Research On Fabrication And Properties Of2024Aluminium Based Hybrid Composites Reinforced With High Content CNTs

In this paper, CNTs reinforced2024Al matrix composites with21vol%,15vol%CNTs were fabricated by squeeze casting. Then hot extrusion deformation of thecomposites was conducted to improve the density and strength. The microstructure andinterface phase of the casted and hot extruded composites were analysised by the OM、SEM、EDS、XRD and TEM respectively. The reaction conditions of CNTs andaluminum were analysised by DSC, and the effects of different heat treatments on thereinforcement and the strength of the matrix interface bonding were alsoconducted. Ambient and high temperature tensile experiments were performed toinvestigate the mechanical properties. The strengthening and toughening mechanism ofthe reinforcement were also explored. Dry friction and wear tests at the ambient andhigh temperature were conducted respectively. The mechanisms of wear under ambientand high temperature were analysised by means of SEM and EDS.The homogeneous distribution of CNTs was achieved by mixing acid, ultrasonictechniques, and agitation. CNTs and SiC whisker were fabricated by wet blending. Thesqueeze casting was performed by optimizing the appropriate processing parameters,and then hot extrusion was conducted. Microstructure observation results show thatthere are clip strips and micro-holes in the cast composites, and the number and size ofclip strips and micro-holes decreased in the squeezing composites. The uniformity anddispersion of the reinforcement have been improved. Heat treatment of composites wasconducted under different phase temperature of2042Al. By comparing insulation at495℃(10h) with520℃(2h), the interface bonding was reinforced. However, a lot ofinterface brittle phase were generated while insulating at700℃(3min), which is notconducive to interfacial bonding.The tensile strength, yield strength and elongation ratio at ambient temperature ofthe hot extruded or aging treatment composites were better than the cast composites.Hot extrusion deformation has led to grain refinement of the matrix, whisker orientationand homogeneous distribution of CNTs. Dispersion strengthening phase precipitated inthe solution and aging treatment to improve the strength of matrix. High temperaturetensile experiments of hot extruded composites show that the tensile strength was up to350MPa at250°C. When the temperature exceeded250℃, the intensity decreased andplasticity increased.Dry friction and wear tests of hot extrusion composites and2024AL alloy wereconducted respectively. The friction and wear characteristics of composites were worsethan aluminum matrix under the conditions of low load and low sliding speed. This isdue to the fact that composites were in abrasive wear and carbon nanotubes have not been self-lubricating under the experimental conditions. However, the friction and wearcharacteristics of composites were much better at high temperature. The mechanism ofwear changed. The aluminum body was softening and the adhesive wear occurred. Atthe same time, the existence of reinforcement in composites can effectively improve thethermal stability and resistance to plastic deformation, and prevent adhesive wear.