Tribological characteristics of magnesium alloy using N-containing compounds as lubricating additives during sliding

The tribological characteristics of a magnesium alloy, AZ91D, were investigated in a sliding lubricating system using various N-containing compounds as lubricating additives on a Timken type tester against a bearing steel (AISI52100) ring. Results indicated that a significant improvement in the tribological performance exists using N-containing compounds as additives. The characteristics of anti-wear, anti friction and load-carrying capacity increased with an increase in the number of amidogen groups in amine molecules. Antiwear and antifriction characteristics were also observed with an increase in the length of the carbon chain in amide compounds. The amide showed a much better performance than the amine in terms of the tribological characteristics of the magnesium alloy. Electromicroscopy revealed that mild abrasive wear was a predominant wear mechanism of the magnesium alloy using an amine (or amide) additive; while the dominant wear mechanism was severe abrasive wear with severe material deformation using only base oil. Analysis showed the formation of a boundary film on the magnesium alloy. XPS analysis suggested the occurrence of tribo-chemical reactions between Mg and N-containing compounds with the formation of a chemically stable complex of magnesium and amine (or amide), as well as the formation of friction polymer.