Processing and mechanical properties of AlB₂ flake reinforced Al-alloy composites

A new process to produce high-purity AlB₂ single crystals in an Al-Cu alloy was developed. This process suppressed the formation of the AlB₁₂ phase by argon quenching from 1300°C to room temperature. The high-temperature heat treatment was coupled with a melt infiltration step to produce AlB₂ reinforced Al-Cu composites, with volume fractions of reinforcement up to 20%. Microstructural examination of these composites indicated that the aspect ratio of the flakes was approximately 30 with a high degree of homogeneity in the as-cast structure. Mechanical properties of the composites were measured and compared with those of the unreinforced matrix alloy. At a volume fraction of 20% reinforcement, the composite showed an 80% increase in strength at room temperature with 1% loss of strength up to 150°C. Higher strengths were obtained by partially aligning the flakes along the tensile axis.