阳极氧化AZ91D镁合金在氯化钠稀溶液中的腐蚀行为

利用盐雾实验、极化曲线扫描、电化学阻抗谱和电化学噪声技术等电化学研究方法结合扫描电镜表面观测技术对AZ91D镁合金氧化膜在1%(w)氯化钠溶液中的耐蚀性能进行了评价. 结果表明, 氧化前后的镁合金腐蚀行为发生明显改变, 如未封孔的阳极氧化膜耐中性5%氯化钠盐雾试验时间超过200 h; 氧化后的镁合金自腐蚀电位明显正移, 点蚀诱导期延长; 阳极氧化膜的高频阻抗约为裸露镁合金的数千倍, 这些变化证明阳极氧化处理使镁合金获取了十分优异的耐蚀性能. 首次利用分形维数Df的变化规律初步描述氧化后AZ91D镁合金的腐蚀过程. 可以发现随着浸泡时间的延长, Df呈现出初期快速增长, 随后出现波动, 最后稍有降低的变化过程. 这种现象对应于氧化后AZ91D 镁合金在1%氯化钠溶液中腐蚀的三个阶段.     

添加氧化铈对AZ91D镁合金表面富镁涂层的保护作用

通过Machu测试、电化学交流阻抗(EIS)和扫描电子显微镜(SEM)等方法研究了添加氧化铈对AZ91D镁合金表面富镁涂层防护性能的影响.氧化铈添加量较少(0.1%,w)时,对涂层耐蚀性无影响;添加量过多(3%)时,涂层耐蚀性降低;添加氧化铈颗粒为0.5%时,涂层的阻抗增大,涂层电容降低,对AZ91D镁合金基体的保护性能明显提高.尽管添加氧化铈不改变富镁涂层对AZ91D镁合金的保护机制,但可显著延长涂层的服役寿命.氧化铈能够降低纯镁颗粒的电化学反应活性,使镁粉腐蚀速率降低,阴极保护时间延长.添加一定量氧化铈后,也有利于涂层屏蔽性能提高,氧化铈能降低AZ91D镁合金表面阳极腐蚀电流密度,提高镁合金腐蚀电位,从而有利于富镁涂层发挥对镁合金基体的阴极保护作用.     

覆有微弧氧化涂层的AZ91D镁合金在氯化钠溶液中的极化行为

由于结构和成分的影响,覆有微弧氧化涂层的AZ91D镁合金的极化曲线有多种不同的表现形式.事实上,覆有微弧氧化涂层的AZ91D镁合金在NaCl溶液中的极化曲线行为不仅与涂层的主要组成和微观结构有关,也与极化曲线测试条件,如氯离子浓度、溶液pH值、阴极极化程度和样品的暴露面积有关,由于微弧氧化涂层的不稳定性,这些因素通过改变氧化涂层的组成和微观结构,继而影响极化曲线的形状.本文用傅里叶变换显微红外成像和对应的光学照片研究了氧化涂层的成分和结构的变化.结合物理表征,我们提出一个模型,用以阐明微弧氧化涂层组成和结构在NaCl溶液中的变化.对于浸泡在NaCl溶液中的AZ91D微弧氧化涂层,阳极溶解和阴极还原反应的速控步骤分别是传质过程和电荷转移过程.所以从极化曲线上拟合出来的腐蚀电流密度不能准确反映腐蚀速率,而且误差也难以避免.     

AZ31和AZ61镁合金在模拟海水中的腐蚀电化学行为

应用极化曲线、电化学阻抗谱方法研究了两种Mg-Al-Zn系合金——AZ31和AZ61在模拟海水中的腐蚀电化学行为.根据两种镁合金在浸泡过程中腐蚀介质pH值的变化以及扫描电子显微镜对合金微观金相组织和腐蚀形貌的观察,讨论了镁合金的腐蚀机理及合金元素Al的含量对镁合金耐蚀性能的影响.结果表明,AZ61镁合金具有比AZ31镁合金更好的耐蚀性能,其原因主要是AZ61镁合金中Al含量较高使合金的微观组织结构更有利于耐蚀性能的提高.     

镁合金表面原位生长有机膦酸盐薄膜及耐蚀行为

利用超声辅助的浸渍涂布方法,在AZ91D镁合金表面原位生长了氨基二乙酸亚甲基膦酸镁铝薄膜,其中包含具有纳米尺度的变形六边形板状颗粒。塔菲尔极化曲线、电化学阻抗谱测量表明,修饰后的AZ91D镁合金的耐腐蚀行为依赖于浸渍所用的膦酸浓度、pH值、温度及时间等。在3.5%NaCl溶液中,未修饰的AZ91D其腐蚀活化能是18.1 kJ.mol-1,而在1.5 mmol.L-1膦酸溶液中pH值分别是1.7、11.5时浸渍涂布有机膦酸盐薄膜后,AZ91D的腐蚀活化能分别是27.9、37.8 kJ.mol-1。     

XPS study of the effect of aluminium on the atmospheric corrosion of the AZ31 magnesium alloy

The surface characteristics and corrosion behaviour of the AZ31 magnesium alloy exposed to a high relative humidity (RH) atmosphere were investigated. During the first 15 days of humidity test at 98% RH and 50 °C, a significant increase of magnesium carbonate and a decrease of magnesium oxide were detected on the surface film by XPS; after this stage, increased exposure times did not produce substantial changes on the relative amounts of these compounds. The surface film of commercially pure magnesium, also examined for comparison purposes, revealed more magnesium carbonate and less magnesium oxide compared with the AZ31 alloy. Unlike the AZ31 alloy, the surface of pure Mg disclosed almost complete substitution of MgO by magnesium carbonate after 30 days of exposure time. Mass gain values of tested specimens and scanning electron microscope characterisation of corroded surfaces indicated lower corrosion susceptibility of the AZ31 alloy compared with the commercially pure Mg, suggesting superior chemical stability of the oxide/hydroxide film formed over the magnesium–aluminium alloy surface. XPS and energy dispersive X‐ray (EDX) analyses did not revealed any substantial enrichment of aluminium in the corrosion products film on the AZ31 alloy after 30 days of testing. Copyright © 2008 John Wiley & Sons, Ltd.     

镁合金化学转化膜的制备及其性能研究

在磷酸钠-磷酸二氢铵-高锰酸钾体系中对镁合金进行化学转化处理.研究了磷酸钠、磷酸二氢铵、高锰酸钾、温度、时间和添加剂对转化膜性能的影响.通过对转化膜结构、成分及性能的测试评价,得到了性能较好的化学转化溶液配方:Na3PO4为5g·L-1,NH4H2PO4为15 g· L-1,KMnO4为1g· L-1,添加剂(NH4)6 Mo7O24为0.5g·L-1.由SEM可观察到转化膜的表面成“干枯河床”状.XRD和EDS检测表明,膜层的主要成分是Mg,Al12 Mg17和无定形相,膜层表面主要有Mn,Mg,K,O和Al等元素组成.腐蚀实验和电化学测试表明,添加剂能够降低转化膜的腐蚀率,转化膜较基体的腐蚀电位正移了0.73 V,提高了镁合金的耐蚀性.     

(NaPO3)6对AZ91D镁合金微弧氧化陶瓷层电化学腐蚀特性的影响

在Na2SiO3-KOH电解液体系中添加一定量的(NaPO3)6, 利用微弧氧化(MAO)技术在AZ91D 镁合金表面制备了原位生长的陶瓷层. 采用动电位极化和电化学阻抗谱(EIS)技术研究了添加(NaPO3)6前后, 制备的陶瓷层在3.5%(w) NaCl溶液中的室温电化学行为. 结果表明, 添加(NaPO3)6后, 陶瓷层的自腐蚀电位显著上升, 自腐蚀电流密度明显减小. 这主要是由于(NaPO3)6增加了反应过程中基体镁合金表面的“氧空位”和溶液中PO3-4的含量, 促使元素Mg在金属/膜层(M/F)界面上快速形成相应氧化物, 从而增加了陶瓷层的厚度和致密性. 根据电化学反应体系和陶瓷层的特殊结构, 建立了合理的等效电路, 并结合EIS 数据, 分析了添加(NaPO3)6提高陶瓷层耐电化学腐蚀性能的机理.     

Plasma electrolytic oxidation of AZ91D magnesium alloy in biosafety electrolyte for the surgical implant purpose

Plasma electrolytic oxidation (PEO) of AZ91D magnesium alloy in biosafety electrolyte was studied. The prepared PEO coating and its stability in the simulated body fluid (SBF) were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentio-dynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion test. The SEM results show that a kind of smooth, compact and well adhesive PEO coating is prepared in the proposed biosafety electrolyte. The electric analytical results show that the corrosion resistance of the PEO coating is excellent even in harsh environment. Immersion test shows that the PEO coating is stable enough in the SBF solution. The weight loss, the average corrosion rate and the pH variation of the PEO treated magnesium alloy are far lower than the untreated ones. From these highly positive results, the proposed PEO process is promising in the treatment of the surgical magnesium alloy materials.     

AZ91D镁合金上钼改性锌系磷化膜的制备、 结构及性能

采用在磷化液中添加钼酸钠及腐蚀抑制剂的方法, 在AZ91D 镁合金表面上制备了均匀细致的锌系复合磷化膜. 用XRD对膜层的化学组成及结构进行了表征,用SEM和EDS对膜层的形貌和组分含量进行分析. 结果表明, 磷化膜主要由Zn3(PO4)2·4H2O和单质Zn组成. 在磷化液中加入钼酸钠使磷化膜组织更加细致而且无裂纹. 磷化液中的钼酸钠含量为1.5 g/L时, 磷化膜的结晶最致密, 单质锌的含量最高, 耐蚀性最好. 还提出了一种快速测量镁合金表面膜层耐蚀性的试验方法, 同时对镁合金上的磷化反应的机理进行了探讨.     

ESEM observation of the process of hydrogen generation around the micro-droplets forming on AZ91 magnesium alloy

The process of hydrogen generation around micro-droplets on as-cast AZ91 magnesium alloy in an atmosphere of water vapor was in situ observed using an environmental scanning electron microscope (ESEM). The procedure for hydrogen generation was described. It indicated that the cathodic or anodic location gradually changed with the generation of hydrogen bubbles and the formation of corrosion products.     

Electrochemical performance of Mg–9Al–1Zn alloy in aqueous medium

A systematic study on the corrosion and passivation behavior of AZ91D alloy in relation to the influence of concentration, temperature, pH, and immersion time was made in aqueous sulfate solution using electrochemical techniques including open-circuit potential, potentiodynamic polarization and impedance spectroscopy. It was found that the corrosion and pitting potentials (E _corr and E _pit) of the alloy drift to more active values with increasing either concentration (0.01–1.0 M) or temperature (278–338 K) of the test solution, suggesting that sulfate solution enhances the alloy dissolution, particularly at higher temperatures. On the other hand, values of the total film resistance (R _T) indicate that neutral solution (pH 7.0) supports the formation of a better protective layer on AZ91D surface than alkaline (pH 12.5) or acidic (pH 1.0) medium. The growth of a protective film on the alloy surface at short immersion times (up to ∼50 h) is evinced by a rapid positive evolution of E _corr and fast decrease in the corrosion rate (i _corr). However, for a long-term exposure (up to 500 h) E _corr drifts negatively and i _corr increases due to breakdown of the protective film, which causes a decrease in the alloy stability. Fitting the impedance data to equivalent circuit models suitable to each behavior assisted to explore the mechanism for the attack of the sample surface at various testing times. The results obtained from the three studied electrochemical techniques are in good agreement.     

Corrosion behavior of Mg,AZ31, and AZ91 alloys in dilute NaCl solutions

Corrosion behavior of extruded Mg, extruded AZ31 alloy, and cast AZ91 alloy was investigated by electrochemical measurements in dilute NaCl solutions. Corrosion products and passivation films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. All specimens exhibit the corrosion and passivation zones in dilute NaCl solutions. The aluminum content and alloy microstructure influence the corrosion and passivation processes. AZ91 alloy shows the broadest passivation zone followed by AZ31 alloy and Mg. AZ91 alloy reveals a highest corrosion resistance, and preferential attack is located at the primary Mg phase. Its relatively fine β-phase (Mg₁₇Al₁₂) network and Al₂O₃/Al(OH)₃ compounds produced on the passivation film are the main factors which limit the corrosion progress as compared with AZ31 alloy and Mg. The thick passivation product on AZ31 alloy is the key factor which restricts the corrosion attack in dilute solutions.     

AZ91镁合金表面稀土转化膜的制备及耐蚀性能研究

采用在镁合金表面形成无毒、无污染的稀土铈转化膜的方法解决AZ91镁合金表面的腐蚀问题。确定了最佳成膜工艺参数，讨论了处理液的浓度、成膜温度和成膜时间等因素对转化膜耐蚀性的影响。利用湿热实验、阳极极化曲线的测定等实验方法评价了转化膜对镁合金表面的防护作用。结果表明，在潮湿温热条件下稀土铈转化膜试样仍能保持膜层的完整性并具有较高的覆盖度，腐蚀现象不明显。腐蚀电势升高，出现钝化现象，腐蚀电流密度下降，稀土铈转化膜可以提高AZ91镁合金的耐蚀性能。用扫描电镜观察了膜的微观形貌，稀土铈转化膜是由基膜和附着的细小颗粒组成，最佳工艺形成的铈转化膜无破碎现象，对AZ91镁合金表面的腐蚀过程的发生有明显的抑制作用。     

Corrosion resistance and durability of superhydrophobic surface formed on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution

The corrosion resistant performance and durability of the superhydrophobic surface on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution were investigated using electrochemical and contact angle measurements. The durability of the superhydrophobic surface in corrosive 5 wt% NaCl aqueous solution was elucidated. The corrosion resistant performance of the superhydrophobic surface formed on magnesium alloy was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the superhydrophobic surface considerably improved the corrosion resistant performance of magnesium alloy AZ31. American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the superhydrophobic film to the magnesium alloy surface. The corrosion formation mechanism of the superhydrophobic surface formed on the magnesium alloy was also proposed.     

AZ31镁合金表面聚吡咯的化学氧化合成及其耐蚀性能

以对甲苯磺酸钠为掺杂剂, 三氯化铁为氧化剂, 用化学氧化聚合法在AZ31 镁合金表面制备聚吡咯(PPy)膜. 采用傅里叶变换红外(FTIR)光谱分析了镁合金表面聚吡咯膜结构, 通过电化学极化曲线、电化学阻抗谱(EIS)研究了其耐蚀性能, 通过扫描电子显微镜(SEM)、X射线能量散射谱(EDS)分析了表面形貌和成分. 和镁合金裸样相比, 聚吡咯膜对镁合金腐蚀有一定的抑制作用. 硅烷预处理改善了镁合金/聚吡咯体系的耐腐蚀性能, 使腐蚀电位较镁合金裸样正移了110 mV, 电流密度减小了约2个数量级.     

Improved Corrosion Resistance of AZ91D Mg Alloy by Cerium-Based Films. Formation of a Duplex Coating with Polypyrrole

Russian Journal of Electrochemistry - In order to improve the corrosion resistance of die-cast AZ91D magnesium alloy in simulated physiological solution, two cerium-based coatings were synthesized....     

SNAP溶胶组成对镁合金涂层耐蚀性的影响

本文利用纳米自组装颗粒工艺(SNAP)在AZ31B镁合金表面制备了防腐涂层。通过透射电镜(TEM)和扫描电镜(SEM)观察及电化学阻抗谱(EIS)、电导率测试等,对SNAP溶胶的纳米粒子形态和电导率,以及SNAP涂层的表面形貌和耐蚀性进行了测试,研究了不同含量的有机硅烷前躯体3-缩水甘油醚丙基三甲氧基硅烷(GPTMS)和正硅酸乙酯基硅烷(TEOS)、溶剂水、助溶剂无水乙醇、交联剂三乙烯四胺(TETA)等对镁合金SNAP涂层耐蚀性的影响。研究结果表明,随着溶胶中TEOS和TETA含量的增大,镁合金涂层耐蚀性呈先增大后减小的趋势;随着溶胶中水含量的增大,镁合金涂层耐蚀性提高;溶胶中无水乙醇的含量较低时,对镁合金涂层耐蚀性的影响较小。     

Corrosion behavior of PEO-treated AZ31 Mg alloy in chloride solution

Corrosion behavior and resistance of plasma electrolyte oxidation (PEO)-treated AZ31 Mg alloy were investigated by immersion and potentiodynamic polarization tests in 0.5 M NaCl solution in view of the PEO film thickness and sealing treatment of the PEO films in boiling water. The PEO films were formed using pulse current for various durations in 1 M NaOH?+?0.5 M NaF solution. Filiform corrosion was observed during the immersion test while pitting corrosion occurred during the potentiodynamic polarization test, irrespective of sealing treatment of the PEO films. Corrosion resistance of AZ31 Mg alloy was improved remarkably by the formation of thicker PEO films and their sealing treatments.     

Film characteristics of anodic oxidized AZ91D magnesium alloy by applied power

This study examined the film characteristics of an anodized AZ91D magnesium alloy by varying the direct current and pulse frequency conditions. In order to evaluate the effect of the pulse frequency on film formation, anodic oxidation was carried out by applying direct current and pulse current at a current density of 300 mA/cm². Compared with the sample groups treated with the direct current, a large number of small arcs were generated continuously on the film treated with the pulse current and the film formation rate was found to increase. Homogeneous and compact pores were formed with increasing frequency, and the rate of formation was increased rapidly to the arrival voltage. The film thickness increased and the surface roughness decreased with increasing anodic oxidation time at a fixed frequency of 125 Hz. However, treatment for more than 3 min led to decomposition of the oxidized film onto the previously formed film, which caused an increase in the number of cracks and pores within the film. The most uniform and smallest pores were acquired when the surface was anodized for 3 min at a current density and frequency of 300 mA/cm² and 125 Hz, respectively. X‐ray diffraction revealed the formation of MgO and Mg₂SiO₄ peaks, with a relative decrease in peak intensity for the MgO and Mg substrate. The Vickers hardness value was higher on the treated groups than on the untreated group, and the potentiodynamic polarization test revealed satisfactory corrosion resistance through a decrease in corrosion density and a large improvement in the corrosion potential. Copyright © 2009 John Wiley & Sons, Ltd.