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The { $$10\stackrel{-}{1}2$$ } twinning characteristic and its related mechanical behavior were examined in a rolled Mg-Al-Zn alloy via compression along the rolling direction (C-RD) and tension along the normal direction (T-ND). The results show that the twinning behavior greatly depends on the loading mode and the twin variant selection is largely dominated by Schmid factor criterion under both deformation modes. Parallel twin bands consisted by single-type variant and/or para variant are frequently observed in C-RD sample, while intersecting twin structures composed by different twin variant types prevail in T-ND sample. Preliminary analysis suggests that the different twinning characteristics should be responsible for the variations in the yield stress and strain-hardening behavior between the two conditions.

Microstructures and impact properties of the rolled Mg-8.10Al-0.46Zn-0.18Mn-0.18Ag (wt.%) alloy were investigated under various thermal conditions including as-rolled, solid solution (T4) and solid solution plus aging (T6) states. The results show that the impact toughness of the as-rolled alloy is slightly enhanced after solution treatment but remarkably reduced by the subsequent aging process, exhibiting a similar trend with the elongation of the alloy. Fractography analysis suggests that the impact toughness variations are closely associated with the changes in the deformation mode: the superior impact toughness of the as-rolled and T4 samples are mainly attributed to the occurrence of profuse twins during impact testing, while, in the T6 sample, the twinning activity is significantly suppressed due to the presence of β-Mg17Al12 phases. In addition, the lamellar-shaped β-Mg17Al12 phases are easy to fracture, which accelerates the crack propagation and thus degrades the impact property.

In this work, deformation behavior of an extruded Mg-Zn-Gd-Y-Zr alloy sheet, including mechanical anisotropy and tension-compression asymmetry, were investigated by conducting tension and compression experiments along different directions. Coupling with the strong texture, the role of long-period stacking ordered (LPSO) phases in the deformation behavior was analyzed based on the microscopic plastic deformation theory. The results showed that LPSO phases with different morphologies played different roles in deformation behavior of the strong textured Mg-Zn-Gd-Y-Zr alloy sheet: (i) the irregular-shaped LPSO phases distributed along extrusion direction (ED) brought anisotropic fiber reinforcement and exacerbated the mechanical anisotropy; (ii) the needle-like LPSO phases filled in the grain interior hindered the propagation of twinning boundaries and decreased the tension-compression asymmetry. The results may provide valuable references for the manufacturing of large size Mg/LPSO alloys with low mechanical anisotropy and tension-compression asymmetry, hence making them better to meet the growing need of engineering application.

A large size Mg-1.2Zn-3.4Y-4.7Gd-0.5Zr (wt%) alloy sheet was manufactured by semi-continuous casting, homogenization and hot extrusion, in which the microstructures were systematically examined. The results showed that: (i) During homogenization, the generation of 14H LPSO phase was mainly achieved by two phase transition processes of “Mg5(Gd,Y,Zn) phase → 14H LPSO phase” and “18R LPSO phase → 14H LPSO phase”. (ii) During extrusion, the evolution of LPSO phases with various morphologies was driven by severe deformation and dynamic recrystallization (DRX). Under severe deformation, the 14H LPSO phases in homogenized alloy were broken down to fragments with various sizes. Under the influence of DRX, the deformation defects of small LPSO fragments were fully eliminated and formed the “sandwich-like” LPSO phase. While the deformation defects of coarse LPSO fragments were less eliminated and formed the “irregular-shaped” LPSO phase. Meanwhile, due to the decreased solubility of Zn, Y and Gd in the extruded alloy matrix, the solution elements of Zn, Y and Gd were impelled to precipitate at the scattering arranged stacking faults (SFs) and formed the “needle-like” LPSO phase. It is found that the gliding of Shockley partial dislocation(s) on basal plane was structurally needed during the precipitation of needle-like LPSO phase. Keywords: Magnesium alloy, LPSO phase, Stacking faults, Extrusion, Recrystallization (DRX)

Twinning-stress correlation of a basal textured Mg-Al-Zn alloy was studied after impact test. The deformed microstructure was characterized using electron backscattered diffraction (EBSD) while the stress analysis during impact process was modeled by finite element method. Results showed that both the tension and compression region of the sample were dominated by high density deformation twins. Various twinning modes and variant selections were determined by trace method and misorientation analysis. Preliminary analysis suggested that some rare twinning modes such as { 10 1 ¯ 1 }-{ 10 1 ¯ 1 } and { 10 1 ¯ 2 }-{ 10 1 ¯ 2 } double twinning likely occurred after deformation.

The microstructure and mechanical anisotropy of the hot rolled Mg-8.1Al-0.7Zn-0.15Ag (wt%) sheets were investigated. Dynamic precipitation and dynamic recrystallization (DRX) are the main features of the microstructures. Compared with the sheet rolled at 673 K, the sheet rolled at 633 K exhibits higher level of dynamic precipitates, finer grain size, more uniform microstructure and better strength. TEM observations reveal that the spherical Mg17Al12 phases which precipitate dynamically do not possess specific orientation with the matrix. Meanwhile, the migration of dynamic recrystallized (DRXed) grain boundaries is retarded by the pinning of fine particles, thereby leading to a remarkable grain refinement. DRX within the compression twins only appear in the alloy sheet rolled at 673 K and give rise to a weakened basal texture. The study on mechanical anisotropy behavior suggests that the reduced anisotropy of the sheet rolled at 633 K may ascribe to the activation of prismatic slip due to the presence of Mg17Al12 phases.

In this study, multi-directional forging (MDF) experiments were conducted to a homogenized Mg-2.36Y-0.98Zn (at%) alloy containing long period stacking ordered (LPSO) phase. Microstructure evolution of the MDFed alloys with different forging passes were systematically investigated, corresponding microhardness development was also concerned. The results revealed that grain refinement, texture weakening and DRX development during MDF were closely relevant to fragmentation of LPSO phase. It was also found that development of average microhardness and mechanical heterogeneity of the MDFed alloys can be attributed to the competition and balance of work hardening, grain refinement and DRX softening. Furthermore, LPSO-related deformation and dynamic recrystallization (DRX) behaviors such as (i) kink-aided DRX (KDRX, this concept was firstly nominated in this study); (ii) particle stimulated nucleation mechanism (PSN) and (iii) pinning effect on DRX nucleus were thoroughly discussed, which should help to understand the unique microstructure evolution of LPSO-containing Mg alloys, and thus offer certain enlightenment for manufacturing LPSO-strengthened Mg alloys with excellent mechanical property.

A Mg–Zn–Y alloy containing long period stacking ordered (LPSO) phases was compressed at temperatures ranging from 623 K to 773 K and strain rates ranging from 0.001 s−1 to 1 s−1. The role of LPSO phase in dynamic recrystallization (DRX) was emphatically studied. The results revealed that: (i) the area filled with kinked LPSO phase is found as potential site favors the initiation of DRX at lower temperatures. (ii) Fragmentation of LPSO phase at initial grain boundaries significantly improves the DRX process via particle stimulated nucleation (PSN) mechanism. (iii) Boundary migration of DRX grains is frequently pinned by LPSO phase at elevated temperature. Understanding the role of LPSO phase in DRX may shed light on manufacturing of Mg–Zn–RE alloys with excellent mechanical property and good corrosion resistance.

Two interaction modes between kinking and { 10 1 ‾ 2 } twinning in a Mg–Zn-Gd alloy containing long period stacking ordered (LPSO) phase are thoroughly investigated: (i) when kinking forms prior to twinning, twins concomitantly nuclear at kink boundaries (KBs) and twinning propagation is frequently restricted by two adjacent KBs. By contrast, (ii) when twinning forms prior to kinking, kink deformation locally breaks the twins’ theoretical misorientation to their adjacent matrixes, during which basal slip plays a vital role in accommodating the asynchronous deformation between kinking and twinning.