Microstructure And Properties Of 5052 Aluminum Alloy Friction Stir Welding

5052 aluminum alloy is a kind of low which has high plasticity and good weldability.5052 aluminum alloy is commonly used in transportation and aerospace,it is a typical rust proof alloy materials.In the connection of aluminum alloy,there are many problems in the traditional welding methods,such as gas hole,crack,non environmental protection,reduction of joint rate,large welding deformation,the need of welding wire filling and unsightly joints,but friction stir welding can solve these problems effectively.In this paper,the 2mm thick 5052 aluminum alloy was chosen as the research object,and the friction stir welding was carried out on it.The welding tool with 12 mm diameter shoulder was designed into truncated cone and its thread is rotate right.According to the rotation speed and welding speed change,in the process of welding by fixed pressing the weight of 0.1mm and the parameters of welding needle inclination of 2.5 degrees,selected in a large scale and rotation speed and welding speed of process parameters.The relationship between process parameters,microstructure and properties was studied by OM,SEM,EDS and electromechanical universal testing machine etc,it can provide the basis for the optimum parameters of the friction stir welding of 2mm thick 5052 aluminum alloy.The results show that:The structure of friction stir welded joint can be divided into 3 regions in 2mm thick sheet: Nugget zone,transition zone and base metal zone.The microstructure of the nugget zone consisted of very fine and equiaxed grains.The transition zone is narrow,which is divided into heat affected zone and heat affected zone,the microstructure of the the heat affected zone is elongated deformed banded structure,the microstructure of heat affected zone is only affected by the welding heat cycle,but it is similar to that of the parent material,the parent zone is not affected as the original structure,the width of the advancing side in transition zone is narrower than that of the retreating side in transition zone.When the rotating speed is 1200 rpm,the welding speed is 120mm/min,240mm/min,360mm/min,480mm/min and 600mm/min respectively,The grain size of the weld zone is small equiaxed grain,and the average grain size is 10.8 m,10.1 m,9.3 m,8.2 m and 7.6 m,respectively.The variation of grain size is as follows: when the rotating speed is constant,the dynamic recrystallization grain size decreases with the increase of welding speed.When the welding speed is 240mm/min,the rotating speed is 600 rpm,800rpm,1000 rpm and 1200 rpm respectively,The grain size of the weld zone is small equiaxed grain,and the average grain size is 8.1 m,9.2 m,9.6 m and 10.1 m,respectively.The variation of grain size is as follows: when the welding speed is fixed,the grain size of dynamic recrystallization increases with the increase of rotating speed.The hardness of the weld is in "W" shape,the hardness of the weld zone is lower than that of the base metal,and the hardness of the heat affected zone is the lowest.The microhardness is mainly determined by the grain size and dislocation density,and the hardness is inversely proportional to the grain size.Because the grain size of the heat affected zone is the largest,the hardness value is the lowest.The tensile strength of the base material at room temperature is 245 Mpa and the elongation is 9%.The mechanical properties of friction stir welded joints were decreased compared with that of base metal.The optimum technological parameter of friction stir welding is the rotational speed of 1200 rpm and the welding speed of 600mm/min.The tensile strength at room temperature can reach 216 Mpa,which is 88.16% of the base material strength,and the elongation is 6.7%.Friction stir welding can be used to realize the solid state joining of 2mm thick 5052 aluminum alloy and the range of welding parameters is large,and the joint with good performance can be obtained when the rotating speed is 1200 rpm and the welding speed is 600mm/min.