Abstract

The fabrication of Metal Matrix Composites (MMCs) using the stir casting technique is the focus of this study. A significant part of the work consists of the design of a specialised rig for this high temperature processing method. Following preliminary tests, graphite was chosen as the mam vessel material, and a crucible was designed with a bottom pouring mechanism. In order to optimise stirring conditions, a computer program was used to stimulate the fluid flow in the process crucible. The mam research challenge was to solve the problem o f poor wettability between particulate SiC and molten aluminium (A359 alloy), materials which are potentially suitable to the proposed fabrication approach as reinforcement and matrix materials respectively. The percentages of SiC particles used were m the range o f 5 to 25 volume percent, samples were cast into ingot or tensile specimen, and some samples were heat treated by precipitation hardening with T6 artificial ageing. It was found that the both increasing the silicon carbide content, and T6 artificial treatment increase the mechanical properties such as hardness and tensile strength of the matrix alloy. Charactenzation of the MMCs produced included observation of microstructure, porosity content measurement, tensile strength, microhardness, and compression strength measurements. The fabrication approach was successful in producing cast MMCs samples which have reasonable mechanical properties The use of clean SiC particles, magnesium as a wetting agent, and continuous stirring while the MMC slurry is solidifying were found to promote the wettability o f SiC and A359 matrix alloy Decreasing the solidifying time was found to improve the wettability significantly.