Zincating Effect on Corrosion Resistance of Electroless Ni-P Coating on Aluminum Alloy 6061

Aluminum and its alloys represent a promising alternative as bipolar plates in proton exchange membrane fuel cell (PEMFC) systems. However, to improve the corrosion resistance they are commonly coated, and electroless Ni-P offers great advantages. The effect of multiple zincating process on the corrosion behavior of electroless Ni-P coatings on AA6061 was investigated. Results of morphological characterization and compositional analysis of the electroless Ni-P coatings showed that as the number of zincating steps increased, the surface became smoother (with decreasing roughness) and the phosphorous content increased. The results of electrochemical impedance measurements and potentiodynamic polarization curves in 0.5M H2SO4 solution showed that the pretreatment used before coating of aluminum with Ni-P has a direct effect on corrosion resistance. The corrosion current density decreased with increasing the number of zincating steps. A significant improvement in corrosion resistance was observed on performing the triple zincating.