Effect of slider materials on the nano-characteristics of the mechanical mixed layer of worn wrought Al-alloys

The work hardening study of four commercial wrought aluminium alloys; AA2124, AA3004, AA5056 and AA6092 against two different sliders (M2 steel and an alumina) under dry sliding conditions at 1m/s over the load range 23N to 140N was carried out. A ferrous slider was used, to promote a mechanical mixed layer (MML), whereas an alumina slider to minimise the formation of an MML due to its inert behaviour, so that the true effect of the work hardening induced by wear can be analysed. It was found that in Al/M2 system, 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 system, the MML was derived from fracture of the slider, and also from transfer and re-transfer of the aluminium alloy. 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. It was found that the average nano-hardness of the MML layer in the Al/Al2O3 decreased with load. Unlike alloys worn against M2 slider, the nano-hardness of the MML in this work was associated with the wear rate. In the case of slider type, the nano-hardness of precipitate-hardened A2124 against Al2O3 showed lower hardness than those MML worn against M2 slider.