Microstructures and Mechanical Properties of Multiphase-Reinforced In Situ Aluminum Matrix Composites

We investigated the microstructures and mechanical properties of multiphase-reinforced in situ aluminum matrix composites (AMCs) prepared with various combinations and contents of Li, Mg, Si, Cu, Zn, Sn, and Ni. The area fractions of the secondary phases in the as-cast AMCs ranged from 26% to 58%, and the types of secondary phases depended on the alloy chemical compositions. The type and amount of secondary phases were more important than matrix strengthening in determining the alloy mechanical properties. Composite hardness and compressive stress increased while fracture strain decreased with increasing total area fraction of the secondary phases up to 40%. The formation of coarse primary and soft/heavy Sn-containing phases significantly deteriorated the alloy mechanical properties. Annealing also influenced the mechanical properties of the AMCs by changing the microstructures of the secondary phases and Al matrices.