For ultra-light Mg-Li alloys with a high Li content, fusion welding is a challenge due to the relatively active main alloying elements Mg and Li. In this study, electron beam welding technology was applied for the first time to join 8-mm-thick forged Mg-12Li-3Al-2Zn-1Si-1Y alloy plates. By controlling the heat input, defects in the welded joints and elemental evaporation were minimized. However, for the Mg-12Li-3Al-2Zn-1Si-1Y alloy, the Mg₂Si eutectic phase segregates at the fusion-zone grain boundaries during rapid solidification of the molten pool, thereby promoting the precipitation of coarse Mg₃(Al, Zn) phases along the boundaries. This segregation weakened intergranular atomic bonding in the fusion zone, leading to reduced deformability. Consequently, tensile fracture of the welded joints occurred in the fusion zone. With increasing heat input, the precipitation of α-Mg phases around Mg₃(Al, Zn) phases at the grain boundaries improved the deformability of the grain boundaries. As the fusion zone and heat-affected zone were strengthened, fracture shifted to the base material, which became the weakest region. Under these conditions (with the heat input ranging from 123.4 to 164.6 J/mm), the joint efficiency exceeded 95 %, and the ultimate tensile strength was approximately 280 MPa. When the heat input was further increased, grains in the heat affected zone coarsened, creating a softened zone where fracture occurred. This study provides a theoretical basis for electron beam welding of high-Li-content Mg-Li alloys, and offers a solution for their joining applications.

In this work, the aging response and mechanism of dual-phase Mg-Li-Al-Zn alloy at various temperatures are investigated. The results show that the strengthening after quenching is primarily attributed to the immediate precipitation of the semi-coherent ~Mg₃Zn phase. The aging softening of the studied alloy is mainly caused by the rapid transformation of the strengthening ~Mg₃Zn phase to the softening MgLi(Al, Zn) phase, along with the coarsening of the α-Mg matrix and precipitates within β-Li matrix. Further analysis indicates that the quick precipitation and transformation of ~Mg₃Zn is a consequence of the high diffusion rate of solute atoms, resulting from dense vacancy concentration in the β-Li matrix. This research bridges a critical gap in the study of aging mechanism in the dual-phase Mg-Li-Al-Zn alloy, providing a theoretical basis for the development and application of high-performance and thermal-stable Mg-Li alloys.

A novel Mg-10Li-3Al (wt.%, LA103) matrix composite reinforced by ex situ micron TiB₂ particles was developed in the present study. The ball milling and cold pressing pretreatment of the reinforcements made it feasible to prepare this material under stir casting conditions with good dispersion. The microstructure and mechanical properties of the composites prepared by different pretreatment methods were analyzed in detail. The TiB₂ particles in the Al-TiB₂/LA103 composite using the pretreatment process were uniformly distributed in the microstructure due to the formation of highly wettable core-shell units in the melt. Compared with the matrix alloys, the Al-TiB₂/LA103 composite exhibited effective strength and elastic modulus improvements while maintaining acceptable elongation. The strengthening effect in the composites was mainly attributed to the strong grain refining effect of TiB₂. This work shows a balance of high specific modulus (36.1 GPa·cm³·g^-1) and elongation (8.4%) with the conventional stir casting path, which is of considerable application value.