High Performance Mg Alloy with Designed Microstructure and Phases.

A high strength and ductile Mg-Gd-Y-Zn-Zr alloy was designed and fabricated. The local strain evolution of the alloys during plastic deformation was analyzed using high-resolution digital image correlation (DIC). The results showed that the ß particles, nano-sized γ' phases, and LPSO phases were distributed in the as-extruded alloy and a bimodal microstructure was exhibited, including elongated un-dynamic recrystallized grains and fine dynamic recrystallized grains. With increasing extrusion ratio, the grain size remained, with the volume fraction of dynamic recrystallization of the as-extruded alloy increasing from 30% to 75%, and the as-extruded alloy exhibited a high strength-ductility synergy, which is attributed to the grain refinement, extensive ß particles, and elongated block-shaped LPSO phases. The strain evolution analysis showed that a strain-transfer from un-DRXed regions to adjacent DRXed regions and LPSO phases can promote uniform plastic deformation, which tends to improve the ductility of the alloy.

Effect of Al Addition on Grain Refinement and Phase Transformation of the Mg-Gd-Y-Zn-Mn Alloy Containing LPSO Phase.

The effect of 0−1.0 at.% Al additions on grain refinement and phase transformation of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy containing a long period stacking ordered (LPSO) phase was investigated in this work. The addition of Al promoted the formation of the Al2RE phase in the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy, and the dominant secondary phases in the as-cast Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn-1.0Al (at.%) alloy were the Mg3RE phase, LPSO phase, and Al2RE phase. With increased Al addition, the area fraction of the Al2RE phase increased monotonously, while the area fraction of LPSO phase and Mg3RE phase decreased gradually. The orientation relationship between the Al2RE phase and the α-Mg matrix was determined to be <112>Al2RE//<112¯0>α-Mg, {101}Al2RE//{101¯0}α-Mg, which was not affected by Zn and Mn concentrations in the Al2RE phase. Since the Al2RE particles with a size more than 6 µm located at the center of grains could act as nucleants for α-Mg grains, the average grain size of the as-cast alloys decreased from 276 µm to 49 µm after 1.0% Al addition. The effect of the Al addition on the grain refinement of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn alloy was comparable to that of the Zr refined counterpart.

Effects of La Addition on the Microstructure, Thermal Conductivity and Mechanical Properties of Mg-3Al-0.3Mn Alloys.

The effects of La addition on the microstructure, thermal conductivity and mechanical properties of as-cast and as-extruded Mg-3Al-xLa-0.3Mn (x = 1, 3 and 5 wt.%) alloys were studied. The results showed that the thermal conductivity of the alloys increased with the addition of La element, which was due to the formation of the Al11La3 phases by consuming the solute Al and the added La element. The yield strength of the as-cast Mg-3Al-xLa-0.3Mn alloys increased with the increase in La concentration. The thermal conductivity of the as-extruded alloys was lower than that of as-cast counterparts owing to lots of defects generated in the process of hot extrusion deformation, particularly the grain boundaries. The anisotropy of thermal conductivity was discovered in the as-extruded alloys on account of the formation of texture. As the La content increases, the tensile strength and yield strength of the as-extruded alloys decreased gradually. In contrast, the elongation first increased and then decreased, resulting from the combined effect of the texture strengthening and second phase strengthening.

Free gait in a shallow pool accelerates recovery after exercise in model mice with fibromyalgia.

This study aimed to determine the effect of pool gait exercise using fibromyalgia-induced model mice. The sensory threshold, locomotive behavior, electrocardiogram, and onset time after the gait test in shallow water using male C57BL/6J mice (weight, 30-35 g; n=21) were investigated. To induce fibromyalgia in model mice, reserpine was injected intraperitoneally into wild-type mice once a day for 3 days. Subsequently, the fibromyalgia-induced model mice were randomly classified into two groups as follows: the control group (n=11) and the pool gait group (n=10). The mice in the pool gait group walked in the same cage containing shallow warm water 5 times per week. Both groups underwent sensory thresholds and video recordings to determine locomotive behaviors weekly. Further, both heart rate and video recordings for observation of a recovery after the gait test in shallow water were undertaken (control group; n=5, pool gait group; n=5). The pool gait did not affect sensory thresholds and locomotive behavior; however, in the pool gait group, both the recovery after the test, such as onset time and gait distance, were considerably better than those of the control group. Furthermore, changes in heart rate and heart rate irregularity after the test were more apparent in the control group than in the pool gait group. The free gait in a shallow pool accelerated recovery after exercise, unlike the sensory threshold.

Excessive exercise induces cardiac arrhythmia in a young fibromyalgia mouse model.

BACKGROUND: Fibromyalgia patients experience cardiovascular complications in addition to musculoskeletal pain. This study aimed to investigate the cardiac effects of a prolonged shallow water gait in a fibromyalgia-induced young mouse model. METHODS: To produce a fibromyalgia mouse model, wild-type mice were administered an intraperitoneal injection of reserpine once a day for three days, and two primary experiments were performed. First, three types of gait tests were performed before and after the reserpine injections as follows: (i) 5 minutes of free gait outside the water, (ii) 1 minute of free gait in shallow warm water, and (iii) 5 minutes of free gait in shallow warm water. Second, electrocardiogram recordings were taken before and after the three gait tests. The average heart rate and heart rate irregularity scores were analyzed. RESULTS: Exercise-induced cardiac arrhythmia was observed at 1-minute gait in shallow water during the acute stage of induced FM in young mice. Further, both cardiac arrhythmia and a decrease in HR have occurred at 5-minute gait in shallow water at the same mice. However, this phenomenon was not observed in the wild-type mice under any test conditions. CONCLUSION: Although a short-term free gait in shallow warm water may be advantageous for increasing the motor activity of FM-model mice, we should be aware of the risk of prolonged and excessive exercise-induced cardiac arrhythmia. For gait exercises in shallow water as a treatment in FM patients. We suggest a gradual increase in exercise duration may be warranted.

Effect of LPSO and SFs on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy.

High performance Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy with high strength and excellent ductility has been successfully developed by hot extrusion. The effect of plate-shaped long period stacking ordered (LPSO) phases and solute-segregated stacking faults (SFs) on the dynamically recrystallization (DRX) behavior was analyzed. The plate-shaped LPSO phases stimulate the DRX by particle stimulated nucleation mechanism, leading to higher DRX ratio and weaker basal texture. While for the alloy with dense fine SFs inside the original grains, discontinuous DRX initially occurs at the original grain boundaries, and the DRX is obviously restricted. Consequently, alloy containing dense SFs exhibits higher strength but lower ductility compared with alloy with plated-shaped LPSO phases.