Microstructure and room- and high-temperature mechanical properties of a bimodal-structured as-extruded Al–La–Mg–Fe alloy with high Fe content

In this study, a bimodal-grained as-extruded Al–11.53La–3.41Mg–3.25Fe (wt.%) alloy was developed based on a near-eutectic Al–La system by incorporating a high Fe content and Mg solid solution. The as-extruded alloy exhibited good strength–toughness balance due to the synergistic effects of multiple strengthening mechanisms, including solid solution strengthening from Mg, Orowan strengthening induced by submicron- and micron-sized Al₁₁La₃ and Al₁₃Fe₄ phases, and high hetero-deformation-induced (HDI) strengthening arising from HDI stress at the interfaces between the matrix and intermetallics as well as between coarse and fine grains. In addition, a layered intermetallic compound was observed, consisting of an Al₁₃(Fe, La)₄ shell and an Al₁₃Fe₄ core, which is primarily attributed to the preferential solidification of the Al₁₃Fe₄ phase and the subsequent enrichment of La atoms. The layered intermetallic compound exhibited excellent coarsening resistance even at 500 °C, and in conjunction with the proven thermally stable strengthening phases (Al₁₁La₃ and Al₁₃Fe₄), it endowed the alloy with outstanding high-temperature mechanical properties, achieving a tensile strength of 155 ± 7 MPa and an elongation of 20.8 ± 3.4 % at 300 °C.