Investigation On Microstructure And Properties Of2024-al Hybrid Composites Reinforced With CNTs And SiCw

In this work, CNTs and SiCw hybrid reinforced2024Al matrix compositeswere fabricated by squeeze casting. Then hot extrusion deformation of thecomposites was conducted to improve the density and strength. The microstructureand interface phase of the casted and hot extruded composites were analysised bythe OM、SEM、EDS、XRD and TEM respectively. Ambient and high temperaturetensile experiments were performed to investigate the mechanical properties. Thestrengthening and toughening mechanism of the reinforcement were also explored.Dry friction and wear tests at the ambient and high temperature were conductedrespectively. The mechanisms of wear under ambient and high temperature wereanalysised by means of SEM and EDS.The homogeneous distribution of CNTs was achieved by mixing acid,ultrasonic techniques, and agitation. The preform with CNTs and SiC whisker werefabricated by wet blending. The aluminum composites were fabricated by squeezecasting, and then hot extrusion was conducted. Microstructure observation resultsshow that there are clip strips、micro-holes and CNTs cluster in the cast composites,and the number and size of clip strips、micro-holes and CNTs cluster decreased inthe squeezing composites. The uniformity and dispersion of the reinforcement havebeen improved and good interfacial bonding between CNTs、SiCw and metallicmatrices. The formation of Al4C3between CNTs and Al matrix, between SiCw andAl matrix, respectively.The tensile strength, yield strength and elongation ratio at ambient temperatureof the hot extruded or aging treatment composites were better than the castcomposites. Hot extrusion deformation has led to grain refinement of the matrix,whisker orientation and homogeneous distribution of CNTs. Dispersionstrengthening phase precipitated in the solution and aging treatment to improve thestrength of matrix. High temperature tensile experiments of hot extruded and agedcomposites show that the tensile strength was up to345MPa and382MPa at200°C,respectively. When the temperature exceeded200℃, the intensity decreased andplasticity increased. High temperature tensile strength of extruded and agedcomposites were better extruded2024Al alloy.Dry friction and wear tests of hot extrusion composites and2024Al alloy wereconducted respectively. It was found that, under ambient temperature and differentloads, the composite displayed lower wear rate and smooth friction coefficient compared to the monolithic alloy. At room temperature and20N, adhesion was thedominant wear mechanism for2024Al alloy, however, abrasion was found to bedominant for the composites. Also, it was clarified that the friction and wearbehavior of Aluminum matrix composites is largely influenced by the applied loadand temperature, and there exists a critical load andtemperature beyond which thewear mechanism were different. The ciritical conditions were200℃、20N and300℃、20N for extruded and aged composites, respectively. At300℃、20N,adhesion and delamination was the dominant wear mechanism for extruded and agedcomposites.