Fine-grained Mg-3Al-Zn alloys with various oxygen contents were prepared by a powder metallurgy process, and the effect of oxygen content on the impact toughness of the fine-grained magnesium alloys was quantitatively investigated. It is found that the impact toughness of magnesium alloys with mean grain size smaller than 3μm is extremely high when the oxygen content is less than 400pp, but it becomes very low as the oxygen content is higher than 1000ppm. Both magnesium oxides and hydroxides are detected in the magnesium alloys. The presence of excessive magnesium oxides and hydroxides deteriorates the dynamic plastic deformation ability of the fine-grained magnesium alloys.
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