Effect Of Rare Earth On Microstructure And Corrosion Resistance Of Ni-based Amorphous Alloy Coatings

The widespread application of the magnesium alloys has been tremendously limitted by the weak corrosion resistance.Owing to the excellent physical,chemicaloptical,properties of rare earth elements,the research and application in the electrodeposition and electroless deposition become deeper.In this study,using AZ91D magnesium alloys as substrates,focused on preparing three protective Ni-P,Ni-W-P,Ni-Mo-P coatings with adding different rare earth compounds(Ce(NO3)3?Nd(NO3)3),aming to improve the corrosion resistance of the substrates.The details and main conclusions in this study are as follows:(1)Attributing to adding rare earth compounds(Ce(NO3)3,Nd(NO3)3),the as-deposited coating presents fine,uniform and compact microstructure,the quality of the plating is superior compared with the plating which does not add rare earth elements.And the grains exhibit refined and cell structure.When the adding concentration is 1.25 g/L of Nd(NO3)3,the overall properties of the plating are best.Meanwhile,the P content reaches 11.6%,corresponding to amorphous structure.The adhesion between the substrate and the plating reached the best.According to the potentialdynamic polarization curves,the corrosion potential of the plating with 1.25 g/L.Nd(NO3)3 is-0.63 V,which increases by 0.42 V compared with the coating adding no rare earth elements.The radium of capacitive arc the plating reached largest,the corrosion rate of the plating is the smallest,corresponding to the most superior anti-corrosion property.(2)The cell structure of Ni-W-P coatings adding rare earth compounds(Ce(NO3)3,Nd(NO3)3),are batter and more compact than that of the coating adding no rare earth elements,with no defects such as cracks and holes.When the adding concentration is 1.00 g/L of Nd(NO3)3,the P content reaches 12.38%,the W content reaches 0.65%,corresponding to amorphous structure.The critical load is 43 N approximately,with the strongly combination of the plating and the substrate.The potentialdynamic polarization curves indicate that the corrosion potential of the plating is-0.29 V,the corrosion density is 0.000829 A/cm2.At the same time,the radium of capacitive arc of the plating reaches the largest,the corrosion rate reaches smallest,corresponding to the best corrosion resistance.(3)The adding rare earth compounds(Ce(NO3)3,Nd(NO3)3),of the Ni-Mo-P ternary coating which completely covers the substrate presented typical cell structure,and the amorphous degree of the coating is improved.The critical load of the coating becomes larger than that of without rare earth element.Meanwhile,the deposition rate is uplifted.When the adding concentration is 1.00 g/L of Nd(NO3)3,the potentialdynamic polarization curves indicate that the value of the corrosion potential is-0.15 V approximately,which demonstrates that the coating has the best anti-corrosion protection.Additionally,the electrochemical impedance plot suggestes that the radium of capacitive arc of the plating was the largest.