Protection Mechanism of Al-Rich Epoxy Primer on Aluminum Alloy 2024-T3

The active aluminum-rich primer (AlRP) was invented and developed at NAVAIR to sacrificially protect aluminum alloys and steels from corrosion. The Al pigments (Al-Zn-In) in AlRP were fabricated from a sacrificial anode alloy, which has a lower open-circuit potential than common aluminum alloys. However, initial results indicated that AlRP undergoes severe self-corrosion. Therefore, the Al pigments were pretreated in a trivalent chromium passivation (TCP) bath to reduce the self-corrosion rate. The objectives of this study are to understand the anti-corrosion properties of AlRP on aluminum alloy 2024-T3 substrate and to evaluate the effect of TCP treatment on the Al pigment particles. The polarization curves of AA2024-T3 and active aluminum alloy (Al-Zn-In) show that TCP-treated active aluminum alloy has lower corrosion potential than AA2024-T3 and thus would sacrificially protect it. The AlRPs were exposed in an accelerated exposure test, GMW14872. Exposed samples were then examined using scanning electron microscopy and energy dispersive x-ray spectroscopy to understand the coating degradation process. The AlRP with TCP-treated pigments outperforms a similar coating with untreated pigments.