Seizure Resistance of Cast Aluminum Alloys Containing Dispersed Graphite Particles of Different Sizes

Abstract

Seizure resistance of the cast graphite particle-aluminum 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 aluminum alloys is more than 2 percent, 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 aluminum matrix and the low flow stress of the graphite particles. During wear, the deforming aluminum 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-aluminum composite alloys. This layer persists even after extensive wear deformation.