Electrochemical measurements of electroless nickel coatings on zincated aluminium substrates

Zincate pre-treatment of aluminium substrates and the effects of deposit th ickness on the corrosion resistance of electroless nickel deposits on alumi nium have been studied by electrochemical methods. The results show the imp ortance of the controlled zincate pre-treatment sep on the induction period for electroless nickel plating. The protective properties of the nickel de posit are evaluated, as a function of thickness, using linear polarisation resistance and zero resistance ammetry techniques. The corrosion resistance of the deposits, which is strongly related to their thickness, is compared to the results of porosity testing on steel substrates. An essentially non -porous deposit is obtained after a thickness of 5-10 microns has been depo sited on aluminium substrates under the experimental conditions.