Surface Protection for Aircraft Maintenance by Means of Zinc Rich Primers

Abstract

The aerospace industry urgently needs environmentally friendly materials and processes for corrosion protection of aluminium alloys in aircraft structures. Until now this has been achieved by hexavalent chromium based compounds in either surface pre-treatments or primers. Due to its carcinogenic properties the use of chromates is restricted and a ban is expected soon. Up to now an all over recognized replacement of chromates is not available for aircraft maintenance, although a lot of research has been done and promising results also exist for some chromium-free conversion coatings and for magnesium rich primers. WIWeB found out in laboratory scale and by flight trials that thin layers of zinc rich primers, if applied with dry film thickness of 10 – 20 µm, can be used successfully to prevent corrosion on aluminium for aircraft. Solvent based as well as water based zinc rich primers have been tested. The major part of the work presented is from further investigations which show, that another great improvement can be achieved, when thin layers of organic adhesion inhibitors like 2-aminopropyltriethoxysilane and 4-t-butylbenzoic acid are applied on the unclad Al 2024 panels, which had been scrubbed with abrasive pads before. This process is followed by the application of the thin film of zinc rich epoxy primer before the usual 2-pack epoxy primer is applied.

Corrosion processes and strategies for prevention: an introduction

“…Liquid-applied paints have four basic components: (a) resin or binder, (b) solvent, (c) pigments and (d) miscellaneous components (dryers, fl ow-control, gloss-control and suspension agents). The resin or binder is based on the organic/polymeric structure and can comprise the following types: acrylics [49,50] , alkyds [51][52][53] , epoxy (novolacs, polyamides) [54,55] , phenolics [56,57] , polyesters [58,59] , polyurethanes [60,61] , silicone [62] , vinyl [63] , zinc-rich inorganics/ organics [64] and magnesium (Mg)-rich organics [65] . The solvent, thinner or diluent refers to their ability to dissolve or reduce the viscosity of the binder or resin in the paint.…”

Non-Chromate Surface Protection for Aircraft Maintenance

“…The high reactivity of Zn powder seems to be the driving force leading to a type of chemical barrier protection. Magnesium (Mg) rich primers have also been reported to be effective [11,12]. It is likely that such products, which also work by cathodic protection, will be available soon.…”