A comparative study of mechanically mixed layers (MMLs) characteristics of commercial aluminium alloys sliding against alumina and steel sliders

Dry sliding of four commercial wrought aluminium alloys; AAA2124, AAA3004, AAA5056 and AAA6092 against two different materials (M2 tool steel and a high purity alumina) at room temperature were carried out. A ferrous slider was used, to promote a mechanically mixed layer (MML). It was found that in Al/M2 tests, the presence of major alloying elements in the Al-alloy that have high solubility in steel promoted a thick mechanically mixed layer. The solubility of these elements in α-Fe is in the order of Si, Mn, Cu, Mg, which roughly approximates the thickness of the MML formed, while the Fe content of the MML also scaled in this order. The MMLs with high Fe content tended to be comprised of fragmented particulate, while a low Fe content tended to be associated with a more homogenous MML. As for the Al/Al2O3 tests, the MML was derived from fracture of the slider, and also from transfer and re-transfer of the aluminium alloy. An alumina slider was used, in principal, to minimise the formation of an MML, so that the true effect of the work hardening induced by wear can be analysed. In contrast to the Al/M2 tests, none of the alloying elements in the aluminium alloy were expected to chemically react with the Al2O3, but the thickness of the MML appears to be controlled by different factors to that against the M2 slider. Detailed analyses of the wear performance and the work hardening effects were also undertaken in order to explain the differences between the tests.