Preparation and corrosion resistance of Ni‐P bilayer on magnesium alloy

Abstract

Ni‐P bilayers were prepared on AZ61 magnesium alloy by electroless plating method in dual baths with pH value of 11.0 and 5.5. The thickness, surface morphology, composition, structure and corrosion resistance of Ni‐P bilayer were observed and determined by scanning electron microscope (SEM), energy dispersive X‐ray spectrometry (EDX), X‐ray diffractometer (XRD) and electrochemical workstation. The results show that Ni‐P bilayer is composed of inner layer in mixed amorphous and nanocrystalline structure with phosphorus content of 3.9–4.0% and outer layer in amorphous structure with phosphorus content of 8.8–10.9%. The plating time of inner layer has a great impact on the morphology and corrosion resistance of Ni‐P monolayer and bilayer, and the corrosion resistance of Ni‐P bilayer is obviously higher than that of inner layer. The optimum plating condition for Ni‐P bilayer is the combination of inner layer's plating time of 30 min and outer layer's plating time of 180 min, under which Ni‐P bilayer gets a dense structure, smooth surface and higher corrosion resistance than that of single inner layer and outer layer.

Fabrication and Corrosion Resistance of a Superhydrophobic Ni–P/Ni3(NO3)2(OH)4 Multilayer Protective Coating on Magnesium Alloy

“…These pores are relevant to the release of hydrogen during plating and are hard to avoid. 24 However, a lot of nanosheets grow vertically on the surface of the Ni–P coating, and some locations appear like 3D flowerlike nanoclusters after the hydrothermal reaction ( Figure 1 c,d). The pores and defects on the surface of the Ni–P coating are repaired by the growth of nanosheets because these positions are preferentially nucleation sites during the hydrothermal reaction due to a higher surface energy than other locations.…”

Tuning Interface to Improve Corrosion Resistance of Electroless Ni-P Coating on AZ31B Alloy

“…A uniform coating prepared by surface treatment methods is usually adopted to modify physical and chemical properties of metal materials, in particular to enhance the corrosion resistance. Electroless nickel (EN) coating is one of the common surface treatment methods, which has been widely employed to produce corrosion-resistant Ni-based coatings [6][7][8][9][10][11]. The corrosion resistance depends highly on the quality of EN coatings.…”

Influence of pickling time on electroless Ni–P coating on magnesium alloy

“…The conventional processing of pretreatment is acid pickling by chromic oxide and nitric acid, followed by activation in hydrogen fluoride. [15,16] However, chromic oxide is forbidden due to its carcinogenic effect and environmental hazards. [17] Therefore, exploiting an environment-friendly pretreatment process has been a research hotspot in recent years for electroless plating of magnesium alloy.…”