Abstract
A kind of corrosion-resistant Ni-Mo-P composite coating was deposited on the surface of AZ91D magnesium alloy substrate by electroless plating method with different concentration of Ce(NO3)3 and Nd(NO3)3. The deposition mechanism of Ni-Mo-P composite coating was explored. Furthermore, the effects of Ce(NO3)3 and Nd(NO3)3 concentration on the microstructure and properties of Ni-Mo-P composite coatings were studied. Results indicated that the Ni-Mo-P composite coatings prepared by adding the optimal concentration of Ce(NO3)3 and Nd(NO3)3 had few defects. Meanwhile, the deposition rate of the composite coatings and the adhesion between the coating and the magnesium alloy substrate were improved. When the concentration of Ce(NO3)3 and Nd(NO3)3 were 0.10 and 1.00 g/L, the Ni-Mo-P composite coatings had the minimum corrosion rate of 0.826 and 0.681 g/m2·h, respectively. Herein, compared with the addition of Ce(NO3)3, the Nd(NO3)3 added Ni-Mo-P composite coating has the maximum arc radius of capacitive resistance and significant improvement corrosion resistance.
Highlights
Magnesium alloys are potentially applied in aerospace, automotive, electronics and biomedical applications due to light weight, low density, high strength, and excellent recyclability[1,2,3,4]
The microscopic morphology of Ni-Mo-P composite coating was analyzed by scanning electron microscope (SEM, JSM-6390A, Japan), and the composition of coating was determined by the energy dispersive spectroscopy (EDS) equipped with SEM.The phase structure of the coating was characterized by X-ray diffractometer (XRD-7000, Shimadzu, Japan) with a Cu Kα radiation (Kα=0.15406 nm) in the 2θ range of 20°~80°
Ni2+ is reduced to metallic nickel by some [H], and part of [H] reduces H2PO2, precipitating phosphorus atoms deposited on the nickel surface
Summary
Magnesium alloys are potentially applied in aerospace, automotive, electronics and biomedical applications due to light weight, low density, high strength, and excellent recyclability[1,2,3,4]. Numerous surface modification techniques such as chemical transformation[8], microarc oxidation[9], chemical vapor depositions[10], Electrodeposition[11,12] and electroless plating[13] are presented for obtaining corrosion resistant coatings on magnesium alloys. For exploring the application of electroless Ni-P coating, co-deposition of metallic elements such as W17,18, Cu19, Ag20, Fe21, Zn22, Mo23, and Co24 formed Ni-X-P ternary alloy coatings with superior hardness, corrosion resistance and wear resistance. The Ni-Mo-P composite coatings with different Ce(NO3)[3] and Nd(NO3)[3] concentration was prepared by electroless plating and special pretreatment on magnesium alloy substrate, aiming to improve the corrosition resistance of magnesium alloys. The deposition mechanism of Ni-Mo-P composite coating was explored
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