Microstructure Evolution of Al6061 Alloy Made by Additive Friction Stir Deposition

In this paper, the phase structure, composition distribution, grain morphology, and hardness of Al6061 alloy samples made with additive friction stir deposition (AFS-D) were examined. A nearly symmetrical layer-by-layer structure was observed in the cross section (vertical with respect to the fabrication-tool traversing direction) of the as-deposited Al6061 alloy samples made with a back-and-forth AFS-D strategy. Equiaxed grains were observed in the region underneath the fabrication tool, while elongated grains were seen in the flash region along the mass flow direction. No clear grain size variance was discovered along the AFS-D build direction except for the last deposited layer. Grains were significantly refined from the feedstock (similar to 163.5 mu m) to as-deposited Al6061 alloy parts (similar to 8.5 mu m). The hardness of the as-fabricated Al6061 alloy was lower than those of the feedstock and their heat-treated counterparts, which was ascribed to the decreased precipitate content and enlarged precipitate size.

Automated summary

The study found that Al6061 alloy samples made with AFS-D exhibited a symmetrical layer-by-layer structure, uneven grain morphology distribution, and lower hardness compared to the feedstock.