The electroless nickel-plating on magnesium alloy using NiSO4·6H2O as the main salt

In this paper, the electroless nickel-plating on magnesium alloy was studied, using NiSO4·6H2O as the main salt in the electroless plating alkaline solutions. The effects of the buffer agent and plating parameters on the properties and structures of the plating coatings on magnesium alloy were investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). In addition, the weight loss/gain of the specimens immersed in the test solution and plating bath was measured by using the electro-balance, to evaluate the erosion of the alloy in the plating solutions. The adhesion between the electroless plating coatings and the substrates was also evaluated. The compositions of the non-fluoride and environmentally friendly plating bath were optimized through Latin orthogonal experiment. The buffer agent (Na2CO3) added to the plating bath was found to be useful in increasing the growth rate of the plating coating, adjusting the adhesion between the electroless plating coatings and the substrates, and maintaining the pH value within the range of 8.5–11.5, which is required for the successful electroless nickel-plating on magnesium alloy with NiSO4·6H2O as the main salt. Trisodium citrate dihydrate was found to be an essential component of the plating bath to plate magnesium alloy, with an optimum concentration of 30 g L−1. The obtained plating coatings are crystalline with preferential orientation of (111), having advantages such as low-phosphorus content, high density, low-porosity, good corrosion resistance and strengthened adhesion.