Low frequency damping capacities of commercial pure magnesium

The amplitude-dependent and temperature-dependent low frequency damping capacities of magnesium with 99.96% purity were studied by a dynamic mechanical analyzer. The pure magnesium alloys include CPM1 and CPM2 castings having textures of columnar grains which extraordinarily influence the damping behaviours. The commercial pure magnesium alloy CPM was re-melted to obtain equiaxed grains, which could remove the effect of texture orientation on the damping behaviours of these pure magnesium alloys. The results of strain amplitude-dependent damping spectrums of these pure magnesium alloys show that the pure magnesium with equiaxed grains possesses the highest damping capacity. In temperature-dependent damping plot for all these three pure magnesium alloys, there are two damping peaks P1 and P2 located at 80 and 230 °C, respectively. These two damping peaks are considered to be caused by the interaction between dislocation and point defects, and the movement of grain boundaries, respectively.

EFFECTS OF TREATMENT TIME ON CORROSION OF DIFFUSION-ALLOYED COATINGS OF PURE MAGNESIUM

The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time （8, 16, and 24h）. The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test （in 3.0% NaCl solution, temperature is （28±1）℃, and time is 96h）. Optical microscopy （OM） and EDS （energy dispersive spectrum） composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones （especially the samples treated for 24h at 480℃）, was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase （WP-zone） of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.

Effect of grain size on the electrochemical behavior of pure magnesium anode

Three kinds of pure magnesium anode materials with different grain sizes were prepared by extrusion at different temperatures.The grain size of each sample was calculated,then the effect of grain size on the electrochemical properties of pure magnesium anode was investigated by chemical immersion hydrogen test,potentiodynamic polarization scanning,constant current discharge and electrochemical impedance spectroscopy.As the extrusion temperature increases from 180℃ to 250℃,the average grain size of pure magnesium increases from 20m to 30m,and the pure magnesium extruded at 250℃ has the best electrochemical performance as magnesium anode,with the discharge potential of−1.571 V(vs.SCE).Plastic deformation process is a convenient method that can change the microstructure and improve the electrochemical behavior of magnesium anode.

Investigation of anti-corrosion property of hybrid coatings fabricated by combining PEC with MAO on pure magnesium

Novel hybrid coatings on pure magnesium were prepared by combining plasma electrolytic carburizing(PEC)with micro-arc oxidation(MAO)to further enhance the anti-corrosion property in this paper.Scanning electron microscopy(SEM)was used to observe the microstructure of the coatings,meanwhile,energy dispersive spectrometry(EDS)and X-ray diffraction(XRD)were separately used to investigate the elemental as well as phase compositions of the coatings.The anti-corrosion property of the coatings was evaluated by potentiodynamic polarization curves as well as electrochemical impedance spectroscopy(EIS).The results show that PEC process is closely related with the effects of adsorption as well as diffusion of the activated carbon atoms,and it can provide a favorable pretreatment surface with predesigned chemical composition to obtain a new kind of phase,namely Si C with superior corrosion resistance and chemical stability,in the following PEC+MAO hybrid coatings.Meanwhile,PEC preprocessing also can afford an excellent micro-structure to increase the coating thickness as well as to improve the compactness of the PEC+MAO hybrid coatings.During the fabrication process of the PEC+MAO hybrid coatings,an overlapping phenomenon in regard to coating thickness can be observed instead of heaping up layer by layer.Compared with both single PEC surface modification layers as well as single MAO coatings,the PEC+MAO hybrid coatings exhibit more superior anti-corrosion property.Especially,the EIS data reveal that the PEC+MAO hybrid coatings can act as an effective protection system to provide relatively excellent long-range anti-corrosion protection.Note also that employing same MAO technique for both single MAO treatment as well as PEC+MAO combining procedure is the key to this research.

Bulk and local textures of pure magnesium processed by rotary swaging

Rotary swaging processing on commercial as-cast pure Mg has been carried out. Bulk texture variation with the processing passes was investigated using large gauge volume by neutron diffraction, of which results showed a combination of different components such as {00.2} basal fibre and two weak {10.0} and {11.0} fibres. Asymmetric distribution of the basal fibre around swaging direction was observed and being related to the processing parameters. Texture gradient analysis by synchrotron radiation demonstrates a non-uniform deformation of the RS processed pure Mg from surface to the centre.

Study on the Properties of TiN Coatings on Previously Ion-Implanted Pure Magnesium Surface by MEVVA Ion Implantation

A metal vapor vacuum arc （MEVVA） is used in ion implantation for substrate preparation before the deposition process which would ensure the improvement of mechanical properties of the coating. Ti ion is implanted into pure magnesium surface by MEVVA implanter operated with a modified cathode. Implanting energy is kept at 45 keV and dose is set at 3 ×10^17 cm^-2. TiN coatings are deposited by magnetically filtered vacuum-arc plasma source on unimplanted and previously implanted substrates. Microstructure and phase composition are analysed using scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The property of corrosion resistance of TiN coatings was studied by CS300P electrochemistry-corrosion workstation, and the main impact factor of the corrosion resistance was also analyzed.

Friction stir welding of pure magnesium and polypropylene in a lap-joint configuration: Microstructure and mechanical properties

A hybrid joint with a satisfactory mixture of pure magnesium and polypropylene(PP)was achieved via friction stir joining(FSW)in a lap-joint configuration.The tool rotational and travel speeds used in this work were 500–700 r/min and 50–100 mm/min,respectively.The mechanical properties and microstructural analysis of the resultant hybrid Mg/PP joint were examined.The results show that the maximum tensile shear strength(22.5 MPa)of the joint was attained at 700 r/min and 75 mm/min due to the optimum percentage fraction of mechanical interlocking(48%)and the presence of magnesium oxide.The interfacial joint center exhibits the maximum microhardness values because of the presence of refined and intertwined Mg fragments and density dislocations in the matrix of the PP.The joint failed via two different modes:interfacial line and weld zone fractures,respectively.

In vitro degradation of pure magnesium-the synergetic influences of glucose and albumin

The biocorrosion of magnesium in the external physiological environment is still difficult to accurately evaluate the degradation behavior in vivo,particularly,in the microenvironment of the patients with hyperglycemia or diabetes.Thus,we explored the synergistic effects of glucose and protein on the biodegradation of pure magnesium,so as to have a deeper understanding the mechanism of the degradation in vivo.The surface morphology and corrosion product composition of pure magnesium were investigated using SEM,EDS,FTIR,XRD and XPS.The effect of glucose and albumin on the degradation rate of pure magnesium was investigated via electrochemical and immersion tests.The adsorption of glucose and albumin on the sample surface was observed using fluorescence microscopy.The results showed that the presence of 2 g/L glucose changed the micromorphology of corrosion products on the magnesium surface by reacting with metal cations,thus inhibiting the corrosion of pure magnesium.Protein formed a barrier layer to protect the magnesium at early stage of immersion.The chelation reaction between protein and magnesium surface might accelerate the degradation at later stage.There may be a critical glucose(albumin)content.Biodegradation of pure magnesium was inhibited at low concentrations and promoted at high concentrations.The synergistic effect of glucose and protein restrained the adsorption of aggressive chloride ions to a certain extent,and thus inhibited the degradation of pure magnesium considerably.Moreover,XPS results indicated that glucose promoted the adsorption of protein on the sample surface.

Degradation and biological properties of Ca-P contained micro-arc oxidation self-sealing coating on pure magnesium for bone fixation

Poor corrosion resistance is one of the main disadvantages for biodegradable magnesium-based metals,especially applied for bone fixation,where there is a high demand of bio-mechanical strength and stability.Surface coating has been proved as an effective method to control the in vivo degradation.In this study a Ca-P self-sealing micro-arc oxidation(MAO)coating was studied to verify its efficacy and biological properties by in vitro and in vivo tests.It was found that the MAO coating could effectively retard the degradation according to immersion and electrochemical tests as well as 3D reconstruction by X-ray tomography after implantation.The MAO coating exhibited no toxicity and could stimulate the new bone formation.Therefore,the Ca-P self-sealing MAO coating could be a potential candidate for application of biodegradable Mg-based implant in bone fixations.

In Vivo Study on Degradation Behavior and Histologic Response of Pure Magnesium in Muscles

When an orthopedics device is implanted into bone injury site, it will contact the soft tissue （skeletal muscle, fascia, ligament etc.） except for bone. Magnesium based biodegradable metals are becoming an important research object in orthopedics due to their bioactivity to promote bone healing. In this study, pure Mg rods with and without chemical conversion coating were implanted into the muscle tissue of rabbits. Implants and their surrounding tissues were taken out for weight loss measurement, cross- sectional scanning electron microscopy observation, elemental distribution analysis and histological examination. The results showed that the chemical conversion coating would increase the in vivo cor- rosion resistance of pure Mg and decrease the accumulation of calcium （Ca） and phosphorus （P） elements around the implants. For the bare magnesium implant, both Ca and P contents in the surrounding tissues increased at the initial stage of implantation and then decreased at 12 weeks implantation, while for the magnesium with chemical conversion coating, Ca and P contents in the surrounding tissues de- creased with the implantation time, but were not significant. The histological results demonstrated that there was no calcification in the muscle tissue with implantation of magnesium for up to 12 weeks. The chemical conversion coating not only increased the in vivo corrosion resistance of pure Mg, but also avoided the depositions of Ca and P in the surrounding tissues, meaning that pure magnesium should be biosafe when contacting with muscle tissues,

稀土盐Er(NO_(3))_(3)掺杂对纯镁微弧氧化膜层耐磨性的影响

针对纯镁耐磨性较差这一问题,通过微弧氧化(MAO)技术在Na2SiO_(3)-C10H14N2Na2O8电解液中对纯镁进行表面改性处理,旨在提高镁的耐磨性。在电解液中添加不同量的稀土盐Er(NO_(3))_(3),研究Er(NO_(3))_(3)添加量对纯镁微弧氧化膜层的相组成、微观结构、显微硬度、临界载荷以及摩擦系数的影响。结果表明,电解液中未添加Er(NO_(3))_(3)时,膜层中主要有Mg、MgO、Mg_(2)SiO_(3)和MgF_(2)相;电解液中添加Er(NO_(3))_(3)后,膜层中检测到Er_(2)O_(3)相。电解液中添加稀土盐Er(NO_(3))_(3)后,膜层表面的孔洞直径减小,当稀土盐Er(NO_(3))_(3)的添加量超过2.85 g/L时,膜层表面出现明显的裂纹。在电解液中添加稀土盐Er(NO_(3))_(3)后,经MAO处理得到膜层的显微硬度均高于未添加稀土盐Er(NO_(3))_(3),当稀土盐Er(NO_(3))_(3)的添加量为2.85 g/L时,膜层的显微硬度值最大,约为185.8±7.1 HV。膜层的临界载荷及摩擦系数随稀土盐Er(NO_(3))_(3)添加量的增加呈现先增加后减小的趋势,在稀土盐Er(NO_(3))_(3)的添加量为2.85 g/L时,膜层的临界载荷及摩擦系数分别约为12.2±0.5 N和0.15。

Difference in formation of plasma electrolytic oxidation coatings on MgLi alloy in comparison with pure Mg

In order to study the substrate lattice structure(Li addition)on the growth of plasma electrolytic oxidation(PEO)coatings,Mg Li alloy(11.36 wt.%of Li,cubic)and pure Mg(hexagonal)were treated under a pulsed direct PEO mode in a phosphate electrolyte for different periods of time.The results revealed that the presence of Li and Li-rich phases in the cubic Mg alloy seems to be essential for the treatment result rather than the original lattice structure.A modified discharge behavior of Mg Li alloy finally led to a different microstructure of the coating.The unstable coatings of Mg Li alloy tended to dissolve rapidly though shared the similar composition to that of pure Mg.Li was incorporated only in the primary conversion products at the interface of coating/Mg Li.In spite of the advanced efficiency of energy input during processing,the more porous and thinner PEO coatings on the Mg Li alloy were less resistant to abrasion and corrosion.

Mechanical properties and damping capacities of magnesium alloys processed by equal channel angular extrusion(ECAE)

Equal channel angular extrusion (ECAE) was applied to commercial pure magnesium and AZ91D alloy. Microstructures of these magnesium alloys before and after ECAE process were observed by optical microscopy (OM). The ultimate tensile strength of pure magnesium and AZ91D alloy processed by ECAE is about 130 and 260MPa, respectively, and it is much higher than that of the as cast alloys. The elongation of them is increased from about 2% to 8%. The strain amplitude dependence damping capacities of these magnesium alloys were investigated by dynamic mechanical analyzer (DMA). ECAE process largely decreases the damping capacities of pure magnesium from 0.033 to about 0.012 (ε=1×10 -4), but does not show obvious influence on that of AZ91D alloy, which is about 0.0015.

电解液配方对纯镁微弧氧化膜层耐蚀性的影响

基于单纯形重心设计改变Na_(2)SiO_(3)、NaOH、KF和NaAlO_(2)四种组分的搭配,在纯镁基体上制备微弧氧化膜层,研究了电解液各组分及其搭配对膜层耐蚀性能的影响。结果表明,拟合得到的回归方程的显著性较好,预测精度高。通过标准化回归系数及帕累托分析可知,KF对膜层点滴及电化学耐蚀性的影响均较大。由响应面分析可知,KF有助于膜层点滴耐蚀性的提高,但高浓度的KF反而不利于电化学耐蚀性的提升。主盐Na_(2)SiO_(3)和NaAlO_(2)可以明显提高膜层的电化学耐蚀性。膜层点滴耐蚀性与电化学耐蚀性的腐蚀机制不同是导致电解质对二者的影响有所区别的根本原因。

预置初始孪晶对ECAP变形纯镁组织和性能的影响

对预置孪晶后的纯镁进行等通道挤压(ECAP),利用光学显微镜、电子万能试验机研究1、2、4道次后组织和力学性能的变化。结果表明在250℃等通道挤压下,预压缩5%的试样比原始试样具有更细的晶粒。2道次挤压后,预孪晶的样品相较于没有预压缩的样品动态再结晶晶粒更多。4道次挤压后晶粒尺寸变得更加均匀。ECAP和预孪晶均能提高纯镁的伸长率。预孪晶4道次挤压后样品的伸长率比原始样品挤压的伸长率提高较大,说明了孪晶在纯镁ECAP变形中起着重要的作用。

纯镁的生物腐蚀研究

镁及其合金作为生物医用材料具有明显的优势,可以利用其耐蚀性差的特点,发展新型医用可降解镁金属材料.本文选择纯镁为主要研究对象,从杂质含量、加工处理状态等方面研究了两种纯镁在生理盐水中的腐蚀规律,表明降低纯镁中杂质元素的含量和细化晶粒可以提高纯镁在生理盐水中的开路腐蚀电位,减缓腐蚀速率.纯镁的腐蚀速率可以通过调整杂质含量、晶粒细化和固溶处理等方法进行控制,适宜发展成为一类新型的医用可降解金属材料.

纯镁在模拟体液中的腐蚀机理

考察纯镁浸泡于模拟体液（SBF）中所发生的化学和物理过程，实验材料为扩散退火态，浸泡时间3-21d。结果发现，镁的腐蚀速率随时间增加而降低，同时溶液pH递增；裂纹和腐蚀坑是材料损伤的主要形貌特征，而MgCl2的局部富积是形成腐蚀坑的重要原因；随着浸泡时间延长，Mg（OH）2沉积于试样表面并逐步增长，成为Ca、P在Mg表面沉积的屏障，因此抑制Mg（OH）2的形成和生长是诱导磷酸钙陶瓷在Mg表面沉积的必要条件。

纯镁基复合材料的阻尼性能

制备了以纯镁为基体、以混杂碳化硅颗粒和硅酸铝短纤维为增强物的一类特殊复合材料，研究了其阻尼性能，发现镁基复合材料的强度优于纯镁，但阻尼性能却降低了，并随增强物含量增加，这种下降越大。镁基复合材料的阻尼性能与其状态关系密切，退火处理和热循环处理提高了复合材料的阻尼性能。

共晶合金中间层连接镁/铝异种金属的界面组织及结合强度研究

采用高温加压,中间加镁铝合金粉末或镁锌合金粉末连接剂的方法,分别在450及360℃温度条件下以不同的压强及保温时间,对纯镁和纯铝进行连接。利用扫描电子显微镜(SEM,配备EDS)对所制备的镁铝连接件进行了显微组织结构观察,通过弯曲试验测试了连接件的结合强度。结果表明:高温加压处理,可成功实现镁铝的连接;压强升高,连接件的结合强度增大;保温时间对结合强度的影响与连接剂有关。

表面改性纯镁的细胞毒性和溶血率

介绍了处理前后纯镁细胞毒性和溶血率试验的结果。试验结果表明,小鼠骨髓细胞与纯镁试样直接接触的细胞毒性实验中,纯镁没有对小鼠骨髓细胞的增殖产生明显的毒副作用;但未处理的纯镁试样出现了严重的溶血现象。经过热-有机表面改性后,纯镁试样的溶血率在生物材料允许的<5%的范围之内。本阶段试验提示,经表面改性后的纯镁可望用作生物材料。