Study On Friction Stir Welding Process Of T2 Copper And 1061 Aluminum Alloy

There are big differences in physical and chemical properties between copper and aluminum.It is difficult to obtain high-quality butt joints by conventional welding.As a new type of welding technology,friction stir welding can ensure that the material does not melt during the welding process,and the welding is completed under the shaping state,effectively reducing the occurrence of defects.Friction stir welding technology has been widely used in the connection between low melting point homogenous or heterogeneous materials such as magnesium alloys and aluminum alloys.With the development of industrial modernization,lightweight is an inevitable trend of future development.The copper-aluminum composite structure can not only combine the advantages of both materials,but also reduce weight and cost,and has high research value.This paper mainly studies the friction stir welding of 3mm thick T2 copper and 1061 aluminum alloy.The experiment was carried out by orthogonal experiment method under the process parameters of 1000-1200 rpm and welding speed of 40-60 mm/min.T2 copper was placed on the receding side,and 1061 aluminum alloy was placed on the advancing side for copper-aluminum friction stir welding.XRD was used to analyze the presence of intermetallic compounds at the welded joint.Combining the pressure changes during the welding process with the surface macro/microscopic morphology,the effects of process parameters,pressure and morphology are explored.A better welded joint sample was selected to study the effects of material flow,temperature field and grain on hardness.Through the experimental test results of tensile strength and fatigue performance of welded joints,the influence of process parameters on the mechanical properties of welded joints was investigated.The K-type thermocouple was used to measure the temperature change during the actual welding process.The transient temperature field model of the workpiece was combined with the actual temperature measurement results to analyze the temperature field distribution during the welding process.The influence of process parameters on heat input was analyzed according to the heat input conditions of different welding parameters.The optimum tensile strength was obtained at a rotation speed of 1100 rpm and Welding speed of 50 mm/min.The tensile strength was 193.155 MPa,which was 85.5%of the strength of the 1061 aluminum alloy base material.The particles of the precipitate at the fracture are larger and the dimples are deeper,indicating that the joint performance is better.Data analysis found that the effect of the rotational speed on the tensile test results is more significant than the welding speed.The fatigue life can reach more than 1×106 which is in line with the needs of practical applications.The fracture locations of fatigue samples mostly occurred at the copper-aluminum interface in the weld zone.The analysis suggested that it was related to the presence of intermetallic compounds and copper particles.Observing the microstructure of the copper-aluminum welded joint,it was found that the aluminum side weld zone(SZ)regularly distributed relatively small copper particles.Under the action of the stirring head,the agitation zone forms a layered structure of copper and aluminum.XRD analysis of some samples found that there may be three brittle and hard intermetallic compounds(IMC)of AlCu,AlCu3 and A14Cu9.IMC will seriously affect the joint performance.Reducing the heat input can reduce the presence of IMC to some extent.The copper side is affected by the heat cycle(HAZ)and the heat affected zone(TMAZ),the grain size becomes larger,the hardness decreases slightly,and the SZ grain refinement hardness increases.The hardness of the aluminum side TMAZ aluminum is significantly increased by the intermetallic compound,and the HAZ becomes soft under the action of thermal cycling,and the hardness decreases remarkably.During the welding process,the temperature field is asymmetrically distributed.The properties of copper and aluminum materials are different.The temperature on the aluminum side is higher than that on the copper side.The maximum temperature is 503.9?,which does not exceed the melting point of 1061 aluminum alloy.The influence of the rotation speed on the temperature peak is basically consistent with the trend of increasing the temperature peak with the increase of the rotation speed,but the difference is small,and is susceptible to external factors such as defects.The rotational speed affects the heat input by affecting the welding time.The influence of the welding process parameters on the heat input can determine the optimum heat input size in order to adjust the welding process parameters according to the environment.Through calculation,it can be determined that the heat input of the defect-free welded joint is 800-835W,and the heat input is 820W under the optimal welding parameters,and the heat input increases with the increase of the rotating speed.