Numerical Simulation And Process Optimization Of Magnesium Alloy AZ61A MIG Welding

This paper takes AZ61 A magnesium alloy for structural parts as the research object and uses ABAQUS finite element simulation software to simulate the MIG welding process between magnesium alloy plates with a size of 300mm×120mm×3mm.In order to make the simulation results more close to the actual welding situation,the response surface optimization method(RSM)was used to optimize the double ellipsoid heat source.Using design expert software to design the central composite design test method of four factors and five levels with the front hemisphere radius,back hemisphere radius,ellipsoid width and heat source efficiency as the factors and the welding temperature and weld width as the evaluation indexes,the mathematical model of the influence of heat source parameters on the welding temperature and weld width is established.The optimized double ellipsoid heat source equation was solved in ABAQUS software,and the temperature field and stress field of simulated welding process were analyzed.The corresponding MIG welding process experiment was carried out.The temperature field detection device and temperature detection method of weldment were designed and developed independently,and the temperature change of each part of weldment was monitored in real time to verify the reliability of numerical simulation results.Optical microscope,scanning electron microscope,micro Vickers hardness tester,universal tensile testing machine and other testing instruments were used to analyze and test the microstructure and mechanical properties of the welding samples,so as to evaluate the corresponding welding parameters.The results show that:(1)In the process of welding heat source verification,the appropriate heat source parameter model is found for the welding heat source under different current,and the mathematical model of welding heat source model parameters and response value has high credibility.(2)By analyzing the temperature field nephogram and thermal cycle curve under different current,it can be found that the effect of this simulation experiment is very good,and the instantaneous temperature can not reach the melting point of magnesium alloy in the arc starting stage,which makes the welding effect poor.As the welding continues,the temperature is gradually stable,which can get better welding effect.The gradient change of longitudinal temperature is obvious,which will greatly affect the formation of weld microstructure.(3)The analysis of welding stress field shows that large welding stress is produced at the beginning and end of welding,and large stress area also appears in the center of weld.The longitudinal stress along the weld direction is tensile stress,the transverse stress is compressive stress at the beginning and end,and tensile stress at the middle stable zone.The longitudinal stress perpendicular to the weld direction is tensile stress at the center and near the edge,while the transverse stress between the center and the edge is tensile stress.(4)Analysis of welding simulation results and actual temperature measurement data shows that the results match well and the relative error is less than 10%.The results show that the weld width increases and the weld reinforcement decreases with the increase of welding current.From the micro morphology analysis,with the increase of welding current,the microstructure of HAZ area becomes larger,the microstructure of FZ area becomes finer and denser,and the microstructure of BZ area changes less.The microhardness of FZ area is the largest,BZ area is the second,and HAZ area is the smallest.By observing the tensile fracture morphology of AZ61 A magnesium alloy plate weldment,it can be judged that the fracture form of welded joint is brittle fracture.With the increase of welding current,the tensile strength of welding area first increases and then decreases.In conclusion,the experimental research not only provides the available heat source model parameters for the numerical simulation of Mg alloy MIG welding process,improves the reliability of welding process simulation,but also obtains the optimization value of main process parameters such as welding current of AZ61 A magnesium alloy plate,and provides guidance for the actual welding process.