Abstract: The numerical simulation of grain growth is an important way to study the evolution of complex microstructure. Studies are less concerned with numerical simulation of grain growth in arc welding based additive forming(AWAM) process. A coupling model of macroscopic heat transfer and microstructure evolution in AWAM process is established by finite element method and cellular automata method. Then, the dynamic evolution of grains during the solidification process of the molten pool is simulated. The simulated results show that the grains nucleate at the fusion line and then grow toward the molten pool center in the first-layer deposition. Under the influence of the temperature gradient direction and crystallographic orientation of the dendritic arms, the competition between the grains becomes strong. When the crystallographic orientation coincides with the temperature gradient direction, the grain growth faster, and the others are inhibited. Ultimately, the grain morphology is characterized by staggered and coarse columnar grains. In adition, the solute enrichment phenomenon appears between the grains. In the second-layer deposition, the grains nucleate on the columnar grains of upper layer, and the subsequent growth process is similar to the upper layer. Beacause the change of temperature gradient direction of molten pool in the second-layer deposition, there is a lilte angle between the main growth direction of the grains between the first-layer and second-layer. The simulated results are verified by metallographic photograph of the experimental test. The conclusions of the above study can provide the basis and reference for the microstructure control and process planning of AWAF process.

Key words: arc welding based additive forming, grain growth, numerical simulation, single-pass two-layer deposition