Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： The microstructure and corrosion morphology of extruded alloys Mg-xZn-yGd (x=1~3, y=0~3) were observed by optical microscopy (OM), scanning electron microscopy (SEM). Results show that after extrusion the microstructure of the alloys is obviously refined and further refined by Gd addition, i.e. the average grain size decreases from (30±3) μm for Mg-3Zn to (10±2) μm for Mg-3Zn-3Gd. The dynamic recrystallization occurs during the extrusion, while the second phase particles tend to distribute as belts along the extrusion direction. Mg-xZn-yGd alloy is sensitive to pitting corrosion in the Hank's solution. Among others the corrosion of Mg-3Zn-2Gd is the fastest, while that of Mg-3Zn is the slowest. After solid solution treatment, the corrosion rate of Mg-3Zn-2Gd and Mg-3Zn-3Gd decreases from (0.605±0.025) and (0.352±0.021) mg/(cm2·h) to (0.085±0.010) and (0.167±0.020) mg/(cm2·h) respectively. With increasing Zn content the corrosion current density decreases and the high-frequency capacitance increases gradually; with the increase of Gd content, the corrosion current density and high-frequency capacitance of the alloys rise firstly and then reduce gradually. Mg-3Zn alloy exhibits aminimum corrosion current density (8.65×10-3 mA/cm2)and a maximum Faraday resistance Rt (3312 Ω).
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：Mg在室温下的强度和塑性较差 其根源之一在于Mg的形变孪晶在极低的应力下即可形核和扩展, 而且研究表明目前应用于Mg合金的时效强化法通常无法显著抑制 形变孪晶. 尽管对>Mg及其合金的力学性能至关重要, 迄今为止, 对形变孪晶的形核和扩展的机制仍存在很大的争议. 本综述论文首先回顾了有关形变孪晶的定义以及孪晶机制的研究历史, 然后着重介绍了最新的基于原位透射电镜的研究成果: 即Mg的形变孪晶迥异于孪晶的经典定义, 它事实上是一种新的室温变形机制, 即塑性的产生可以通过局部的晶胞重构来完成, 而不需要孪晶位错的参与; 由晶胞重构机制所产生的界面为界面(BP界面), 而且该界面在三维空间呈现梯田状的不规则形貌. 晶胞重构机制迥异于基于位错的孪晶变形机制, 因此基于对该机制进行抑制的设计思路可能是开发未来高强韧Mg合金的关键.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To reduce the weight of car body, Al-Mg-Si-Cu alloys have been used to produce outer body panels of automobiles due to their relatively good formability in the solution treated condition and high strength in the age hardened condition. However, their formability is significantly poor compared to that of steels, which are the major drawbacks to wide-scale application of aluminum in the automotive industry. The microstructural characteristics developed during recrystallization, most notably grain size and crystallographic texture, play a dominant role in controlling the mechanical properties and formability of sheet in the T4 condition. In this work, the effect of particles with different sizes on the mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloys was studied through tensile test, OM, SEM, TEM and EBSD measurement. The results reveal that with increase of solute concentration, the average plastic strain ratio rˉ, yield strength and ultimate tensile strength increase, but the elongation decreases and with different extents in the three directions. In addition, the number of observed particles with different sizes in the alloy matrix such as Mg2Si, Al15Mn3Si2 and a-Al(Fe, Mn)Si phases also increases. When the size and concentration of the se particles are controlled appropriately, lots of finer recrystallized grains can form during solution treatment due to the particle stimulated nucleation (PSN) effect of coarse particles and pinning effect of finer particles. The main texture components include CubeND18, Goss{011}<100>, P{011}<122> and Cu{112}<111> for the alloy with fine-grained structure. At last, according to the relationship among alloy composition, thermomechanical processing and microstructure, the model of nucleation and growth of recrystallized grains affected by the particles with different sizes was also proposed.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Since electrochemical impedance spectroscopy, polarization curve and hydrogen collection were the main technologies for corrosion research of Mg and its alloy. However, those methods only provide the mean information of entire surface of corrosion electrode. In this work, H2 evolution and active sites of pure Mg from localized sites (point, line and surface) in NaCl and Na2SO4 solution based on generation/collection and feedback modes of scanning electrochemical microscopy (SECM) were studied. The results indicate that both cathodic and anodic polarization are in favor of H2 evolution in NaCl and Na2SO4 solution, which is well in line with the negative difference effect by the classical H2 collection, but the SECM results show that the H2 evolution in localized sites is not uniform and stable. The H2 evolution rate increases with NaCl concentration increasing, which is opposite in Na2SO4 solution. The higher NaCl concentration, anodic polarization and lower pH value accelerate the formation of active sites on pure Mg surface.
Subjects: Digital Publishing >> New Media submitted time 2023-10-08 Cooperative journals: 《中国传媒科技》
Abstract：MG动画是近年来出现的新型信息可视化设计方式，它融合平面设计、动画设计等多种表现形式，拥有独特的设计语言和丰富的包容性，表现出较高的传播效率。MG动画在当前新媒体时代凭借简约化、扁平化、制作快捷化等优势占据传播市场一席之地。本文旨在分析MG动画在新媒体时代的传播优点及当前面临的传播困境，尝试提出解决策略，期望推动MG动画在新媒体环境中的高效传播和可持续发展。
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： The microstructure of Mg-10Gd-2.5Nd-0.5Zr (mass fraction, %) alloy after solid solution and aging treatment were characterized by means of OM, XRD, TEM and SEM. The average corrosion rate in 3.5% (mass fraction) NaCl solution was measured for 0~96 h. The results show that the microstructure of the as-cast alloy is composed of α-Mg matrix and coarse dentritic crystal β phase. After heat treatment, the β phase has experienced a course of dissolution and then precipitation, while the discontinued net-like β-phase transformed into cuboid-shaped particles due to the solution and aging treatment. The heat treatments are beneficial to the corrosion resistant of the alloy in 3.5% NaCl solution, while its corrosion rate was 0.74 mg·cm-2·d-1 for the as-cast, 0.41 mg·cm-2·d-1 for the solid solution treated and 0.35 mg·cm-2·d-1 for the aging treated ones respectively. The corrosion products of the alloy is mainly composed of Mg(OH)2.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： A series of micro-arc oxidation (MAO) films were prepared on Mg-Mn-RE alloy by an alternating current with symmetric voltage in different alkaline solutions containing aluminate, phosphate or silicate and then the MAO films were characterized by SEM and XRD. The corrosion resistance of MAO films was evaluated by EIS potentiodynamic polarization. The results indicated that the MAO films prepared in phosphate or silicate systems have low thickness with obvious cracks, leading to poor corrosion resistance. In the contrast, the MAO films prepared in aluminate system exhibit the better corrosion resistance due to the compactness and higher surface quality, which shows a good prospect for the application.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To reduce the weight of car body, Al-Mg-Si-Cu alloys have been widely used to produce outer body panels of automobiles due to their favorable high strength-to-weight ratio, corrosion resistance, weldability and good formability. Al- Mg- Si- Cu alloys belong to age- hardenable aluminium alloys, whose strength derives mainly from the matrix precipitation during aging treatments. However, their bake hardening response still need to be further improved to enhance their dent resistance. A novel thermo-mechanical treatment consisting of conventional pre-aging, pre-deformation and re-aging was developed to enhance the tensile properties and bake hardening increment of Al-Mg-Si-Cu alloys. In this work, the effect of pre-deformation on the precipitation behaviors of Al-Mg-Si-Cu alloy was studied by DSC, mechanical property measurement and TEM. The results show that, the GPzone dissolution rate decreases with increasing pre-deformation during the slow heating up process for the pre-aged alloy, the corresponding activation energies of 0, 5% and 15% pre-deformed alloy calculated by Avrami-Johnson-Mehl method are 137.1, 189.5 and 141.3 kJ/mol, respectively. If the pre-deformed alloys are directly bake hardened at 185 ℃ for 20 min, precipitation and bake hardening increment can be greatly improved by pre-deformation (the highest bake hardening increment is 160 MPa), but the bake hardening increment rate gradually decreases if the pre- deformation is above 10%. In addition, the GP zone dissolution rates of pre- deformed alloys after bake hardening treatment are much lower when the heat treatment temperatures are below one certain value, but if the treatment temperatures above it, the corresponding GP zone dissolution rates are higher than that of alloy without pre-deformation, finally, the activation energy changes from high value to low value even can be observed in the ln[(dY/dT)f/f(Y)]-1/T curve. For the β″ precipitation in the alloys, with increasing pre-deformation, its activation energy gradually decreases, corresponding gradually increase of precipitation rate.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：采用DSC、力学性能测试及TEM研究了预变形对Al-Mg-Si-Cu合金析出行为的影响。结果表明，预时效态合金在慢速率升温过程中，GP区溶解速率均随预变形量的增加而降低，利用Avrami-Johnson-Mehl方法求得经0%、5%和15%预变形后合金的GP区溶解激活能分别为137.1KJ/mol、189.5KJ/mol和141.3KJ/mol；若合金经不同预变形后直接进行185℃/20min烤漆硬化，预变形可有效促进沉淀相析出，提高烤漆硬化增量，最高达160MPa，不过预变形量大于10%时合金烤漆硬化增幅减缓；此外，经预变形处理后烤漆态合金的GP区溶解速率在一定温度下均较低，但高于某一温度后，相应的GP区溶解速率均高于未经预变形处理的，最终获得的ln[(dY/dT)φ/f(Y)]-1/T曲线甚至会出现高激活能向低激活能转化现象；不过随预变形量增加，β〃相析出激活能不断降低，析出速率不断增加，相应的TEM组织观察结果与此非常吻合。
Subjects: Nuclear Science and Technology >> Nuclear Materials and Techniques submitted time 2023-06-18 Cooperative journals: 《Nuclear Science and Techniques》
Abstract： The chlorination of rare earth oxides by MgCl2 was investigated in the molten chlorides. To reduce the solvent salt volatility, the LiCl-NaCl mixture was selected as a solvent by comparing the mass loss of the LiCl-NaCl with LiCl-KCl melts after the addition of MgCl2 in the temperature range of 873 K to 1073 K. The dissolution behavior of La2O3 was investigated in the LiCl-NaCl-MgCl2 melts by XRD measurements and ICP-AES analysis of the melts, which indicated that La2O3 was chlorinated by MgCl2 to produce LaCl3. The reduction peak of La(III) in the LiCl-NaCl-MgCl2-La2O3 melts was observed from cyclic voltammogram and square wave voltammogram. The Mg-La alloy obtained by galvanostatic electrolysis in the LiCl-NaCl-MgCl2-La2O3 melts was characterized by XRD and SEM-EDS, indicating that the Mg-La alloy consisted of Mg and La2Mg17 phases.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： The effect of extrusion temperature on the tensile properties and fracture toughness of an Al-Zn-Mg alloy was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile tests and Kahn tear tests. The results showed that after extrusion the alloy possesses a surface layer composed of fine equiaxed grains with higher toughness in the L-T orientation than that of its center layer, which composed of fiber-like texture and recrystallized grains, while the tensile strength of the center layer is higher than that of the surface layer. When the extrusion temperature increases from 440-450℃ to 480-490℃, the dynamic recrystallization becomes more serious, and the tensile properties and fracture toughness become lower and higher respectively. After aging the precipitates in grains become smaller and the precipitates at grain boundaries are coarsening and discontinuous. Taking the central layer for example, the volume fraction of recrystallized grains increases from 14.8% to 52.3%, correspondingly σ 0.2 increases from 280 MPa to 314 MPa, while UIE decrease from 229 N·mm-1 to 204 N·mm-1.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The as-extruded Mg-1Zn-1Ca (mass fraction, %) alloys was fabricated successively by alloying, homogenization treatment and hot extrusion. The corrosion behavior of the alloy in simulated body fluid (SBF) solution was evaluated by electrochemical test and immersion test. The microstructure and morphology of corrosion product were observed by OM and SEM. Compositions of corrosion layer and different phases were investigated by EDS analysis. Fourier Transform infrared spectroscopy was also conducted to identify the functional groups in the corrosion products and XRD was also used to determine the phase constitutes of the corrosion products. The results show that Mg-1Zn-1Ca alloy consists of three phases, i.e. a-Mg, Mg2Ca and Ca2Mg6Zn3. After immersion in SBF solution for 72 h, the corrosion products is composed of HA (Ca10(OH)2(PO4)6), CaCO3, MgCl2 and Mg(OH)2. During the stage of immersion, the high active Mg2Ca phases act as the anode and corrode first, so they protect the around a-Mg substrate; the Ca2Mg6Zn3 phases are the lowest active, so they accelerate the corrosion of around α-Mg substrate. The corrosion resistance of as-cast Mg-1Zn-1Ca alloy are better than as-extruded alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of linear heating aging process and the Cu content on the performance and the formation of precipitates of Al-Zn-Mg-(Cu) alloy was investigated by means of differential scanning calorimeter (DSC), hardness tester, transmission electron microscopy(TEM) and three- dimensional atom probe (3DAP). The results show that with the increase of the aging temperature the hardness rises firstly and then decreases after reaching a peak. After aging at every selected temperature of the linear heating aging treatment process, all the relevant hardness of the Al-Zn-Mg-Cu alloy is higher than that of the Al-Zn-Mg alloy. After aging at peak point by linear heating, the main precipitates are η' phase, while there exists small quantities of η phase and GP zone for the two alloys Al-Zn-Mg and Al-Zn-Mg-Cu. However the addition of Cu may induces certain change of the composition and morphology of the precipitates and delay their transition from metastable state to stable state.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-14 Cooperative journals: 《中国腐蚀与防护学报》
Abstract：使用高速电弧喷涂技术在Q420基体上制备了新型Zn-22Al-Mg-Re合金涂层，通过扫描电镜(SEM)、铜加速乙酸盐雾试验、电化学工作站等手段研究了其微观组织形貌、结合强度、耐蚀性能，并与纯锌、Zn15Al涂层进行了比较。试验结果表明，Zn-22Al-Mg-Re合金涂层的结合强度高、腐蚀电位低、腐蚀电流小，腐蚀产物较为稳定，呈细小致密的针状，具有良好的自封闭性，合金涂层的阴极保护能力和耐蚀性能均优于纯锌、Zn15Al涂层。
Subjects: Biology >> Biophysics submitted time 2016-05-12
Chen, Xuemin
Pu, Hua
Fang, Ying
Wang, Xiao
Zhao, Shun
Dai, Huai-En
Liu, Lin
Chen, Xuemin
Pu, Hua
Fang, Ying
Wang, Xiao
Zhao, Shun
Lin, Yajing
Gong, Weimin
Zhang, Min
Gong, Weimin
Abstract： Tetrapyrroles, including haem and chlorophyll, play vital roles for various biological processes, such as respiration and photosynthesis, and their biosynthesis is critical for virtually all organisms. In photosynthetic organisms, magnesium chelatase (MgCh) catalyses insertion of magnesium into the centre of protoporphyrin IX, the branch-point precursor for both haem and chlorophyll, leading tetrapyrrole biosynthesis into the magnesium branch1,2. This reaction needs a cooperated action of the three subunits of MgCh: the catalytic subunit ChlH and two AAA(+) subunits, ChlI and ChlD ( refs 3-5). To date, the mechanism of MgCh awaits further elucidation due to a lack of high-resolution structures, especially for the similar to 150 kDa catalytic subunit. Here we report the crystal structure of ChlH from the photosynthetic cyanobacterium Synechocystis PCC 6803, solved at 2.5 angstrom resolution. The active site is buried deeply inside the protein interior, and the surrounding residues are conserved throughout evolution. This structure helps to explain the loss of function reported for the cch and gun5 mutations of the ChlH subunit, and to provide the molecular basis of substrate channelling during the magnesium-chelating process. The structure advances our understanding of the holoenzyme of MgCh, a metal chelating enzyme other than ferrochelatase.
Peer Review Status:
Awaiting Review
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： An alloy Mg94Cu4Y2 with a large quantity of long-period stacking ordered (LPSO) phases bearing Cu and Y was designed and prepared in this paper. The microstructural transformations and the hydrogen absorption/desorption properties of the alloy were characterized during hydrogenation and dehydrogenation processes. The cast Mg94Cu4Y2 alloy consists of phases such as Mg, Mg2Cu and LPSOs with 18R or 14H type. The LPSOs decomposed at the first hydrogenation, and in situ formed highly even dispersed nanocomposite (MgH2+MgCu2+YH3). The Mg/MgH2 was the main reaction during the subsequent dehydrogenation cycles. The alloy exhibits excellent hydrogen absorption and desorption kinetics because the nano-sized and even dispersed Mg2Cu and YH2 catalyzed effectively the Mg/MgH2 reactions.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Mg-Zn-Gd base alloys possess much superiority, such as, high strength, light weight, low cost, etc., and favorable for the application in various airframe components. Two kinds of eutectic phases, such as, W(Mg3Zn3Gd2) and I(Mg3Zn6Gd), can be usually found in Mg-Zn-Gd alloy under the traditional casting conditions. The interface between W phase and a(Mg) is incoherent and thus weak. However, I phase has quasiperiodic lattice leading to a coherent interface between I phase and a(Mg). Therefore, compared with W phase, I phase is more effective to obstruct dislocations slipping and so efficiently strengthening the alloy. So, controlling the solidification path, i.e., controlling the relative amount of I phase and W phase, is critical for increasing the heat resistant of Mg-Zn-Gd magnesium alloy. In this work, the solidification path of Mg-4.58Zn-2.6Gd ternary casting alloy was investigated by experiments and numerical analysis. Experimental results showed that at lower cooling rate (≤0.75 K/s), a+W(Mg3Zn3Gd2) eutectic will be formed first, while at higher cooling rate (≥7.71 K/s), a(Mg)+I(Mg3Zn6Gd) eutectic will be formed first. A numerical model for predicting solidification path of the primary phase in multi-component alloy with considering the effects of solute diffusion in liquid phase and the cooling rate was developed. The thermodynamic data in the computation model was obtained by using the database of Thermo-Calc. The numerical results were in favorable agreement with the experimental ones. The numerical model established in this work provides a direct and easy way to predict solidification path of Mg-Zn-Gd alloy for different casting conditions. The validity of this model was further confirmed by other three different Mg-Zn-Gd alloys, i.e., Mg-3.8Zn-2.0Gd, Mg-5.5Zn-2.0Gd and Mg-5.5Zn-4Gd. It is also found that for Mg-Zn-Gd alloy, the higher Zn-content and the higher cooling rate will promote the formation of I phase. However, higher Gd-content and the lower cooling rate is favorable for the formation ofWphase.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：本文采用实验方法和数值计算方法，以Mg-4.58Zn-2.6Gd为例，研究了Mg-Zn-Gd三元铸造镁合金的自由凝固路径选择问题。不同铸型条件下的实验表明，当铸型冷却速率较小时，实验合金生成α(Mg) + W(Mg3Zn3Gd2)共晶组织；随着铸型冷却速率的增大，实验合金生成α(Mg) + I(Mg3Zn6Gd)共晶组织。建立了综合考虑合金液相扩散和冷却速率因素的多元合金初生相凝固路径计算模型。耦合热力学计算软件Thermo-Calc及其数据库获得实验合金凝固路径计算所需热力学数据，发现计算结果与实验结果吻合良好。
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The corrosion behavior of the newly developed Al-Mg alloys was investigated in terms of their alloying element and thermo-mechanical treatments by means of intergranular corrosion test, exfoliation corrosion test, scanning electron microscopy and transmission electron microscopy. The results show that, with the increase of Mg content the mass loss of the alloys in concentrated nitric acid increased, correspondingly their intergranular corrosion resistance decreases. Zn addition to the Al-Mg alloys led to the formation of Mg32(Al, Zn)49 phase at the grain boundary, which dramatically increased the intergranular corrosion resistance of the alloys. The corrosion resistance of the alloys was also modified by thermo- mechanical treatment. Both intergranular corrosion resistance and exfoliation corrosion resistance of the alloys were dramatically increased by a proper post stabilizing treatment after cold rolling reduction. The residual stress, higher dislocation density and morphology of elongated grains after cold rolling reduction can lead to more continuous precipitation at the grain boundary, thus decrease the corrosion resistance of the alloys.
Subjects: Medicine, Pharmacy >> Preclinical Medicine submitted time 2017-12-27 Cooperative journals: 《南方医科大学学报》
Abstract： Objective To explore the effects of ghrelin on learning and memory abilities and expressions of DKK-1 and β-catenin in the hippocampus of diabetic rats. Methods Sixty male SD rats were randomly assigned into 4 groups, namely the control group, diabetic group, ghrelin-treated diabetic group (DM1 group), and ghrelin- and D-lys3-GHRP-6 (a GHSR-1a receptor antagonist)-treated diabetic group (DM2 group). Diabetic rat models were established by a single intraperitoneal injection of streptozotocin (65 mg/kg). The learning and memory abilities of the rats were assessed with Morris water maze (MWM) test. The ultrastructure of the hippocampal CA1 area of the rats were observed with electron microscopy. Serum levels of DKK-1 were examined by ELISA, and the expressions of DKK-1 and β-catenin in the hippocampus were examined by quantitative real-time PCR and Western blotting. Results Compared with the control group, the diabetic rats exhibited significantly impaired learning and memory abilities (P<0.05), increased expression of DKK-1 and lowered β-catenin expression in the hippocampus (P<0.05), significant ultrastructural injuries and disordered arrangement of neurons with the nuclear pycnosis in the hippocampal CA1 area. Ghrelin treatment of the diabetic rats obviously improved their learning and memory abilities (P<0.05), reduced DKK-1 and increased β-catenin expressions (P<0.05), ameliorated ultrastructural damages in the hippocampal CA1 area and restored normal neuronal alignment with clear cell layers. Such effects of ghrelin were antagonized by treatment with D-lys3-GHRP-6 in the diabetic rats. Conclusion Ghrelin can alleviate learning and memory dysfunction in diabetic rats possibly by down-regulating the expressions of DKK-1 and activating the WNT signaling pathways.
Hits
Hits
Downloads
Comment
YES