Microstructure Evolution Of CNTs/Al Composites Prepared By Rotating Friction Extrusion

The CNTs/2024 Al composites were fabricated by Rotational Friction Extrusion(RFE), with 2024-T4 aluminum alloy as the base material. The effects of CNTs content and strain on the forming of the composites were studied. The crystal orientation, grain size, grain boundary, misorientation distribution and texture of composites were also determined. The effects of CNTs content and strain on the microstructure of the composites were studied. The main results show that as following.The process parameters which mainly affect the forming of the composites are the rotational speed, CNTs content and strain during RFE processing. When the rotational speed is 315r/min and the content of CNTs is 2%, the composites which have well shape and length of 210 mm can be fabricated. However, with the increase of the CNTs content,the surface of the composites becomes worse. With the increase of the strain, the surface morphology of the composites becomes smoother and the length of the composite is longer. But when the strain increases to 84.3%, the forming of the composites will become worse.The organization of the original aluminum matrix is coarse strip, the average grain size of it is 48.67μm and the large angle grain boundary content of it is 24.4%. After RFE processing, the average grain size of the RFE aluminum matrix decreases to 3.92μm, while the content of large angle grain boundary increases to 75.6%. Dynamic recrystallization of the aluminum matrix is occurred during the RFE processing. With the increase of CNTs content, when the content of CNTs is increased to 5%, the grains of the composites become finer equiaxed grains. The average grain size is gradually reduced to 2.35μm and the large angle grain boundary content is increased to 83.2%with increasing of CNTs content. CNTs can promote the dynamic recrystallization of the composites.RFE processing can reduce the rolling texture intensity and decrease the Copper type {112}<111> texture content of the RFE aluminum matrix, while the shear texture B011}211{?? and the brass R type texture 385}236{?? content of the newly formed recrystallization grains increase obviously, so the recrystallization texture components of the RFE aluminum matrix increase. With the increase of CNTs content, the sheartexture and the brass R type texture content decrease. The recrystallization textures of the composites are weakened by the addition of CNTs.As the strain increases, the organization of composites which consist of equiaxed grains gradually evolves into irregular long thin strips. The average grain size of the composites increases first and then decreases, and the content of large angle boundary of the composites increases. With the increase of the strain, the composite has no obvious preferred orientation and the maximum polar density of the composites increases from 1.94 to 2.10 until 2.16, in that the texture intensity increases while the increase is small.