The displacement reaction between Al and SiO2 in an Al-3wt%Cu-3wt%Si-9wt%SiO2 powder mixture has been studied when the mixture had been ball-milled, and compared with the reaction in the as-mixed powder. Diffusion couples consisting of Al/SiO2 were formed during ball milling. The size of the composite powder particles and the diffusion couples was reduced by increasing the ball milling time. Differential thermal analysis and X-ray diffraction results showed that the displacement reaction between Al and SiO2 did not occur in the as-mixed powder, but occurred in the as-milled powders in the temperature range of 640-680 degrees C. Furthermore, the onset temperature of the displacement reaction shifted to lower temperatures after increasing the ball milling time. On the basis of these results the milled powder was sintered at 640 degrees C in order to produce an Al-Cu-Si matrix composite reinforced with homogeneously distributed submicron-sized Al2O3 particles. This is much lower than the temperature required for the same reaction in other processes which are used to produce such composites, such as the melting infiltration process.