Pure magnesium (Mg) develops a strong basal texture after conventional processing of hot rolling or extrusion. Consequently, it exhibits anisotropic mechanical properties and is difficult to form at ...room temperature. Adding appropriate alloying elements can weaken the basal texture or even change it, but the improvement in formability and mechanical properties is still far from expectations. Over the past 20 years, considerable efforts have been made and significant progress has been made on wrought Mg alloys at the fundamental and technological levels. At the fundamental level, textures formed in sheets and extrusions of different alloy compositions and produced under different strain paths or thermomechanical processing conditions are relatively well established, with the assistance of the advanced characterization technique of electron backscatter diffraction. At the technological level, room temperature formability of sheet has been significantly improved, and tension–compression yield asymmetry of extrusion is also remarkably reduced or eliminated. This paper starts with an overview of dislocations, stacking faults and twins, and deformation of single crystals of pure Mg along different orientations and under different loading conditions, followed by a review of microstructure (texture and grain size) and deformation of polycrystalline pure Mg with different textures, grain sizes, and loading conditions. With this information as a base, texture, grain size, and deformation of polycrystalline Mg alloy sheets and extrusions produced under different processing conditions are systematically examined and compared. Remaining and emerging scientific and technology issues are then highlighted and discussed in the context of texture and grain size. The need for better-resolution diffraction and spectroscopy techniques is also discussed in the relationship between texture change and grain boundary solute segregation.
Summary
Background
Magnetic resonance enterography (MRE) has been proposed as a non‐ionising alternative method to computed tomography enterography (CTE). Some studies have directly compared CTE and ...MRE in patients with small bowel Crohn's disease (CD) with variable results.
Aim
To compare the overall diagnostic accuracy in assessing the activity of small bowel and complications.
Methods
MEDLINE, EMBASE and Cochrane databases were searched for studies on the accuracy of MRE and CTE, as compared with a pre‐defined reference standard. Pooled sensitivity, specificity, the weighted area under the curve (AUC), incremental yield (IY) and other diagnostic indices were evaluated.
Results
A total of 290 CD patients from six different studies were analysed. The pooled sensitivity and specificity for MRE in detecting active small bowel CD was 87.9% 95% confidence interval (CI), 81.8–92.5 and 81.2% (95% CI: 71.9–88.4) respectively. The AUC under the summary receiver‐operating characteristic (sROC) of MRE was 0.905 (SEM 0.03, standard error of the mean). Likewise, the pooled sensitivity and specificity of CTE in detecting active small bowel CD was 85.8% (95% CI: 79.2–90.9) and 83.6% (95% CI: 75.3–90.1) with the AUC of 0.898. The AUC of MRE in detecting fistula, stenosis and abscess was 0.936, 0.931 and 0.996, respectively, compared to 0.963, 0.616 and 0.899 of CTE. No statistically significant IY for MRE vs. CTE was found (fixed model, P > 0.05).
Conclusions
Magnetic resonance enterography has a diagnostic effectiveness comparable to computed tomography enterography, thus may serve as a radiation‐free alternative for evaluation of patients with Crohn's disease.
Texture evolution in cold-rolled Mg-0.3Zn-0.1Ca, Mg-0.4Zn and Mg-0.1Ca (at.%) alloys during static recrystallization is monitored using a quasi-in-situ electron backscatter diffraction (EBSD) method. ...The quasi-in-situ EBSD results show that most of recrystallized grains formed in the early stage of recrystallization have randomised orientations in the ternary alloy and they grow uniformly during the recrystallization process. The formation and uniform growth of these recrystallized grains with randomised orientations give rise to a weak texture in fully recrystallized samples of the ternary alloy. A weak recrystallization texture also forms in the early stage of recrystallization in the two binary alloys, but it is gradually replaced by a strong basal texture via the preferential growth of recrystallized grains with specific orientations. The grain size in the ternary alloy is smaller than those in the two binary alloys at each stage of recrystallization, and the grain size distribution in the ternary alloy is significantly narrower than those in the two binary alloys after full recrystallization. Solute segregation to grain boundaries is observed in all three alloys in the fully recrystallized state. It is hypothesised that Zn and Ca atoms in the ternary alloy segregate strongly to high-energy boundaries of the recrystallized grains that would otherwise grow preferentially in the counterpart binary alloys, and that this co-segregation would significantly reduce the boundary mobility, by reducing grain boundary energy and enhancing solute dragging effect, and therefore lead to a more uniform growth of recrystallized grains with randomised orientations.
Display omitted
To explore the characteristics of Helicobacter pylori resistance in China and the association between antibiotic resistance and several clinical factors.
H. pylori strains were collected from ...patients in 13 provinces or cities in China between 2010 and 2016. Demographic data including type of disease, geographic area, age, gender and isolation year were collected to analyse their association with antibiotic resistance. Antibiotic resistance was detected using the Etest test and the Kirby-Bauer disc diffusion method.
H. pylori were successfully cultured from 1117 patients. The prevalence of metronidazole, clarithromycin (CLA), azithromycin, levofloxacin (LEV), moxifloxacin, amoxicillin (AMO), tetracycline and rifampicin resistance was 78.2, 22.1, 23.3, 19.2, 17.2, 3.4, 1.9 and 1.5%, respectively. No resistance to furazolidone was observed. The resistance rates to LEV and moxifloxacin were higher in strains isolated from patients with gastritis compared to those with duodenal ulcer and among women. Compared to patients ≥40 years old, younger patients exhibited lower resistance rates to CLA, azithromycin, LEV and moxifloxacin. The resistance rates to CLA and AMO were higher in strains isolated more recently, and we also found that the prevalence of resistance to metronidazole, CLA, azithromycin and AMO were significantly different among different regions of China.
The resistance rates to metronidazole, CLA and LEV were high in China. Patient age, gender, disease and location were associated with the resistance of H. pylori to some antibiotics. Furazolidone, AMO and tetracycline are better choices for H. pylori treatment in China.
The present study seeks to clarify the mechanism by which dilute additions of zinc (Zn) and calcium (Ca) improve ductility of Mg alloy sheet. Herein, the ductility and microstructure of fully ...annealed pure Mg and Mg-0.1Ca, Mg-0.4Ca, Mg-0.4Zn, and Mg-0.3Zn-0.1Ca (at.%) alloy sheet were systematically investigated and compared. It is found that the ternary alloy displays better ductility than either pure Mg or binary Mg-alloys, when fully recrystallized and possessing similar grain size. In the deformed grains of the ternary alloy, traces of basal and pyramidal slip and {101̅2} twins are observed, whilst only basal slip traces and {101̅2} twins are observed in the pure Mg and binary alloys. Grain boundary cracks are observed in all the tensile-tested alloys. However, significantly less grain boundary cracks are observed in the ternary alloy, posited to be due to enhanced grain boundary cohesion. These observations suggest that the combination of enhanced pyramidal slip and suppressed grain boundary cracking leads to the appreciably improved ductility of the Mg-0.3Zn-0.1Ca alloy sheet.
•A new class of ternary Mg-Zn-Ge alloys presented, with excellent balance of corrosion resistance and strength.•Metallurgical additions of Ge to Mg-Zn alloys were successfully able to decreasing the ...net cathodic (HER) kinetics.•Mg-Zn-Ge alloys revealed low mass loss and hydrogen evolution relative to Mg-alloys to date.•AESEC testing revealed that combined Zn and Ge alloying additions reduced the partial anodic dissolution rate of Mg.
Satisfactory corrosion resistance remains an issue in the widespread implementation of magnesium (Mg). The use of alloying to improve mechanical properties of Mg generally accelerates corrosion due to microstructural heterogeneity. However, recent works have revealed that additions of elements serving as ‘cathodic poisons’ such as arsenic (As) and germanium (Ge) can reduce cathodic reaction rates and suppress cathodic activation - imparting corrosion resistance. The effect of Ge was translated into a ternary (and mechanically relevant) Mg-alloy system for the first time, revealing an alloy system with a balance of properties, and low rate of corrosion relative to Mg-alloys to date.
Display omitted
Effects of alloying additions on deformation texture in Mg sheet alloys are still controversial. In this study, a quasi-in-situ electron backscatter diffraction method is used for the ...first time to monitor the texture evolution during the cold rolling process of Mg–Zn–Ca and Mg–Zn alloys. It is found that the Ca addition does not cause any texture weakening effect — it only delays the development of a strong basal texture by reducing the growth of deformation twins.
A family of alloys based on the Mg-Al-Zn-Ca-Mn system (Mg-3Al-1Zn-1Ca-0.3Mn, Mg-3Al-1.5Zn-0.5Ca-0.3Mn, and Mg-3Al-1Ca-0.3Mn, wt pct) was developed for extrusion. Their mechanical properties were ...evaluated by tensile testing at room temperature, and compared to those of the benchmark Mg-alloy Mg-3Al-1Zn-0.3Mn (AZ31). The microstructures of the extruded alloys were characterized in detail in order to reveal the effect of Ca on microstructural evolution, and consequently the alloy strength. The addition of Ca to the AZ31 stifles dynamic recrystallization and grain growth, with only ~30 pct recrystallization and a recrystallized grain size of ~480 nm. In contrast, the benchmark alloy is essentially completely recrystallized with an average grain size of ~2.3
μ
m. A high density of low-angle grain boundaries (LAGBs) and dislocations were observed in Ca-containing alloys, and were identified as a major factor in the observed strengthening. Such LAGBs form cellular subgrains predominantly along initial grain boundaries, or newly formed boundaries that are closely spaced (~ 600 nm) and nearly parallel to the extrusion direction. The subgrains have an ultrafine size of 100 to 400 nm, and difficult to convert to recrystallized grains. Solute segregation to grain boundaries was also observed. It is hypothesized that it is the Ca segregation to dislocation cores along LAGBs that decreases the dislocation mobility and stabilizes LAGBs, by thermodynamically decreasing the dislocation energy and/or kinetically imposing a solute drag effect.
Display omitted
Magnesium sheet alloy of dilute composition, Mg–0.3Zn–0.1Ca (at.%), does not exhibit any hardening response during heating. However, an annealing treatment at 80–200°C, after some ...plastic strain in tension, leads to a remarkable strengthening, rather than softening, effect. By using electron backscattered diffraction and scanning transmission electron microscopy, it is found that the strengthening effect is caused by the pinning of gliding basal dislocations by GP zones and possibly solute atoms segregated to the dislocations.
Display omitted
•Li dissolves from Mg-Li-(Y-Al-Zr) while Mg forms oxygen deficient oxide film (MgO1-x).•Li+ doping of MgO1-x slows down transformation MgO→Mg(OH)2.•Li2Al2(OH)62·CO3·nH2O (LDH), ...LiAlO2, Y2O3 and Mg(OH)2 grow locally on cathodes.•Cathodic activity is expected to be weakened on Li-doped MgO and LDH.•Li2CO3 formed on Mg-Li-(Y-Al-Zr) in air exposure can be a reservoir of Li+.
The aqueous stability of a corrosion resistant Mg-Li(-Al-Y-Zr)-alloy was investigated by combining in-situ confocal Raman Microscopy, Atomic Emission SpectroElectroChemistry, ex-situ Photoluminiscence Spectroscopy, Auger Electron Spectroscopy and Glow Discharge Optical Emission Spectroscopy. Li and Mg dissolved from visually intact anodic areas, leaving a Li-depleted metallic layer under approximately 100 nm thick Li-doped MgO. The transformation MgO→Mg(OH)2 was inhibited. Li2Al2(OH)62·CO3·nH2O, LiAlO2, Y2O3 and Mg(OH)2 accumulated locally around active cathodic sites. New corrosion mechanism is proposed, which associates the improved corrosion resistance of Mg-Li alloys with an enhanced chemical stability and modified catalytic activity of MgO in presence of Li+.
PDF
