The design of high-strength and high-thermal-conductivity magnesium alloy sheets is challenged by the inherent contradiction between strength and thermal conductivity, as well as the complex variables involved in the rolling process. In this study, Mg-xZn-0.5Gd-0.5Y (at.%) (1/x = 0.5, 1.0, 1.5) alloys were developed by adjusting the atomic ratio of rare earth (RE) elements to Zn. In the subsequent multi-pass hot rolling process, the influence of various factors on the microstructure and comprehensive properties of alloys with different compositions was obtained. With the decrease of RE/Zn atomic ratio, the W phase gradually dominates, which ensures the high thermal conductivity throughout the preparation process. Additionally, the thickness reduction per pass plays a decisive role in the properties of alloys by affecting the precipitates, dislocations and grains. The reheating between passes plays a coordinating role in the whole rolling process through the twin-induced static recrystallization mechanism. The findings indicate that leveraging the advantages of large thickness reduction per pass and effectively coordinating strain accumulation is a viable strategy for progressively enhancing the strength of high-thermal-conductivity magnesium alloys, ultimately leading to superior comprehensive performance. This study provides systematic research results for the composition design and process optimization of high-strength and high-thermal-conductivity magnesium alloy rolled sheets, which is helpful to promote the performance breakthrough and application expansion in this field.

The ductility and toughness of peak-aged (PA) Mg-RE alloys are significantly influenced by their grain structure characteristics. To investigate this issue, we examined PA Mg-8.24Gd-2.68Y (wt.%) alloys with two distinct grain structures: an extruded-PA sample with dynamic recrystallized (DRXed) fine grains and coarse hot-worked grains, and an extrusion-solution treated and PA sample with grown large equiaxed grains. The results showed that the extruded-PA sample demonstrated a favorable combination of tensile strength (426 MPa) and ductility (7.0 %). Although intergranular microcracks nucleated in the DRXed region due to strain incompatibility, crack propagation was impeded by the DRXed fine grains, inducing intrinsic and extrinsic toughening mechanisms. On the other hand, the hot-worked grains in the extruded-PA sample initiated transgranular cracks after a relatively high strain, attributed to the strain partitioning effect, ultimately leading to failure. In comparison, the solution-treated-PA sample exhibited lower tensile strength and ductility (338 MPa and 3.7 %, respectively). Intergranular cracks nucleated in the CG sample before necking, and the readily formed critical crack, facilitated by the large grain size, exhibited unstable crack growth, resulting in premature failure. This work offers valuable insights for designing high-performance PA Mg-RE alloys and preventing premature failure in practical applications.