Experimental and numerical studies of re-stirring and re-heating effects on mechanical properties in friction stir additive manufacturing

Friction stir additive manufacturing is studied experimentally and numerically. Different to conventional friction stir welding, re-stirring and re-heating can be found for friction stir additive manufacturing. The new generated phenomena are investigated by new integrated model, which is established based on Monte Carlo method and precipitate evolution model with combination of finite element model. Corresponding experiments are performed. Results indicate that different grain morphology and size, different hardness, and different yield strength can be found in different layers. The re-stirring and re-heating to the formed layers can lead to enhancement of mechanical properties with smaller grains and with higher hardness and yield strength. In comparison with first layer, the hardness and yield strength on second layer are increased due to the decrease of the peak temperature. After 2-3 layers, the mechanical properties of formed layers are not further affected by the new added layers.