Cast aluminium-silicon alloys containing graphite particles are
reported to offer the potential for use as bearing and cylinder block
materials due to low friction and wear characteristics, good thermal
conductivity and resistance to corrosion. However, a fundamental problem
exists in dispersing graphite particles because liquid aluminium alloys
do not wet graphite and so particles are rejected by the melt.
The first section consists of a literature survey which examines
the potential for graphite aluminium alloys, and reviews various methods
for dispersing graphite particles. The potential for the use of recently
developed methods of casting semi-solid alloys as a means of retaining
graphite particles in melts is then considered.
The second section reports on an investigation into the production
of aluminium-silicon alloys which contain graphite particles and an
evaluation of the mechanical and tribological properties of the composites
produced with various silicon and graphite contents. Processing semisolid
alloys produced an even dispersion of graphite particles without
segregation, agglomeration or rejection. Solidification under pressure
(squeeze casting) was used to optimise the mechanical properties of the
composites. The evaluation of mechanical and tribological properties showed
that strength and ductility were reduced in alloys which contained
graphite. Wear tests showed that graphite additions provided increased
load carrying capacity, reduced coefficient of friction, reduced steady
running temperature and reduced damage to mating components. There
was no evidence of a deterioration in corrosion from corrosion tests
and machinability tests showed that machinability was greatly improved
by the addition of graphite particles.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.