Review on properties of hybrid aluminum–ceramics/fly ash composites

Abstract

The production and characterization of metal matrix composites reinforced with fly ash is a very active research area. This paper presents a review on the properties of hybrid aluminum–SiC/fly ash, hybrid aluminum–B4C/fly ash, hybrid aluminum–Al2O3/fly ash, hybrid aluminum–graphite/fly ash and hybrid aluminum–BN/fly ash composites. The major production route utilized by the various authors was stir casting technique and its variant; powder metallurgy was also utilized by few authors. Improved mechanical properties were observed in the hybrid composites, compared to the composites filled with single reinforcements. It was observed that the properties of the composites were influenced by both the volume fractions of the reinforcements in the matrix and the percentage of replacement of the ceramic reinforcements with fly ash in the hybrid reinforcement mixture. In most of the reports, beyond 40 wt% of replacement of ceramic reinforcements by fly ash, the wear resistance, strength and ductility of the hybrid composites excessively reduced (high brittle tendency), while corrosion tendency increased. Generally, the mechanical properties and wear resistance of the hybrid composites were reported to increase with increase in weight fractions of the reinforcement in the composites until about 15 wt%, beyond which the properties depreciate. At the right ratio of the reinforcements in the hybrid mixture and up to about 15 wt% weight fractions of reinforcements in the composites, the reinforcements were reported to distribute uniformly in the matrix. The major observation was that most of the reports focused on the mechanical properties and wear behavior. Reports are lacking on the thermal and electrical properties of hybrid aluminum–ceramics/fly ash composites. Other areas such as hybrid TiC/fly ash composites are yet to be explored.