A method was developed for applying an inorganic conversion coating on that is procedurally similar to chromate conversion coating methods; this method, however does not use or involve hazardous/toxic chemicals. The coating forms by precipitation involving Al(sup 3+) Li(sup +), OH(sup (minus)), CO(sub 3)(sup 2)(minus), and possibly other anions. This polycrystalline coating is continuous, conformal and persistent in aggressive environments. Coating thicknesses range from several tenths to ten micrometers. Although the outer portions of the coating are porous, the pores do not penetrate to the substrate interface. These coatings do not match the levels of performance offered by commercially available chromate conversion coatings, but are capable of meeting many of the corrosion resistance, electrical resistivity, and paint adhesion requirements established in MIL-C-5541E ''Chemical Conversion Coatings on Aluminum and Aluminum Alloys.'' In this paper, methods for producing the talc coating on aluminum alloys 1100 and 6061-T6 are described and compared to traditional chromate conversion coating methods. Resulting coating structure and composition are described. Performance data for the talc coatings in MIL-C-5541E required tests are presented along with data commercial chromate-based coatings.
展开▼
