Bimodal microstructure evolution and strength-ductility co-enhancement of hot-extruded Al–La–Mg–Mn alloy

Novel heat-resistant Al-(La, Ce) alloys are strengthened via alloying with high Mg; however, their ductility deteriorates due to the formation of coarse intermetallics. In this work, a conventional hot extrusion process was used to refine the microstructures of Al–La alloy with a high Mg addition. Bimodal intermetallic and grain structures were observed in the as-extruded alloy. Of note, the coarse intermetallics were decorated with high-density microcracks. The as-extruded alloy achieved a good balance between strength and ductility, exhibiting a high ultimate tensile strength (360 ± 2 MPa) and good elongation (9.6 ± 0.6%). The high strength was mainly attributed to the strong strain-hardening ability and the load-transfer effect. Good elongation arises from the propagation of pre-existing microcracks, microstructure refinement, and increased strain-hardening ability. These findings reveal that a combination of pre-existing microcracks and a matrix with strong strain-hardening ability is a promising feature for microstructural design with increased ductility.