Investigation On Fabrication,Microstructure And Mechanical Properties Of Carbon Nanotubes/Mg Composites With A Biomimetic Laminated Microstructure

This paper aims to prepare CNTs/Mg composite materials with a layered configuration by constructing carbon nanotube/magnesium layered elements to solve the contradiction between the strength and toughness of the composite materials.CNTs/Mg layered composite materials with different layered structure parameters were prepared by spray deposition-stacked cold pressing-hot pressing-reciprocating extrusion-hot extrusion process,and the structure,properties,toughness and toughness of the composite materials were strengthened.The mechanism was explored.First,the ultrasonic-assisted mixed acid treatment method was used to solve the problem of pre-dispersion of CNTs.The CNTs/Mg layered composite element was constructed by spray deposition process.The CNTs/Mg layered composite material was realized through cold pressing,hot pressing and reciprocating extrusion process Preparation and control of layered structure parameters.With the help of OM,SEM,EBSD,TEM and room temperature tensile test,the microstructure and mechanical properties of pure magnesium and composite materials with different layer structure parameters were studied,and the influence of layer spacing on the properties of composite materials was studied.Through finite element simulation of the stress and strain distribution of pure magnesium and composite materials during the three-point bending deformation process,the strength and toughening mechanism of the composite materials was revealed.The successfully prepared CNTs/Mg composite element was cold-pressed to achieve preliminary mechanical bonding,hot-pressed to achieve further metallurgical bonding,and finally through reciprocating extrusion to achieve the successful preparation of composite materials and the adjustment of layered structure parameters.The composite materials were hot extruded into rod-shaped materials to study the structure and mechanical properties.The effects of reciprocating extrusion pass on the structure and properties of composite materials and the effect of CNTs content on the structure and properties of composite materials were mainly studied.When the content of CNTs is 0.3wt%,after 5,10,and 20 reciprocating extrusions,the yield strength of the composite is increased to 195 MPa,208MPa,and 242 MPa,respectively,while the elongation is maintained at about 5.4%.The characterization of the tissue revealed that the layer spacing decreased with the increase of the reciprocating extrusion pass.When the reciprocating extrusion pass was 20,the layered structure disappeared.The grain size was also reduced from 4.9 ?m and 4.2 ?m to 3.1 ?m.At the same time,the texture of the base surface gradually decreases with the increase of the reciprocating extrusion pass.Fracture analysis showed that a good interface combination was achieved after reciprocating extrusion.When the reciprocating extrusion pass is kept unchanged,the yield strength of the composite materials with pure magnesium and CNTs content of 0.13%,0.27% and 0.36% are 152 MPa,186Mpa,197 MPa and 214 MPa,respectively.The composite material with CNTs content of 0.36% has a yield strength increase of 40.7% compared with the pure matrix of the comparative matrix,while the elongation is slightly improved.The layered configuration is the key to the simultaneous improvement of the strength and toughness of composite materials.Through theoretical calculations,it is found that the main strengthening mechanisms of composite materials are layered interface strengthening,fine grain strengthening and thermal mismatch strengthening.In addition,there are load transfer strengthening and interlayer Mg O strengthening.The extraction,bridging and crack deflection of CNTs in composite materials can inhibit crack propagation and contribute to the improvement of toughness.Through the finite element simulation of the stress-strain distribution of the composite material during the three-point bending deformation process,it was found that the presence of the layer relieves the strain concentration and delays the fracture of the composite material,thereby improving the toughness of the composite material.