EFFECT OF HUMIDITY ON FRICTION AND WEAR OF AL-SI EUTECTIC ALLOY AND AL-SI ALLOY-GRAPHITE COMPOSITES

The influence of moisture content in air on the unlubricated sliding w ear of an Al-Si eutectic alloy and an Al-Si alloy-graphite composite m aterial containing 55 vol% graphite particles has been investigated. E xperiments were conducted in a relative humidity (RH) range of 1-95% u sing a cast iron counterface. In the humidity range of 1-70% RH the mi ld wear of the Al-Si alloy was characterized by the formation of an ir on-rich compacted surface layer. On increasing the humidity content fr om 70% to 95%, the wear rate decreased by two orders of magnitude owin g to the in situ formation of an oxide-rich surface film. The tribolog ical behavior of the Al-Si alloy-graphite composite material closely r esembled that of graphite. In ambient air its coefficient of friction was low (0.2-0.25) and its wear rate was three orders of magnitude low er than that of the base alloy. However, an abnormally high friction a nd wear behavior was observed for the composite material at 1% RH.