关键词： AZ80   Magnesium alloys   Aggressive ions   Corrosion behavior  

摘要： Magnesium alloys can work as biomedical materials due to their Young's modules similar to that of bone. Nevertheless, in a human plasma, one of the major drawbacks of these materials is the low corrosion resistance. Here, AZ80 corrosion in the solutions containing chloride, bicarbonate, sulphate and hydrogen phosphate ions were investigated by a short-term immersion test and electrochemical techniques. The results showed that bicarbonate and hydrogen phosphate could retard corrosion rate, while chloride and sulphate accelerated corrosion rate. During the early immersion stage, the corrosion rate increased with the presence of bicarbonate. It was caused by the reaction of bicarbonate and hydroxide promoting the dissolution of magnesium and accelerating corrosion. In the later stage, the reduced corrosion rate was due to the formation of various protective films. The sample formed a new sparse porous MgSO4 center dot 5H(2)O compounds in the sulphate ion solution, which could not effectively prevent chloride ions from entering the matrix and thus accelerated the dissolution of magnesium. With the presence of hydrogen phosphate, magnesium phosphate with a much lower solubility was formed, preferentially precipitated on the surface and was not influenced by the chloride ions. The corrosion mechanisms of magnesium alloys in above ions were proposed.

关键词： chloride ion concentration   electrochemical impedance spectroscopy   focused ion beam   magnesium   magnox   pH   potentiodynamic   scanning electron microscopy   scanning vibrating electrode technique   temperature   x-ray diffraction  

摘要： Magnesium (Mg) nonoxidizing alloy, known as Magnox, was historically used as a fuel cladding material for the first generation of carbon dioxide gas-cooled nuclear reactors in the United Kingdom. Waste Magnox is currently stored in cooling ponds, pending final disposal. The corrosion resistance of Mg and its alloys is relatively poor compared to modern cladding materials, such as zirconium alloys, so it is important to have a knowledge of the chloride concentration/pH dependence on breakdown and localized corrosion characteristics prior to waste retrievals taking place. These results show that Magnox exhibits passivity in high-pH solutions, with charge transfer resistance and passive film thicknesses showing an increase with immersion time. When chloride is added to the system, the higher pH maintains Magnox passivity, as shown through a combination of potentiodynamic and time-lapse/post-corrosion imaging experiments. Potentiodynamic polarization of Magnox reveals a -229 mV/decade linear dependence of breakdown potential with chloride ion concentration. The use of the scanning vibrating electrode technique enabled the localized corrosion characteristics to be followed. At high pH where Magnox is passive, at low chloride concentrations, the anodes that form predominantly couple to the visually intact surface in the vicinity of the anode. The high pH, however, means that visually intact Magnox in the vicinity of the anode is less prone to breakdown, restricting anode propagation such that the anodes remain largely static. In high-chloride concentrations, the higher conductivity means that the anode and cathode can couple over greater distances, and so propagation along the surface can occur at a much faster rate, with the visually intact surface acting as a distributed cathode. In addition, the chloride anion itself, when present at high concentration, will play a role in rapid passive film dissolution, enabling rapid anode propagation.

关键词： ZK60 Mg alloy   PTCAP   Ultra-fine grain   Microstructure   Mechanical properties   Predictive intelligent-based techniques  

摘要： Ultrafine grained ZK60 magnesium (UFG-ZK60 Mg) tubes were successfully fabricated by a parallel tubular-channel angular pressing (PTCAP) process. The number of pass effects on the phase composition, microstructural features and mechanical properties were examined. Also, two types of Artificial Neural Network known as Radial Basis Function (RBF) and Multi-Layer Perceptron (MLP) were employed to accurately estimate mechanical behavior of the PTCAP-processed ZK60 Mg alloy. The results showed that all the processed tubes had more refined microstructure with similar to 7 to 0.9 mu m grain sizes, which consist of an average crystallite size between 68 +/- 8 and 51 +/- 8 nm, compared to the as-received specimen with a mean grain size of similar to 90 mu m. Similar XRD profiles were achieved following different PTCAP passes, however, some discrepancies were observed as the number of passes increased, which corroborated the structural changes during the PTCAP process. The microscopic observations also revealed the microstructural changes by increasing the PTCAP passes. The hardness of the processed tubes increased with the number of PTCAP passes, from 77 +/- 2 HV for the unprocessed alloy to a maximum of 111 +/- 2 HV at three PTCAP passes. The PTCAP process increased not only mechanical strength but also the ductility of the processed tubes, where the highest yield strength (sigma(YS) = 320 MPa), ultimate tensile strength (sigma(UTS) = 397 MPa) and elongation to failure (delta = 14%) values were obtained at the second pass of PTCAP. However, with increasing number of PTCAP passes to three, delta reached 4% and sigma(YS) and sigma(UTS) decreased by 31% and 11%, respectively. Findings from the neural based-predictive models indicated that both RBF and MLP can be employed for accurately estimating the mechanical properties of the PTCAP-processed ZK60 Mg alloy. Graphic

关键词： Magnesium   Polarization   EIS   XPS   Passive film  

摘要： Magnesium is the world's lightest structural metal, with a significant growth potential in view of the accelerating demand for light-weighting portable devices and transportation (aerospace, automotive), amongst other. The effect of carbonate ions on corrosion protection of AZ31 magnesium alloy was studied in 0.1 M NaCl solution saturated in Mg(OH)(2) using Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization measurements, hydrogen evolution tests and SEM-EDX analysis. X-ray Photoelectron Spectroscopy (XPS) was used in order to investigate the top-surface composition. The inhibitive effect of CO32- ions on corrosion of AZ31 magnesium alloy was highlighted and the underlying mechanisms discussed.

关键词： Magnesium alloy pellets   Bisphosphonates coating   Osteosarcoma   Multicellular spheroids model   Mevalonate pathway  

摘要： Osteosarcoma (OS) remains one of the most threatening primary malignant human tumors of the bone, especially in the first or second decade of life. Unfortunately, the clinical therapeutic efficacy has not substantially improved over the past four decades. Therefore, to achieve efficient tumor eradication, a new approach to prevent tumor recurrence is urgently needed. Here, we develop a new bisphosphonate (BP)-loaded microarc oxidation (MAO) coated magnesium-strontium (Mg-Sr) alloy pellet that can inhibit OS, and we illuminate the cellular and molecular mechanisms of the inhibiting effect. To generate such pellets, nitrogen-containing BP is chemically conjugated with a MAO coating on hollow Mg-Sr alloys. We demonstrate that BP coated Mg pellet has multiple desired features for OS therapy through in vitro and in vivo studies. At the cellular level, BP coated Mg pellets not only induce apoptosis and necrosis, as well as antitumor invasion of OS cells in the two-dimensional (2D) cell culture environment, but also damage the formation of multicellular tumor spheroids by OS cell lines in the three-dimensional (3D) cell culture environment. At the in vivo level, BP coated Mg pellets can destroy tumors and prevent neoplasm recurrence via synergistic Mg degradation and drug release. It is further suggested that the superior inhibitory effect on OS of our pellet is achieved by inhibiting the mevalonate pathway at the molecular level. Hence, these results collectively show that the BP coated Mg pellet is a promising candidate for future applications in repairing defects after tumor removal in OS therapy. Statement of significance Osteosarcoma (OS) is prone to metastases and unfavorable prognosis and the clinical therapeutic efficacy has not substantially improved over the past four decades. It is of high demand in developing new materials that can not only repair the bone defects but also inhibit OS in the lesion location. To solve these problems, we design a hollow Mg-Sr allo

关键词： ZK60 magnesium alloy   Flow softening   Microstructure   Deformation twinning   Dynamic recrystallization  

摘要： In this work, a commercial extruded Mg-6Zn-0.5Zr (ZK60) magnesium alloy was compressed to investigate the correlations among flow curve shape, microstructure evolution and loading parameters in terms of strain rate and deformation temperature. According to the results, twinning played an important role during deformations below 250 degrees C and the number of twinning bands increased with the increase in strain rate. Twinning caused initially softening followed by hardening. The flow curve shape before peak stress was determined by the number of twinning bands that were initiated. Dynamic recrystallization (DRX) was initiated during deformations at temperatures higher than 150 degrees C, and the DRX grain size decreased with strain rate and increased with deformation temperature. At 400 degrees C, twinning was not initiated and the microstructure of the specimens was composed of both DRX and SRX (static recrystallization) grains.

关键词： Magnesium alloy   Precipitate   Twinning   Elongation   Fracture mechanism  

摘要： Effects of discontinuous precipitate (DP) and continuous precipitate (CP) on the tensile elongation and fracture mechanism of aging-treated AZ91D Mg alloy were investigated via quantitative microscopy and fractography. Specimens with various distributions of DP and CP were prepared under a wide range of aging conditions. As quantitative microstructural factors of DP and CP, area fraction of DPs and CP/alpha-Mg interfaces per unit volume were measured by optical microscopy (OM) and scanning electron microscopy (SEM). To explain the tensile fracture mechanism, a deformation twinning behavior was analyzed using OM and electron back-scattered diffraction, and area fraction of stepped cleavage facet was quantitatively measured on a large number of fractographs. An increase in the area fraction of DPs caused a slight decrease in the tensile elongation and this reduction was attributed to cracking at the DP along grain boundary. For the specimens with high CP/alpha-Mg interfaces per unit volume, a large number of fine {10-12} tension twins were produced within a few percent of tensile elongation as well as premature fracture occurred. In this investigation, the premature fracture mechanism of the aging-treated AZ91D alloy with a large amount of fine CP distribution was explained in relation with the increased probability of {10-12} tension twin boundary cracking, although activation of {10-12} tension twinning can be a way to facilitate deformation of some Mg alloys in previous researches. Validity of the suggested premature fracture mechanism was supported by the quantitative measurement of area fraction of the stepped cleavage facet on the fractography as indirect evidence of the twin boundary cracking.

关键词： additive manufacturing   fatigue   friction stir welding   magnesium alloy   mechanical properties  

摘要： This work examines the grain refinement and mechanical properties of additive friction stir layer welding (AFSLW) of a Mg Alloy. The AFSLW process was used to additively fabricate a seven-layer tall build using 5-mm-thick plates of AZ31 Mg alloy, with each layer containing three parallel welding passes. This multipass AFSLW process demonstrates the ability of this additive method to produce tall and wide structures free of volumetric defects. While the AFSLW material was found to have lower monotonic tensile and fatigue strengths as compared to wrought Mg AZ31-H24, this result was expected due to the heat input from the additive layer welding process that relaxed the cold work strengthening mechanisms. Metallography cross sections and analysis via scanning electron microscopy revealed that the AFSLW build did not contain any detectable defects in any of the 21 weld passes. Furthermore, postmortem fractography found fatigue crack initiation mechanisms to be similar in both the AFSLW and wrought AZ31-H24. The results of this study indicate that large, defect-free builds with predictable mechanical properties can be achieved using the AFSLW process.

关键词： biocompatibility   biological activity   coating   magnesium alloy   silicon  

摘要： Among biomaterials, the mechanical properties of magnesium and its alloys are closest to those of human bone tissue, making these ideal materials for bone tissue repair and replacement. In order to further improve the biocompatibility and biological activity of the magnesium alloy AZ91D, micro-arc oxidation with a constant-current power supply mode was employed in this study in a silicate electrolyte solution. The resultant coating surface had a porous structure, and silicon was evenly distributed in it. Further, the results of in vitro experimental studies showed that the silicon-doped magnesium coating on the surface of the magnesium alloys has no obvious cytotoxicity, and it can induce the proliferation of osteoblasts and promote actin stretching. In addition, it has good biological activity and biocompatibility. Thus, the novel method developed in this study improves the potential for clinical applications of magnesium alloys.

关键词： Extrusion-shear deformation   ZC61 alloy   Dynamic mechanical property   Deformation mechanism   Shear accommodation  

摘要： In this study, Mg-6Zn-1Cu-0.6Zr (ZC61) alloy was fabricated using a novel extrusion-shearing process that combines traditional hot extrusion with equal-channel angular pressing (ECAP). The behavior and microstructure of the alloy were investigated in the extrusion area (EA) and forming area (FA) at different temperatures (25-200C) under dynamic compression. The experimental results reveal that the microstructure mainly consists of fine dynamically recrystallized grains in both the EA and FA with an average grain size of 4.45 mu m and 2.61 mu m, respectively. Under dynamic compressive loading at a strain rate of 1300 s(-1), the true stress-true strain curves exhibit a typical sigmoidal shape (concave upwards) due to activation of the {10 (1) over bar2} extension twinning mode typical of textured ZC61 alloys. At room temperature, extension twinning is the main deformation mechanism in both the EA and FA. As the loading temperature increased, {11 (2) over bar2} <1<(12)over bar>3> secondary order pyramidal slip and {10 (1) over bar1}-{10 (1) over bar2} double twins coordinated the dynamic deformation in the EA and FA, respectively.