showed that the major strengthening mechanism in alu- minum matrix composites reinforced Al203 is the orowan strengthening by particles; however, he found that when clusters of these ceramic particles were present, the particle strengthening effect diminished. This is the reason why the parameters ofthe MM process need to be studied and optimized in order to obtain a fine dispersion of partially yttria-stabilized zirconia through the AA 7075 matrix by using mechan- ical ball milling and to characterize its microstructural evolution through the process. 2. Materials and experimental procedure The matrix powders were obtained from a commercial bar AA 7075- T6. The bar was annealed for 48 h at 415 oct 5 c in a Felisa furnace followed by a slow cooling in order to remove the high hardness caused by the T6 heat treatment. During this heat treatment it is promoted the presence of stable m (Mgzn2) phase instead of (Mgzn), lowering the hardness of the alloy by this way.The matrix powders were obtained by Table 1 Average partide size of Zroz powders after ball milling with two milling media