| Magnesium and magnesium alloys are widely used because of their advantages of low density,high specific strength,high damping capacity,noise reduction,and so on.Pure magnesium has the best damping capacity,but with poor mechanical properties,such as low hardness,low yield strength and tensile strength which limits its range of application.Friction stir processing（FSP）is a new kind of solid phase processing technology.The change of grain size and grain orientation during the friction stir processing is an important factor affecting the damping performance of magnesium alloys.Therefore,friction stir processing provides a great possibility to solve the contradiction between the mechanical properties and damping performance of magnesium alloy.In this paper,the ZrO2/Mg composites were prepared by friction stir processing.The effects of ZrO2 contents and friction stir processing pass on the microstructure,mechanical properties and damping properties of ZrO2/Mg composites were investigated.Well-formed ZrO2/Mg composites can be prepared by friction stir processing.The distribution of ZrO2 was well-distributed in AZ31 magnesium alloy.After friction stir processing,there were uniform fine equiaxed grains in the center of friction stir zone of ZrO2/Mg composites.The addition of ZrO2 reinforced phase can significantly and effectively refine the grain size.After 3 passes of friction stir processing,the average grain size of SZ of ZrO2/Mg composites with the groove width of 0.6mm was 10.26 μm.After friction stir processing,the hardness of AZ31 magnesium alloy was lower than the hardness of base metal,the overall strength decreased and the elongation was increased.The increase of the hardness of ZrO2/Mg composites was mainly due to the effect of ZrO2 reinforced phase.After 4 passes of friction stir processing,ZrO2 reinforced phase had the most uniform distribution,the hardness distribution was more smoothly.The addition of ZrO2 reinforced phase had important influence on the tensile strength and elongation of ZrO2/Mg composites.After 4 passes of friction stir processing,ZrO2/Mg composites with the groove width of 0.8mm had the tensile strength of 233.58 MPa,which was increased by 17.38% than that of the AZ31 magnesium alloy after 4 times of friction stir processing.After friction stir processing,the ZrO2/Mg composites had good damping properties.After comparison,when the groove width was 0.6 mm and 0.8 mm,after 4 times of friction stir processing,the ZrO2/Mg composites had the better damping properties.The damping values（ε=10-4）of the ZrO2/Mg composites with a groove width of 0.8mm was 0.01178,which was increased by 21.44% than that of the AZ31 magnesium base alloy.The damping values（ε=10-3）of the ZrO2/Mg composites with a groove width of 0.8mm was 0.02299,which was increased by 19.12% than that of the AZ31 magnesium base alloy.In the temperature-damping test,there was a P1 internal consumption peak between 150-180 ° C.The damping peak P1 was a relaxation process.With the increasing of ZrO2 contents,the activation energy of damping peak P1 gradually increased.In the strain-damping test,the damping behavior of ZrO2/Mg composites followed the G-L theory.The average distance of strong pinning point LN and the average distance of weak pinning point LC increased with the increasing of the pass of friction stir processing. |
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