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Reducing the yield asymmetry is very important concern for wrought Mg-Li alloys. In this study, Mg-5Li-3Al-2 Zn (LAZ532) alloy was successfully produced by hot-extrusion followed by multi-pass rolling at 573 K. Microstructure evolution, mechanical properties and yield asymmetry reducing of LAZ532 alloys at different rolling passes were studied. By observing microstructure using transmission electron microscopy showed that a small amount of ultra-fine AlMg4Zn11 and nano Li3Al2 phases existed in the alloy. With the increasing of rolling passes, the grains of the alloys were obviously refined, and comprehensive mechanical properties were dramatically improved. Meanwhile, it also showed an excellent tension and compression yield symmetry (TYS/CYS was about 1). The results showed that the combined action of the weak {0001} basal lamellar texture, grain refinement and addition of Li element could effectively improve the yield symmetry. Furthermore, based on theoretical analysis, the yield strength in the alloys mainly depended on the strengthening contributions of LAGBs and HAGBs, and strengthening effect of HAGBs most (∼50%) to the yield strength improvement.

In order to compare the workability of AZ80 magnesium alloy casted with and without variablefrequency ultrasonic field (VUF), uniaxial hot compression tests were carried out in the temperature range of 523-673 K and the strain rate range of 0.001-1 s(-1) on a Gleeble-3500D thermo-mechanical simulator. The flow stress, constitutive relation, DRX kinetic model and processing map were analyzed based on the experimental data. The results show that, the VUF samples have lower peak stress and peak strain than DC samples at low strain rates, while the opposite situation can be observed at high strain rate. The calculated activation energy Q and stress exponent n for DC samples are 192.38 kJ/mol and 7.30158, which are higher than the calculated values for VUF samples, showing the figures of 165.30 kJ/mol and 7.30158, respectively. The VUF casted samples start DRX earlier and easier, and can obtain complete DRX structure at high strain rate. The VUF samples have larger workability range but smaller instability region than DC samples. Dense and irregular bulges can be observed on side surfaces of DC samples after compression, while surfaces of VUF samples are smooth. (C) 2019 Elsevier B.V. All rights reserved.

In this study, a novel multi-microalloying MgAlCoCrFeNi alloy was extruded at 300 ˚C with different extrusion speeds (0.2, 1, and 2 mm/s). The microstructure evolution, tensile properties and work-hardening behavior of the alloy were studied. Results showed that increasing the extrusion speed could improve the homogeneity of the microstructure, transitioning from a bimodal microstructure (fine recrystallized grains and elongated un-recrystallized grains) at 0.2 and 1 mm/s to a fully recrystallized one at 2 mm/s. The lower extrusion speed could improve the YS of the alloy, which possesses a maximum YS of ~213 MPa at 0.2 mm/s, an increase of ~12% compared to the YS at 2 mm/s, which was mainly attributed to the fine grain strengthening and dislocations (residual dislocations) strengthening. Moreover, the work hardening capacity of the alloy increases with the extrusion speed. As the extrusion speed increases from 0.2 mm/s to 2 mm/s, the work hardening exponent n increased from 0.08 to 0.14, and the work hardening capability Hc increased from 0.31 to 0.52. The analysis results showed that the improvement of work hardening ability was mainly due to the increase of dislocation storage rate caused by grain coarsening.

In this study, the microstructure evolution and mechanical anisotropy of the extruded Mg-2Zn-0.4Mn-0.4Ce alloy tube during tensile loading along the extrusion direction (ED), 45° towards extrusion direction (45°ED) and transverse direction (TD) were investigated, respectively. The results showed that the initial extruded alloy tube had an obvious {0001} basal fiber texture with the symmetrical pole position deviating about 20° from the RD to ED, which resulted in mechanical anisotropy of the tensile yield stress (TYS) when tensile loading along the ED, 45°ED and TD. The deformation behavior of the alloy tube consisted of three stages. In the yield process, the deformation was dominated by prismatic slip under tensile loading along the ED, while the deformation was dominated by basal slip, next were prismatic slip and pyramidal slip under tensile loading both along the 45°ED and TD. In the initial stage after yielding, some extension twin (ETW) formed when tensile loading along the three direction, and the deformations were still dominated by the previous slip systems. In the later part of the deformation, the activation of prismatic slip and the nucleation and expansion of ETW gradually reached saturation under tensile loading along the ED. The dominated prismatic slip was gradually replaced by pyramidal slip, and accompanied with a small content of contraction twin (CTW) and double twin (DTW), thus forming a typical texture of [0001]⊥ED. For the deformation both along the 45°ED and TD, dominated prismatic slip and subdominant pyramidal slip gradually became the main deformation mode after the saturation of basal slip and ETW, and a small content of CTW and DTW also formed, thus forming the texture of [0001]∥ED-RD plane.