Microstructure and mechanical properties of extruded Mg-Gd-Y-Zn-Zr alloys filled with intragranular LPSO phases

A comparison has been made on the dynamic recrystallization (DRX), texture, and mechanical properties of the Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr (wt%) alloys extruded with different ratios (ER, 36 and 7.1). Intragranular long period stacking ordered (LPSO) phases strongly restrict the DRX by restraining the lattice rotation of alpha-Mg grains and hindering the migration of the boundaries of DRX-ed grains. Extrusion with ER of 36 can widely break the intragranular LPSO phases and create a fully DRX-ed microstructure with a relatively random texture, while the lower ER of 7.1 fails to break the LPSO and leads to a bimodal microstructure with a strong basal fiber texture. Finer DRX-ed grains and smaller LPSO phases account for the superior tensile yield strength and elongation of the ER36 alloy. However, the ultimate tensile strength of the ER7.1 alloy catches up because its larger grain size causes an increase in the strain hardening rate.