Development of Corrosion Resistant Coatings for Aerospace Aluminium Alloy AA2024- T3

Abstract

Five organic molecules, namely, (E)-2-(2-hydroxybenzylidene) hydrazinecarbothioamide (2-MHC), (E)-2-(2,4-dihydroxybenzylidene) hydrazinecarbothioamide (2,4-DHC), (E)-2-(3,4-dihydroxybenzylidene) hydrazinecarbothioamide (3,4-DHC), (E)-2-(2,3,4-trihydroxybenzylidene) hydrazinecarbothioamide (2,3,4-THC) and Bis[[3,4-Dihydroxyphenylmethylene]- carbonothioic dihydrazide] (3,4-DCT) were synthesized and their corrosion inhibition actions on 2024-T3 aluminium alloy were studied in 3.5% NaCl solution. The synthesized inhibitors were found to provide corrosion protection on AA2024-T3 by forming adsorbed layers on the alloy surface. To explore the possibility of using the synthesised inhibitors for corrosion detection applications, the initial studies were carried out on all the five inhibitors. It was found that only 3,4-DHC qualified in the tests, by imparting the colour change at the corrosion sites. From the five inhibitors studied for their inhibition action, the three most effective inhibitors were employed for coatings applications. An oxide layer was created on the aluminium alloy by anodizing the surface in 10 wt % sulphuric acid and was sealed with the three inhibitors, namely, 2,3,4-THC, 3,4-DHC and 3,4-DCT to evaluate their role in the enhancement of corrosion resistance. The order of the corrosion protection efficiencies of the anodised layer is: Ox < Ox-2,3,4-THC < Ox-3,4-DHC < Ox-3,4- DCT. The effect of corrosion inhibitor addition on the anticorrosion properties of primer coatings on aluminium alloy 2024-T3 was investigated. 3,4-DCT, 3,4-DHC and 2,3,4-THC were supplemented to epoxy primer. The addition of 2,4-DCT and 3,4-DHC to primer coating, offered good barrier properties. The addition of 2,3,4-THC provided active corrosion protection along with good barrier properties. The synthesised inhibitors 3,4-DHC and 2,3,4-THC were added to the hybrid sol to study their effect on the corrosion protection efficiency of the sol-gel coating. Addition of corrosion inhibitors to the coating enhanced the corrosion protection abilities of sol-gel coatings. The order of the corrosion protection efficiencies is: Uncoated < sol-gel coated < sol-gel + 2,3,4-THC coated < sol-gel + 3,4-DHC coated.