Squeeze-casting conditions of Al/Al2O3 metal matrix composites with variations of the preform drying process

The characteristics of the preform play a role in determining the final properties of MMCs. Effects of organic binder and microwave drying on preform microstructure have been examined by SEM. In the preform with organic binder, flocking processes are observed during drying. The preform has a uniform distribution of binder and dries quickly with microwave drying owing to its internal and volumetric heating patterns. The fundamental manufacturing process and controlling parameters of squeeze casting, including preform temperature, mould temperature, applied pressure and molten metal temperature, have been studied in Al/Al₂O₃ composites. MMCs have poor mechanical properties with too high temperatures of preform and molten metal due to thermal shocking of the preform, oxidation of the matrix and thermal damage to the fibers. Mould temperature barely affects the tensile strength of MMCs. High applied pressure reduces voids and solidifies the matrix faster. Conditions for squeeze casting to achieve optimal processing, are suggested. The tensile strength of MMCs can be improved by up to about 20% compared with the unreinforced matrix alloy.