Creep behavior of a cast 359/SiC/10p aluminum composite

Abstract

Aluminum 359/SiC/10p composite was processed via ingot metallurgy using ultrasonic techniques to refine the grains, fragment the dendrite and the primary silicon and to disperse the uniform silicon carbide particles within the matrix. The relatively low melting temperature coupled with short stirring time and high solidification rate resulted in composites having high strength with adequate ductility. The tensile creep behavior of the heat treated (T61) composite has been investigated over a temperature range of 523–723 K. It is shown that the composite exhibits threshold creep behavior up to at least 750 K. The origin of the threshold stress is not well understood, however, the concepts of load transfer to particulate and the long range internal back stress generated in creep were discussed. The stress exponent varies from 5 to 9, depending on the test temperature. The activation energy for creep was estimated as ∼250 kJ/mol, which is quite high when compared with 142 kJ/mol, the value for self-diffusion in pure Al. The difference is accounted for by the temperature dependence of the threshold stress.