1991-02-01

New Processes for Corrosion Control of Active Metals in Severe Environments 910922

The corrosion of active metals such as magnesium and aluminum continues in spite of the recent development of more corrosion resistant alloys. Much of the corrosion occurs due to chloride ion attack aggravated by design problems that produce crevices and other corrosion prone surfaces. Many components made of obsolete alloys remain in service.In this paper basic protection schemes are reviewed for both magnesium and aluminum. Pretreatments and coating systems typically used are outlined with emphasis on problems at overhaul and reassembly. A novel coating primer/sealer process is described which provides a significantly more corrosion resistant surface for both magnesium and aluminum alloys. A mechanism for the operation of the coating film is offered; how it is combined with pretreatments to seal and prime the active metal surface is described. Data is supplied indicating corrosion resistance in salt spray tests, humidity tests and exposure to aerospace fluids. Compatibility with MIL-R-3043 sealant is described as well as MIL-P-23377 and MIL-C-83286 type epoxy polyamide/urethane paint systems.Components are described that utilize the process, including alloy, pretreatment and final use of components.

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