In-situ formation of SiC-reinforced Al-Si alloy composites using methane gas mixtures

Theoretical and experimental studies on the in situ formation of an Al-Si alloy composite using a methane gas mixture were carried out. An Al-Si alloy composite with in situ formed SiC as a reinforced phase was produced by bubbling methane gas at temperatures from 1223 to 1423 K. An optical microscope, scanning electron microscope (SEM), and electron microprobe were used for the product characterization. Primary and eutectic silicon were observed in the samples taken from the top part of the crucible, and only eutectic silicon was observed in the samples taken from the bottom of crucible. The SiC formation rate increased with the decrease in the bubble size. A silicon concentration gradient existed at different vertical positions of the liquid alloy. The silicon concentration close to the top of the liquid alloy was higher than that at the bottom. The SiC concentration was very low in the bulk alloy. The bubbling of the gas mixture in the melt resulted in the formation of a layer of foam on top of the crucible. Formed SiC particles were enriched in the foam and carried out of the crucible by the overflow foam to a composite collector located under the crucible. The foam in the composite collector was broken, and composites in the foam contained up to 30 wt pct SiC. The particle size of the SiC is in the range of 1 to 10 microns. The bubbling process resulted in the unevenness of the silicon concentration and the different crystallizing processes. The SiC formation rate was found to be about 12.5 mg/(L /s). A kinetic model was developed. The model-predicted results are in very good agreement with the experimental results. (Author)