حسین اسکندری

In the present study, the wear behavior of ultra-fine grained (UFG) Al-Mg alloys produced by a severe plastic deformation (SPD) method was assessed and compared against the annealed coarse-grained alloy. To this end, weight loss, wear resistance, friction coefficient, and morphology of the worn surfaces was investigated. Constrained groove pressing-cross route (CGP-CR) process, an SPD technique, was implemented at ambient temperature up to two passes to impose an equivalent plastic strain of about 4.64. Formation of a UFG structure with an average sub-grain size of  350 nm with an enhanced tensile strength of up to  225 MPa and indentation hardness of up to  95 HV were achieved upon two passes of CGP-CR process. The pin-on-disk dry wear sliding testing was conducted up to a distance of 1000 m under normal loads of 5, 7, and 9 N at a constant sliding speed of 0.5 m/s. The trends measured for the evaluation of wear properties/mechanisms are discussed based on the microstructural features and mechanical property of UFGed alloys. The results showed that by employing the CGP-CR process and through the formation of UFG structure, the wear resistance was considerably increased. This was even beyond two times ( 100%) larger depending on the normal loading with the lowest coefficient of friction around 0.6. Observation and study of the morphology of the worn surfaces under field emission-scanning electron microscopy (FE-SEM) revealed a change in the wear mechanism from sticking followed by formation of plastic deformation bands and delamination in the coarse-grained annealed alloy into a combined abrasiveadhesive behavior in the UFG material.