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

• Published in: Materials and corrosion Vol. 68; no. 12; pp. 1377 - 1388
• Main Authors: Yuan, J., Gao, Y., Wang, J. H., Hu, W. B.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.12.2017
• Subjects: Amorphous structure; Bilayers; Corrosion resistance; Corrosion resistant alloys; Electroless plating; magnesium alloy; Magnesium base alloys; Morphology; Nickel base alloys; Ni‐P bilayer; Phosphorus; Phosphorus content; Plating baths; structure; Thickness
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.201709515

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. A Ni‐P bilayer was prepared on AZ61 magnesium alloy by electroless plating method in dual baths with pH value of 11.0 and 5.5. Ni‐P bilayer is composed by inner layer with low phosphorus content and outer layer with high phosphorus content. The plating time of inner layer has a great impact on the morphology and corrosion resistance of Ni‐P bilayer.