A review on high stiffness aluminum-based composites and bimetallics

The Young's modulus of aluminum-based materials is one of the most important mechanical properties in controlling structural performance. The improvement of the Young's modulus of castable aluminum-based materials is essential for improving their competiveness in light weighting structural applications. Currently, there are limited options for cast aluminum alloys with outstanding Young's modulus. Also, for further stiffness improvement and thereby weight lightening, in-depth understanding of the relevant mechanisms for modulus improvement in aluminum alloys is necessary. This review focuses on the Young's modulus of cast aluminum-based composites, as well as aluminum alloys reinforced with continuous metallic fibers (bimetallic materials). The effect of different chemical elements in cast alloys, the constituents of in-situ and ex-situ formed aluminum matrix composites, and the wire-enhanced bimetallic materials on the Young's modulus of aluminum-based materials are reviewed. The Young's modulus of cast aluminum alloys can be improved by: (a) introducing high modulus reinforcement phases - such as TiB2, SiC, B4C, and Al2O3 - into aluminum by in-situ reactions or by ex-situ additions; and (b) forming bimetallic materials with metallic wire/bar reinforcement in the aluminum matrix. The performance of a stiff aluminum alloy depends on the volume fraction, size, and distribution of the high modulus phases as well as the interface between reinforcement and Al matrix. One of the major concerns is the reduction of the ductility of castings after adding specific high modulus phases to increase the Young's modulus. Further research into the improvement of Young's modulus and the ductility of aluminum alloys is necessary through proper selection of reinforcement, optimizing interface, and distribution of reinforcement.