Preparation, Microstructures, and Corrosion Resistance of Ni-Mo-P Ternary Amorphous Coating

Protective Ni-Mo-P ternary composite coating was deposited on AZ91D magnesium alloy substrate by electroless plating with different concentrations of Na2MoO4. The effect of Na2MoO4 concentration on deposition rate, microstructures, adhesion between the Ni-Mo-P coatings and the substrates, corrosion morphologies and corrosion resistance of Ni-Mo-P coatings were systematically investigated. Moreover, the growth and corrosion resistance mechanisms of the composite coatings were explored. The results revealed that the Ni-Mo-P coating possessed a uniform and dense structure, and the adhesion between the coating and the magnesium alloy substrate was improved. The x-ray pattern and EDS demonstrated that the Ni-Mo-P coating with the addition of 0.4 g/L Na2MoO4 presented amorphous structural characteristics. Furthermore, when the concentration of Na2MoO4 was 0.4 g/L, the Ni-Mo-P coating presented superior corrosion resistance, among which Ecorr was − 0.26 V and Icorr was 8.725 × 10−3 A/cm2. In addition, the Ni-Mo-P composite coating was corroded slightly at this concentration, with the lowest corrosion rate of 0.68 g/m2·h. The results were attributed to the addition of molybdenum elements to improve the amorphous degree for the coating, which improved the corrosion resistance for Ni-Mo-P composite coatings.