Experimental Investigation On Laser Welding Dissimilar Materials Between Galvanized Steel And Carbon Steel Plates

With the deterioration of global environment and growing energy crisis,"Lightweight" and "Security" are paid great attention in the automotive industry.Energy saving becomes a crucial issue in automotive design and manufacture. Tailorwelded blanks are widely used in auto body molding. The technique can connect twoor many steel plates, which are copied with different kinds of steel,variousthicknesses, diverse strength and different surface appearances. Not only a reasonablestrength and number body can be designed, but also the body weight and productioncost can be reduced.In this paper, the theory and experiment of laser welding of dissimilar metalplates between galvanized steel and carbon steel are researched. Firstly, thetemperature field of dissimilar metal plates between galvanized steel and carbon steelis analyzed in the condition of the moving heat of3D transient finite element. Notonly the relation of laser power and critical welding speed, but also the influence ofparameters’ variation such as laser beam power and welding speed to the width anddepth of welding seam are simulated. The reference for the choice of welding processparameters is provided. Secondly, the fiber laser and equipped robot are used toconnect the galvanized steel and carbon steel in the study of experiments. Finally, themicrostructure and mechanical properties of joints are analyzed and detected. Themajor conclusions are summarized as the followings:(1) Mathematic model of thermal conduction of laser welding is established inthis paper, the finite element software ANSYS is used to analysis the temperaturefield of laser welding in the condition of the moving heat of3D Transient finiteelement. The influence of parameters’ variation such as laser power and weldingspeed to the temperature field of surface and interior are simulated. The temperaturefield of surface is found to be elliptical, the temperature field of interior is found to beparabolic. When the center of laser beam is located in the both plates’ center, thedistribution of temperature field is asymmetric, offseting to the side of galvanizedsteel. By studying the transition, the relation of laser power and critical speed in laserpenetration welding of galvanized steel and carbon steel is acquired, the influence ofparameters variation such as laser power and welding speed to the width and depth ofwelding seam are simulated. (2) Based on the theoretical analysis results, using the orthogonal experimentalmethod, the fiber laser and equipped robot are used to connect the galvanized steeland carbon steel in the experiment. After joint quality detection of the specimen andwelding process parameters’ adjustment in the experiment, an optical and reasonablewelding parameters are attained.Under this circumstances, the tensile strength andyield strength of joints are more prominent.(3) The surface of joints is detected, and when the center of laser beam is locatedin the both plates’ center, the joints’ center is clined offset to the galvanized steel. It isadvisible that laser beam center offset a bit to the carbon steel side so as to prevent theuncoinciding between the centerline of joint and butt caused by the materials’physical properties difference, and to keep the continuity of strength and performancein the joint during the laser welding dissimilar materials between galvanized steel andcarbon steel. The microstructure of welded joints are detected, and the defects suchas stomata and crack are not found in the joints.The surface hardness in the weldedjoint are higher than that of base materials, and heat affected zone softening is notfound. The tensile strength of the welded joint is reasonable equal to that of thecarbon steel under the experimental conditions.