Lithium and Cerium based sol-gel coatings for corrosion protection of AA2024-T3

Abstract

Due to the demand of reducing the weight of aircrafts to reduce the carbon consumptions without compromising the mechanical properties, aluminium alloy AA2024-T3 has been widely applied in the aircrafts’ manufacture. However, the alloying elements which ensure the mechanical properties also could increase the susceptibility of localized corrosion. The chromate conversion coatings (CCCs) have been used as the efficient anti-corrosion protection for aluminium alloys. Due to their toxicity, many countries and regions in the world have been banned CCCs from many industries. Numerous alternatives were studied for decades to replace the CCCs. Among all of them, the sol-gel technology is a promising method to inhibit the corrosion of aluminium alloy AA2024-T3. Furthermore, the addition of corrosion inhibitor into the sol-gel coating additionally increases active corrosion protection of aluminium alloys. This thesis focuses on the sol-gel coatings corrosion protection of aluminium alloy AA2024-T3 with the incorporation of lithium and cerium salt as corrosion inhibitors. The corrosion protection for the intact coatings was analyzed by potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). An active corrosion protection for the scribed coatings was investigated by observation of immersion test with digital optical microscope and the electrochemical impedance spectroscopy (EIS). The main findings of the present work are the following: (1) the sol-gel coating decreases the corrosion. (2) the addition of corrosion inhibitors, LiNO3 and Ce(NO3)3, into the solgel coating decreases the corrosion current. (3) the combination of LiNO3 and Ce (NO3)3 provides the best corrosion protection for intact coatings applied on AA2024-T3.