| Cast aluminum alloys contain higher alloying elements.For example,aluminum-silicon alloys usually contain more than 6% silicon.Phases with different electrode potentials are formed in the alloy structure,making the alloy more prone to corrosion.The phosphate ceramic coating has excellent corrosion resistance.However,the preparation temperature is generally above 300°C,and the aging temperature of cast aluminum alloys is mostly in the range of 145-175°C.A higher preparation temperature will cause the cast aluminum alloy to lose the heat treatment effect of the early stage.A steam-assisted curing method is used to prepare ceramic coatings on the surface of cast aluminum alloys,and the preparation temperature is reduced to 120?,which can be used as the final surface treatment of cast aluminum alloys or pretreatment before painting.In this paper,the morphology and corrosion resistance of coatings prepared with different compositions of Al(H2PO4)3,Mg(H2PO4)2 and Zn(H2PO4)2 binders were compared,and the effects of addition of different TEOS,CeO2,and TiO2 was investigated.Finally,the effects of KH560 and BTSE on the sealing treatment of the coating was explored.The thickness of the coating prepared with binders of different compositions is about 5?m.The coating surface is relatively flat but there are microcracks.The aluminum-magnesium phosphate coating has the densest surface,the best corrosion resistance and durability;the aluminum-zinc phosphate coating has the flattest surface,but the corrosion resistance is reduced;The surface of the aluminum-magnesium-zinc phosphate coating is relatively flat and dense,and its durability is lower than that of the aluminum-magnesium phosphate coating.The best binder composition is m(AHP):m(MHP)=3:1.At this time,the composition of the coating is AlPO4·2H2O,AlPO4 and Mg3(PO4)2.The coating is tightly combined with the substrate,the icorr is 5.165×10-6A·cm-2,which is two orders of magnitude lower than the substrate,and the inhibition efficiency?reaches 97.96.The corrosion resistance of the coating can be improved with the addition of proper amount inorganic fillers of TEOS,CeO2 and TiO2,and the order of the effect of the fillers is CeO2>TEOS>TiO2.The optimal addition amount of TEOS is 5%.At this time,the coating is tightly bonded to the substrate,and the microcrack width is about 0.3?m.The optimal addition of TiO2 is 3%,and the microcracks on the surface of the coating slightly increase.The optimal addition amount of CeO2 is 3%,the surface of the coating is smooth and compact tightly combined with the substrate,and the size of the microcracks has no obvious change,which the coating possesses the optimum properties was gained,the icorr is 2.518×10-6 A·cm-2,and the inhibition efficiency?reaches 99.01.Using KH560 and BTSE silanes to seal the coating can cover the microcracks on the coating surface.When the KH560 concentration is 30%,the micro-cracks on the coating surface are completely closed,and a layer of silane film with a thickness of about 2.5?m is formed on the coating surface.When the BTSE concentration is 30%,the microcracks on the coating surface are reduced to about 0.5?m,and a layer of silane film with a thickness of about 2?m is formed on the coating surface.At the same concentration,the treatment effect of KH560 is better than that of BTSE. |
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