Abstract
Creep features of two cast aluminium alloy composites reinforced by Al2O3 short fibres randomly oriented in the matrices have been studied at 300 °C and several stress levels. The presence of short-term negative creep in primary creep is an important feature for the composites, which resulted from randomly oriented fibres strongly resisting dislocation creep in the matrix. However, the negative creep magnitude depended on both the applied stress and the nature of the material. There was a critical stress for the presence of the short-term negative creep. When the applied stress had exceeded the critical value, the negative creep disappeared. Fibres traversing grain boundaries can reinforce and resist grain boundary sliding at elevated temperature. The effect of stress on creep rate for the composites is not so strong as that for unidirectional metallic matrix composites. During the creep, some intermetallic phases in the Al2O3/Al-5Si-3Cu-1 Mg composite were precipitated and most of them were segregated at grain boundaries, leading to a small increase of the creep rate.
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