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： 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： 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： 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.

关键词： grain refinement   magnesium alloy   microsegregation   quasi-crystalline phase   subrapid solidification  

摘要： The evolution of the microstructure and microsegregation in a new type of Mg-6Al-4Zn-1.2Sn (wt%) cast magnesium alloy solidified at cooling rates from 4.5 x 10(1) degrees C s(-1)to 2.3 x 10(3) degrees C s(-1)is investigated. The results indicate that the secondary dendrite arm spacing and the average grain sizes decrease from 14.3 to 2.9 mu m and from 187 to 78 mu m, respectively, as the cooling rate increases from 4.5 x 10(1) degrees C s(-1)to 2.3 x 10(3) degrees C s(-1). The relationship between the secondary dendrite arm spacing (lambda(2)) and cooling rate (R) is fitted as lambda(2) = 69.7 x R-0.42. When the alloy solidifies in the range of cooling rates, a new quasi-crystalline I phase is formed due to faster solidification. The microsegregation ratios of Al, Zn, and Sn elements decrease significantly with the increase in cooling rate. Compared with the specimen solidified at 4.5 x 10(1) degrees C s(-1), the microsegregation ratios of Al, Zn, and Sn of that solidified at a cooling rate of 2.3 x 10(3) degrees C s(-1)decrease by 37.4%, 45.7%, and 31.6%, respectively.

关键词： HPDC parameters   Defect band   Porosity   3D   Tensile fracture  

摘要： For understanding the processing-microstructure-properties correlation of high pressure die casting (HPDC) AZ91D alloy, 3D reconstruction was carried out to characterize the microstructural morphologies of castings produced by four designed HPDC processes. The influence of different parameters (vacuum, slow-shot speed, fast-shot speed) on porosity volume and morphology, defect band width and average externally solidified crystals (ESCs) size of castings were systematically studied. Microstructural characterization revealed that the defect band width was strongly related with the size and quantity of ESCs, rather than the porosity volume. Meanwhile, ESCs were mainly influenced by the slow-shot speed in shot sleeve (ESCs growth time) and fast-shot speed into the die cavity (shear stress of melt flow). Tensile fracture revealed that cracks easily propagated within the defect bands due to the accumulated ESCs and connected irregular pores, while the cracks were restrained in center zone. The mechanical properties of HPDC castings was inversely proportional to the defect band width, and is not dependent on the average volume fraction porosity.

关键词： AZ31 magnesium alloy   Cross variable thickness rolling   Edge crack   Edge curve   Microstructure  

摘要： According to the MAS rolling and cross rolling theory, the hot rolling experiments were carried out on the AZ31 magnesium alloy specimens at the initial rolling temperature of 350 degrees C, and the grain distribution and edge damage of the strip after rolling by a controlled rolling reduction in different regions were analyzed. Meanwhile, the edge curves were designed to improve the edge crack and grain refinement of magnesium alloy during cross variable thickness rolling. The results indicated that the variable thickness rolling with the edge curve could effectively reduce the edge crack of magnesium alloy. The results also indicated that different edge curves could produce varying degrees of grain refinement at the strip edge and realize the ideal grain refinement in different regions during the rolling process;meanwhile, the optimization of the edge curve during cross variable thickness rolling could provide a theoretical basis for improving the magnesium alloy edge crack.