Effect of consumable stud microstructure on friction surfacing: Comparison between friction extruded and hot extruded AA2024 studs

Friction surfacing is a solid-state layer deposition process that shows high potential as a coating and an additive manufacturing technique for aluminum alloys. Avoiding high temperatures, it does not suffer common challenges of fusion-based techniques, such as hot cracking. Friction surfacing and other solid-state processes commonly use studs from conventional hot extrusion, which are characterized by long elongated grains. However, limited research focused on different consumable materials. In this study, friction surfacing is successfully employed for the first time on friction extruded AA2024 studs and compared to hot extruded ones with respect to process behavior and resulting deposit. Friction extrusion produces rods characterized by a refined grain structure, illustrating the effect of a different microstructure on the friction surfacing process. Despite a completely different initial microstructure, the analysis of the deposits showed similar ultra-fine grain sizes (1.4μm). However, results show strong effects of the consumable stud microstructure on the FS process behavior as well as the resulting deposit geometry. The fine-grained friction extruded studs feature 80% higher stud consumption rate, but 15% lower bonded width compared to hot extruded studs. These findings are of high value to successfully adapt the deposition parameters in case different consumable materials are employed, considering the high recycling potential of friction extrusion.