Microstructure and mechanical properties of an AA6060 aluminum alloy after cold and warm extrusion

Severe plastic deformation techniques can produce ultrafine-grained aluminum alloys with high strength and ductility, but further processing often requires costly and/or time-consuming machining. In this study, we investigate the potential of an alternative processing route that operates below recrystallization temperature and that can produce fine-grained materials. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature or at 170 °C (which corresponds to the aging temperature of the alloy, and allows for simultaneous forming and aging). The materials were then subjected to an aging treatment. Electron microscopy and mechanical testing were performed to characterize the resulting microstructural features and mechanical properties. Both extruded profiles exhibit similar, strongly graded microstructures with submicron-sized grains in the highly deformed surface layers, and a mixture of coarse and fine grains in the center regions. Despite different processing routes (i.e., cold vs. warm extrusion), both materials are characterized by similar mechanical properties in terms of maximum hardness, strength and ductility; these results are discussed in the light of the relevant microstructural deformation and precipitation mechanisms.