2A12/6061 Dissimilar Aluminum Alloy Friction Stir Joining Process Research

With the development of automobiles,ships,aerospace and other fields,lightweight has become one of the important ways to reduce energy consumption,reduce pollution and improve fuel utilization.As aluminum alloys commonly used in these fields,2xxx series and 6xxx series aluminum alloys have good corrosion resistance and machinability,low density,high specific strength,and have been used in complex structural parts in a variety of manufacturing fields.When the traditional fusion welding process is adopted,the mechanical properties of aluminum alloy will be greatly reduced,and friction stir joining(FSJ),as a new type of solid phase joining method,has received widespread attention because of its few defects,small deformation,low residual stress,and other properties.In this studying,and the influence of joining process parameters on the microstructure of the joining area is analyzed,as well as the flow and microstructure evolution of materials during the joining process.The mechanical properties and corrosion resistance of the joining zone under different joining process parameters were analyzed.The temperature field during the joining process is numerically simulated,and the joining process parameters are optimized using the response surface method.The main research contents and conclusions are as follows:(1)The surface quality of the joining zone with too high heat input is worse and there are more flashes;The microstructure can be divided into the base metal base metal of the retreating side,the affected area of the retreating side,the Thermomechanica effect zone of the retreating side,the joining center area,the Thermomechanica effect zone of the advancing side,the heat-affected zone of the advancing side and the base metal area of the advancing side.After EBSD analysis,the grain is refined,the overall size of the grain is smaller than the joining core area,the grain boundary orientation angle is the smallest in each region,and the residual stress is large and belongs to the weak region.The material flow phenomenon in the joining area can be divided into three regions from top to bottom,each area has different flow behavior,and the influence zone of the shaft shoulder is squeezed and suctioned,resulting in the downward flow of the material on the advancing side at the top of the joining zone and the upward suction of the retreating test material.The affected area of the shaft shoulder and stirring pin is affected by the extrusion and suction effect and the stirring pin,so that the two materials in this area are fully mixed.Since the bottom of the joining zone is only affected by the stirring pin,the material flow distance is reduced and the degree of stirring is reduced.(2)The hardness level of the 2A12 side is higher than that of the 6061 side,there is a significant hardness gradient change on the 6061 side in the center of the joining area,and the hardness of the central layer of the joining area has a strong consistency,and the overall "W" shape is "W" shaped,but the shape is slightly distorted due to the different material properties on both sides;The increase of the speed of the stirring tool will lead to grain refinement,and the heat input of the joining will increase,the former will benefit the strength of the joining area,the latter will lead to the coarsening of the precipitation phase and reduce the strength of the joining zone,so there is a certain optimal interval in the speed;The corrosion potential and corrosion current of electrochemical corrosion cannot be analyzed to find its corrosion law,and the corrosion potential and corrosion current cannot be better judged by its corrosion resistance.The salt spray corrosion rate in the 12 h joining area was lower than that of 24 h aluminum alloy,and all were higher than the base metal,and the salt spray corrosion corrosion products were mainly aluminum hydroxide according to the atomic ratio of energy spectrum.(3)The joining at the beginning and end is the joining in an unstable state,the isotherm gradually forms an oval shape due to the residual heat influence after joining,the temperature under the shaft shoulder is gradually stabilized during the joining process,the highest heat point is located at the back of the shaft shoulder of the stirring tool,and there is a slight difference in the temperature of the advancing side and the retreating side.Based on the CCD response surface method,the mathematical model of the joining process parameters was established to verify the accuracy of the mathematical regression model through variance and experiment,and the combination of the process parameters with the highest tensile tensile strength under the condition of stirring head rotational speed of 590 tool rpm and feed speed of 460 mm/min under the shoulder pressure of 0.184 mm was obtained.