Short alkyl chain imidazolium ionic liquid additives in lubrication of three aluminium alloys with synthetic ester oil

Abstract

In this study the authors have compared the tribological behaviour of three aluminium alloys (ASTM 2011 T3, ASTM 6061 T6 and ASTM 7075 T6) lubricated with two room temperature ionic liquids (ILs) with the same short alkyl chain imidazolium cation, 1-ethyl-3-methylimidazolium, and two different anions, tetrafluoroborate (BF₄) (L102) and bis(trifluoromethylsulfonyl)imide {[(CF₃SO₂)₂N]; NTf} (LNTf102). The ILs were used as 1 wt-% additives of the synthetic ester base oil propylene glycol dioleate (PGDO) in reciprocating sliding tests. The results are discussed in terms of the properties of the lubricants and the hardness of the aluminium alloys. Plastic deformation, wear mechanisms and surface interactions have been studied by electron microscopy (SEM), energy dispersive (EDS) spectroscopy and three-dimensional profilometry. The tribological performance of both ionic liquids is similar, and depends on hardness values and on the degree of plastic deformation of each alloy. Reductions of more than 40% in the wear rate and surface roughness with respect to the base oil are achieved for both additives only for the hardest alloy Al7075. The performance of the additives is independent of the contribution of the different anions due to the absence of extensive tribocorrosion processes.