On the Impact Toughness of AI-B4C MMC: The Role of Minor Additives and Heat Treatment

Two base alloys of Al-15 vol% B4C and 6063-15 vol% B4C metal matrix composites (MMCs) were produced using a powder injection technique. Alloying additions of 0.5wt% Ti, 0.35wt% Zr and 0.35wt% Sc were made to the base alloys to produce various compositions of the two MMCs. For the purpose of investigating the effect of reinforcement/matrix (B4C/Al) interaction on the composite toughness, ten compositions of pure Al-15 vol% B4C and 6063-15 vol% B4C with various additions of Ti, Zr and Sc were produced. A metallic L-shaped mold was used for casting the aluminum MMCs. Reinforcement/matrix interface interactions in the produced composites were investigated as a function of the alloying elements added using field emission gun scanning electron microscopy (FEGSEM) and energy dispersive x-ray (EDX) techniques. The results show that the toughness of a given composite is controlled by the type of heat treatment and amount of added elements or refractory materials. Introduction of Ti alone leads to reaction with some of the B4C particles, converting them to Al-Ti-B or Al-Ti-C compounds. The addition of Zr reacts with Ti forming Al-3 (Ti,Zr) which minimizes the particle/matrix interaction. Repeated remelting of the composite coupled with a high stirring speed may cause fragmentation of the B4C particles.