Microstructures and mechanical properties of a hot-extruded Mg−8Zn−6Al−1Gd (wt%) alloy

Microstructural evolution and mechanical properties of a Mg−8Zn−6Al−1Gd (wt%) alloy were thoroughly investigated in this work. The results indicate that the dominant intermetallic phases in the as-cast sample are ϕ-Al₂Mg₅Zn₂, τ-Mg₃₂(Al,Zn)₄₉, i-Mg₄₄Al₁₅Zn₄₁ and Al₂Gd phases and almost free Gd was detected in the former three phases. After extrusion, the sample has a fully recrystallized microstructure with the average grain size being ~1.5 µm, and exhibits a weak rare earth texture. Additionally, fine particles were approximately homogeneously dispersed in the fine-grained structure. Most of them are quasicrystal phase (i-phase) but have no identical orientation relationship with Mg matrix regardless of whether they distribute at grain boundaries or inside grains. Finally, the as-extruded sample exhibits good strength-ductility balance in both tension and compression and simultaneously has a slight reverse tension/compression asymmetry. Microstructural observations indicate that the excellent mechanical performance of the studied alloy is highly related to its fine grains, weak RE texture, and numerous homogeneously distributed fine particles.