Interfacial reaction and its effect on strength of Al₁₈B₄O₃₃/Al composites

Aluminium alloy 6061, AC8A, Al-1Mg, Al-9Cu and pure aluminium composites reinforced with aluminium borate whiskers were fabricated by a squeeze casting process. The interfacial reaction in the composites and its effect on the bending strength are discussed, together with the results from SEM, TEM, and X-ray diffraction. A slight interfacial reaction is favourable for composite strength as it has the effect of anchoring the whiskers. A T6 treatment can enhance the strength of an Al-9Cu matrix composite, but is not efficient for magnesium containing 6061 and AC8A matrix composites. Furthermore, if heated at temperatures higher than 793 K for a long time, the composite strength drops rapidly owing to whisker damage and shortening during the interfacial reaction. It is suggested that the interface in an Al₁₈B₄O₃₃/Al alloy composite is stable below 623 K which is the temperature requirement for automobile engine components.