A multi-technique characterization of ZDDP antiwear films formed on Al (Si) alloy (A383) under various conditions

Abstract

The simulation of the lubrication of aluminum-silicon (Al-Si) alloy cylinder-bore conditions is an important goal in automotive tribology. This study describes the use of X-ray absorption near edge structure (XANES) to determine the macro-chemistry of zinc-dialkyl-dithiophosphates (ZDDPs) antiwear (AW) films formed on A383, an Al-Si alloy. The temperature dependence of the chemistry and mechanical properties were examined using X-ray photoelectron emission microscopy (X-PEEM), and imaging indentation techniques. Our findings suggest that ZDDPs break down to form polyphosphate glasses, which have different chemical natures and depend on the underlying substrate. Furthermore, the chemical nature of the films appears temperature dependent on both the macro-and micro-scale. Not only are the chemical species different, but the mechanical properties also differ, depending on the region upon which an AW pad is formed. Through the use of focused ion beam (FIB) milling, we can determine the film thickness, which was previously estimated from the P K-edge XANES areal density of samples with known thicknesses.

Tribological performance of an Al—Si alloy lubricated in the boundary regime with zinc dialkyldithiophosphate and molybdenum dithiocarbamate additives

“…In Al-Si alloys, the ZDDP tribofilm is not effective in wear reduction as it is in Fe-based materials. This is also observed by Pereira et al [6] where it is suggested that this is due to the low tenacity of the film to the AlSi material. The reason for the low tenacity is because the Al-Si material can not provide thick oxide layer on the surface, therefore the ZDDP film is unable to bind to the surface via oxide as it does on the steel surface.…”

“…The study of Al-Si alloys against steel lubricated by commercial engine oils under boundary lubrication conditions has been reported occasionally since the 1960s and 1970s [2,3], with research focused mainly on the tribological performance of Al-Si alloys lubricated by zinc dialkyl dithiophosphate (ZDDP) [4][5][6]. The challenge in understanding fully these interactions lie mainly in the research being performed using different Al-Si alloys and under different testing conditions.…”

“…Performance of this additive in maintaining low wear is due to its interaction with the ferrous material resulting in formation of a layered phosphate/sulphide tribofilm at the interface. Formation of the ZDDP tribofilm in Al-Si alloys has been recently studied [4][5][6] and, although the findings are still not conclusive, an insight on the interaction between this additive and the Al-Si alloy has started to develop. It is demonstrated that polyphosphates form on both Al and Si material [6] while the higher Si content promotes formation of the polyphosphates from the ZDDP additive [4].…”

A Semi-deterministic Wear Model Considering the Effect of Zinc Dialkyl Dithiophosphate Tribofilm

“…Antiwear additives are generally known to form protective tribofilms on the surface of contacting bodies. The most common such additive is zinc dialkyl dithiophosphate (ZDDP) [16], which can form tribofilms on various materials including steel, diamond-like carbon (DLC) and Si/Al alloys [17][18][19][20][21][22][23][24][25][26][27]. Though extensively studied, the specific processes involved in formation and removal of tribofilms in these different systems are not yet fully understood.…”

Model scale generation and microscopic characterisation of tribofilms formed on Fe and Cu alloys

“…11 summarise the results of surface characterisation for the Fe/Cu-system for both the steel ring and the CuPb22Sn2 disc. Results of elemental analysis (EDX) are expressed in mass percent.…”