Al–20Sn–1Cu self-lubricating alloy: Correlations between microstructure coarsening, mechanical, and application properties

This study investigated the microstructure, microhardness, tensile strength, and dry wear behavior of the cast Al–20Sn–1Cu alloy (wt. %), focusing on the relationship between β-Sn phase morphology and the results. The Al–Sn–Cu alloys have been shown to be promising for plain bearing applications due to their self-lubricating properties. However, those alloys exhibit peculiar behaviors contrary to the classical Archard equation, which relates hardness to wear resistance, or to the typical behavior of metallic alloys, where increasing strength generally leads to a reduction in ductility. This can be attributed to the morphology, fraction and distribution of the β-Sn phase, a component of low hardness and strength but essential for self-lubricating functionality. In this study, the Al–20Sn–1Cu alloy solidified under a wide range of cooling rates varying from 1.0 to 28.9 °C/s was investigated. Dendritic spacing was measured using an automated method proposed in this study. The results showed that more refined samples had better tensile properties but compromised wear behavior. When the microstructure was refined up to dendritic spacing of 15.7 μm, a good combination between strength and ductility was achieved: a tensile strength of 72 MPa and an elongation of 14 % were obtained. These results can be explained by the increased contact area between the α-Al and β-Sn phases, which favors a strain hardening mechanism. However, these samples have very small β-Sn particles, which are insufficient to form an effective lubricating layer, resulting in severe wear due to adhesion. Despite that, it achieved a lower wear coefficient compared to other self-lubricating alloys reported in the literature.