Improvement of surface properties of an Al–Sn–Cu plain bearing alloy produced by rapid solidification

Abstract

Al–Sn based alloys are widely used as plain bearings in several engineering applications, particularly in internal combustion engines. The microstructures of these alloys are composed by two main phases, α-Al and β-Sn. The latter provides the low friction coefficient required for bearing applications. The new combustion engines and hybrid systems impose harder working conditions to plain bearings, thus the bearing materials need to be stronger with improved friction properties. The conventional Al20Sn1Cu (wt.%) alloy produced at different cooling rates by means of different casting processes such as Belt Casting, Twin Roller and Single Roller Melt Spinning techniques was studied. The effects of the cooling rate and of the Mn addition on the microstructure and properties were studied. The samples produced by the melt-spinning technique with cooling rates higher than ∼5 × 105 K/s conducts the alloy to a solidification pathway in a metastable condition through a miscibility gap. A microstructure characterized by an homogeneous small rounded β-Sn particles distributed in a refined α-Al grain size matrix is obtained. Samples produced with cooling rate higher than ∼1.4 × 106 K/s show an anisotropic microstructure of a <100> α-Al crystallographic texture in a columnar microstructure. The melt-spun samples with an isotropic microstructure reach a Vickers hardness 86% higher and an improved wetting property than the alloy produced by the traditional Belt-Casting technique. However the melt-spun samples with crystallographic texture showed a downfall in the properties. The addition of Mn leads to a more homogeneous and refined microstructure independently of the casting technique used.