Investigation on effect of heat treatment on hardness and corrosion behavior of electroless Ni-P plating on AZ31 magnesium alloy

In this study، Ni-P coating on the surface of AZ31 Mg alloy was proposed by electroless plating due to improve in surface hardness and corrosion resistance. Electrochemical polarization test was done before and after coating on base alloy، with and without coating in 3/5wt%NaCl solution. The hardness of EN coating and base alloy also were evaluated before and after heat treatment، and surface morphology was studied by scanning electron microscopy (SEM). Also، microstructural changes were evaluated by X-ray diffraction (XRD) analysis. The results of this study showed that EN coatings with low phosphorus content were nano-crystalline and hard and the hardness of the coating could be increased with increasing temperature in heat treatment process، while the hardness of base alloy decreased due to grain growth and the rate of the corrosion increased. So the best range for Heat treatment of mg alloys was 230-270˚c. heat treatment in this range would increased 110 HV hardness of the coating and decreased only 14BHN hardness of the base alloy.