Processing, As-Cast Microstructure and Wear Characteristics of a Monotectic Al-Bi-Cu Alloy

Ternary Al-based monotectic alloys have a good combination of wear resistance and mechanical strength. While self-lubricating soft elements guarantee an adequate wear resistance, the modification with third elements can increase the ability to support load. In the present investigation, a collection of microstructures is generated through transient directional solidification of the Al-3.2wt.%Bi-3.0wt.%Cu alloy. Samples with different Bi spacing have been subjected to micro-adhesive wear ball tests. A relationship linking the wear volume, V, the microstructural spacing and the test time is proposed for Bi spacing higher than 16 μm, according to which V decreases with the decrease in Bi spacing. It is observed that wider and deeper grooves emerged on the surface of the samples related to more refined Bi and Al₂Cu phases, that is, associated with Bi spacing and Bi diameter lower than 16 and 2.4 μm, respectively. A reverse trend is noted for these finer microstructures, for which V increases with further decrease in Bi spacing. This can be caused by the detachment of the very fine and less cohesive Al₂Cu lamellas as the Al₂O₃ oxide breaks up forming debris, with the presence of these lamellas as loose debris at the interface acting as third-body abrasives.