This is a copy of the slides presented at the meeting but not formally written up for the volume.

The pressure infiltration of densely packed alumina particle preforms with molten aluminium produces defect-free composites containing roughly equal proportions of metal and ceramic. The process affords considerable latitude in microstructural design of the resulting composites. In particular, the matrix can be kept microstructurally simple, and the size of the reinforcement can be varied roughly between 3 and 100 µm. Despite their high ceramic loadings, these composites display appreciable plasticity, often deforming in tension to elongations of several percent before breaking. Beyond yield, their flow stress is largely governed by that of the matrix; this matrix, in turn, is a metal deforming between hard inclusions only a few micrometres apart. As is well-known from the composite literature, the high constraint imposed by the reinforcement on matrix deformation is manifest in a “size-effect”, whereby the matrix, and hence the composite, flow stress can depend on the microstructural scale of the composite. We present recent results from a recent investigation of this phenomenon on pressure-infiltrated alumina reinforced aluminium composites. We describe a methodology of analysis of the effect that takes into account both the complexity of the underlying mechanical problem and the influence of internal damage, which often develops extensively in these materials. We then present back–calculated in-situ flow curves of the matrix within such composites, showing that there is a strong and systematic size effect with pure aluminium, but not in solutionized binary Al-Cu alloys.