The Formation Mechanism And Corrosion Resistance Behavior Of Plating Ni-P Film On The Surface Of Al₁₈B₄O₃₃W/Al Composite

This research is on the formation process of electrodeposited Ni-P amorphous alloy on the surface of the Al₁₈B₄O₃₃w/Al composite materials. The influence of pretreatment on the structure and properties of electrodeposition coatings is analyzed. The corrosion of Ni-P alloy electrodeposition coatings and corrosion resistance of element P is analyzed. The testing methods of SEM, TEM, EDS and XRD are used to study the surface morphology and microstructure of coatings. Potentiodynamic polarization testing and soak experiment are used to indicate the corrosion resistance.The results show that the electrodeposition process and the settled coating of composite materials are significantly different from that of pure metal. The initial Ni-P alloy particles are crystalline, which nucleate on the surface of Aluminum body rather than the crystal whiskers and then transform into amorphous ones when they get bigger. With the increasing of electrodepositing time, the thickness of the deposition film on the composite substrate increases, and the particle groups aggregate more tightly which make the surface of deposited composite becomes more flat. The corrosion resistance of the deposited composite also improved. The corrosion properties of the deposited composite did not change with the deposition time keep on increasing.The experimental results confirm that for composite materials, pretreatment is also a necessary step before the electrodeposition. Different pretrefments have diverse impacts on the structure and the property of electrodeposition coatings. Corrosion resistance is control by both the quality and the connection of Ni-P alloy.The corrosion mode of Ni-P alloy electrodeposition is pitting corrosion. P absorbs the surface of Ni-P alloy, which prevents the dissolution of Ni. Within a certain range, the corrosion resistance is enhanced by the rise of content of P. By the way of adjusting pH value, Ni-P graded alloy layer is successfully obtained, which greatly changes the short-term corrosion mechanism of the material. The forming and development of corrosion holes is delayed, and its corrosion resistance is improved.