Preparation And Mechanical Properties Of Carbon Nanotubes Reinforced 7075 Aluminum Matrix Composite

7xxx series aluminum alloys are widely used in automobile manufacturing,electronic communications,military and other fields because of their high specific strength,specific rigidity and good thermal processing performance.However,because of the rapid development of society,people's requirements for high-performance materials are getting higher and higher.At this time,aluminum matrix composite materials with excellent performance come in handy.This article uses 7075 aluminum alloy as the matrix material,and carbon nanotubes as the reinforcement.The surface modification method of electroless plating is used to coat a layer of TiO₂ particles on the surface of the carbon nanotubes to improve the wettability between the CNTs and the Al matrix,so that the CNTs can be successfully dissolved into the matrix.Then the Al-TiO₂@CNTs intermediate preform was prepared by the method of ball milling and powder mixing and hydraulic pressure.With the assistance of high-energy ultrasonic vibration,the Al-TiO₂@CNTs intermediate preform was added to the molten 7075 alloy to prepare the as-cast0.9wt.%7075-TiO₂@CNTs composite material.However,because the composite material prepared by melt casting will inevitably lead to the segregation of elements in the 7075 matrix and weaken the strength and hardness of the material,the composite material was processed with a T6 heat treatment process,and the effect of aging temperature and aging time on the mechanical properties of composite was explored.Dry sliding friction and wear tests were carried out on the as-cast and T6composite materials.The wear rate,wear coefficient and wear surface of the material were analyzed,and the wear mechanism of the material was explored.Dry sliding friction and wear tests were carried out on the as-cast and T6 composites.The wear rate,wear coefficient and wear surface of the composites were analyzed,and the wear mechanism of the composites was explored.The experimental results show that0.9wt.%TiO₂@CNTs reinforcing phase is added to the 7075 melt,and the reinforcing phase can disperse uniformly along grain boundaries in the matrix under the assistance of high-energy ultrasonic vibration.Compared with 7075 matrix,the strength and microhardness of 7075-0.9wt.%TiO₂@CNTs composite have been greatly improved.The ultimate tensile strength,yield strength and microhardness of the composite are 261.79 MPa,201.22 MPa,126.02 HV,respectively.Compared with the matrix material,increased by 31.99%,40.93%,and 32.22%,respectively.In order to eliminate the element segregation in the as-cast material and further improve the strength and microhardness of the composite material,T6 heat treatment was carried out to reduce the grain boundary segregation.The experimental results show that the second phase elements segregated along the grain boundary in the composite material gradually merge into the matrix after solution treatment,and only a small amount of insoluble second phase is still segregated in the matrix.The solution treatment has achieved solid solution strengthening.effect.The yield strength,ultimate tensile strength and microhardness of the composite material after solution treatment are 240.39 MPa,301.13 MPa and 159.3 3HV,respectively.Compared with the as-cast composite material,improved by 19.47%,15.02%and13.16%respectively.The main purpose of the solution treatment is to prepare for the subsequent aging treatment.During the low temperature aging process,the supersaturated solid solution gradually formed the size about the nanoscale MgZn₂strengthening phase.The strengthening phase is in the form of a dispersion distribution,which plays the role of dispersion strengthening,and the interacts between the fine strengthening phase and the displacement dislocations inhibits the movement of the dislocations.The increase of dislocation density also greatly improves the mechanical properties of the composite material.After T6 heat treatment,there are many dimples of different sizes on the fracture of the composite material.At this time,the material is mainly ductile fracture.The friction and wear properties of the as-cast composite materials and composite under heat treatment were tested by the friction and wear tester.The properties,such as the wear rate and the wear coefficient were studied.The friction and wear mechanism were analyzed by observing the wear surface and wear debris via scanning electron microscope.The experimental results show that adding0.9wt.%TiO₂@CNTs reinforcing phase to 7075 melt can effectively reduce the wear rate and wear coefficient of the material,because CNTs can be used as a solid lubricant to cover the wear surface of the sample and reduce wear The contact surface between the surface and the friction pair,thereby greatly improving the wear resistance of the material.After T6 heat treatment,the strength and microhardness of the composite material have been greatly improved.The higher the hardness of the material,the better the wear resistance of the material.Under the same wear conditions,the wear rate of the composite material after T6 heat treatment is one order of magnitude less than that of the as-cast composite material,and the wear coefficient of the material is also reduced a lot.The SEM analysis of the wear surface morphology shows that the material is mainly based on abrasive wear as the main wear mechanism.Compared with the wear debris of the as-cast material,the wear debris of the composite material after the T6 heat treatment becomes very fine,which also fully shows the composite material after T6 heat treatment has better wear resistance.