Fabrication of particulate aluminium-matrix composites by liquid metal infiltration

Abstract

Aluminium-matrix composites were fabricated by liquid metal infiltration of porous particulate reinforcement preforms, using AlN, SiC and Al₂O₃ as the particles. The quality of the composites depended on the preform fabrication technology. In this work, this technology was developed for high-volume fraction (up to 75%) particulate preforms, which are more sensitive to the preform fabrication process than lower volume fraction whisker/fibre preforms as their porosity and pore size are much lower. The technology developed used an acid phosphate binder (with P/Al molar ratio=23) in the amount of 0.1 wt% of the preform, in contrast to the much larger binder amount used for whisker preforms. The preforms were made by filtration of a slurry consisting of the reinforcement particles, the binder and carrier (preferably acetone), and subsequent baking (preferably at 200 °C) for the purpose of drying. Baking in air at 500 °C instead of 200 °C caused the AlN preforms to oxidize, thereby decreasing the thermal conductivity of the resulting Al/AlN composites. The reinforcement-binder reactivity was larger for AlN than SiC, but this reactivity did not affect the composite properties due to the small binder amount used. The Al/AlN composites were superior to the Al/SiC composites in the thermal conductivity and tensile ductility. The Al/Al₂O₃ composites were the poorest due to Al₂O₃ particle clustering.