Finite Element Simulation On The Mechanical Properties Of Resistance Spot Welded AA6111 Aluminum Joint

6000 series aluminum alloy is an ideal lightweight material for automobiles,with high corrosion resistance and formability.Resistance spot welding is the most widely used joining method for automotive aluminum alloy components.Because aluminum alloys have high thermal conductivity,electrical conductivity and thermal expansion coefficient,it is more difficult to control the performance of aluminum alloy spot welded joints.Destructive testing methods are commonly used for joint performance testing,and analyzing the joint performance is time-consuming and labor-intensive.The purpose of this paper is to construct a reliable mechanical model of spot welded joints and simulate the process of joint stretching and correctly predict the fracture strength and displacement of spot welded joints.In this dissertation,AA6111 aluminum alloy sheet is used,and shear tensile joint(TS)and peel tensile joint(CP)are used as model prototypes.The microstructure and properties of spot-welded joints are systematically analyzed and tested.Aluminum alloy spot welded joints can be divided into three areas: base metal zone,thermo-mechanical affected zone(TMAZ),and nugget zone.The base metal zone has the highest strength and hardness,followed by the thermo-mechanical affected zone and the nugget area is the lowest.The construction of the numerical model is mainly processed from the following three aspects: model geometry,model mesh,and material parameters.For the model geometric size,it fully refers to the geometric dimensions of the joints in the experimental test sample to ensure the dimensional accuracy.For the model's mesh,the mesh size and the mesh division method are considered.Combining the calculation time with calculation accuracy,0.15 mm mesh size is used for TMAZ zone,nugget zone,and the base metal zone close to TMAZ.Elasticity,plasticity and fracture are the three main material parameters that the needs to be inputted into model.Elasticity and plasticity are used to guide the elastic deformation and plastic deformation behavior of the joint deformation.The fracture model adopts the Coulomb Moore's Modification Criterion(MMC3),and the fracture model is calibrated by simulation and the experiments.After the model are constructed,we compare the simulated data with the experimental data.For the 2 mm×2 mm TS joint,the model's peak fracture load is about6100 N,the maximum fracture displacement(gauge change)is about 1mm,and the simulated fracture model is interface failure model,which is in good agreement with the experimental data.For the 2 mm×2 mm CP joint,the model has two peak loads before fracture,which are 1095 N and 1108 N,respectively.The simulated fracture model is a pullout failure model,which is in good agreement with the experimental data.By comparing model simulations for different nugget thicknesses,we found that when fixing a nugget width(interface failure model)and increasing a nugget thickness,which means a larger welding penetration,the fracture strength predicted by the model will be slightly reduced;but as the penetration depth increases to certain critical thickness,the fracture mode will change from an interface failure model to a pullout failure model,and both the fracture strength and fracture displacement will increase as well.