New High Durability Sol-Gel Surface Pretreatments for Aluminum

Conversion coatings, which both inhibit metallic corrosion and promote coating adhesion have long been a key component in aircraft maintenance. Commercially available conversion coatings and primers contain toxic and corrosive chemicals, most notably,hexavalent chromium compounds. In order to achieve the same type of surface chemistry and morphology necessary for effective corrosion inhibition without chromates, a novel pretreatment method is proposed. The objective of the Phase I program is toidentify candidate materials which meet the goals of low toxicity, simple application, removal on command, adhesion promotion, and corrosion inhibition of non-ferrous alloys. This involves synthesizing novel corrosion-inhibiting compounds and formulatingnew ionic self-assembling monolayer-based coatings. A novel combination of metal surface-active compounds and sol-gel precursors will be used to form self-assembling coatings that possess optimum barrier properties, primer coat adhesion and suppression ofelectrochemical reactions. These properties will be tested on common aircraft aluminum alloys for salt fog resistance and paint adhesion. Potentiodynamic electrochemical analysis will be used to study the corrosion inhibiting mechanisms. A system willbe devised for rapidly removing the protective coatings. The pretreatment systems are designed to be easily applied and removed, chromium-free, and to form long lasting interfaces between metals and coatings. An effective, corrosion inhibiting material or process which excluded chromium compounds would provide the DoD and commercial aviation with a cost-effective process for maintaining an aging aircraft inventory. Potential commercial applications wouldinclude corrosion prevention treatments for the aerospace, electronics, automotive and marine industries.