Research On Microstructure And Properties And Plastic Material Flow Of Cu/Al Butt Joints By Friction Stir Welding

In power,electronics,appliances and other relative fields,both copper and aluminum are good conductor material.Because the Cu/Al joint has the advantages of high connection strength,excellent corrosion resistance and good appearance,copper and aluminum are usually connected by Cu/Al joints.As a solid-phase welding,Friction Stir Welding（FSW）has a great potential for the preparation of Cu/Al joints.In this paper,4mm thick copper T2 and 1060 pure aluminum were chosen as the experiment object.Cu/Al butt joints were manufactured by friction stir welding.The microstructure and phase composition of Cu/Al joints were explored.The effect of welding parameters and stir tool’s shoulder diameter on weld surface formation,mechanical properties and electrochemical corrosion properties were studied.And,the flow behavior of weld material was studied by means of experiment and numerical simulation.With reasonable rotating speed and welding speed,the Cu/Al joints with good forming quality could be obtained.In Cu/Al joints,the grain size of Shoulder Affect Zone and Weld Nugget Zone were fine and uniform.The grain size of Thermo-Mechanically Affected Zone on the side of copper and aluminum were also fine.The Heat Affected Zone on the side of aluminum was narrow and the grain size was larger.And there was no obvious grain growth in Heat Affected Zone on the side of copper.Intermetallic phases CuAl₂ and Cu₉Al₄ existed in Cu/Al joints.The type of phase compositions did not change with different welding parameters.When the heat input was low,the fracture mechanism of Cu/Al joints was brittle fracture.With increase of rotating speed or decrease of welding speed,the tensile strength of Cu/Al joints increased.When the heat input was large,the fracture mechanism of Cu/Al joints changed to plastic fracture.With increase of heat input,the tensile strength of Cu/Al joints decreased slightly.When shoulder diameter of stir tool was 20 mm,rotating speed was 800 rpm and welding speed was 50mm/min,the well weld was formed and the connection of Cu/Al joint was tight.The tensile strength of Cu/Al joint prepared by optimum welding parameter was 116.4MPa,which reached 82.6% of aluminum 1060.The corrosion potential of Cu/Al joint decreased with increase of rotating speed or decrease of welding speed.However,there was no direct relation between corrosion current density and welding parameters.The intensity of metal flow in shoulder effect area was highest and a large number of copper materials got into aluminum side.In Weld Nugget Zone,copper material transferred to the bottom of Cu/Al joint,and only a small amount of copper material existed.In the bottom of Cu/Al joint,the copper material could also get into aluminum side,but material flow intensity was low and material flow behavior was extremely unstable.Meanwhile,a three-dimensional flow model was established based on fluid mechanics theory.FLUENT software was used to carry out the simulation study.In shoulder effect area,the material flow intensity was high,and the mixing zone was a regular and uniform transition zone.In Weld Nugget Zone,aluminum was shunted in front of the stirring pin,and some aluminum flowed into the Advancing Side.In the bottom of Cu/Al joint,the material flow intensity was low and the mixing zone was small.The numerical simulation results agree basically with the experimental results.