EFFECTS OF ALLOYING ELEMENTS ON SIC DISPERSION IN LIQUID ALUMINUM

The effects of alloying elements on dispersion of SiC particles into molten aluminum were investigated. The time required for incorporation of SiC particle into molten aluminum was defined as an incorporation time. The incorporation time of SiC was shortened by alloying magnesium, or by alloying titanium together with tin. These alloying elements have strong affinity for SiC and are able to form silicide as a result of reaction with SiC. Magnesium silicide was detected by EPMA, although the existence of titanium silicide could not be conformed. The incorporation time of SiC was prolonged by adding zinc, copper and tin which have no affinity for SiC. Moreover, particulate dispersion is considerably influenced by surface-active elements. The incorporation time of SiC particle was shortened by adding lithium which is a surface-active element with strong affinity for SiC, whereas it was prolonged by adding surface-active elements with weak affinity for SiC such as lead and bismuth. This is probably because lead and bismuth adsorb at the interface and hinder the wetting between SiC particle and molten aluminum. The addition of silicon into aluminum prolonged the incorporation time of SiC because the dissociation of SiC, that might be necessary for good wetting, was retarded by the existence of silicon.