Evaluation of Pressure Die Castings Produced in a Graphitic Hypereutectic Aluminium — Silicon Alloy

Summary

The paper describes a method of incorporating graphite particles within a partially solid aluminium alloy developed specifically for the production of automobile cylinder-block castings. The application of the compocasting technique, in which the alloy was agitated vigorously as it cooled below its liquidus, enabled the non-wetting graphite particles to be retained within the melt. The partially solid composite was shaped into a simple casting by cold-chamber pressure die casting. Graphite particles of between 353 and 50 μm were incorporated successfully within the melt at addition levels of up to 7.5 weight % and the effects of particle size and addition level on the mechanical properties of the alloy were established by tensile and hardness tests. Data on the friction and wear characteristics of the composites were obtained by a pin on discwear test. The results for the composite alloy were compared with those for graphite-free control samples produced by: sand casting; gravity die casting; pressure die casting; a combination of rheocasting and pressure die casting. From the results it was concluded that improvements in the tribological properties of the alloy could be obtained by graphite additions, but at the expense of mechanical properties.