Effects of Trace Al Addition on the Microstructure, Hot Deformation Behavior and Mechanical Properties of High-Strength Mg-Gd-Y-Zn Magnesium Alloy

The effects of 0.2 wt pct Al addition on the microstructure, hot deformation behavior and mechanical properties of Mg-8Gd-4Y-1Zn alloy were investigated. The results showed that the Al addition obviously refined the grain structure and increased the 18R long period stacking ordered (LPSO) phase. In addition, a little Al₂(Y, Gd) phase formed in the as-cast Al-doped alloy. After solid solution treatment, the Al₂(Y, Gd) phase and Mg₅(Gd, Y, Zn) eutectic phase were dissolved, and both 18R- and 14H-type LPSO phases could be observed at the grain boundaries of the Al-doped alloy. For the Al-free alloy, the 18R LPSO phase disappeared, and lamellar 14H-LPSO was generated in the grain interior. The calculated results showed that the Al-doped alloy had higher hot deformation activation energy and better hot workability. Under the same extrusion condition, the Al-doped alloy showed faster dynamic recrystallization but similar fully recrystallized grain size as the Al-free alloy. The average tensile strength, yield strength and elongation of the extruded alloy were concurrently improved from 329 MPa, 268 MPa and 6.0 pct to 365 MPa, 281 MPa and 11.1 pct by trace Al addition.