Thermodynamic Analysis of Electroless Plating Nickel for 5383 Aluminum Alloy

Electroless nickel plating was conducted on surface of 5383 cast state aluminum alloy with one time and two times zinc dipping process.Kinds of coatings were investigated with scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS) analysis and X-ray diffraction(XRD) under the conditions of different pH value and temperature.According to the electrochemical corrosion experiment,the corrosion resistance of coating in 3.5wt% NaCl solution has been tested.According to thermodynamic analysis of the chemical plating nickel,the influences of the plating bath temperature and pH value to the coating were analyzed.The experimental results indicate that after two times zinc dipping process,the content of zinc became lower and the coating became well-distributed and denser,compared with 5383 aluminum alloy surface of the one time.The key reaction step of electroless nickel plating is H2→2Had.The pH value is the main factor of the thickness of electroless nickel plating.The content of P element under acidic conditions is higher than that under alkaline conditions,and the Ni-P alloy coating is amorphous phase.The corrosion resistance of nickel plating is optimal as the pH value is 4.5 and temperature is 90 ℃.