Abstract: The structure of compounds and the microstructure of as-extruded Mg₉₈Zn_1.2Y_0.8 alloy were investigated through OM， SEM， TEM and XRD. The dynamic behavior at high strain rate conditions of as-extruded Mg₉₈Zn_1.2Y_0.8 alloy was also researched through the tensile test and fracture surface observation. The results show that the complete dynamic recrystallization occurs in the Mg₉₈Zn_1.2Y_0.8 alloy during extruding process at a temperature of 300℃ and a reduction ratio of 16∶1. The fine particles of compound H-phase dispersively distribute in the Mg-based solid solution with fine grain size， and the particles of Z-phase mainly distribute along the grain boundaries. At room temperature， the yield strength and the tensile strength rise with the increase of strain rates from 100/s to 667/s， and the elongation also increases from 9.2% to 13%. Ductile fracture with some proportion of brittleness fracture occurs in the as-extruded Mg₉₈Zn_1.2Y_0.8 alloy at room temperature and strain rate 100/s -667/s.

Key words: Mg-Zn-Y alloy, microstructure, high strain rate, mechanical behavior, fracture mode