Evaluation of Corrosion Resistance of Electroless Ni-P/Ni-W-P Double Layer Coatings on 6061 Aluminium Alloy

The electroless Ni-P/Ni-W-P double layer coating in as-plated condition on 6061 aluminium alloy substrate were prepared. The morphology of the prepared Ni-P/Ni-W-P double layer coatings were found out from SEM analysis and phases were found out using XRD. The corrosion resistance of the Ni-P/Ni-W-P coatings were compared by electrochemical impedance spectroscopy and potentiodynamic polarization studies in 3.5 wt.% NaCl solution. Microhardness of the Ni-W-P has the better hardness value than Ni-P coating. The values of EIS and potentiodynamic polarization studies indicate that the corrosion resistance values for Ni-P/Ni-W-P coatings were higher when compared to Ni-P coatings. This may be due to presence of W elements on the aluminium substrates. The results indicate that the Ni-W-P coating can be a better corrosion protection material on aluminium alloys than Ni-P coatings.