Rare earth mercaptoacetate corrosion inhibitors for AA2024-T3

The corrosion inhibition of the aluminium alloy AA2024 using rare earth mercaptoacetate inhibitors was investigated to elucidate the mechanisms of protection. The strong susceptibility towards localised corrosion by AA2024 has in the past been mitigated through the use of chromate-based inhibitors, however their toxic and carcinogenic nature has meant a reduction of use in all applications, including aerospace applications. Rare earth-organic compounds have shown promising successes in limiting the corrosion on AA2024, but the process of inhibition is currently not well understood. It was hypothesised that the incorporation of a thiol-containing organic into the inhibitor could lead to deposition of the inhibitor, through the sulfur, at Cu-rich sites in the AA2024 surface and effectively limit corrosion. This has led to the exploration of corrosion protection with rare earth mercaptoacetate compounds. In the current work, electrochemical testing and surface characterization techniques were utilised to examine the behaviour of rare earth mercaptoacetate inhibitors in 0.1 M sodium chloride solution. The praseodymium mercaptoacetate compound was found to reduce the average corrosion current density to a greater extent than that of the cerium mercaptoacetate compound in neutral pH conditions. The differences between the two inhibitors will be discussed.