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The effect of primary silicon refinement on the microstructure and properties of hypereutectic aluminum-silicon alloys. Wootton, George Claude


The effect on microstructure and strength properties of hypereutectic aluminum - 20% silicon alloys of various refining additions has been studied by means of metallographic observations, hardness tests and a quantitative determination of the interparticle spacing for the primary silicon. A mechanism has been proposed to explain the observed coarsening of the eutectic which accompanies primary silicon refinement, and the combined effect of the improvement of primary dispersion and increased eutectic coarseness on strength properties has been discussed. Refining mechanisms for the refining additions used have been suggested and the reasons for the observed effect of the various refining additions on the shape of primary silicon have been presented. An explanation is offered for the increase in primary refinement which results from an increase in the time the alloy is held molten after fluxing with phosphorus penta-chloride. The apparently anomalous behavior of phosphorus-copper refined alloys has been explained on the basis of the degree of dissemination of the phosphorus in the molten alloy.

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