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Powder metallurgical composites consisting of atomized Al–Si–X powder and Saffil δ-alumina fibres were previously consolidated by hot extrusion using various reduction ratios. The microstructure at the fibre–matrix interface, as well as the fibre chemistry of some of these composites, were investigated. The results point towards a relation between mechanical fibre damage during extrusion, extrusion reduction ratio, fibre volume fraction and matrix solute enrichment of fibres. Arguments are forwarded to support the view that the fibres' specific internal texture (porosity/surface), their chemical surface activity at the temperature of extrusion and mechanical fragmentation, allowed the rapidity of the chemical interaction. The mechanical fibre damage partly arose from abrasion by equally hard silicon particles. The implications are that the strength and reinforcing potential of fibres in composites like these can be greatly reduced.