To pursue wide applications of Mg-Li alloys in aerospace field, bringing in reinforcement phases reasonably and manufacturing efficiently have become paramount. Herein, a novel rotation friction extrusion process was proposed to fabricate FeCoNiCrCu high entropy alloy reinforced Mg-Li matrix composites, which were enhanced by newly formed nano-sized AlCuMg phase particles. The grain size of Mg-Li matrix composites was 4.19 μm. Meanwhile, a 69.03 nm thickness amorphous layer was obtained, which was composed of amorphous and nanocrystalline structure. The maximum tensile strength reached 201.3 MPa, which was improved by 43.9 % compared with LAZ933 Mg-Li alloy. It can be attributed to fine grain strengthening and dispersion strengthening, which resulted from dynamic recrystallization in Mg-Li alloy and Cu segregation from the interior of high entropy alloy. This work shows a novel processing and original reinforcement phase, providing a peculiar way to fabricate Mg-Li matrix composites.

Friction stir lap welding (FSLW) was adopted to join successfully dissimilar AZ31B Mg alloy and TC4 Ti alloy with Sn foil addition of 30 µm thickness. Interfacial microstructure, tensile shear performances and bonding mechanism of the joints obtained using three different rotation speeds were studied. High-performance FSLW Mg/Ti dissimilar joints with maximum tensile shear strength of 593.3 N/mm were produced at 1180 r/min, and which was mainly attributed to ultrastrong reaction interlayer consisting of 125.9 nm thick (Mg₂Sn+Mg) transition layer and discontinuous (Ti₆Sn₅+Ti₃Al) IMCs layer with 6.58 nm thickness at the interface. The formation of the reaction interlayer was beneficial for high interfacial strength, resulting in significantly improving the joint strength. The fracture of all FSLW joints located on AZ31B Mg stirred zone adjacent to (Mg₂Sn+Mg) transition layer or along the crack propagation direction of the AZ31B/TC4 interface with different fracture mechanisms, and which could be consistent with interfacial microstructure.