Numerical Simulation And Study On Forming Mechanism In EBW Of Aluminum Alloy

Electron beam welding will produce weld reinforcement, under theprecondition of without adding filler material and with large metal evaporation, thegeneration of the reinforcement must be caused by the volume expansion of themolten pool during the welding process. Therefore, the size of reinforcement isdirectly related to the organization loose in the weld, further to the weldperformance. Therefore, based on the solidification shrinkage and feeding theory,numerical simulation and experimental verification methods are used to study theforming of reinforcement for electron beam welding.Based on the requirements for thick-plate welding of high strength aluminumalloy,20mm thick2219Al-Cu alloy is used for this study. In the numericalsimulation study, using half of the symmetric model for modeling to improve thecomputational efficiency. The study find that the conventional discrete and loadingmode for heat source is not equivalent for the process of half and whole modelingsimulation. Take the middle points between conventional discrete points as the newdiscrete points to improve the discrete way of heat source, in this way, can not only realizethe equivalent of the two discrete modes in the whole modeling, also can realize theequivalent simulation during half and whole modeling.In this study, the simulation of reinforcement is based on the shrinkage andfeeding theory during the solidification process of weld pool, using the combinedcriterion of critical solid fraction and G/R Kto judge the feeding of elementduring the solidification process, and show the not feeding volume as thereinforcement.The simulation results show that the composite heat source model can wellsimulate the nail and deep penetration shape of electron beam welding, and the sizeof melt pool is fit quite well with the actual weld. Under different processparameters, the simulation and test results have the same change trend, that is: withthe increase of beam current the reinforcement increases, but the volume expansionreduces after the first increases, with the maximum in60mA.With the increment ofthe welding velocity, the reinforcement decreases, but the volume expansion rateremains increase slightly; but the simulation value of reinforcement and volumeexpansion rate are respectively4%-19.3%and10.55%-23.67%smaller than themeasured one.Based on the experimental and simulated results to analysis the formationmechanism of reinforcement. The presence of voids in the upper weld, which is caused by interdendritic feeding difficulties,which is also basis of the numericalsimulation.There are nail points and incomplete fusion defects under the weld. Grainrefinement and reticular precipitation of the second phase along interdendritic causethe increase of loose structures. Supersaturation point defects (such as vacancy)residues in the weld, caused by the fast cooling speed. All of the above factors,which cause the volume expansion of weld, are just the formation mechanism ofreinforcement in electron beam welding of aluminum alloy.