Research On Post Weld Electropulsing Treatment Of Friction Stir Welding Joints Of 2024 Aluminum Alloy

Friction stir welding(FSW)technology has attracted the attention of many scholars at home and abroad since its invention,and has been widely used in various fields.At present,there are still some problems in FSW of aluminum alloy,such as low strength and poor plasticity of joints.Although some scholars have solved the above problems by using post-weld heat treatment,the traditional furnace heating treatment will bring others problems,such as aluminum alloy materials are prone to oxidation and deformation at high temperature,and the size of parts is limited by the heating furnace.As a novel technology,electric pulse treatment has been proven to replace furnace heating for heat treatment of metal materials and has unparalleled advantages of conventional heat treatment.Therefore,in this paper,the FSW joint of 2024 aluminum alloy was treated by electropulse,and its effect on the microstructure and properties of the joint was studied.Firstly,the FSW experiment was carried out on the 2024-T4 and 2024-O aluminum alloy sheets.The influence of welding speed on the structure and properties of the joints was studied,and the better process parameters were obtained.Secondly,aiming at the poor plasticity of the 2024-T4 aluminum alloy FSW joint,the electric pulse regression and re-aging treatment of the joint were attempted.The effects of electrical pulse regression and re-aging treatment on the microstructure and properties of joints were investigated.Thirdly,aiming at the low strength of the 2024-T4 aluminum alloy FSW joint,the joints were subjected to electric pulse solid solution and re-aging treatment.The effects of different current density electric pulse solid solution treatment and different re-aging methods on the microstructure and properties of joints were studied.Finally,in order to solve the problem of poor plasticity of the 2024-O aluminum alloy FSW joint,the electric pulse annealing treatment of the joint was attempted.The effects of electrical pulse annealing treatment on the microstructure and properties of the joint were studied.In this paper,the microstructures and properties of the joints were analyzed by means of metallographic,hardness,tensile and scanning electron microscopy.The results show that in the FSW experiment of 2024-T4 aluminum alloy,with the increase of welding speed,the coarsening of the strengthening phase in the thermal mechanical affect zone of the joint was decreased continuously,the strength and elongation were increased first and then decreased.In the FSW experiment of 2024-O aluminum alloy,with the increase of welding speed,the solubility of the strengthening phase in the nugget zone of the joints was continuously reduced,and the strength of the joint was not changed significantly,but the elongation was continuously improved.In the experiment of electric pulse regression treatment,as the current density and the number of pulses increase,the dissolution degree of Cu-Mg clusters in each region of the joint was increased.Compared with the welded joint,the elongation of the joint was increased by 31.1%after electric pulse regression treatment with the current density of 150A/mm~2 and the number of five pulses.In the re-aging stage,after natural aging treatment,the strength of the joint was restored to near the level of the welded joint.In the experiment of electric pulse solid solution treatment,with the increase of current density,the solubility of the strengthening phases in each region of the joint was increased continuously,which leads to the decrease of strength and the increase of elongation of the joint.In the re-aging stage,after artificial aging treatment,compared with the welded joint,the tensile strength of the joint was increased by 8.3%and the yield strength was increased by 8%.And after natural aging treatment,compared with the welded joint,the tensile strength of the joint was increased by 4.1%and the yield strength was increased by 2.8%.In the experiment of electric pulse annealing treatment,with the increase of current density,the coarsening of strengthening phases in the nugget zone and the thermal mechanical affect zone was aggravated,so that the elongation of the joint was improved continuously.When the current density reached 160A/mm~2,the elongation of the joint was increased by 84.9%compared with the welded joints.