Effect of Convection on Weld Pool Shape and Microstructure

摘要

The role of convection in weld pools is of great interest due to its effect on weld pool shapes and weld defects. A quantitative understanding of convection in the weld pool is being developed. In this part of the effort major emphasis has been to model surface tension driven flow. The Lorentz force effect is incorporated towards the end of the two year effort. The significant achievements of the program are: a) stagnation flow analysis for center of the weldpool which provided algebraic expressions for temperature and velocity. This solution clarifies the scaling problems. b) Three dimensional axisymmetric model for surface tension driven flow with flat surface assumption which predicted the pool shape for stationary heat source such as in the case of spot welds. c) Three dimensional perturbation model for surface tension driven flow with flat surface which predict velocity field, temperature field, effect of trace elements and self-consistent prediction of the pool shape and cooling rate. d) Three dimensional model with flat and free surface which predicted same as above with more realistic boundary condition. This model can also predict effect of Lorentz Force. A series of controlled experiments has been carried out to verify pool shape and liquid velocity. This verified the trend predicted by the model.