Study On Preparation Processes Of Ceramic Coating On Aluminum Surface

The preparation of ceramic coating on aluminum surface is the efficient way to enhance the surface performances of aluminum, of which the normal methods are thermal spraying technology, PCD, CVD, Plasma micro-arc oxidation etc. But the preparation of ceramic coating on aluminum surface with sol-gel is a real new area, whose purpose is to explore a preparation of ceramic coating with low cost and high performances. So the paper mainly studied the preparation and main performances of the coating.First is to explore the preparation processes of a ternary complex sol as coating binder, using TEOS, aluminum nitrate, chromium nitrate and so on to obtain Si-Al-Cr hybrid sols. In the process of mixing, added acetylacetone as chelator to make sure the stability of the ternary complex sol. Then added the milled and graded inorganic metal oxides have the same components with the sol system and the other additives to obtain a homogeneous inorganic ceramic coating after sufficient mixing and milling. The research showed, the content of solvent ethanol in SiO2 sol would change the concentration of the reaction system and influence the film forming ability. So the reasonable ratio of SiO2 sol is TOES: H2O: EtOH=1:1:10. And different atomic ratios of Si, Al and Cr can influence the viscosity of the ternary complex sol. When atomic ratio increased, the sol viscosity became larger, the coating film-forming property deteriorated, the dry heat treatment was easy to crack, and the linear expansion coefficient difference between coating and substrate increases can lead to cracking of the interface, so the reasonable atomic ratios of Si, Al and Cr should be Si: Al: Cr=2:1:1.Secondly, the paper studied the influences of rare earth and borax on the coating performances. The coating’ micro hardness of different ratios are all above of the aluminum substrate after the addition of rare earth and borax, of which the highest one is up to 137.75 Hv, increased 62.95 Hv compared with substrate. When the content of borax is less than 3%, the more content of rare earth the better performance of coating’ wear resistance. When the content of borax is more than 5%, the wear resistance would firstly increased and then weaken with the increase of borax content and got the best performance at 16% borax. The adhesion of the coating also got beneficial effect from borax, destructive nature of coating change from attached failure of large areas to the cohesive failure of smaller area. But the corrosion resistance of the coating is not very ideal, need to be further improved and strengthened. And when the rare earth activated substrate surface and refined coating granules, it also generated Y3Al5O12, Y2Si2O7 and other new phases by reacting with the sols simultaneously, which promoted coating densification and played the role of solid sintering. So we can get from the contrast of coating performances that: when borax’ amount is about 15% of fillers, rare earth’ amount is 5%, base ceramic powders are 27%~30% of total coating, can obtain the coating of best overall performances.