Study on the preparation principle and strengthening mechanism of in-situ synthesized Mg-Li matrix composites through the La2O3→La→AlmLan route

In this study, low-cost La 2 O 3 powder modified with LiF-LiCl flux was used as a precursor and introduced into Mg-5Li-3Al-2Zn (LAZ532) alloy melt. Through a series of reactions, in-situ formed Al m La n phase-reinforced LAZ532 matrix composites were successfully prepared. The surface modification of La 2 O 3 powder by molten salt and the related reduction reaction mechanism in the alloy melt, as well as the effects of different La 2 O 3 additions on the microstructure and mechanical properties of the composites, were systematically investigated. First-principles calculations revealed that during precursor preparation, the Cl/F heteroatoms in the flux chemically destabilize La-O bonds, forming LaOF/LaOCl intermediates. Subsequently, Li atoms with low electronegativity and high reactivity in the melt preferentially combined with O/Cl/F, driving the reduction reactions. The reduced La then preferentially bonded with Al, predominantly forming the stable Al 3 La phase, along with small amounts of Al 11 La 3 and Al 2 La phases. Microstructural analysis showed that as the La 2 O 3 content increased from 0.3% to 2.0 wt.%, the yield rate of La in the composite rose from 8% to 23%. Furthermore, the dispersed micro/nano-sized Al m La n phases formed an atomically bonded interface with the matrix, and their size initially decreased and then slightly increased with increasing volume fraction. These phases promoted recrystallization through heterogeneous nucleation and grain boundary pinning, leading to texture weakening and grain refinement in the composites. The mechanical properties of the composites first improved and then deteriorated with increasing La 2 O 3 addition. Among them, the composite with 0.7 wt.% La 2 O 3 exhibited excellent comprehensive mechanical properties, with tensile strength, yield strength, and elongation reaching 278.3 MPa, 182.5 MPa, and 23.6%, respectively. The enhancement in yield strength was mainly attributed to the synergistic effects of grain refinement, precipitation strengthening, and texture strengthening. This study offers a novel design concept for in-situ synthesized Mg-Li matrix composites, holding significant scientific value.