X-ray absorption spectroscopy of antiwear films on aluminum alloys generated from zinc dialkyldithiophosphate

Abstract

The boundary lubrication of Al alloys 6061 (Al-6% Si) and A-390 (Al-18 wt% Si), by a sec-ZDDP (zinc dialkyldithiophosphate) oil blend was examined at 60 and 100°C. The wear performance in the ZDDP blend was an improvement on base stock. At 100°C the ZDDP prevented scuffing, though no antiwear films could be detected due to the severe wear. At 60°C all samples showed initial scuffing followed by a more controlled wear given by an embedded antiwear film. P L-edge X-ray near-edge structure (XANES) spectroscopy using synchroton radiation was used to characterize the antiwear and thermally generated deposition films on the Al alloys. P L-edge XANES results of the antiwear films at 100°C showed the absence of a polyphosphate film. A well-developed polyphosphate film was indicated at 60°C, very similar to that formed on steel at 100°C. P L-edge XANES results of the thermal deposition films showed the presence of only unchanged sec-ZDDP at 125°C with no polyphosphate present. A polyphosphate film was present at 200°C, similar to the antiwear film for Al alloy at 60°C and steel at 100°C.