Influence of matrix hardness on the dry sliding behaviour of 20%vol Al2O3 particulate reinforced 6061 Al metal matrix composite

In the present investigation the wear behaviour of the 6061 Al alloy reinforced with 20 vol.% Al2O3 particles dry sliding against a tool steel counterface was studied as a function of load and with reference to different values of the matrix hardness, obtained by submitting the extruded composite to thermal and forging treatments. The obtained wear rates were interpreted on the basis of the analysis of the surface and subsurface damage to the composite due to sliding. If the hardness of the materials is increased by a treatment, their wear rate also increases, because of the occurrence of subsurface softening and the formation of surface mixed scales prone to leaving the tribological system. On the other hand, the as-extruded composite is characterized by a lower matrix hardness (and thus a higher ductility) which prevents the conditions for subsurface softening and formation of the mixed scale from being reached. In this case a transfer layer mainly consisting of iron oxides then forms and protects the composite, thus reducing its wear rate.