Study On The Process And Mechanical Properties Of Pinless Friction Stir Welding Joints Of 6016 Aluminum Alloy

Friction stir welding is a new type of solid-state connection technology,for the reason that welding temperature is relatively low,this technology can be used to weld a variety of light alloy materials,which traditional welding methods are difficult to weld.At present,the research on friction stir welding is mainly focused on the 2000 series and the 7000 series aluminum alloy in the world,and there is little research on the 6000 series aluminum alloy,especially the research of the 6016 aluminum alloy used in the automobile is less.With the increasing popularity of the concept of automotive lightweight,it is very important to find out the key technology of friction stir welding process.In this paper,the 6016T4 P sheet aluminum alloy whose thickness is 1mm is used as the research object,and completed an experimental study on butt joint and lap joint of pinless friction stir welding.Using the tensile testing machine,the optical microscope,the micro hardness tester,the scanning electron microscope and other modern analysis methods.The macro and micro structures,tensile and shear properties,vivtorinox hardness,internal defects,fracture mode and fracture mechanism of the joints were studied.Experimental results shows that if the welding parameters are optimal,good shape of welds can be achieved,otherwise,peeling and back gap will appear.In the experiment of butt welding,the weld performance and weld macro forming trend are basically same.When rotating speed of the mixing head is 1200 r/min and the welding speed is 400 mm/min,the weld strength reaches the maximum,which is about 218 MPa and up to 90.8% of the base metal.In the welding experiment,weld seam forming performance is quite different from the macro trend,because the lap welding is particular.When the rotating speed is 1600 r/min and the welding speed is 200 mm/min,the weld strength is highest as 223 MPa,which is 92.9% of the base material.The hardness of the weld zone is lower than that of the base metal zone,and the hardness of the weld nucleus is higher than that of THAZ and the HAZ.The lowest point of hardness is near the HAZ.The hardness of the upper plate in the welding area is greater than that of the lower plate,and the hardness of the HAZ is greater than that of the upper plate,the hardness of lower plate is greater than the upper plate of HAZ.When the heat input is insufficient,the defects such as hole,back gap,interface migration are found in the joints.The better mechanical properties of weld fracture sample is ductile fracture;The fracture form of welds with poor mechanical properties is mixed fracture of ductile fracture and brittle.The grain size of the nugget zone is obviously refined and the microstructure is uniform.The deformation of the grain in TMAZ is elongated and the grain size of HAZ is slightly coarser than that of the base metal.