The effect of microstructure length scale on dry sliding wear behaviour of monotectic Al-Bi-Sn alloys

Abstract

The addition of third elements to Al-based monotectic alloys can increase the alloy load capacity, and depending on the nature of the third element can also improve the tribological characteristics. In the present investigation 1.0 wt.%Sn is added to Al-Bi alloys of hypomonotectic, monotectic and hypermonotectic compositions, giving rise to microstructures typified by droplets of a self-lubricating mixture of Bi and Sn embedded in the Al-matrix. These alloys were directionally solidified with a view to permitting microstructures with a wide range of interphase spacings to be obtained. Micro-adhesive wear tests were carried out and experimental equations relating the wear volume, V, to the interphase spacing are proposed. A more homogeneous distribution of Bi/Sn droplets in the microstructure is shown to be conducive to lower V. The lowest wear rates and wear volumes are shown to be related to the monotectic composition (Al-3.2 wt.%Bi-1wt.%Sn alloy). The presence of higher fraction of Fe-oxide areas interrupting the Bi/Sn lubricant layer, is shown to induce inferior wear resistance for the hypermonotectic alloy (Al-7.0 wt.%Bi-1wt.%Sn) when compared with that of the monotectic alloy.