CNTs/Mg Composite And Damping Properties By Friction Stir Processing

0.7~8.0vol%carbon nanotubes reinforced magnesium matrix composites wereprerare by friction stir processing (FSP).The effect of CNTs contents on macromorphology and microstructure was investigated. The mechanics properties and thedamping properties of the composites were tested.The influence of contents ofCNTs on the mechanics properties was analyzed.The damping and strengtheningmechanism of composites were studied.The results show that the CNTs/Mg composites with different CNTs contentswere sucessfully prepared by FSP.The base material is made up of the coarse crystalgrains uneven distributionand a few fine grains located at the grain boundaries.Thecomposite is made up of fine dynamic recrystallization grains and a little blackparticles thought to be segregation of CNTs.With increase of the content ofCNTs, the black particles gradually increase.The results of mechanics properties show that with increase of the volumefraction of CNTs, the hardness and tensile strength increase. The trends of incrementof the tensile strength decrease while the elongation decreased.The highest tensilestrength is282.3Mpa,1.26times of the parent material when the content of CNTs is4.0%. Fracture analysis showed that the characteristics low-stress brittle fracture isshowed when the volume fraction of CNTs is lower.With the increasing of the contentof CNTs, a typical brittle fracture can be observed.Study on damping properties of composite materials show that the increasingof the content of CNTs, decreasing of the influence of strain amplitude on dampingproperties of magnesium matrix composites at room temperature. The frequency is thehigher, the different degrees of growth effect of the parent metal and magnesiummatrix composites damping properties is showed.Under the high temperature,different conditions of frequency, its damping mechanism plays a different role, thenaffecting composites damping properties. When the temperatures rises to a certainvalue, the damping value of magnesium matrix composites has a significantlyimprovement affecting composites damping properties. First peak between150~210℃mainly caused by the dislocation damping mechanism.The second peakbetween300~350℃mainly caused by the interface damping mechanism.After450℃,damping of the composites mainly resulted by dislocation damping interaction damping and grain boundary.TEM observations show that microstructure of magnesium matrix compositesis fine equiaxed grains while the grain sizes are even. In magnesium matrix metalare uniform distribute in the magnesium matrix composites, of which local areahave CNTs of aggregation and wreckage. There are large numbers of dislocationsand dislocations tangles distributed in the interface. CNTs mainly distributedwithin the magnesium grains. There are not observed CNTs in grain boundary.