Study of structural changes in the surface layers of Al–Si–Cu aluminum alloys during their deformation in the friction process

Experimental antifriction aluminum alloys based on the Al–5%Si–4%Cu system with the addition of Bi, Pb, In, and Cd low-melting components were studied. An optimal heat treatment mode was selected: hardening at 500 °С with further aging at 175 °С. Tribological tests were carried out according to the «shoe–roller» scheme (investigated material – Steel 45) (at pressures of 0.5, 1 and 2 MPa) simulating the bearing assembly operation. It was shown that all the experimental alloys have similar tribological properties. However, their mechanical properties (in particular, hardness) differ. A cadmium containing alloy had the highest hardness. Electron microscopic studies of the shoe and roller surfaces were carried out for samples made of this alloy before and after tribological tests including the study of topography and elemental composition. The process of active mass transfer in the contact zone during friction was revealed. At the same time, the roller demonstrated a film formed of secondary structures on the roller and its parameters were determined  (uneven pattern of location on the surface, considerable relief with the maximum thickness up to 200 μm). It was shown that such a film leads to score formation with the friction modes used. It was determined that for all experimental alloys scoring occurs after testing at pressures above 1 MPa. Shoe nanoindentation (with 10–100 mN loads) showed increased hardness in the surface layer with a thickness of about 30 μm. This may be connected with the material hardening as a result of plastic strains occurred in the friction zone.

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