ON THE CASTABILITY OF AL-SI SIC PARTICLE-REINFORCED METAL-MATRIX COMPOSITES - FACTORS AFFECTING FLUIDITY AND SOUNDNESS/

This paper presents results of studies carried out to determine the ef fect of melt and mold temperatures on the castability of four Al-Si/Si C(p) reinforced metal-matrix composites containing two levels of silic on (7 and 10%wt) and two levels of SiC (10 and 20% vol.), in terms of the fluidity and soundness. These were assessed by monitoring the Al4C 3 formation, SiC distribution, porosity volume fraction and melt clean liness (in terms of the oxide content) in specimens prepared under dif ferent melting and casting conditions. The results show that a low sil icon content coupled with a high SiC level accelerates the formation o f Al4C3 which is detrimental to the fluidity and hence castability of the composite alloy. Increasing the silicon level from 7 to 10%wt impr oves the castability through a significant decrease in Al4C3 content. Increasing the SiC content from 10 to 20%vol. results in a relatively homogeneous distribution of the particles within the matrix, even at l ow cooling rates of about 10-degrees-C s-1. The presence of oxides in an otherwise fluid composite melt considerably reduces the castability .