FRACTURE MECHANISMS OF A 2124 ALUMINUM MATRIX COMPOSITE REINFORCED WITH SIC WHISKERS

This study was aimed at investigating the effects of microstructure on the fracture behavior of a 2124 aluminum composite reinforced with SiC whiskers. Particular emphasis was placed on the role of matrix intermetallic particles, inhomogeneous distribution of whiskers, and whisker breakage in the fracture process. Various tests were conducted on the composite to identify the micromechanical processes that were involved in microvoid or microcrack formation. Detailed microstructural analyses showed that the aluminum matrix contained a significant amount of coarse manganese-containing particles of various sizes which could have been formed during composite processing. In situ scanning electron microscope (SEM) fracture study of the crack initiation and propagation processes clearly showed that these coarse particles fractured prior to matrix/whisker decohesion or whisker breakage, suggesting that the manganese-containing particles significantly accelerated crack initiation in the 2124 Al-SiC(w) composite. For a better matrix alloy for use in the composite, it is suggested that microalloying elements must be monitored to prevent the formation of the coarse intermetallic particles.