Rationale for composition-specific ageing schedules for particle-reinforced metal-matrix composites

Optimised age-hardening treatments are vital if aluminium-based particle-reinforced metal-matrix composites (PRMMCs) are to achieve widespread use as an engineering material. This paper shows that for some PRMMCs ageing may not be optimised, and suggests why this is the case. Composites of a 7xxx-series aluminium alloy containing a number of volume fractions of SiC were investigated. On ageing, the materials were found to fall into two groups: (i) the 10% SiC composite, which followed an ageing sequence similar to the unreinforced alloy, and (ii) those containing greater than 15% SiC, which followed a different sequence. The implication of this work is that substantially different ageing schedules need to be devised for the two different groups of materials if the full potential of age-hardenable composites is to be realised in the higher volume-fraction materials.