Numerical Study On Microstructural Evolution In The Molten Pool Of Laser Beam Welding For Al-Li Alloy

In the aluminum alloy laser welding structure,the microstructure of the aluminum alloy weld plays a decisive role on the performance of the welded joint.The existing experimental research methods is difficult to conduct dynamic observation and quantitative detection.To make it,the computer technology to simulate the evolution of the weld pool solidification microstructure is conducted to further study the microstructure evolution.First of all,based on the kinetics of dendrite solidification and the consideration of the actual welding process parameters,the Cellular Automaton(CA)method constitutes the Micro-macro coupling model of dendritic growth in solidification process of Al-Li alloy laser welding pool.The micro-scale dendritic growth CA model is based on the theory of conservation of dendrite tip solute and the growth kinetics of dendrite.Considering the constitutional undercooling and the unbalanced solute redistribution,the established model can better reflect the actual physical nature of crystallization process during the welding solidification.What's more,based on the established Micro-macro model of dendrite solidification in weld pool,the microstructure evolution of 2060-T8 Al-Li alloy laser weld pool was solved.The simulation results reproduce the dendritic growth morphologies and solute distributions in different regions during different periods.In addition,the competitive growth processes of equiaxed oriented columnar crystals,the equiaxed and columnar crystals were simulated,and the morphological evolution of competitive growth dendrites was analyzed.Moreover,laser welding experiment of 2060-T8 Al-Li alloy sheet was designed and implemented in this paper.Through the detection and analysis of the macroscopic,microstructure and mechanical properties of the workpiece after welding,optimal laser welding process parameters were selected.On the one hand,the experimental results are compared with the simulation results of the welding thermal cycle,so that the heat source model used in the calculation of the macro-temperature field is validated.On the other hand,the microstructure evolution of laser welded 2060-T8 Al-Li alloy was simulated by using the CA-FE coupled model of dendrite growth during the weld pool solidification process after verification,and the simulation results were in good agreement with the experimental results.Therefore,the numerical model and the calculation process established in this paper had certain rationality,and laid the foundation for the research on the quantitative,accurate and multi-physical field aluminum alloy laser welding process.