SOLIDIFICATION BEHAVIOR OF AL-SI/SIC MMCS, DURING WEDGE-MOLD CASTING

The solidification behavior of particulate reinforced Al-Si/SiC MMCs was studied using wedge-mold casting. The results suggest that both rejection and entrapment of SiC occurred as a result of interactions with the S/L interface. Three types of entrapment mechanisms of SiC were observed: (i) particulate engulfment by the S/L interface at high interfacial velocities; (ii) particulate trapping between secondary dendrite arms; and (iii) particulate trapping between primary dendrite arms. The segregation behavior of the SiC was noted to depend on the particular interaction mechanisms. Accordingly, the first mechanism did not result in significant redistribution of SiC; the second mechanism caused limited segregation; and the third mechanism led to severe segregation of SiC. Furthermore, the presence of SiC resulted in a refinement of the secondary dendrite arms of the alpha-Al phase. Consequently the distribution of SiC was more uniform in high volume fraction MMCs, relative to that present in low volume fraction MMCs.