Seizure resistance of cast aluminium alleys containing dispersed graphite particles of differing sizes

Abstract

Seizure resistance of the cast graphite particle‐aluminium composite alloys, containing graphite particles of varying sizes has been studied using a Hohman wear tester. The size of the spheroidal graphite particles was varied from 30 µm to 400 µm, and in one case 80 µm size flake graphite was used to observe the effect of shape of graphite. When the graphite content of graphitic aluminium alloys is more than 2 per cent, these alloys can be self‐mated under condition of boundary lubrication without seizing. The size and shape of the graphite particles had no significant effect on the seizure resistance of these alloys, in the range of conditions investigated in this study. This is attributed to the extensive deformation and fragmentation of graphite due to the low yield strength of the aluminium matrix and the low flow stress of the graphite particles. During wear, the deforming aluminium matrix accentuates the deformation and fragmentation of subsurface graphite particles and causes them to come to the mating surface, thus providing continuous lubrication and preventing seizure. Even after a short run‐in period, a continuous layer of graphite is observed on the mating surfaces of graphite particle‐aluminium composite alloys. This layer persists even after extensive wear deformation.