Interface structure and solute-segregation behavior in the high-strain-rate superplastic SiCp/2124 and SiCp/6061 Al composites were investigated. Evidence for interfacial reaction between reinforcement and Al matrix, which was evident in the superplastic Si3N4p,w/2124 Al and Si3N4p,w/6061 Al composites, could not be detected in the current SiC-reinforced Al composites. Instead, strong solute segregation was observed at SiC/Al interfaces. Extensive formation of whiskerlike fibers was observed at the fractured surface of tensile samples above the critical temperature where particle weakening began to be seen. These results suggest that partial melting occurs at the solute-enriched region near SiC interfaces and is responsible for the particle weakening. The absence of reaction phase in the SiC-reinforced composite may explain why no endothermic peak for partial melting appears in its differential scanning calorimetry curve and why its optimum temperature for superplasticity is generally higher than that of the Si3N4-reinforced composite.