Filiform corrosion imaged beneath protection layers on Al alloys

Abstract

Aluminium alloys used extensively in aircraft, ships and land transport vehicles are typically protected by a thin conversion coating based on chromium compounds followed by a surface protection layer of polymer paint. Breeching of the protection layer and exposure to a salt spray induces the growth of filiforms from the breech across the aluminium surface under the protective layers. The growth of the filiform is promoted by the formation of a galvanic cell based on chlorine chemistry. In this paper we study the elemental composition of the filiforms using a nuclear microprobe with 3 MeV proton beams. The deep penetration of this beam allows the composition of the intact filiform to be prob..