Control Of Microstructure And Properties On Aluminum Alloy Under The Integrated Large Strain Technology Of Extrusion-Bc Route Equal Channel Angular

In recently years,the state has promulgated the strategic plan of “Made in China 2025” to rapidly research and develop high-performance materials.The key areas include highperformance medical equipment,aerospace equipment and advanced rail transit equipment.The demand of ultra-high strength Al-Zn-Mg-Cu alloys is increased constantly in many fields because of the high comprehensive performance and low cost.But how to develop and manufacture efficiently the aluminum alloy with low cost and high-performance has become a hot topic today.Based on the equal channel angular pressing(ECAP)technology,the paper proposes a new type of large strain technology that integrates the extrusion process and Bc route into the ECAP technology,and designing,manufacturing and assembling the integrated mold of extrusion-Bc route ECA independently.Then Simulating and analyzing it by using DEFORM,and optimizing the structure of the mold according to the results.The paper studied the effect of the integrated technology of extrusion-Bc route ECA on the microstructure and mechanical properties of extruded 7075 aluminum alloy and verify the reliability of the numerical simulation.In addition,in this paper,the extruded ultra-high strength aluminum alloy(Al-8.70Zn-2.05Mg-2.01Cu-0.198Zr)which was developed by our research group was used as the experimental material.The influence of the integrated technology of extrusion-Bc route ECA on the microstructure and properties of the alloy was studied in the paper and the changing rule of the microstructure and porperies on X?Y?Z direction was explored.The particular research contents and conclusions are shown below:(1)The finite element simulation and parameter optimization of the integrated large strain technology of extrusion-Bc route ECA on was studied by using DEFORM software.The results showed that the maximum effective strain(when the extrusion ratio is less than 3)and the maximum load of the workpiece increase almost linearly with the decrease of shear angle and the increase of extrusion ratio.With the increase of friction factor,the maximum effective strain and load of the workpiece increase parabolically.The shear angle(37)=135°,the extrusion ratio ?=2 and outer arc angle ?=45° can achieve efficient,continuous and smooth processing of extrusion-Bc ECA integrated large strain.From the microstructure simulation analysis of workpiece,the morphology evolution and recrystallization of the interal grain were revealed visually in the process of the extrusion-Bc route ECA.(2)The die of extrusion-Bc route ECA integrated large strain technology was designed and manufactured successfully,and finished the processing of continuous extrusion-Bc ECA integrated large strain technology in the paper.The main dimensions of the die core are as follows: inlet diameter D=20mm,?=2,H/D=2~3,L2/d=0.7~0.85,shear angle ? =135°,outer arc angle ?=45°,die core taper is 4°~8°(seeing Chapter IV for the specific parameters).(3)The microstructure and mechanical properties of 7075 aluminum alloy processed after the integrated large strain technology of extrusion-Bc route ECA and heat treatment were studied.The results showed that after the process of deformation and solution treatment,the grain distribution of the alloy is different in each stage of the extrusion process on the Y direction.The distribution and size of the grains gradually become uniform and small from the clutter and large,the average grain size decreases from 17.31?m to 9.31?m.The recrystallization phenomenon in the process of extrusion-Bc route ECA is found that is similar to the results of numerical simulation of 7075 aluminum alloy,which venifies the reliability of numerical simulation.After the process of the deformation and solution-aging treatment,the hardness of the alloy increased from 186.88 HV to 200.10 HV and the tensile strength in X direction reduced from 571.4MPa to 517.6MPa,but the elongation up to 18.58% which was approximately 2 times higher than the original alloy.The plasticity of the alloy was improved greatly.The depth of the intergranular corrosion increased from the initial 32.61 ?m to 59.93 ?m.The intergranular corrosion resistance was decreased,but the intergranular corrosion rank is three that indicates the influence on the intergranular corrosion was not obvious.(4)The influence of the extrusion-Bc route ECA integrated technology on the internal microstructure and mechanical properties of the ultra-high aluminum alloy(Al-8.70Zn-2.05Mg-2.01Cu-0.198Zr)independently prepared by our research group was studied.The results showed that the microstructure of each area on the Y direction was different after the process of the deformation and heat treatment.The final grains on the A7 position were refined and homogenized significantly,and the equiaxed grains were increased,the average size of the grains reduced from 12.13?m to 6.93?m.The microstructure of the alloy was different on the X?Y?Z direction in the same position(just A7area).The microstructure on the X direction was the arc shape with some fine grains,the grain in the Y direction was homogenized and the Z direction was zonal distribution and oblong,which indicated the internal structure of the alloy shows a significant anisotropy.The hardness of the alloy in the X?Y and Z directions exceeds 215 HV,and the maximum in the Y direction is 222.34 HV.The tensile strength in X direction of the alloy reaches 561.8MPa and the elongation up to 24.5% that is nearly 2 times than the original.The plasticity is significantly improved.The depth of intergranular corrosion at each position in the Y direction of the alloy is different,and the end of the alloy is 39.66?m.The rank of intergranular corrosion is from four to three and the corrosion resistance is enchanced.The rank of intergranular corrosion in the X?Y?Z directions at the A7 position all belong to the third level,which indicates that the intergranular corrosion resistance in three directions is similar.In conclusion,the integrated large strain technology of the extrusion-Bc route which is proposed creatively in the paper not only can control and refine effectively grains of aluminum alloy,but also increases its plasticity,and improve its hardness and intergranular corrosion resistance in some degree.