Investigation Of Arc-sprayed Aluminium Coating On 6061 Al Alloy And Its Sealing Treatments

Al alloys are more and more extensively used in various fields like aviation and marine applications for their competitive advantages including low weight,high corrosion resistance in combination with their good workability.They have perfect corrosion resistance in the air, however,will be pit corroded in marine atmosphere rich in chloride.To extend the life-span of AI alloy with large structures,the economic and efficient twin-wire arc-spray technology is employed for the deposition of pure aluminium coatings.For further corrosion resistance elevation,two new sealing methods are applied.One is the hydrothermal sealing(HTS),which is more simple and less expensive than the HTS of Al anodic film,and which can fulfill the sealing of comprehensive structures as the boiling water can reach anywhere.The other is Al-rich epoxy resin based paint,electric conductive and corrosion resistant.Here,salt solution immersion test(SSIT) and polarization curves as well as optical microscope,scanning electron microscopy(SEM) coupled with Energy-dispersive X-ray analysis system(EDX),X-Ray diffraction,electron probe microanalysis(EPMA) and Raman spectroscopy are employed for the corrosion behavior investigation of the unsealed coating and the sealed ones with the two new methods.A dense coating well joined with the substrate 6061 Al alloy is achieved using twin wire arc thermal spray system assembled by our laboratory with optimum parameters fixed:voltage 28V,arc current 100A,spraying distance 100mm,spraying angle 90°and air pressure 0.6MPa. The coating corrodes fast and gradually more and more slowly,protecting the substrate in the long run.With the analyses of series of corrosion experiments,a corrosion behavior model is established of the substrate and the coating,providing technological bases for the marine applications of A1 alloys with large structures.The HTS coating is covered with a continuous film of aluminium hydroxide structures, and some deionized water manages to penetrate.Besides,pores in the surface as well as in the inner part get smaller and fewer.In SSIT,the HTS coating has a similar corrosion process to the unsealed one,but corrodes much more slightly.After SSIT,the HTS coating exhibits small changes in polarization curves,and still displays a wide passive region,implying slight corrosion in 90 days immersion and proving much higher corrosion resistance than the unsealed coating in the whole immersion process.In a word,the HTS treatment is a successful sealing treatment for the arc sprayed Al coating.Al-rich epoxy resin based paint with acceptable surface is attempted for the first time to prepare on the arc-sprayed aluminium coating surface,corrosion resistant and electric conductive.When the Al powder reaches 50wt.%,an electrical network is formed,making the paint with good electric conductivity.Proper addition of Al particles neither degrades the adhesive properties of epoxy resin nor weakens its barrier type protection of the coating substrate.Because of the close Al particle-resin integration and the tight adhesion in the paint/coating interface,strong adherence of corrosion products on Al particles,as well as probable passivation of Al particles,the paint showed no worse corrosion resistance properties than the epoxy resin and corroded at a similar rate to the epoxy resin,slowly and slightly, protecting the coating base as a barrier type film.