ZDDP and its interactions with an organic antiwear additive on both aluminium–silicon and model silicon surfaces

•Aluminium–silicon alloy was lubricated with ZDDP and an organic antiwear additive.•Silicon crystal was used to replicate contact conditions within the Al3Si alloy.•The resultant tribochemistry was similar to ferrous surfaces lubricated with ZDDP.•ZDDP tribofilm formation was enhanced with the use of an organic antiwear additive.•The combination of ZDDP and OAW improved wear protection compared to ZDDP.

The boundary lubrication of an aluminium–silicon alloy using zinc dialkyldithiophosphate (ZDDP) or ZDDP and an organic antiwear additive (OAW) has been investigated. Contact conditions on silicon grains within the aluminium alloy were replicated using a model silicon surface. On either substrate, ZDDP tribofilms did not form readily and possessed poor lubricating characteristics, but the addition of the organic additive improved film formation and wear performance. An increase in film thickness, surface coverage and mechanical properties of the ZDDP+OAW tribofilm was accredited with the wear improvement. The tribochemistry of worn aluminium–silicon and silicon surfaces was similar to ZDDP-lubricated ferrous substrates.