Wear behavior of Mg–5Al–0.8Zn alloy was studied using a pin-on-disk type wear apparatus within a load range of 20–380 N and a sliding speed range of 0.1–4.0 m/s. Analyzes on morphology and chemical composition of worn surfaces were undertaken using scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) for determination type of wear mechanism. Investigations on microstructure, plastic strain, and hardness in subsurfaces were carried out using optical microscope and hardness tester for understanding changes in the microstructure and hardness before and after mild to severe wear transition. The subsurface microstructure beneath the worn surface was subjected to a large plastic strain, and experienced strain hardening, dynamic recrystallization (DRX), and melting successively with increasing load or sliding speed. The transition between mild and severe wear was controlled by microstructure transformation from a strain-hardened into a thermal soften DRX microstructure in subsurface. A contact surface DRX temperature criterion is proposed for prediction of transition between mild and severe wear in Mg–5Al–0.8Zn alloy. The mild to severe wear transition loads were predicted under various sliding speeds using DRX kinetics. The validity of the proposed method for prediction of transition between mild and severe wear is also verified in AZ31 and AZ61 alloys.