Preparation Of Aluminum- Phosphate Coatings And Its Corrosive And Tribological Properties

Phosphate coating is an aqueous inorganic coating,compared with organic coating,inorganic phosphate coating has excellent high-temperature resistance,oxidative resistance,oil resistance and strong adhesion.Phosphate coatings can be used as anti-corrosion materials,wear-resistant materials,refractory materials,which have been widely used in the automotive,aerospace,marine vessels and other fields.However,there is no systematic research on the corrosion behavior and corrosion mechanism of phosphate coatings,as well as silica sol modified phosphate coatings.In terms of phosphate coatings with the addition of ceramic,the friction and wear properties as well as the effect of lubricant medium on phosphate coatings were still lack of research.In this paper,based on the relevant research,aiming at the problems existing in corrosion resistance and wear resistance of phosphate coatings,aluminum phosphate binder was prepared to study the mechanism of binder film formation.Aluminum phosphate coatings,aluminum-phosphate/silica-sol coatings were prepared to study the corrosion resistance of the coating and the effect of silica sol on the corrosion performance.Aluminum phosphate/silicon-carbide coatings,aluminum-phosphate/?silicon-carbide+graphite?coatings were prepared to study the friction and wear behavior of the coatings,and the effect of lubricating medium on its tribological performance.The innovative results achieved are as follows:Aluminum phosphate binder was prepared by chemical synthesis,using thermal analysis and phase analysis to study the adhesive curing mechanism of the film.There were phase transitions occurred during the heat treatment.The structure is stable at 400?and the main phase of binder is Al?PO₃?₃.Aluminum phosphate coating has a good shielding effect to the corrosive medium,which could protect the substrate for a long time.The binder with aggregate to form a continuous film,hindering the corrosive medium from contacting with the substrate.After 120 days soak test,the corrosion resistance of the coating gradually decreased,the corrosion potential decreased from-0.351 to-0.684 V,and the corrosion current increased from 1.366 to 2.4?A·cm^-2?In the Impedance spectrum,the impedance arc radius decreases,the impedance value decreases but still superior to the matrix.The composite coating with 10%silica sol exhibits excellent corrosion resistance.The appropriate amount of silica sol can promote the production of coating network structure,so that the coating combines the low temperature bonding strength of the silica sol and the high temperature bonding strength of the aluminum phosphate binder,which improves the coating quality and further improves the corrosion resistance.The corrosion potential of coating with 10%silica sol increased from-0.351 to-0.23 V,and the corrosion current decreased from 1.366 to 0.561?A·cm^-2.Aluminum-phosphate/silicon-carbide coatings with a silicon carbide aggregate ratio of 0.8 have the best wear resistance.The adhesive can just fill the gap of the aggregate,so that has the highest chimeric strength.The hardness of the coating reached 500 HV and the wear rate was 0.13×10^-3mg·m^-1·N^-1,the coating has the best wear resistance.Coatings with the mass ratio of graphite to aggregate range from 8 to 10%have good overall performance.The addition of 8-10%graphite reduced the coefficient of friction?from 0.8 to 0.35?,and the hardness of the coating remained high?300-350 HV?,while the wear rate remained low(from 0.198 to 0.216mg·m^-1·N^-1).