Abstract: A process is described for forming a composite cast article comprising an aluminum-silicon alloy matrix containing a modifying amount of strontium and a preform of bonded-together reinforcing fibres incorporated in the matrix, in which the preform of reinforcing fibres is infiltrated under pressure by a melt of the alloy and the composite article thus formed is allowed to solidify by cooling. According to the novel feature, the fibres of the preform are coated with strontium, preferably in the form of SrO, before being infiltrated by the alloy melt. The strontium on the fibres is free to react with the Al-Si melt and thus modify the structure in the region of the preform such that an excess of silicon particles adjacent the fibres is avoided.