Effect of RE/Zn atomic ratio on the microstructure of Mg-Zn-Gd-Y alloys during rolling process: A new composition design strategy for high-strength and high-thermal-conductivity magnesium alloy

• The effects of alloy composition and rolling parameters on the microstructure and comprehensive properties of Mg-Zn-Gd-Y alloys were systematically studied. • A design criterion for Mg-Zn-Gd-Y alloy sheet with high strength and high thermal conductivity was proposed. • The large thickness reduction of per pass realizes the improvement of the comprehensive performance by promoting dynamic precipitation, dislocation accumulation and grain refinement. • A large amount of W phases enhance the thermal conductivity and strength by reducing the solid solution atom content and promoting the dislocation pile-up. 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- x Zn-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.

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