Effect 3D Characteristics Of Weld Holes On Fatigue Properties Of Steel-Aluminum Welded Joints

Steel-aluminum hybrid body material is an effective solution to achieve lightweight car.Steel-aluminum laser welding combines the advantages of light aluminum quality,high degree of laser welding automation,fast welding speed,and small thermal damage to materials.Steel-aluminum laser welding as an ideal technical means to solve the steel-aluminum connection of automobile body,it has become a hot spot in recent years.However,steel-aluminum dissimilar metal laser lap welding will produce many holes defects in the weld during the actual welding process.These holes will cause local stress concentration,which will lead to the initiation of fatigue cracks.Three-dimensional(3D)Xtomography can be used to explore the 3D shape of the holes in the weld and extract the 3D feature data.Then combined with finite element simulation and fatigue test,it is an ideal way to analyze the influence of microscopic holes on the joint fatigue performance.In this paper,the laser welding test was carried out with SGC440 highstrength alloy steel and 6016 aluminum alloy as the base material to prepare fatigue specimens.Then,the 3D X-ray tomography technique is used to obtain the 3D characteristic data of the weld holes,and the distribution characteristics of the weld holes are analyzed.Finally,several sets of main parameters of the weld holes are selected as variables.The finite element model of steel-aluminum welded joint is established in ABAQUS software,and the finite element analysis of the 3D characteristic parameters of 125 different holes is carried out.According to the calculation results of stress and the equivalent stress theory,the influence of 3D features of the holes on the fatigue performance of the weld is systematically studied.The results show that the stress value at the stress concentration on the weld surface shows a regular change with the change of the threedimensional characteristic parameters of the holes.The size of the holes,the distance from the holes to the stress concentration point,and the spatial position of the holes have an important influence on the surface stress of the laser lap weld.In the case where other parameters are constant,the larger the hole or the smaller the distance from the hole to the stress concentration point,the greater the stress at the stress concentration point.Finally,the influence of the 3D features of the hole on the fatigue life of the weld is derived.