Subsurface modifications in powder metallurgy aluminium alloy composites reinforced with intermetallic MoSi2 particles under dry sliding wear

The effect of dry sliding wear on the subsurface of six AA6061/MoSi2/15p composites processed by powder metallurgy with varying mixing methods (wet blending, rotating cube and ball milling) and reinforcement sizes was investigated. Three regions could be distinguished: the tribolayer or mechanically mixed layer (MML), the elasto-plastically deformed layer, where deflection of material occurs, and the unaffected bulk. The MML was not uniform along the surface and no relation could be found between the size/shape of MML areas and processing variables or applied loads. In the second region, particles close to the MML were found to be fragmented only in the composites processed using low energy. These composites were the only ones to show hardening, together with the similarly processed unreinforced alloy. It can be concluded that, although the subsurface of these composites are noticeably affected by dry wearing through formation of a mechanically mixed layer and material deflection, the ball milled composites do not suffer subsurface hardening and their reinforcing particles do not break during the test. It is also evident from the present research that no simple correlation exists between the size/shape of the tribolayer and deflection parameters and processing variables or applied loads.