Numerical simulation of dynamic recrystallization and hardness distribution in friction stir welding process

Elastic viscoplastic rate dependent constitutive model was used to simulate the friction stir welding process. The effect of process parameters on the continuous dynamic recrystallization phenomenon and hardness in the nugget zone was studied in details. Results indicate that the distributions of microhardness on the top surface and on the bottom surface of the friction stir weld are different. The former exhibits that the microhardness near the welding line is smaller, and the one outside of the nugget zone becomes bigger and then is equal to the hardness of the parent metal, which can be fitted well with the experimental tests. For the latter the above distribution law is not exhibited. The rotational speed of the welding tool only has little effect on the hardness distribution but the hardness in the nugget zone can be increased with the increase of the translational speed of the welding tool. The grain size near the bottom surface in the nugget zone is smaller than that in the middle of the weld. The size of the grain in the nugget zone becomes more homogeneous with the increase of the angular velocity of the pin.