Fluidity of Al based metal matrix composites containing Al2O3 and SiC particles

The flow behaviour of aluminium alloy matrix composites containing Al2O3 and SiC particles is studied. A357 aluminium alloy was the matrix alloy common to both metal matrix composites (MMCs). Reinforcing particles were similar in shape and size (40 mu m). Both MMCs were made by the stir casting process using parameters optimised so far as possible. The flowability of the MMCs was studied by measuring the fluidity of strips cast in a permanent mould. The results showed that the fluidity of both MMCs appeared to be reduced by increasing percentage addition of particles and further reduced by increasing times and temperature. It is proposed that much of this behaviour is not the result of the added reinforcing particles but the result of oxide films necessarily entrained by the stir casting process. The agglomeration of additions commonly seen in particulate MMCs is also attributed to the entrainment of clusters of additions as they enter the liquid through the surface oxide film.