Electroless Ni-P On Magnesium Alloys

Magnesium alloys have lots of desirable features such as lightness, high strength to weight ratio, excellent castability , ability to dampen electromagnetism and shock waves and being reclaimed easily, so they have been widely used in many fields such as aerospace, automobile, electronics components, mechanical and so on. However, poor corrosion resistance is one of main causes to restrict their applications.Electroless nickel plating is an excellent surface treatment, the plating layer has many advantages such as good corrosion and wear resistance, deposit uniformity, good electrical and thermal conductivity and solder ability etc. But the technics of the electroless nickel plating on magnesium alloys is not mature yet, especially for the technics of the direct-electroless nickel plating which is simple in the process and of low cost. In this paper, the process of the pre-treatment and the deposition, the characters of the plating layer, the passivation after the deposition and other aspects related are discussed.The surface of the pre-treated magnesium alloys is characterized by weight loss method, optical microscopy, scanning electron microscopy (SEM) and so on. Results show that in the whole pre-treatment process, loss of the weight and the size of the substrate mainly occurs during the etch process, while in the alkaline cleaning and activating process, there is almost no loss of the weight because of the formation of the passivation film. So it is necessary to choose the etch acid carefully when treating the accessories which require high quality and the precision of the size. Compact and well combined plating layer is achieved by using the HF acid as the activation addition.The influence of the additives(nickel salt, reducer, complexant, wetting agent,etc) and the conditions(temperature, PH values,etc) to the stability of the plating solution ,the deposition speed and the properties of the plating layer is discussed in the paper. Results indicated that increasing of the nickel salt and the reducer, PH values and the temperature can speed the deposition but reduce the stability; while the increasing complexant increases the stability but lower the deposition speed. Wetting agent reduces the porosity effectively. As the stability and the deposition speed cannot be increased at the same time using citric acid as the complexant, the co-complexant of citric acid and lactic acid is studied. The orthogonal test is used to optimize the dispensation of the direct-electroless nickel plating on magnesium alloys.