Tribological Properties and Structure of Aluminum—Lithium Alloys

Resumo

This paper presents the results of a study of structural transformations and the main tribological properties (coefficient of friction and wear rate) of Al–2.2 Li and Аl–3.1 Сu–2.0 Li–0.1 Zr (wt %) alloys. Optical metallography and transmission electron microscopy have been used to examine the alloy structure after heating and friction. Tribological tests of the alloys in pair with steel are carried out by sliding friction using a pin-on-plate scheme during reciprocating motion of a sample. The sliding velocity is 0.07 m/s and the load is 294 N. Friction is carried out in air and in a nitrogen gas at room temperature. Alloying of the Al–Li alloy with copper (3.1 wt %) and zirconium (0.1 wt %) is shown to significantly increase the wear resistance, enhance the frictional hardening, and reduce the friction coefficient of the alloys. The positive effect of this alloying on the tribological properties of the Al–Li alloy is caused by friction-induced severe strain hardening. A high-strength nanocrystalline structure consisting of a mixture of matrix crystals and a metastable δ' (Al₃Li) phase is formed in a surface layer to 10 μm thick. Planar dislocation slip is observed in both alloys. This sliding mechanism is assumed to be related to the low (f ~ 0.25) coefficient of friction of both alloys. Artificial aging carried out under different four regimes increases the hardness of alloys, but significantly reduces their resistance to wear. This paper offers an explanation for the effects obtained.