On dry sliding wear of ECAPed Al-Mg-Zn alloy: Wear rate and coefficient of friction relationship
Maged Elhefnawey, G.L. Shuai, Zengyi Li, M. Nemat-Alla, D.T. Zhang, Li Li
Abstract
Equal channel angular pressing (ECAP) of AA7075 alloy, at room temperature, with six numbers of passes, has been successfully processed. Microstructure observations, microhardness experiment, wear test, and worn surface morphology examination were performed to investigate the increasing passes number’s effect on wear behaviors. Increasing the number of passes leads to the observation of refined grains, high-density dislocations, dispersed nanoparticles, and continuous improvement of microhardness to 223 HV at six passes. The SEM results of the specimens after the wear test showed that delamination, plastic deformation, and adhesion mechanism were dominated wear mechanisms in the before-ECAP sample. However, with the increased pass number, the delamination gradually transformed into the ploughing bands, which were the dominant wear mechanism in 5 passes because of the hardened aluminum matrix. After six passes of ECAP, the abrasion wear was founded to start work as a significantly important wear mechanism. Besides, the oxidation plays a remarkable role in the wear mechanism in all the tested samples. The coefficient of friction increased as the increase of passes number due to the deceased lubricant effect acted by delamination, which was gradual shrank from aggregation to debris. Nevertheless, the wear rate decreased with the increased passes number owing to the low applied wear load and increased hardness after ECAP. Based on the study of the inverse correlation between the coefficient of friction and the wear rate, a relation between them was introduced for the ECAPed aluminum alloy.