Effect of Mn on the elevated temperature mechanical properties of Al-La alloys

Highlights: • The primary Fe-rich phases changed from Al₁₃Fe₄ to Al₆(Mn, Fe) with Mn addition. • The precipitation of Al₆(Mn, Fe) dispersoids was found in Mn-containing Al-La alloys. • A remarkable improvement in yield strength was achieved with dispersoids strengthening. • The Al-La based alloys exhibited a high retention ratio of mechanical properties at 300 °C. -- Abstract: In the present work, Mn was added to strengthen the Al-La alloys by the precipitation of Al₆(Mn, Fe) dispersoids. The evolution of microstructures, precipitation of dispersoids and their effect on mechanical properties at elevated temperatures were systematically studied. The results demonstrated that the Al-Al₁₁La₃ eutectic structures were similar in the experimental alloys, while the primary Fe-rich phases changed from Al₁₃Fe₄ to Al₆(Mn, Fe) with Mn addition. A significant dispersoids strengthening effect was achieved during the aging treatment, leading to a remarkable increment in the yield strength at both room temperature (RT) and elevated temperature (300 °C). Besides, the Al-La based alloys retained over 50% of its yield strength (YS) at 300 °C in comparison with that at RT, which was induced by the excellent thermal stability of Al₁₁La₃ phase and Al₆(Mn, Fe) dispersoids. The great compatibility between Al-La system and Al₆(Mn, Fe) dispersoids provides a potential approach to further develop the novel Al-La alloys with the superior performance at elevated temperatures.