Improving strength-ductility of Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr magnesium alloy due to bimodal LPSO and <c + a> dislocations

Rare-earth (RE) magnesium alloys have attracted lots of attention due to their excellent mechanical properties. In this work, the microstructure and mechanical properties of as-extruded 8.5Gd-4.5Y-0.8Zn-0.4Zr magnesium alloy under different solution treatment were examined with the optical microscope (OM), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), electron back-scattered diffraction (EBSD) and Instron testing machine. The results show that the ES12 alloy (solution treatment for 12 h at 520 degrees C) has the highest ultimate tensile strength (UTS) of 390 MPa with a fracture elongation of 24.5% at the cost of a minor drop in yielding strength (YS) compared to the as-extruded alloy. During solution treatment, the block-shaped long period stacking ordered (LPSO) in as-extruded alloy evolves into plate-shaped LPSO, which disperses at grain boundaries (GBs), and lamellar LPSO, which distributes in grains. The coexistence of plate-shaped and lamellar LPSO, which impedes the dislocations movement, and the activated <c + a> dislocations are regarded as the primary reasons for mechanical properties improvement. Furthermore, the (11-21) <1-100> texture in as-extruded alloy transforms into the (11-20) <0001> texture in ES12 alloy. The average grain size increases from 3.45 mu m in as-extruded alloy to 18.70 mu m in ES12 alloy. The Schmid factors of {0001} <11-20>, {10-10} <11-20>, {10-11} <11-20>, and {11-22} <11-23> increase, which indicate that slip systems are more easily activated in plastic deformation. The dynamic recrystallization (DRX) grains fraction increase to 92.8% for ES12 alloy due to the particle-stimulated nucleation (PSN) mechanism triggered by block-shaped and plate-shaped LPSO. The freshly DRXed grains further weaken the texture, and reduce the dislocation density. All of these factors increase elongation of RE magnesium alloy. (c) 2024 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.