The effect of matrix properties on reinforcement in short alumina fibre-aluminium metal matrix composites

Abstract

The effect of the alloy matrix on room-temperature strengthening in δ-alumina-reinforced aluminium alloys has been investigated. Alloy matrices fell into two families exhibiting significantly different fibre-strengthening response. The first gave rise to little or no improvement in the room-temperature strength, while the second gave significant improvements by up to 300%. It is shown that a simple Rule of Mixtures (ROM) strength analysis, modified to account for the discontinuous and random orientation of the reinforcement, can adequately explain these responses. Little or no reinforcement occurs when the matrix properties result in a high value for the critical volume fraction VCRIT which must be exceeded to produce any increase in strength. However, by careful selection of the matrix alloyV CRIT can be reduced, thus giving significant reinforcement of the room-temperature strength. This analysis shows that for optimum room-temperature reinforcement the matrix alloys should exhibit a low rate of work-hardening. In certain alloys reinforcement levels were in excess of those predicted by the ROM analysis. It is proposed that this occurs in relatively low-strength matrices as a result of dispersion strengthening of the matrix due to the presence of the fibre array.