Abstract:The friction stir additive manufacturing (FSAM) is a new solid-state manufacture technology. The re-stirring process is a remarkable feature of FSAM. Under the action of severe deformation and thermal coupling, the grains of base metal were crushed and refined layer by layer to form a new recrystallized structure, and finally an additive forming component was formed. AZ31 magnesium alloy sheet for FSAM process was taken as the research object. Firstly, computational fluid dynamics model of FSAM was established. The influence of rotation speed on material rheology, temperature field and strain rate was studied, and compared with the experimental results. Secondly, the Zener-Hollomon parameters of the hot deformation process of the magnesium alloy material in the additive zone were calculated. Then, the Z parameters and the recrystallized grain size of in additive zone were correlated by empirical formula method. Finally, combined with the micro-hardness test results at 1000 r/min, a fast prediction algorithm for the recrystallized microstructure of the FSAM was proposed. The results indicate that, with the increase of layers, the average grain size and the average hardness in the additive zone decrease. With the increase of the rotation speed, the strain rate and recrystallized grain size of the material in the additive zone gradually increase, but the micro-hardness shows a downward trend.

Key words: friction stir additive manufacturing; numerical simulation; grain size; micro-hardness