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

Abstract

Interface is crucial to enable desirable service performances of coatings on substrates. In this paper, Ni-P coatings were prepared on AZ31B alloy by using electroless plating, with the coating/substrate interface being tuned to improve the corrosion resistance. The interface tuning involved a phosphate treatment prior to the electroless plating, which created a uniform surface of the Mg substrate and finally led to Ni-P plating coatings with enhanced density during the electroless plating. Electrochemical testing was performed to compare the corrosion properties between the Ni-P coatings with and without phosphate treatment. The experimental results evidently showed that the introduction of phosphate treatment, especially after an annealing treatment, greatly improved the corrosion resistance. The underlying mechanisms, revealed by microstructural examinations, were that the phosphate treatment reduced the substrate surface roughness and likely promoted a high and uniform nucleation intensity of the Ni-P coating. Corrosion processes of the unannealed and annealed Ni-P coatings with an interfacial phosphate layer were further clarified for comparison.

A study on the local corrosion behavior and mechanism of electroless Ni–P coatings under flow by using a wire beam electrode

“…The reason for forming this spherical shape is that the Ni-P precipitates tend to reduce their energy associated with the surface. These results were consistent with the study by Ma et al 21 Fig. 4(b) shows the cross-section microstructure (SEM) of the Ni-P coating.…”

Investigation of the Supercapacitive Behavior of Electroless Ni-B Coatings

“…Ni-based electroless coatings, namely Ni-P and Ni-B, have been extensively studied in recent years due to their useful properties for industry. Ni-P coatings have relatively high hardness, good solderability, and are resistant to corrosion, while Ni-B coatings are well-known for their excellent mechanical characteristics, such as their high resistance to wear and surface stress, which exceed even those of hard chromium coatings [1][2][3][4][5][6][7].…”

Erosion-Corrosion Behavior and Mechanism of Heated Electroless Ni–P Coating under Flow

“…4,5) It has been widely used in automobiles, aviation, computers, electronics, machinery, chemicals, light industry, petroleum industry, etc. 6,7) Since developed in the 1940s by A. Brenner and G. Riddell, 8) the method of electroless NiP coating had been a relatively mature technology by overcoming many difficulties such as bath regeneration, bath stability, coating performance test. 9,10) The advantage of electroless NiP coating is that it can obtain a uniform thickness of alloy film on any complex shape of the substrate, and it has the characteristics of economy, low energy consumption and convenient operation.…”