EFFECT OF MELT, SOLIDIFICATION AND HEAT-TREATMENT PROCESSING PARAMETERS ON THE PROPERTIES OF AL-SI-MG/SIC(P) COMPOSITES

With the recent renovations in casting technology and foundry procedures, Al-Si-Mg alloys reinforced with SiC particulates are being increasingly employed in automotive and aerospace applications. The SiC reinforcement particles influence the solidification process in various ways, affecting the fluidity and castability of these composites. This articles reviews the results of an extensive study carried out on different aspects of Al-Si-Mg/SiC(p)-type metal-matrix composites containing 7 or 10 wt % Si, reinforced with either 10 or 20 vol% SiC particulates. Aspects investigated include the castability and soundness in terms of melt fluidity, the effect of the solidification rate and of inclusions on the mechanical properties, and optimization of the heat-treatment parameters with regard to these properties. The influence of the processing parameters on the mechanical properties was determined by monitoring the microstructural changes taking place during the various stages of processing, by measurements of the dendrite arm spacing, porosity and SiC-particle content and distribution in the castings obtained, as well as the amount of oxide inclusions and other harmful reaction products such as Al4C3 present therein. The effect of employing the fluxing procedure commonly used in Al-Si-Mg alloys on the mechanical properties of one of the four composites studied is also reported.