Studies on Structural Changes in the Surface Layers of Aluminum Alloys Based on the Al–Si–Cu System under Frictional Deformation

• Published in: Russian journal of non-ferrous metals 2020, Vol.61 (1), p.99-107
• Main Authors: Shcherbakova, O. O., Muravyeva, T. I., Zagorskiy, D. L., Shkalei, I. V.
• Format: Article
• Language: English
• Subjects: Alloy systems; Aluminum alloys; Aluminum base alloys; Antifriction bearings; Chemistry and Materials Science; Copper; Deformation; Film thickness; Friction; Hardening; Hardness; Heat treatment; Lead; Mass transfer; Materials Science; Mechanical properties; Metallic Materials; Nanoindentation; Physical Metallurgy and Heat Treatment; Scuffing; Silicon; Surface layers; Tribology
• ISSN: 1067-8212; 1934-970X
• DOI: 10.3103/S1067821220010149

Experimental antifriction aluminum alloys based on an Al–5% Si–4% Cu system with the addition of low-melting components such as Bi, Pb, In, and Cd have been studied. An optimal heat treatment mode has been adjusted, including the hardening at a temperature of 500°С with further aging at 175°С. The tribological testing have been carried out according to a pad–roller scheme (Steel 45 as the material under study) at a pressure of 0.5, 1.0, and 2.0 MPa to simulate the operation of a bearing mount assembly. It is shown that all the experimental alloys have similar tribological properties, but their mechanical characteristics, in particular, hardness, are different. Of greatest importance is an alloy containing cadmium. Using electron microscopy, the topography is studied and the elemental composition is determined for the surfaces of a roller and a pad made of this material before and after tribological testing. A process of active mass transfer in the contact zone under friction is revealed. In this case, the formation of a film consisting of secondary structures on the roller is observed. The film has the following features: an uneven distribution on the surface with a developed relief and a maximum film thickness reaching 200 μm. It is shown that, under the friction conditions that are used, such a film promotes the formation of scuffing. It has been found that the scuffing occurs after testing at a pressure higher than 1 MPa for all the studied experimental alloys. The nanoindentation of a pad performed at a load ranging from 10 to 100 mN has shown an increase in the hardness of a surface layer about 30 μm thick. This could be connected with the hardening of the material owing to plastic deformations in the friction zone.