Abstract The paper addresses studies of the subsurface region originated in dry sliding of aluminium casting alloy AK 12 and alloy composite; AK 12 with Al 2O 3 particles. We found the inverse correlation between the wear rate in these materials and the total depth of the subsurface region detected by the positron annihilation technique. The microhardness profile and scanning electron microscopy used in our studies, generally underestimated the total depth of this region in comparison to that obtained using the positron annihilation technique. The total depth of this region for AK 12 was about 300 μm and for the composite it was 60 μm. In the latter, the immersed reinforcement particles effectively prevented deeper expansion of the damaged region.