Study On Microstructure And Interface Characteristics Of CNTs/Mg Composites By Rotational Friction Extrusion

The carbon nanotubes reinforced magnesium matrix?CNTs/Mg?composites with different content of CNTs were fabricated by Rotational Friction Extrusion?RFE?with AZ91 D magnesium alloy as the substrate and CNTs as the reinforcing phase.The grain size,orientation difference distribution,orientation imaging and texture of the composites were measured by EBSD technique.The micro-strcture of second phase and interface characteristics about the composites were observed by TEM.The hardness and tensile strength of the composites were tested.The effects of CNTs on the microstructure,interface and mechanical properties of Mg matrix composites were studied.The results show that the magnesium matrix composites which have good forming can be prepared by RFE,and the distribution of CNTs in the composites is uniform.The dynamic recrystallization of magnesium alloy occurs after RFE processing,which is composes of small equiaxed grains,and large angle grain boundaries ratio is 47.4%.The higher the content of CNTs in the composites,the smaller the grain size.The grain size of 5% CNTs/Mg composites is 2.8?m,the large angle grain boundary ratio is 72.9%.CNTs promote the dynamic recrystallization of composites.The crystal orientation of AZ91 matrix is<0001> and<01???0> crystal,with a small amount of <???2???0>crystal.The crystal orientation of the<0001> crystal direction increase,the<01???0> crystal decrease,the texture of substrate <0001> is enhanced and the maximum polar density is reduced.The <???2???0>and<01???0>crystal orientation increase,<0001> crystal orientation decrease of composites,and the more the CNTs,the more <???2???0> and <01???0> crystal orientation,the less the<0001> crystal orientation,and the maximum polar density and the texture strength of the composites were lower than those of AZ91 magnesium matrix.The crystal orientation of 5% CNTs / Mg composites is almost completely <???2???0>crystal orientation and<01???0> crystal orientation.The damaged CNTs in the composites interact with the alloying elements Al in the matrix forming Al₄C₃.The interplanar spacing is 0.227 nm,which is close to the?104?crystal plane of Al₄C₃.The CNTs at the reaction site are well integrated with the matrix interface.The interface between?2??????3?_Mg and ?104?AL₄C₃ ,?104?AL₄C₃ and ?111?_CNTs,?2??????3?_Mg and ?111?_CNTs is semi-coherent.The hardness of composites increase first and then decrease with the increase of CNTs content.When CNTs is 2%,the hardness of CNTs/Mg composites is 101.3HV which is the maximum hardness of composites,and 40.3% higher than that of magnesium matrix.When CNTs is not higher than 2%,the tensile strength of the composite is higher than that of the original magnesium matrix,the maximum tensile strength is 228.0MPa,which is 31.3% higher than that of magnesium matrix.The composite material is reinforced by the combination of fine grain strengthening,the second phase strengthening,CNTs strengthening and synergistic strengthening.