High-energy milling changes the compressibility of powder material due to the work hardening effect and the changes in the powder morphology. Aluminium 6061 powder alloy reinforced with AlN was mechanically alloyed for different lengths of time and the compressibility of the obtained powder was determined. The results are explained in terms of the plastic deformation capacity of the powders, which is influenced by the hardness and the morphology of the powder. With increased milling time, powder compressibility is reduced. The equiaxed morphology of the as-received unreinforced aluminium powder also induces low compressibility, which is improved by the simple addition of reinforcement particles. (C) 2003 Elsevier Science B.V. All rights reserved.355416715055