Preparation And Wear, Corrosion Resistance Of Electroless Plating Ni-based Coating On Magnesium Alloy

Because of their low density,high specific strength and specific modulus,magnesium alloys are highly valued in the fields of aviation,aerospace,national defense,automobile and electronics.However,the poor wear and corrosion resistance of magnesium alloys hinder the wide application in industrial field.This paper adopts electroless plating process.First,the AZ91D magnesium alloy matrix was pretreated with tinate conversion,then the low and high phosphorus double layer Ni-P electroless plating was carried out,and finally,double layer Ni-P coating,Ni-Mo-P coating,Ni-Mo-P alloy coating and Ni-Mo-P/CNT composite coating were prepared by electroless plating.The properties of double Ni-P and Ni-Mo-P coatings were compared and studied,and the effects of Na2MoO4 and CNT additions on microstructure,composition,adhesion,phase composition,wear resistance and corrosion resistance of Ni-Mo-P alloy coating and Ni-Mo-P/CNT composite coating were studied.(1)The surface of the double layer Ni-P、Ni-Mo-P coating,the Ni-Mo-P alloy coating and the Ni-Mo-P/CNT composite coating all show different cell-like structure,without cracks,holes and other obvious defects.(2)The content of outer P of double layer Ni-P、Ni-Mo-P coating is 13.13 wt%and 10.62 wt%,respectively,which are high phosphorus,showing typical amorphous structure.T he friction coefficients are 0.67 and 0.58,respectively.The polarization curve and impedance spectroscopy results show that the self-corrosion potential of the Ni-Mo-P coating is corrected than that of the double layer Ni-P coating,and the self-corrosion current is smaller;the arc resistance radius is larger.Therefore,Ni-Mo-P coating has better wear resistance and corrosion resistance than double layer Ni-P coating.(3)Compared with 0.2,0.3,0.4 and 0.6g/L Na2MoO4 in the electroless plating solution,when the Na2MoO4 addition is 0.5 g/L,the cell structure of the alloy coating is the smallest and the microstructure is the most compact;the friction coefficients of the alloy coating is the smallest,which is 0.404.The polarization curves and impedance spectra results show that the self-corrosion potential of the Ni-Mo-P alloy coating prepared by 0.5g/L Na2MoO4 addition is the most positive,which is-0.8273V,the minimum self-corrosion current is 2.3041 ×10-6A/cm2;and the arc resistance radius reaches the maximum.Therefore,the wear and corrosion resistance of the Ni-Mo-P alloy coating prepared with 0.5g/L Na2MoO4 addition is the best.(4)Compared with 0.1,0.2,0.3 and 0.5g/L CNT in the electroless plating solution,when the CNT addition is 0.4g/L,the cell-like structure of the Ni-Mo-P/CNT composite coating is the smallest,and the friction coefficient of composite coating is the smallest,which is 0.201.The polarization curve and impedance spectroscopy results show that the self-corrosion potential of the Ni-Mo-P/CNT composite coating prepared by 0.4g/L CNT addition is the most positive,which is-0.1673V,the minimum self-corrosion current is the most positive,which is 2.3041×10-6 A/cm2;and the arc resistance radius reaches the maximum.Therefore,the wear and corrosion resistance of the Ni-Mo-P/CNT composite coating prepared with 0.4g/L CNT addition is the best.