Study On The High Temperature Mechanical Properties Of Nano-Al₂O₃/6061 Aluminum Matrix Composites

Aluminum matrix composites have the characteristics of low density,good plasticity,high specific strength,high specific stiffness,good wear resistance and fatigue resistance,and are widely used in aerospace,electronics and automotive industries.However,the high temperature mechanical properties of aluminum matrix composites are low,which limits their application in high temperature environments,and how to improve high temperature performance has become a research hotspot.Adding nanoparticles to the aluminum matrix can significantly improve the high-temperature mechanical properties of the material.In this paper,nano-Al₂O₃ was selected as the reinforced phase and 6061aluminum alloy was used as the matrix,and sintered nano-nano-Al₂O_3p/6061Al composites with different nano-Al₂O₃ contents were prepared by high-energy ball milling combined with hot pressing sintering,and the effect of nano-Al₂O₃ particle content on the microstructure and properties of the composites was studied.In order to further improve the performance of the material,the heat treatment process of the extruded material was further studied,and the microstructure and mechanical properties of the extruded and heat-treated composites were systematically studied,and the optimal heat treatment system was obtained,which improved the high-temperature mechanics of the composite.The main findings are as follows:（1）Under the ball milling process with a ball milling time of 50 h and a spherical ratio of 10:1,the particle size and morphology of composite powders with different nano-Al₂O₃ content changed significantly.With the increase of the volume fraction of nano-Al₂O₃ particles,the size of powder particles and grains gradually decreases,and the shape of the powder gradually changes from sheet to irregular granules,the addition of nano-Al₂O₃ enhanced particles will accelerate the fracture process of Al matrix particles.（2）Sintered Al₂O₃/6061Al composites with different nano-Al₂O₃ particle content were prepared by vacuum hot pressing sintering.Microstructure analysis showed that the grain size of the composite decreased with the increase of nano-Al₂O₃ content,and no pores were found in the material,and the nano-Al₂O₃ particles were uniformly distributed in the matrix,without obvious agglomeration,and the interface with the matrix was clean and well bonded.With the increase of nano-Al₂O₃ content,the hardness and strength of the composite material are significantly improved,but the plasticity of the material is reduced to a certain extent.Among them,the tensile strength and yield strength of the sintered 5vol.%Al₂O₃/Al composites reached 497 MPa and 463 MPa,respectively,and the elongation was 4.6%.（3）The Al₂O₃/6061Al composite with different nano-Al₂O₃ content was extruded and deformed.It is found that the internal holes and other defects of the composite material are reduced after extrusion,and the relative density and hardness of the material are further improved.After hot extrusion,the grain size of Al₂O₃/6061Al composites with different nanometer Al₂O₃ content was finer than that of the sintered state,and a large number of subgrain boundaries were found.The high temperature tensile test results show that the 6061Al composites with different Al₂O₃ content in the extruded state have excellent tensile strength and good plasticity.Among them,5vol%Al₂O₃/6061Al composite material can reach 176 MPa at 300°C with a tensile strength of 280 MPa and400°C.（4）The effect of solution aging treatment on the microstructure and high temperature mechanical properties of extruded nano-Al₂O₃/6061Al composites was studied.The heat treatment results showed that the hardness of different nano-Al₂O₃ content composites reached peak after solution treatment at 530°C×1 h.In the aging stage,the sequence of aging precipitation is:α-Al supersaturated solid solution-GP region-β’’phase-β’phase-βphase.With the increase of nano-Al₂O₃ content,the optimal aging temperature of the composite increased,and the addition of nano-Al2O3 delayed the aging precipitation process of the second phase.The heat treatment further improved the high-temperature mechanical properties of the composites,and the tensile strength was higher than that of the extruded composites at the same temperature.