Study On Corrosion Resistance Coating Of Magnesium Alloy

In this paper,cermet coatings were deposited on AZ91D magnesium alloy by electrophoretic deposition technique.The microstructure,adhesion strength and electrochemical corrosion resistance of Al₂O₃/Ni and YSZ/Ni cermet coatings with different ratios were studied mainly.In addition,the effect of cermet coatings with ball peeling treatment of substrate was researched.The results show that the cermet coating of Al₂O₃:Ni=1:3 has the lowest surface porosity,the addition of Ni has filled part of the gap and decrease the agglomeration of Al₂O₃powder.The additional of nano Al₂O₃particles affected the crystallization process of Ni particles,Ni particles were refined and the organization is more uniform and compact.There was obvious cracks on the interface of pure Al₂O₃coating and substrate which made the coating is easier to be peeled off and cracked,however,the Al₂O₃/Ni cermet coating has no obvious cracks and the bond strength has increased,this is due to a small amount of Ni from the coating diffuses into the substrate,which reducing the thermal expansion coefficient mismatch of the substrate and the coating.Through the electrochemical polarization curve and impedance spectrum test,the corrosion resistance of Al₂O₃:Ni=1:3cermet coating is the best.The results show that the thickness of YSZ/Ni cermet coating with three different ratios decreases with the decrease of nano YSZ powder in the suspension under the same experimental conditions.The Ni elements exist in the form of solid solution in Zr O₂,which promotes the diffusion of Zr elements,which makes the coating more compact and homogeneous.The cermet coating of YSZ:Ni=1:1 has good adhesion with the substrate,uniform structure,compact coating and low porosity which can separate the substrate from the corrosive environment effectively,and has the best protection for the substrate.Compared with cermet coatings without ball peeling treatment of the substrate,the results show that the bonding strength of ball peeling coating samples has increased from3.2 N（Al₂O₃:Ni=1:3）and 2.7 N（YSZ:Ni=1:3）to 3.5 N and 3.1 N respectively.The EDS mapping analysis indicated that more Ni elements were diffused from the coating to the substrate,and an transition layer was formed at the interface between the coating and the substrate.The research shows that the cermet coatings with ball peeling treatment of the substrate has superior adhesion and and corrosion resistance.