Research On Heat Treatment And Properties Of A Hot Extruded Rapidly Solidified 6061 Aluminum Alloy

The rapidly solidified 6061 aluminum alloy bar was prepared by the single roll melt rotating cooling（melt spining）combined with hot extrusion process,and compared with the conventional casting combined with hot extrusion process.Metallographic and X ray diffraction,scanning electron microscopy,transmission electron microscopy,backscatter electron diffraction,energy spectrum and density,hardness and tensile tests were used to analyze microstructures and mechanical properties of aluminum alloy bars fabricated by melt spinnig+hot extrusion and conventional casting combined with hot extrusion.Also,the heat treatment process was explored.The main results were as follows.（1）The microstructure of the ribbons fabricated by melt spinning was uniform and fine,and the average garin size was smaller than 1μm.Alloying elements were almost dissolved in aluminum alloy matrix,little second phases could be observed obviously under scanning electron microscope.The castings were a typical dendrite structure with an average size of 100μm,and acicularβ-AlFeSi and granular Mg₂Si could be observed from SEM iamges.In the process of hot extrusion,a large amount of Mg₂Si was precipitated from matrix of the ribbon,while the formation of AlFeSi was suppressed.The tensile strengths of the aluminum alloy bars fabricated by melt spinning+hot extrusion and casting+hot extrusion were 198.8 MPa and131.7 MPa,respectively.（2）In the process of hot extrusion,the dynamic recrystallization was likely to occur at the greater extrusion ratio and the higher extrusion temperature,generating new grains and orientations,making the<111>fiber texture deflecte.The best performance of the aluminum alloy bar could be obtained while the extrusion ratio was 16 and the temeparature was 500 ℃ by means of melt spinning+hot extrusion.Its tensile strength was 216.8 MPa,the elongation was 26%,and the fracture morphology was completely equiaxed dimple.（3）The optimum heat treatment process of aluminum alloy bar fabricated by melt spinning combined with hot extrusion with an extrusion ratio of 16 at 400 ℃ was solid solution at 560 ℃ for 2 h combined with aging at 185 ℃ for 1h.The tensile strength and yield strength were 321.2 MPa and 232.9 MPa,respectively,the elongation was 15%.After the heat treatment,the grain size remained to be the same.Due to the precipitation of theβ"phase the tensile strength increased 60%（¹21 MPa）,while the elongation decreased by 6%.The combination between ribbons could not be improved by heat treatment.