Finite Element Simulation In Tensile Fracture Process Of Magnesium/Steel Butt-welded Joint And Weld Shape Optimization

Tailor welded blank(TWB)technology is one of the ways to realize the lightweight of automobiles.TWB made of light metal and steel can not only reduce the weight of the whole vehicle,but also ensure the strength of the parts.In the manufacturing process of tailor welded blanks,special welds will be produced because of different welding parameters.Most of the light metals and steel can not be melted in the welding process,which makes tailor welded blanks easy to fail at the interface between the weld and the motherboard.Magnesium alloys,as one of the lightest metal structural materials,have the advantages of small density,excellent processing performance and abundant resources.They are suitable for the background of global energy saving and environmental protection,and have been widely used in automobile manufacturing industry.In this paper,magnesium steel tailor-welded blank is selected as the research object.Laser-arc hybrid heat source is used to weld magnesium steel heterogenous metals.The mechanical parameters of weld material are obtained through experiments,and the effects of weld shape and interface strength between weld and base plate on the tensile properties of tailor-welded blank are further explored.Firstly,the material at the weld of magnesium steel tailor welded blank is selected to make the micro-tensile specimen and the tensile test is carried out.The material parameters at the weld are obtained by digital image correlation technology,and the parameters are input into the finite element simulation model for verification.Then Cohesive element is used to construct the finite element model of the interface between weld and base metal.The effect of the joint strength of each part of the interface on the tensile fracture position and tensile load of tailor welded blanks was investigated by dividing the interface into different zones and setting different joint strength.Finally,the parametric model of tailor-welded blank is established.Four parameters are used to control the weld shape of tailor-welded blank.The relationship between each parameter and the tensile displacement is studied in detail through the experimental design method.An approximate model based on neural network is established to optimize the shape parameters with the maximum tensile displacement as the objective.The results of finite element simulation show that the minimum bonding strength of the interface between the weld and the base plate affects the fracture location of the tailor-welded magnesium steel sheet.When the fracture occurs in the weld,the maximum bonding strength at the interface determines the maximum tensile load during the tensile process of the tailor-welded sheet.The length of the weld spread on the steel plate is the main factor affecting the tensile properties of the tailor-welded sheet,when the fracture occurs on the steel side base plate.At the same time,the tensile properties of tailor welded blanks can be optimized.