Cerium chemical conversion coating on a novel Mg-Li alloy

A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO₂ in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.     

Corrosion behavior of amorphous/nanocrystalline Al-Cr-Fe film deposited by double glow plasmas technique

In order to improve the corrosion resistance of AZ31 magnesium alloy, the amorphous/nanocrystal Al-Cr-Fe film has been successfully prepared on AZ31 magnesium alloy by double glow plasma technology. The amorphous/nanocrystalline consists of two different regions, i.e., an amorphous layer on outmost surface and an underlying lamellar nanocrystalline layer with a grain size of less than 10 nm. The corrosion behavior of amorphous/nanocrystalline Al-Cr-Fe film in 3.5% NaCl solution is investigated using an electrochemical polarization measurement. Compared with the AZ31 magnesium alloy, the amorphous/nanocrystalline Al-Cr-Fe film exhibits more positive corrosion potentials and lower corrosion current densities than that of AZ31 magnesium alloy. XPS measurement reveals that the passive film formed on the Al-Cr-Fe film after the anodic polarization tests is strongly enriched in Cr₂O₃, Fe₂O₃ and Al₂O₃ at outer surface of the film and in the inner layer consists of Cr₂O₃, FeO and Al₂O₃. Supported by the National Natural Science Foundation of China (Grant Nos. 50571045 and 50704022) and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2007591)     

Ce改性AZ91的微弧氧化膜制备及其耐蚀性能

利用交流恒压微弧氧化技术, 通过Ce改性镁合金基体制备高耐蚀微弧氧化膜. 在100、120和 140 V的外加电压下, 对3种试样: AZ91, 质量分数w(Ce) 分别为0.92%和1.80%改性的AZ91微弧氧化过程、微观结构和组成及氧化膜的耐蚀性能进行研究. 应用电子扫描显微镜(SEM), 电子能谱（EDS）和X射线衍射（XRD）等表征氧化膜的微观结构和化学组成. 利用稳态极化曲线和电化学阻抗谱（EIS）测试了氧化膜在质量分数w(NaCl)为3.5%的溶液中的腐蚀过程. 实验结果表明氧化膜成膜过程可以分为3个阶段; 氧化膜主要由MgO组成, 镁合金中的稀土元素Ce促进成膜过程, 增加膜层的致密性; 稀土改性后镁合金氧化膜的耐蚀性比镁合金基体提高4个数量级, 腐蚀电流密度低至10^-8 A/cm2．     

表面活性剂对镁合金基体上的非铬化镀镍涂层的腐蚀特性的作用

在镁合金AZ91D化学沉积了镍涂层,研究了非铬化预处理及表面活性物质对涂层腐蚀特性的影响。通过盐水试验(1mol/L HCl)和电化学极化试验(3.5%NaCl)检测了腐蚀性能。试验表明:化镀镍溶液中添加的表面活性剂可提高镁合金镍涂层上的抗腐蚀能力。此外,表面平整均匀的纳米和非晶相涂层提高了其抗腐蚀能力。极化试验表明,其腐蚀电位向正方转移,且腐蚀电流密度减低。浸泡试验和电化学极化试验都表明阳离子表面活化剂具有更好的提高抗腐蚀性能的作用。     

Localized electrochemical impedance spectroscopy study on the corrosion behavior of Fe-Cr alloy in the solution with Cl− and SO4 2−

The corrosion behaviors of Fe-Cr alloy under three different pH values solutions with Cl- and SO42- were investigated by localized electrochemical impedance spectroscopy (LEIS) measurements and the corrosion products were analyzed by laser Raman spectrometry. The results show that the high corrosion resistance of Fe-Cr Alloy is attributed to a passive film which is formed more easily when the alloy contains a large quantity of Cr element. However, its corrosion resistance varies in the solutions with different pH values, especially in the initial corrosion. The average impedance values in neutral and alkaline solution are much higher than that in acidic solution because the passive film is more likely to dissolve in the acidic condition. Moreover, the destructive effect of Cl- and SO42+ ions on the passive film is also demonstrated in corrosion process through the change of the impedance value with the steeping time.     

磁控溅射TiCN薄膜对Al-Cu-Mg-Ag合金组织与性能的影响

基于正交试验设计，在铝合金表面磁控溅射沉积TiCN薄膜，采用盐雾腐蚀、电化学腐蚀、硬度测试等探究磁控溅射工艺参数（钛靶功率、碳靶功率、氮氩比）对Al-Cu-Mg-Ag合金硬度与抗腐蚀性能的影响规律，并结合扫描电镜（SEM）、X射线衍射（XRD）等对其机理进行探讨。结果表明：磁控溅射工艺参数对合金的膜层硬度、盐雾最大腐蚀深度、腐蚀电流密度、膜基结合力的影响顺序分别为：氮氩比>C靶功率>Ti靶功率；C靶功率>氮氩比>Ti靶功率；C靶功率>氮氩比>Ti靶功率；Ti靶功率>C靶功率=氮氩比。C靶功率200 W、Ti靶功率100 W、氮氩比为1：40时，可以获得耐蚀性、硬度和膜基结合力综合性能优良的TiCN膜层。     

Preparation and electrochemical properties of Pb-0.3wt%Ag/Pb-WC composite inert anodes

We prepared Pb-0.3wt%Ag/Pb-WC(WC stands for tungsten carbide,the same below) composite inert anodes by double-pulse electrodeposition on the surface of Pb-0.3wt%Ag substrates,and investigated the electrochemical properties of the composite inert anodes,which were obtained under different forward pulse average current densities from 2 A/dm~2 to 5 A/dm~2 and WC concentrations from 0 g/L to 40 g/L in bath.The kinetic parameters of oxygen evolution,corrosion potential and corrosion current of the composite inert anodes were obtained in a synthetic zinc electrowinning electrolyte of 50 g/L Zn~(2+) and 150 g/L H_2SO_4 at 35 ℃,by measuring the anodic polarization curves,Tafel polarization curves and cyclic voltammetry curves.The results show that Pb-0.3wt% Ag/Pb-WC composite inert anodes obtained under forward pulse average current density of 3 A/dm~2 and WC concentration of 30 g/L in an original acid plating bath,possess higher electrocatalytic activity of oxygen evolution,lower overpotential of oxygen evolution,better reversibility of electrode reaction and corrosion resistance in [ZnSO_4+H_2SO_4] solution.The overpotential of oxygen evolution of the composite inert anode is 0.926 V under 500 A/m~2 in [ZnSO_4+H_2SO_4] solution,and 245 mV lower than that of Pb-1% Ag alloy;the corrosion current of the composite inert anode is 0.95×10~(-4)A which is distinctly lower than that of Pb-1%Ag alloy,showing the excellent corrosion resistance.     

NaCl 溶液中回收AZ31 镁合金的腐蚀和电化学特性

利用熔炼工艺,将回收镁合金型材(RMA)进行了制备。在回收过程中,添加适量的Al、MnCl_2,最终得到合金AZ31,其中各元素质量分数如下:Al 3.31%、Zn 0.82%、Mn 0.27%、Fe 0.002%、Cu 0.004%、Ni 0.000 7%,剩余为Mg。研究了RMA的结构、在NaCl溶液中的腐蚀和电化学特性,并与商业化镁合金(CMA)进行了对比。X射线衍射仪和金相显微镜表明, RMA和CMA主要由镁基底组成,另外还有少量的Mg_(17)Al_(12)第二相。在NaCl溶液中进行的腐蚀试验和电化学特性研究表明, RMA抗腐蚀特性差于CMA,这可能与RMA中有更多的第二相有关。将两种合金作为镁电池原型器件的负极材料,进行放电性能测试。结果表明, RMA的放电时间和放电容量优于CMA。当NaCl电解质溶液浓度从0.6 mol/L增加至0.9 mol/L时,两种合金材料的放电时间和放电容量都得到了增加。     

Growth characterization of anodic film on AZ91D magnesium alloy in an electrolyte of Na2SiO3 and KF

Anodization of AZ91D magnesium alloy in the electrolyte solution of 0.5 mol/L of sodium silicate and 1.0 mol/L of potassium fluoride was investigated. The anodic films were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The corrosion resistance of the various anodized alloys was evaluated by a fast corrosion test using the solution of hydrochloric acid and potassium dichromate. The results showed that the addition of KF resulted in the presence of NaF in the anodic film. The thickness of the anodic film formed under a constant current density of 20 mA/cm2 for 16 min at 60℃ exceeded 100 μm. The growth of the anodic film could be divided into three stages based on the anodizing time; the growth rate was much faster during stage Ⅱ than in stages Ⅰ and Ⅲ. The anodic film exhibited the highest corrosion resistance for the AZ91 alloy,which is attributed to the fact that the anodization was maintained until the end of stage Ⅱ.     

The influence of Ce(NO3)3·6H2O on the inhibitive effect of Ca(NO2)2 in simulated concrete pore solution

The effects of cerium nitrite on corrosion behaviors of carbon steel in simulated concrete pore solutions were studied with the methods of linear polarization, electrochemical impedance spectroscopy and surface analysis. In pore solutions in the presence of Ce(NO3)3?6H2O, the corrosion potential, polarization resistance and impedance of carbon steel obviously increased in contrast to the situation in the absence of cerium salts. The pore solution with [NO2-] / [Cl-] = 0.3 and 0.1% Ce(NO3)3?6H2O, carbon steel shows better corrosion resistance than that in the pore solution with [NO2-] / [Cl-] = 0.6, which indicates that a small amount of Ce(NO3)3?6H2O in pore solutions can effectively promote passivation of the steel and reduce the threshold [NO2-] / [Cl-] ratio for corrosion control. The surface layer formed in cerium salt containing pore solutions is more compact and smooth and 1.36%Ce is examined on the sample surface. The addition of 0.1% Ce(NO3)3?6H2O in pore solutions can decrease the corrosion rate of steel in pore solutions and has little influence on pH change of the solutions. However, more cerium nitrate addition above 0.1% may result in pH decrease of the solution.     

Formation mechanism of an aluminium-based chemical conversion coating on AZ91D magnesium alloy

An environmentally clean aluminium-based conversion coating on AZ91D magnesium alloy was studied in aluminium nitrate solutions. The morphology, composition, structure, and formation mechanism of the coating were investigated in detail using scanning electron microscopy/energy dispersion spectrometry, X-ray diffraction, transmission electron microscopy, and electrochemical corrosion tests. The results show that the conversion coating is composed of magnesium, aluminium, and oxygen, and shows an amorphous st...     

Cerium Chemical Conversion Coating on a Novel Mg-Li Alloy

A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a m...     

钨酸钠的缓蚀作用及其复配协同效应研究

用开路电位测试、Tafel极化曲线测试和失重法研究了模拟海水中钨酸钠对AZ31镁合金的缓蚀作用.研究结果表明,当钨酸钠浓度为0.03 mol/L时具有较好的缓蚀效果,缓蚀效率为60％.钨酸钠通过与镁合金腐蚀产物共同成膜而起到保护作用.将钨酸钠与有机型缓蚀剂六次甲基四胺进行复配,其缓蚀性能仍主要由钨酸钠决定,缓蚀性能没有显著提升.     

Corrosion protection of AM50 magnesium alloy by Nafion/DMSO organic coatings

The effectiveness of the corrosion protection of Nafion/Dimethysulfoxid （DMSO） organic coatings for AM50 magnesium alloy prepared by simple immersion and heat treatment was investigated. Its corrosion resistance and morphologies of the Nafion/DMSO organic coatings were studied by electrochemical corrosion testing and optical microscopy. The results show that Nafion/DMSO organic coatings can improve the corrosion resistance of AM50 magnesium alloy effectively. Also, the corrosion resistance increases with the surface density of the organic coatings.     

Technology of black coloring for stainless steel by electrochemical method

The technology of black coloring for stainless steel by electrochemical method was studied. The optimum bath compositions and operating conditions were obtained as follows. 40 - 50 g/L K2Cr2O7, 15 - 20 g/L MnSO4, 15 -20 g/L （NH4）2SO4, 20 -40 g/L H3BO3, 20 -30 g/L additive A, 2 g/L （NH4）6Mo7O24 ; time 9 -20 min; temperature 15 - 30 ℃ ; potential 3 V and current density 1 - 2 mA/cm^2. The effects of the compositions of the bath on the quality of black colored film were discussed. The influences of passivation process on the black coloring velocity and performances of black colored film layer were investigated. The results show that the passivation process can improve the corrosion resistance and the stability to bear color-change; （NH4）2 SO4 can control the black coloring velocity and prolong black coloring bath life remarkably; and additive A can improve the evenness and compactness of black colored film layer. The results of scanning electron microscopy and energy dispersive spectra show that the microstructure is of cylindrical lump, the filling process can decrease the crackles, and the main elements of black colored film are Fe, Cr, Mn and Ni.     

Corrosion mechanism and corrosion model of Mg-Y alloy in NaCl solution

Corrosion of Mg–Y alloy was studied using electrochemical evaluations, immersion tests and SEM observations. Corrosion mechanisms of Mg-(0.25 and 2.5) Y alloy and Mg-(5, 8, and 15) Y alloy were uniform corrosion and pitting corrosion respectively, and the content of Mg_(24)Y_5 phases determined its effect acting as cathode to accelerate the corrosion or corrosion barrier to inhibit the corrosion. Corrosion resistance of Mg-(0.25, 2.5, 5, 8, and 15) Y alloys was as follows: Rt(Mg-0.25Y) Rt(Mg-8Y) Rt(Mg-15Y) Rt(Mg-5Y) Rt(Mg-2.5Y). Y could significantly improve the corrosion resistance of the Mg-Y alloy, but the excess of Y deteriorated the corrosion resistance of the Mg-Y alloy. The optimum content of Y in the studied alloys was 2.5%.     

Microstructure and corrosion resistance of modified AZ31 magnesium alloy using microarc oxidation combined with electrophoresis process

A top electrophoresis coating was deposited on the surface microarc oxidation (MAO) modified ceramic coating on AZ31 magnesium alloy. Microstructure and corrosion resistance of this composite coating were studied by SEM, electrochemical potentiodynamic polarization, and acid corrosion test. The results showed that the composite coating with a top electrophoresis coating on the surface of ceramic coating exhibited a better corrosion resistance compared with the coating formed by chemical conversion film combined with electrophoresis process. Corrosive ions could permeate into the substrate with corrosion time, and the composite coating was firstly destroyed around the scratch. The formation of composite coating with a higher adhesive force due to the porosity of the ceramic coating contributed to the improved corrosion resistance property.     

锌合金表面稀土转化膜的组成与性能研究

通过在铈盐溶液中进行化学转化处理在电池锌合金表面获得了稀土转化膜，测量了膜的结合强度、在氯化钠溶液中的极化曲线，极化电阻和腐蚀速率，利用XPS、XRD和SEM对稀土转化膜的化学成分和组织结构进行了分析，结果表明，稀土转化膜的形成使锌合金的耐蚀性大大提高，已达到普通铬酸盐转化膜的耐蚀水平，稀土转化膜主要由CeO2、Ce2O3、ZnO等氧化物组成。     

Alkaline treatment kinetics of calcium phosphate by piezoelectric quartz crystal impedance

Calcium phosphate film was prepared by electrochemical deposition technology. Subsequently, the alkaline treatment process of calcium phosphate film in 0.1 mol/L NaOH solution was monitored on real time by the piezoelectric quartz crystal impedance (PQCI) technique. The variations of morphology and composition for the alkaline treatment products were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. The dynamic variations of calcium phosphate can be characterized by the change of equivalent circuit parameters. The results show that the forming process of hydroxyapatite (HA) is composed of three stages: (1) acidic calcium phosphate dissolution; (2) phase transformation; and (3) HA formation. Furthermore, the correlative kinetic equations and parameters are obtained by fitting the static capacitance (C _s)—time curves. Foundation item: Project(2005CB623901) supported by the Major State Basic Research and Development Program of China     

Electrochemical behavior of Mg-Al-Pb alloy in 3.5% NaCl solution

An investigation on electrochemical behavior of Mg-5%Pb alloy, Mg-6%Al alloy and Mg-6%Al-5%Pb alloy(mass fraction) in 3.5% Na Cl(mass fraction) solution was conducted using electrochemical measurements and corroded morphology observation, in which solid solution and the as-aged state of each alloy were compared to discuss the influence mechanism of lead and aluminium on the electrochemical properties of alloys. The X-ray diffraction(XRD) analysis was performed to make microstructure characterization. The electrochemical results indicate that the corrosion of Mg-5%Pb alloy is predominated by homogeneous pitting and dissolution of PbCl_2 film due to Cl ions attack, while corrosion crevice propagates along grain boundaries in solid solution of Mg-6%Al alloy and the micro galvanic corrosion also plays vital role in Mg_(17)Al_(12) phase containing experimental alloys. The co-existence of lead and aluminium in magnesium alloy increases corrosion current density and electrochemical activity as well. The comparison between solid solution and the as-aged state demonstrates that Mg_2 Pb and Mg_(17)Al_(12) somewhat increase corrosion resistance but lighten anodic polarization by facilitating corrosion product flaking off.