Microstructures and mechanical properties of a novel Al-5Mg-3Zn alloy with the combined additions Sc and Zr

The study investigated the impact of Sc and co-addition of Sc and Zr on the dispersoids, subsequent grain structures and aging precipitations, and the ultimate mechanical properties of Al-5Mg-3Zn-xSc-yZr (x + y = 0.2 wt%) alloys were studied. The results indicate that the co-addition of Sc and Zr produces the highest number density of dispersoids among the three alloys. The Al-5Mg-3Zn alloy mainly comprises fully recrystallized equiaxial grains (close to 100 %) after solution treatment. In contrast, the recrystallization ratio of Al-5Mg-3Zn0.1Sc-0.1Zr remarkably decreases to 9 % owing to the presence of fine and dense Al3M dispersoids to impede the mobility of sub-grain boundaries. Adding the Sc element alone reduces the number density of the T-Mg32(Al, Zn)49 and enhances their size during the subsequent aging treatment, while the co-addition of Sc and Zr elements shows an opposite trend. The primary factor contributing to this result is that the microalloying of Sc and coaddition of Sc and Zr affects the diffusion of Mg and Zn solute atoms in Al-5Mg-3Zn alloys. Consequently, the peak-aged Al-5Mg-3Zn-0.1Sc-0.1Zr alloys exhibit a yield strength of 481 MPa, an ultimate tensile strength of 547 MPa, and an elongation of 12 %, which is superior to the reported Al-5Mg-3Zn alloys. The good strengthductility synergy can be attributed to the combination of a high number density of dispersions, grain refinement, and high-volume fraction nanoprecipitates.