Constructing heterogeneous microstructures has been demonstrated as an effective strategy to overcome the strength-ductility trade-off in magnesium (Mg) alloys. Here, a dual-heterogeneous microstructure was fabricated in a Mg-6.49Gd-2.74Y-0.45Zr (wt.%) alloy via additive friction stir deposition (AFSD), featuring alternating fine grain (FG) bands embedded with dense nanoscale multiphase clusters and coarse grain (CG) bands containing sparse clusters. This unique architecture leads to simultaneous enhancement of strength and ductility. The AFSD alloy exhibits an elongation of 19.5 % and a yield strength of 262.2 MPa, which can be enhanced to 411.0 MPa following peak aging treatment. The formation mechanisms of heterogeneous microstructures and their influence on mechanical properties were systematically investigated. Fragmented rare earth (RE)-containing eutectic phases at grain boundaries induced recrystallization via particle-stimulated nucleation (PSN). Their subsequent complete and rapid dissolution led to the formation of supersaturated RE solid solutions, which promoted the precipitation of nanoscale multiphase clusters with pronounced pinning effects, ultimately leading to the growth of differential grains and the formation of dual-heterostructures. Furthermore, CG/FG interfaces were found to activate non-basal slip systems within adjacent grains, while the nanoscale multiphase clusters can effectively hindered dislocation motion. The synergic effect of these mechanisms contributed to the simultaneous enhancement of strength and ductility. This study provides fundamental insights for developing high-performance Mg-RE alloys.

Nanomodification is an effective method to solve the thermodynamic and kinetics limitation of Magnesium (Mg)-based materials, which shows promising application prospects in hydrogen energy field. However, the role of the grain size of pure Mg on the hydrogen-induced performance of the hydrogen sensitive thin film under cyclic hydrogen loading/unloading process at room temperature has rarely been studied systematically. To study the relationship between the structure of Mg layer and the hydrogen-induced optical performance of fluorocarbon (FC)/Pd/Mg films, a series of Mg with different internal structures were prepared by changing the velocity of sputtered atoms under different sputtering powers. The FC/Pd/Mg (40 W) film with fine nanostructure showed faster hydrogenation/dehydrogenation kinetics as well as a larger optical conversion range, which can be attributed to the large population of grain boundaries with high grain boundary energy and more hydrogen diffusion path. As sputtering power gradually increased from 40 W to 300 W, the grain inside films grew larger. The FC/Pd/Mg (300 W) film had more columnar-like regions inside and less grain boundaries with lower energy contributing to slower hydrogen absorption/desorption kinetics and lower optical conversion range.