Ultrafine-grained Al–La–Mg–Mn alloy with superior thermal stability and strength-ductility synergy

Ultrafine-grained (UFG) structures are highly desirable in microstructural design for their substantial improvements in strength and ductility; however, they often face challenges such as thermal instability and high manufacturing costs. In this work, powder hot-extrusion was employed as a cost-effective method to fabricate an Al–La–Mg–Mn alloy with a UFG structure (∼0.8 μm). The as-fabricated alloy exhibited a high-volume fraction of bimodal sub-micron intermetallics, with coarse intermetallics (∼270 nm) distributed primarily along the grain boundaries and fine ones (＜80 nm) in the grain interior. This unique structure cooperatively retarded the grain growth, resulting in a UFG structure with excellent thermal stability. The grain size grew slightly to 1.08 μm after thermal exposure at 400 °C for 100 h. Moreover, the UFG structure exhibited an excellent combination of strength and ductility, with yield strength, ultimate tensile strength, and elongation of 365 MPa, 543 MPa, and 13%, respectively. The UFG structure, decorated with bimodally distributed intermetallics, presents a promising microstructural design for UFG-structured alloys with excellent thermal stability and mechanical properties.