Friction Stir Lap Welding Process And Mechanical Properties Improvement Of Dissimilar Aluminum Alloys

7005 aluminum alloy has high strength and good comprehensive mechanical properties,5083 aluminum alloy has good molding processability and excellent corrosion resistance.The connection of dissimilar aluminum alloys can meet the needs of different working conditions while playing their respective excellent performance.However,the physical properties and chemical composition of dissimilar aluminum alloys differ greatly,and traditional welding methods are prone to defects such as porosity and cracking.Friction stir welding(FSW)as a solid-phase joining technique that can effectively avoid these defects,but the heat input generated during the welding process can still dissolve or roughen the precipitated phase in heattreatable reinforced aluminum alloys,reducing the joint performance.Aluminum alloy FSW lap joints are prone to hook defects,deteriorating the shear strength of the joint,how to obtain highquality heterogeneous aluminum alloy FSW lap joints is an urgent problem to be solved.In this paper,we have taken 5083-H112 and 7005-T6 aluminum alloys as the research objects,changed the process parameters and the position of the base material to carry out the FSW lap joint test of dissimilar aluminum alloys under conventional conditions,analyzed the factors affecting the forming and mechanical properties of the joint,and on this basis,changed the cooling conditions to investigate the effect of cooling conditions on the microstructure and mechanical properties of the lap joint,in order to improve the microstructure of the joint through the morphology of the joint interface and hook defects and microstructure control.This study was carried out to investigate the effect of cooling conditions on the microstructure and mechanical properties of lap joints,and to provide a theoretical basis for improving the mechanical properties of FSW lap joints of dissimilar aluminum alloys through joint interface morphology and hook defects and microstructure control.A study was conducted on the formation and microstructure of FSLW joints of dissimilar aluminum alloys to investigate the influence of process parameters and plate position on the surface defects and flying edge morphology,interface morphology and hook defects,tissue distribution and grain morphology of the joints.The results showed that the process parameters and plate position significantly influenced the flow behavior of the plasticized material of the weld and thus the joint formation.The lap joint showed large flutter on the receding side of the surface,hook-like defects and incomplete breakage of the interface on the inside.With the same process parameters,5083 is the top plate with larger flying edges,hooked defects migrate downward a greater distance,and internal hole defects appear at higher speeds.Decrease the speed or increase the welding speed can reduce the size of the flying edge,reduce the vertical expansion of the hook-shaped defects,while reducing the degree of interface fragmentation.The mechanical properties of FSW lap joints of dissimilar aluminum alloys were studied by microhardness testing,tensile and shear properties testing,analyzing the differences in mechanical properties of the joints at different plate positions,and analyzing the factors influencing the mechanical properties of the joints in combination with the interface morphology and hook defects and microstructure distribution.The results show that the shear strength of the joint increases and then decreases with the increase of the rotational speed and welding speed for both plate positions.High speed and low welding speed,7005 for the top plate joint strength is higher;low speed and high welding speed,5083 for the top plate joint strength is higher,when the speed of 1050 rpm,welding speed 175 mm / min,5083 for the top plate when the hook-shaped defects down migration distance is smaller,the interface is broken to a higher degree,then the joint strength reaches the maximum.In order to continue to improve the mechanical properties of the joint,cooling conditions of heterogeneous aluminum alloy FSLW joint organization and mechanical properties research,and compared with conventional joints.It was found that FSLW under cooling conditions could improve the joint hardness by regulating the coarsening of the tissue,and the hardness increase was more obvious with the enhancement of the cooling effect.Compressed air cooling inhibits the downward migration of hook-like defects while the degree of interface fragmentation is higher,and improves the interface structure,which increases the shear strength of the joint.Water cooling inhibits the flow and mixing of the two plates,reduces the degree of interface fragmentation,decreases the lap interface bearing capacity and thus reduces the shear performance.It is shown that the appropriate cooling rate can refine the grain structure of the joint,reduce the migration of hook-like defects and improve the degree of interfacial fragmentation,and realize the regulation of mechanical properties of the lap joint.