Study On Microstructure And Mechanical Properties Of Nano-Al₂O₃p/7075 Aluminum Structure Composites Prepared By Powder Metallurgy

Traditional ceramic particles reinforced aluminum matrix composites have higher strength and lower plasticity.The addition of ceramic particles hinders the plastic deformation of the composite material and improves the strength of the composite material.However,once a crack emerges at the boundary between the ceramic particles and the matrix,the crack is easily connected and expanded,which reduces the plasticity of the composite material.Research in this area is a research hotspot,in which the periodic non-uniform dispersion of ceramic particles in the matrix proves to be an effective means of toughening.Because 7075 aluminum alloy has the highest strength compared to other grades of aluminum alloy,and the price of nano-scale Al₂O₃ is low,this paper uses 7075 aluminum alloy and nano-Al₂O₃ as the matrix and reinforcing phase.In order to obtain a high-strength,high-toughness and low-cost aluminum-based composite material in this paper,it is designed to add or form coarse-grained particles in Al₂O₃p/7075 aluminum-based composite material,through mechanical ball milling powder mixing,cold pressing into agglomeration,vacuum sinter And the extrusion process,a nano-Al₂O₃p/7075 aluminum-based configuration composite material toughened by fibrous aluminum grains was prepared.The sintering process,extrusion process and different coarse crystal content of the composite materials were used to study the microstructure,density,elastic modulus,hardness and compressive strength,and compression fracture deformation rate of the composite materials.The specific research content and results are as follows:By studying the effects of sintering at 620?,630?,and 640?in air,the sintering time of 0 min,10 min,30 min,and 60 min on the microstructure of nano-Al2O3p/7075 aluminum matrix configuration composites was compared with that of vacuum sintering on composites.The effect of determining the best sintering process.Studies have shown that with the increase of sintering temperature and the extension of sintering time,the remelting of the matrix in the composite material increases and the structure becomes more uniform.When sintering in the air,there is extravasation of the aluminum liquid,which results in a large number of holes in the composite material,but there is no extravasation in the vacuum condition.The effect of temperature sintering(620?,630?,640?sintering,sintering for60 min,extrusion ratio of 4:1)on the structure and properties of nano-Al₂O₃p/7075aluminum matrix composites was investigated.The research shows that the density is above 98%,and the hardness,compressive strength and elastic modulus are improved relative to the matrix;the fracture deformation rate of the 640?fired structural composite material is 15.9%,and the fracture deformation rate of the homogeneous composite material is increased by 38.7%;According to the compression fracture analysis of the configuration composite material,the fracture mode of the configuration composite material is the cleavage fracture in brittle fracture,and the fracture mode of the composite material is not changed after heat treatment.The effects of extrusion ratio(extrusion ratio of 8:1,4:1,620?,630?,640?sintering,holding 60min)on the structure and properties of nano-Al₂O₃p/7075aluminum matrix composites were studied.The research shows that the sintering temperature is the same,and as the extrusion ratio increases,the density of the configuration composite material further increases,resulting in an increase in the material's hardness,elastic modulus,compressive strength,and plasticity.Both the compressive strength and the fracture deformation rate of the material are improved.The compressive strength of the composite material with a sintering extrusion ratio of 630?at 8:1 is 874.1Mpa.The fracture deformation rate is 20.7%.Combined with the analysis of the structure and fracture morphology of the composite material,with the increase of the extrusion ratio,the fracture mode of the composite material has not changed.The effect of coarse crystal content(coarse crystal content of 5 wt%,10wt%,15wt%,sintering at 475?,holding temperature 360 min,extrusion ratio 4:1)on the structure and properties of nano-Al₂O₃p/7075 aluminum matrix composites was investigated.Studies have shown that as the content of coarse crystals increases,the hardness of the material decreases,holes appear in the material,and the density of the material decreases slightly,resulting in a decrease in the compressive strength of the material.Smooth,the material's fracture deformation rate gradually increases,the material's hardness gradually decreases,direct addition of coarse crystals compared with high-temperature sintering process,direct addition of coarse crystals will inevitably reduce the compressive strength of the material,while the direct high-temperature sintering process first increases the compressive strength After the reduction,and the fracture deformation rate is much higher than the direct addition of coarse crystals.Among them,the compressive strength of the composite material at 15%coarse crystal content is 775.9 MPa,the fracture deformation rate is 14.6%,and the composite material at 15%coarse crystal content reduces the compressive strength by 1.0%and the fracture deformation rate by 10.7%compared with sintering at 640?In the high temperature sintering process,when the strength of the configuration composite material is flat,the fracture deformation rate of the configuration composite material can be greatly improved.The mechanism research shows that when the crack propagates to the coarse crystal,the crack cannot pass through the coarse crystal area,and can only propagate along the interface between the coarse crystal area and the composite area,thereby changing the crack propagation path and significantly improving the plasticity of the material.