搅拌摩擦焊中动态再结晶及硬度分布的数值模拟

使用率相关弹粘塑性本构模型模拟了搅拌摩擦焊接过程，并着重研究了过程参数对搅拌摩擦焊接动态再结晶过程以及搅拌区内材料硬度的影响．结果表明，在搅拌区内焊接构件上、下表面沿垂直于焊缝方向的硬度分布规律不同．焊接构件顶部材料的硬度分布符合实验得到的结果，即焊缝中心线附近材料硬度较低，热力影响区外材料硬度逐渐升高并最终达到母材的硬度；但是在焊接构件下表面并不显示这一硬度分布规律．搅拌区内材料的硬度与搅拌头转速无明显关系，但随焊速的增加而增加．焊接构件中部材料的晶粒尺寸大于焊接构件底部材料的晶粒尺寸，且搅拌区内晶粒尺寸随搅拌头转速的增加趋于均匀．

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.