Protic Ionic Liquids Used as Metal-Forming Green Lubricants for Aluminum: Effect of Anion Chain Length

Among the applications for protic ionic liquids (PILs), lubrication is one of the newest and the most promising. In this work, ammonium-based protic ionic liquids were tested as lubricant fluids for aluminum-steel contacts. PILs were synthesized with 2-hydroxyethylamine (2HEA) and a carboxylic acid (formic and pentanoic), aiming to understand the effect of two different anion chain lengths on the lubricant behavior. The synthesized PILs were characterized by RMN, FTIR and TGA. Wear tests, conducted using a ball-on-plate configuration, showed that the increase of the anion carbon chain length in the PIL structure reduced significantly the coefficient of friction value. Besides, after the wear tests, the PILs structural integrity was not affected. In the same way, bending under tension (BUT) tests evidenced that the performance for stamping conditions of the PIL with the longest anion carbon chain was similar to that of the commercial lubricant. Since, both formed a uniform tribofilm, developed the same lubrication regime and the drawing forces values were close and constant. Hence, the ionic liquid obtained with 2HEA and pentanoic acid (2HEAPe) is as suitable as the commercial lubricant for metal forming processes.