Solid-state additive manufacturing of aluminum and copper using additive friction stir deposition: Process-microstructure linkages

Among metal additive manufacturing technologies, additive friction stir deposition stands out for its ability to create freeform and fully-dense structures without melting and solidification. Here, we employ a comparative approach to investigate the process-microstructure linkages in additive friction stir deposition, utilizing two materials with distinct thermomechanical behavior-an Al-Mg-Si alloy and Cu-both of which are challenging to print using beam-based additive processes. The deposited Al-Mg-Si is shown to exhibit a relatively homogeneous microstructure with extensive subgrain formation and a strong shear texture, whereas the deposited Cu is characterized by a wide distribution of grain sizes and a weaker shear texture. We show evidence that the microstructure in Al-Mg-Si primarily evolves by continuous dynamic recrystallization, including geometric dynamic recrystallization and progressive lattice rotation, while the heterogeneous microstructure of Cu results from discontinuous recrystallization during both deposition and cooling. In Al-Mg-Si, the continuous recrystallization progresses with an increase of the applied strain, which correlates with the ratio between the tool rotation rate Oand travel velocity V. Conversely, the microstructure evolution in Cu is found to be less dependent on O, instead varying more with changes to V. This difference originates from the absence of Cu rotation in the deposition zone, which reduces the influence of tool rotation on strain development. We attribute the distinct process-microstructure linkages and the underlying mechanisms between Al-Mg-Si and Cu to their differences in intrinsic thermomechanical properties and interactions with the tool head.

Automated summary

The study investigates the process-microstructure linkages in additive friction stir deposition using aluminum-magnesium-silicon alloy and copper, showing that the microstructure in aluminum-magnesium-silicon evolves primarily through continuous dynamic recrystallization, while copper exhibits heterogeneous microstructure due to discontinuous recrystallization. The differences in microstructure evolution are attributed to intrinsic thermomechanical properties and interactions with the tool head.