Sliding behavior of selected aluminum alloys

Abstract

This project was undertaken to achieve three principal objectives: to improve understanding of the behavior of selected aluminum-based bearing materials used in sliding applications, to develop improved guidelines for the design of such bearings, and to respond to increasing environmental concerns about the use of lead in bearing materials. Unlubricated sliding tests have been conducted using disks of Al-Sn and Al-Pb binary alloys as well as multicomponent alloys produced with the aid of an MHD (magnetohydrodynamic) technique at the Institute for Solid State Physics, Chernogolovka, Russia. For comparison, commercial alloys produced by Glacier Vandervell Inc. have also been tested. The counterface in each case was a hardened 52100 ball. Sliding speeds were kept low (15-30 mm s-1) to limit frictional temperature increases. Normal loads ranged from 0.8 to 1.2 kgf. Earlier results on Pb-Sn and babbitt alloys demonstrated that the environment strongly affects the friction coefficient, the smoothness of sliding and the hardness and hardness gradient at the surface. Therefore we have performed tests in vacuum (as a reference condition) and in air. A range of complementary techniques ( optical and electron microscopy, X-ray fluorescence analysis using energy dispersive spectroscopy (EDS), microhardness) was used for structural and chemical characterization of debris and of surface and near-surface material. In all cases, sliding in vacuum was smooth and the wear rates were low. In fact, the rate of production of debris during the vacuum tests was negligible. However, the friction coefficient, the fluctuations in friction and the wear rate were all much higher for tests in air. The reasons for this behavior are associated with dramatic differences in structure and composition which develop near the surface of the bearing material. The effects of environment are larger than those associated with changes in composition for the alloys studied. © 1997 Elsevier Science S.A.