关键词： Pulsed laser   Laser hole-cutting   Magnesium alloys  

摘要： The magnet-assisted laser hole-cutting in magnesium alloys was explored systematically with and without using water immersion, including femtosecond laser multilayer center-oriented hole-cutting and millisecond laser helical hole-cutting of both blind holes and through holes. The effect of the magnetic field and water immersion on laser hole-cutting quality, efficiency and performance is first reported for magnesium alloys with mechanism analysis and comparable discussion. It was shown that the magnetic assistance and/or the water medium improved the hole wall formation especially for underwater laser cutting of blind holes. Compared to laser hole-cutting in air, the underwater laser hole-cutting generated higher-quality holes in magnesium alloys. For laser hole-cutting in magnesium alloys in water, it is first reported that the magnetic field increases the entrance diameters for blind and through holes while decreases the blind-hole depth. The water cooling-insulating effect prevented the molten and vaporized material from re-solidifying and re-depositing onto the workpiece, and the laser-induced ignition and explosion were also prevented by water. The local laser-induced ignition and explosion were weakened when increasing the magnetic flux density. The local oxidation and carbonization reactions in air as a result of the laser-induced ignition and explosion were suppressed while the laser hole-cutting efficiency was enhanced by using the transverse magnetic assistance. The blind-hole recast layer was significantly reduced nearly without accumulated residues and carbonized or oxidized debris by using underwater laser hole-cutting, indicating that the water suppressed the laser-induced melting, vaporization, ignition and explosion and blocked the re-solidification and re-deposition surrounding the hole entrance and onto the hole wall for the recast layer formation. The average grain size number in the heat affected zone (HAZ) near the hole was improved for grain re

关键词： Hydroxyapatite Coating   Fluorinated Magnesium Alloy   Hydrothermal Growth   Biomaterial  

摘要： In order to explore the hydrothermal growth mechanism of hydroxyapatite (HA) coating on fluorinated magnesium alloy, the changes of morphology, composition and crystal phase of the calcium phosphate coating during the hydrothermal treatment were studied. And the change of electrochemical impedance spectroscopy (EIS) of the coating specimen of different hydrothermal treatment time was discussed to further understanding the change of the coating structure. The results demonstrated that calcium phosphate could rapidly nucleate on fluorinated AZ31 magnesium alloy. The crystal phase of calcium phosphate coating was mainly octacalcium phosphate (OCP) at the early stage of hydrothermal treatment. Then the content of OCP decreased and the content of HA increased with hydrothermal time. The coating consisted of only HA after hydrothermal treatment for about 4h. The HA coating composed of rod-like crystals exhibited an obvious double layer structure. The rod-like crystals of inner layer arranged into dense bundles and the rod-like crystals of outer layer arranged into loose chrysanthemum-like clusters. Fluoride conversion layer acted as an intermediate transition layer to connect magnesium alloy and HA coating into a whole. The results of immersion test in simulated body fluid demonstrated that HA crystals dissolved slowly. No peeling occurred of HA coating during the 12 days' immersion. Pitting corrosion was still the mainly corrosion mode of magnesium alloy substrate due to the electrolyte infiltration during the immersion.

关键词： Controlled release   Corrosion resistance   Cytotoxicity   Ibuprofen   Implant   Magnesium alloy   Narrow pH response  

摘要： An intelligent narrow pH-triggered multilayer film was prepared on magnesium alloys, aiming to solve the implant infections during the implantation period and improve the corrosion resistance of magnesium alloys. The encapsulation of ibuprofen by chitosan (IBU@CS) makes the release of IBU sensitive to narrow pH (pH 6.8-7.4). Positive charged IBU@CS was assembled with heparin (Hep) to fabricate (Hep/IBU@CS)(10) film on AZ31 alloys using layer-by-layer method. The microstructure, composition and anticorrosion properties of the film were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and electrochemical experiments. Cellular activity was studied by MTT cell viability assay. The results showed that the Hep/IBU@CS multilayer films improved the corrosion resistance of magnesium alloys. The in vitro test demonstrated that the release of IBU in the film presented narrow pH sensitivity. The films showed no obvious signs of cytotoxicity conformed by the MTT assay and presented antibacterial properties. These preliminary results demonstrate the potential use of the Hep/IBU@CS multilayer films on magnesium-based implants.

关键词： AZ31 Mg alloy   ECAP   grain refinement   ultrasonic   texture  

摘要： An intermittent ultrasonic-assisted equal channel angular pressing (IU-ECAP) technique for grain refinement is proposed in this study. AZ31 Mg alloy samples were divided into two groups (IU-ECAP and ECAP) and processed using four passes along route B-C, and the effects of ultrasonic vibration on the mechanical properties and microstructure were examined. Mechanical testing revealed that IU-ECAP significantly reduced the extrusion force relative to that for ECAP, whereas the microhardness and ultimate tensile strength were strengthened. The maximum true ultimate tensile strength and microhardness of the IU-ECAPed specimens were achieved using ultrasonic vibration with an amplitude of 35 mu m and intermittent time of 2 s. In addition, the microstructures were the most homogeneous for the smallest grain sizes. The IU-ECAPed specimens also possessed less high-angle grain boundaries because of the lower temperature of the IU-ECAP die. Texture analysis revealed that after the 4th pass, the texture of the IU-ECAPed specimens along the (0001) crystal plane exhibited maximum reduction;furthermore, the textures along the (0001), (01 (1) over bar0), and ((1) over bar2 (1) over bar0) crystal planes were scattered homogeneously. These findings may be related to ultrasonic-induced grain boundary rotation.

关键词： beta-Mg17Al12 gamma 2-Al8Mn5   Microstructure   Transmission Kikuchi diffraction (TKD)   Fractography   X-ray tomography  

摘要： The presence of intermetallic constituent particles strongly influences the deformation and fracture characteristics of as-cast magnesium alloys. The present study investigates the two-dimensional (2D) and three-dimensional (3D) microstructure of these intermetallic particles in a direct chill as-cast AZ91 alloy and their effect on the tensile deformation of the alloy. Electron backscattered diffraction (EBSD) was employed to characterize the non-equilibrium eutectic beta-Mg12Al12 phase, which further assisted in hypothesizing the solidification process of the alloy. Transmission Kikuchi diffraction (TKD) indicated the small-sized spherical Mg12Al12 precipitates, formed adjacent to the non-equilibrium eutectic precipitate, did not exhibit any orientation relationship reported in the literature. Further, micron-sized Al-Mn inclusions were observed to be single phase gamma(2)-Al8Mn5 particles exhibiting a cyclically twinned structure with {20 (2) over bar1} habit plane. Additionally, optical microscopy (OM) in the dark-field (DF) and differential interference contrast (DIC) mode, in assistance with high resolution - transmission electron microscopy (HR-TEM) confirmed that the nano-sized gamma(2)-Al8Mn5 particles resulted in a bimodal grain size distribution of the alloy. The three-dimensional (3D) spatial distribution of these intermetallic constituent particles along with fractography facilitated in understanding the damage process of the alloy in uniaxial tension.

关键词： aluminum fumarate   corrosion   EIS   ethylene glycol   magnesium alloy   MOF  

摘要： The aluminum fumarate metal-organic framework (MOF) was synthesized for the application as a corrosion inhibitor of AM60B magnesium alloy in 30% ethylene glycol solution containing 0.5 M NaCl. The prepared MOF was characterized using the XRD and FTIR spectra, as well as SEM images and TGA. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques were used to evaluate the inhibitor performance in a concentration range of 50-400 ppm. The results indicated that the inhibition efficiency enhanced with increasing inhibitor concentration and reached 88.35% at 400 ppm, indicating the high potential of the proposed MOF.

关键词： Magnesium alloys   fly ash   metal matrix composites   drilling   wear   corrosion  

摘要： In the present work, fine grained AZ91 magnesium alloy - fly ash composite has been successfully fabricated by friction stir processing. Microhardness measurements show marginally higher hardness with uniform distribution compared with the base material. No significant difference in the mean cutting force was observed during drilling of the base metal and the composite. However, lower cutting forces were recorded in the sub-surface region of the composites. Interestingly, decreased corrosion resistance was noticed for the composite compared with the base material. Lower mass loss has been observed for the composite during reciprocating wear experiments. The results strongly suggest that the surface composite of AZ91 magnesium alloy - fly ash exhibits better mechanical and wear properties. However, decreased corrosion resistance is a significant observation that warns the applicability of these composites in corroding environment.

关键词： rolling   magnesium alloy   sheet   defects detection   computer vision  

摘要： In the rolling process of magnesium alloy sheet, defects such as edge crack, fold and ripple are easy to appear on the surface of the sheet. These defects will affect the product yield and quality, and cause waste of resources. In this paper, computer vision technology is used to analyze the image of rolling magnesium alloy sheet in real-time, extract its defect features, and Bayesian classifier and Random Forest (RF) classifier are used to identify defects. The experimental results show that the comprehensive defect recognition rate of the RF algorithm is up to 92,4 %, which is much higher than the accuracy of Bayesian classifier, and it is more suitable for the recognition of surface defects of magnesium sheet.

关键词： Dynamic recrystallization  

摘要： Dynamic recrystallization always occurs during hot forming of magnesium alloys and largely controls their microstructure evolution. In this study, we developed a new dynamic recrystallization kinetics model with one undetermined parameter based on isothermal compression tests of a cast-homogenized Mg-8Gd-3Y alloy (GW83) at temperatures ranging from 300 degrees C to 450 degrees C and strain rates from 0.001 to 0.1 s(-1), and measured its dynamic recrystallization volume fractions. The undetermined parameter could be determined by parameter regression. The adaptability of the new model was further examined by comparison with the published data of isothermal compression experiments of AZ31B and ZK60 alloys. The predicted results were well consistent with the experimental results. By integrating the new model with finite element software, we investigated the dynamic recrystallization kinetics of upsetting and plane strain forging of GW83 alloy. The predicted distributions of the dynamic recrystallization volume fraction agreed very well with the experimental values under four different sets of isothermal deformation conditions. These results indicated that the new dynamic recrystallization kinetics model affords highly accurate predictions of the kinetics of cast-homogenized magnesium alloys.

关键词： 术后粘连   甲壳素水凝胶   力学性能   生物相容性   生物降解性  

摘要： 目的:粘连是腹盆腔手术后常见的并发症,可以导致肠梗阻,女性不育,慢性疼痛等,严重影响患者生活质量,甚至危害生命。水凝胶是一种良好的物理屏障,可以有效地预防术后粘连的形成。然而水凝胶力学性能、生物安全性和生物降解能力难以协调,限制了其在术后粘连中的进一步应用。甲壳素是自然界含量第二丰富的天然多糖,基于甲壳素构建的水凝胶拥有良好的生物安全性和生物降解能力,但力学性能较弱,影响了其在生物医学中的应用。因此,我们拟通过绿色改性的方法来增强甲壳素水凝胶的力学性能,从而制备理想的抗粘连水凝胶物理屏障。 方法:(1)制备与表征:依次使用绿色化学交联剂KH560和95%乙醇水溶液物理凝固浴来制备双交联甲壳素水凝胶。我们使用扫描电镜(SEM)和原子力学显微镜(AFM)来观察水凝胶的表面形态,使用紫外分光光度计(UV)、能谱分析仪(EDS)、傅里叶变换红外光谱(FT-IR)和X射线衍射(XRD)测量水凝胶的透明度、元素组成、官能团和结晶度的变化,使用拉伸试验和溶胀试验测试水凝胶的力学强度和吸水性能;(2)生物相容性和生物降解性探究:使用体内外实验验证水凝胶的血液相容性、细胞相容性、生物降解性和生物安全性;(3)抗粘连作用探究:使用SD大鼠盲肠侧壁-腹膜损伤肠粘连模型探究甲壳素水凝胶预防术后粘连的作用。 结果:双交联甲壳素水凝胶具有高透明性、均一致密的三维网络结构、优异的力学强度和吸水性能及良好的生物相容性、生物降解性和生物安全性,在SD大鼠术后粘连模型中发挥了优异的抗粘连物理屏障效应。 结论:我们成功构建了双交联甲壳素水凝胶并解析了其形成机理,验证了其在SD大鼠术后粘连模型中的抗粘连作用。