Tribo-Induced Surface Deformation Mechanisms Govern Friction and Wear in Ultralight HCP and Duplex Mg-Li Alloys

Abstract

Adding lithium into Mg can activate more deformation modes in both hexagonal close packed (hcp) and body centered cubic (bcc) Mg-Li alloys. In this work, friction and wear tests were performed on coarse-grained Mg-xLi-3Al-3Zn (x = 4 and 10 wt. %) alloys and detailed surface deformation mechanisms were uncovered. Compared with the duplex Mg-10Li alloy, the friction coefficient of hcp Mg-4Li is lowered by ~ 40%, and the wear rate is strikingly lowered by nearly one order of magnitude. The low wear rate stems from formation of hard and stable nanograined surface layer through rapid grain refinement of the hcp grains upon sliding. While for the dual-phase alloy, dynamic recrystallization (DRX) dominates the deformation of bcc grains, unavoidably causing its cracking and delamination within the ultra-fine grained DRX layer. Our results are suggestive in designing wear resistant ultra-light Mg-Li alloys through in-depth understanding of tribo-induced surface deformation mechanisms.

Keywords: magnesium alloys, Friction, Nanostructure, Dynamic recrystallization