Use of rare earth salts as electrochemical corrosion inhibitors for an Al–Li–Cu (8090) alloy in 3.56% NaCl

Abstract

Alloys used in the aeronautical industry, mainly of the series 7xxx and 2xxx, are liable to suffer several types of corrosion attack due to the fact that they are exposed to humid atmospheres of different aggressiveness. For this reason they are protected by surface treatments that can lengthen their service life. These treatments are mainly based on the use of chromates in anodic films, in conversion layers, or as inhibitor pigments in paint system primer coatings. However, in view of the high toxicity of chromates, viable alternatives are being researched to replace them. The literature includes a number of studies focused on the use of rare earth salts as inhibitors that can offer good levels of protection on Al–Zn–Mg–Cu and Al–Cu–Mg alloys. On the other hand, the need to reduce the weight of aeronautical structures means that research continues to be carried out on lightweight aluminium alloys such as Al–Li. The authors have not found references on the inhibition of this type of alloys, which may be of interest in the future. This work presents the results of localized corrosion inhibition on the Al–Li–Cu alloy 8090 T-8171 in 3.56% NaCl by means of the addition of CeCl 3 and LaCl 3 as inhibitors. The corrosion/inhibition mechanism and kinetics have been studied using electrochemical and surface analysis techniques (SEM, EDS, XPS). The inhibiting ability of the two salts in this system has been compared for the inhibitor concentrations used.