| 6061 aluminum alloy has many excellent properties,such as good weldability,strong corrosion resistance and good formability.6061 aluminum alloy is widely used in aerospace and automotive fields,and is a hot material for lightweight materials in the future.The severe plastic deformation technique can refine the grains and prepare an ultrafine grain structure material.Equal channel angular pressing(ECAP)is the most representative of the severe plastic deformation technology.Therefore,it is of great significance to study the micro structure evolution,grain refinement mechanism and mechanical properties of 6061 aluminum alloy during equal channel angular pressing.In this paper,6061 aluminum alloy sheet was taken as the research object.At room temperature,6061 aluminum alloy was ECAPed four passes with A,Bc,C routes.Evolution of microstructure of 6061 aluminum alloy were studied by means of(TEM),(EBSD),(XRD)and other methods to observe the testing of universal tensile machine,and the evolution of microstructure and grain refinement mechanism during extrusion.The main results are as follows:(1)The original material is a typical rolled grain.After one single ECAP extrusion of 6061 aluminum alloy,the grain refinement is remarkable,the grain is elongated along 45°,and the grain orientation is obvious.After the ECAP,the 6061 aluminum alloy forms intertwined deformation bands and shear bands,and the large grains are broken into many fine grains.After the four-pass ECAP of the 6061 aluminum alloy by Bc path,the grain refinement is more remarkable due to further shearing action,forming fine nearly equiaxed crystals.(2)The tensile strength of 6061 aluminum alloy sheet is 332.23MPa,the hardness is 72.41HV,and the elongation is 24.97%.After one extrusion,the tensile strength was 469.65MPa and the tensile strength was increased by 41.36%.the hardness was 90.37HV,an increase of 24.80%.After one pass,the elongation quickly dropped to 6.41%,a drop of 18 percentage points.After one-pass extrusion of 6061 aluminum alloy,the dislocation density increases,the grain refines,the grain boundary increases,and the hindrance to dislocations increases,so the tensile strength and hardness increase,and the plasticity decreases.(3)From the analysis of tensile strength,hardness and elongation of 6061 aluminum alloy,the Bc path is the best process path among the three paths.And from the analysis of tensile strength and elongation,the Bc path obtained better mechanical properties after the fourth pass extrusion.The tensile strength of 6061 aluminum alloy is 541.73 MPa,which is 63.05%higher than the original material,and the hardness is 122.76HV.Compared with the increase of 69.53%,the elongation is 10.35%,which is 14.45%lower.(4)The starting material is a typical rolled grain with an average grain size of about 30.35μm.After extrusion,the grains of 6061 aluminum alloy are elongated,and the large grains are broken into many small grains.The grain refinement is obvious.The average grain size after extrusion is about 6.17 μm.The grain refinement was more remarkable after four passes,and the average grain size was about 0.72μm.Ultrafine grained material can be formed after four passes.(5)The grain orientation difference in the 6061 aluminum alloy raw material is mainly concentrated in 1°-5°,mainly the small-angle grain boundary.After four passes,the grain orientation difference is between 15°-55°,mainly due to the high angle grain boundary.After one extrusion,the deformed grains increase,and the substructure and recrystallized grains decrease.However,after four passes,the deformed grains are greatly reduced,and the substructure is significantly increased.As the deformation increases,more sub grains favor recrystallization nucleation. |
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