Abstract: In order to clarify the reason behind the mild to severe wear transition for AZ system alloys, dry sliding wear tests are performed on AZ31 and AZ51 alloys within a sliding speed range of 0.1-4.0 m/s. Effects of load and sliding speed on wear rate and wear mechanism are investigated, wear transition maps are established, changes in subsurface microstructure and mechanical property are analyzed. Results show that oxidation, abrasion and delamination operate in the mild wear regime, severe plastic deformation and surface melting prevail in the severe wear regime. Subsurface material experiences the plastically deformed to dynamic recrystallization (DRX) microstructural transformation and the strain hardening to DRX softening transformation. The mild to severe wear transition is determined by realization of DRX in subsurfaces of AZ system magnesium alloys, and a criterion is established using DRX dynamics for prediction of critical DRX temperatures and transition loads at different sliding speeds.

Key words: magnesium alloy, mechanical properties, microstructure, wear mechanism