Study On Microstructure And Properties Of ZrO₂@CNTs/2A70 Aluminum Matrix Composites

As the cornerstone of manufacturing industry,materials are the realistic basis and forerunner of social development and progress.The development of materials have a significant role in promoting automobile,aviation,information and other industries.With the development of science and technology,more and more industries are limited by the performance of materials and enter the bottleneck stage of development.The performance of traditional materials is gradually falling behind the requirements of advanced manufacturing industries for materials.How to improve the performance of materials to better meet the requirements of the industry is particularly important.The coating mechanism of ZrO₂ceramic particles on the surface of CNTs was studied.ZrO₂@CNTs/2A70 composite was prepared by high-energy ultrasonic assisted casting,and the microstructure,mechanical properties and strengthening mechanism of the composites were analyzed.The ZrO₂@CNTs/2A70 composite was processed by hot extrusion.The effects of the CNTs and hot extrusion on the microstructure,mechanical properties and friction behavior were compared by hardness test,tensile test and wear test,and the strengthening mechanism was theoretically analyzed.The results show that the contact angle between ZrO₂@CNTs and 2A70 melt decreases from 140.70°to 116.85°after ZrO₂ particles coated on the surface of CNTs.Although the wetting angle of ZrO₂@CNTs is non-wetting,the high-energy ultrasonic assisted casting adopted in the experiment can supplement energy to promote the wetting of ZrO₂ particles.When the content of ZrO₂@CNTs is lower than 2wt.%,ZrO₂@CNTs can disperse in the matrix.When the content of ZrO₂@CNTs is 1.5wt.%,the hardness and ultimate tensile strength of the composite reach the maximum,which respectively increase by 26.0%and 21.5%,compared with matrix.When the content of ZrO₂@CNTs reach 2wt.%,obvious agglomeration appeare in the microstructure of composites.The ZrO₂ particles on the surface of CNTs can form semi-coherent interface with aluminum matrix to strengthen the interfacial bonding strength of CNTs to Al.The improvement of mechanical properties of 2A70 composite with the addition of ZrO₂@CNTs is attributed to the synergistic effect of grain refinement strengthening,orowan strengthening,thermal mismatch strengthening and load transfer mechanism.The casting defects were eliminated by hot extrusion to obtain ZrO₂@CNTs/2A70composites with excellent properties,and the dispersion of reinforcement phase was also improved.The results show that the eutectic phase of composite is broken and dispersed uniformly under the action of shear force after hot extrusion.The broken eutectic phase and ZrO₂@CNTs reinforcement flow along the extrusion direction under the action of extrusion,presenting a linear arrangement orientation.The Al-Cu phases and Al-Cu-Mg phases in the composites are solidly dissolved into matrix during hot extrusion at 460℃,while Fe-Ni phase is broken into particles or blocks under the action of extrusion shear force.The ZrO₂@CNTs phases in the extruded composites flows evenly along the extrusion direction under the action of extrusion.After the hot extrusion process,the mechanical properties of extruded composites have been significantly improved,the hardness and ultimate tensile strength of extruded composites are increased by 23.7%and 20.9%,respectively,compared with the as-cast composites.In addition,the plastic elongation of extruded composites is significantly improved by 152.7%compared with that of as-cast composites.The tribological behavior features test were carried out on 2A70 and ZrO₂@CNTs/2A70 composite in different states.The results show that the wear rate of the composites in both as-cast and extruded state can be reduced by adding 1.5wt.%ZrO₂@CNTs/2A70.Under the low normal load（1.3Mpa）,the wear mechanism of as-cast composites is mainly abrasive wear.With the deterioration of friction and slip conditions,the wear mechanism changes to adhesive wear mechanism.The wear rate of as-extruded composite is significantly lower than that of the as-cast composite in the same wear environment.The as-extruded composite exhibit stable abrasive wear mechanism under experimental load and velocity.The wear analysis of the as-cast and extruded composites under different friction conditions can be summarized as follows.The wear rate of as-cast and as-extruded composites increases with the increase of normal load and friction velocity.In addition,with the increase of normal load,the friction coefficients of the as-cast and as-extruded composites show an upward trend,and the upward trend of as-extruded composite is higher than that of the as-cast composite.However,with the increase of friction velocity,the coefficient of friction of composites decreases slightly.The amplitude of the COF of as-extruded composites is much smaller than that of as-cast composites under different friction slip conditions.