Effects of sodium tungstate on properties of micro-arc coatings on magnesium alloys

Anodic coatings were prepared by micro-arc oxidation on AZ91HP magnesium alloys in a base solution containing 10 g/L NaOH and 12 g/L phytic acid with addition of 0-8 g/L sodium tungstate. The effects of sodium tungstate on the coating thickness, mass gain, surface morphology and corrosion resistance were studied by eddy current instrument, electronic scales, scanning electron microscope and immersion tester. With the addition of sodium tungstate, the electrolytic conductivity increases and the final voltage decreases. The sodium tungstate has a minor effect on the coating thickness, but lightens the coating color. With increasing sodium tungstate concentration, the size of micropores on the coatings is enlarged and the corrosion resistance of the anodized samples decreases.     

甘油磷酸钙浓度对钛合金MAO涂层性能的影响

目的 提高医用钛合金的生物活性。方法 在含葡萄糖酸钙(Ca Glu₂)、葡萄糖酸镁(MgGlu₂)、植酸钠(Na₁₂Phy)和磷酸(H₃PO₄)的基本溶液中,分别添加8、10、12 g/L甘油磷酸钙(Ca-GP),采用MAO方法在Ti-6Al-4V表面制备3种涂层。使用SEM、EDS、XRD、XPS和AFM检测涂层表面形貌、化学成分、物相结构、元素存在状态和表面粗糙度,并测试涂层的接触角、结合强度以及体外生物活性。结果 经过MAO处理后,钛合金表面可成功生长出多孔陶瓷涂层,Ca-GP参与了MAO涂层形成。当Ca-GP的质量浓度为8 g/L时,涂层非常粗糙,Ca和Mg的原子数分数分别为7.56%和1.74%。随着Ca-GP浓度的增加,微孔均匀性变好,表面微裂纹减少,且钙磷原子比(Ca/P)显著提高。在含8、10 g/L的Ca-GP溶液中,制备的涂层以Ti、锐钛矿和金红石型Ti O2组成为主;在12g/L的Ca-GP溶液中生成的涂层,Ca/P原子比可达1.77,含有Ti P     

Effects of electric parameters on corrosion resistance of anodic coatings formed on magnesium alloys

Anodic coatings were obtained by micro-arc oxidation on AZ91HP magnesium alloys in a solution containing 10 g/L NaOH and 8 g/L phytic acid. The effects of electric parameters including frequency, final voltage, duty cycle and current density on the corrosion resistance of anodic coatings formed on the magnesium alloys were investigated by using an orthogonal experiment of four factors with three levels. The results show that the final voltage plays a main role on the coating properties. The orders of affecting corrosion resistance and coating thickness are separately ranked from high to low as, final voltage>duty cycle>current density>frequency and final voltage>current density>frequency>duty cycle. The final voltage influences the corrosion resistance of the anodized samples mainly by changing the surface morphology and coating thickness.     

化学镀镍层缓蚀工艺研究

目的提高化学镀Ni-P镀层的耐蚀性能。方法在钢铁基体表面化学镀Ni-P镀层,采用植酸、硅酸钠、钼酸铵和双氧水中的一种或多种复配对镀层进行钝化处理。通过硝酸点滴法、贴滤纸法分析镀层耐蚀性的变化,并通过正交实验确定四种物质复配的最佳浓度。结果以植酸、硅酸钠、钼酸铵和双氧水为主要成分配制的复合缓蚀剂能使镀层耐硝酸效果良好,电化学实验表明,复合钝化膜的腐蚀电流密度降低和阻抗值增加都超过1个数量级。结论所研究的复合缓蚀剂各组分间存在协同效应,最佳配方为:6 g/L植酸,6 g/L硅酸钠,4 g/L钼酸铵,30 mL/L双氧水。     

Characterization and corrosion behavior of ceramic coating on magnesium by micro-arc oxidation

In this study, the commercial pure magnesium was coated in different aqueous solutions of Na₂SiO₃ and Na₃PO₄ by the micro-arc oxidation method (MAO). Coating thickness, phase composition, surface and cross sectional morphology and corrosion resistance of coatings were analyzed by eddy current method, X-ray diffraction (XRD), scanning electron microscope (SEM) and tafel extrapolation method, respectively. The average thickness of the coatings ranged from 52 to 74 μm for sodium silicate solution and from 64 to 88 μm for sodium phosphate solution. The dominant phases on the coatings were detected as spinal Mg₂SiO₄ (Forsterite) and MgO (Periclase) for sodium silicate solution and Mg₃(PO₄)₂ (Farringtonite) and MgO (Periclase) for sodium phosphate solution. SEM images reveal that the coating is composed of two layers as of a porous outer layer and a dense inner layer. The corrosion results show the coating consisting Mg₂SiO₄ is more resistant to corrosion than that containing Mg₃(PO₄)₂.     

Formation of Microcracks During Micro-Arc Oxidation in a Phytic Acid-Containing Solution on Two-Phase AZ91HP

Micro-arc oxidation (MAO) is an effective method to produce ceramic coatings on magnesium alloys and can considerably improve their corrosion resistance. The coating properties are closely related with microcracks, which are always inevitably developed on the coating surface. In order to find out the formation and development regularity of microcracks, anodic coatings developed on two-phase AZ91HP after different anodizing times were fabricated in a solution containing environmentally friendly organic electrolyte phytic acid. The results show that anodic film is initially developed on the α phase. At 50 s, anodic coatings begin to develop on the β phase, evidencing the formation of a rough area. Due to the coating successive development, the microcracks initially appear at the boundary between the initially formed coating on the α phase and the subsequently developed coating on the β phase. With the prolonging treatment time, the microcracks near the β phase become evident. After treating for 3 min, the originally rough area on the β phase disappears and the coatings become almost uniform with microcracks randomly distributed on the sample surface. Inorganic phosphates are found in MAO coatings, suggesting that phytate salts are decomposed due to the high instantaneous temperature on the sample surface resulted from spark discharge.     

K2ZrF6对镁合金微弧氧化膜抗点燃性能的影响

目的 降低镁合金在高温环境下起火燃烧的风险,同时探索微弧氧化膜是否具有抗点燃的热防护功能.方法 采用添加不同含量K2ZrF6的碱性硅酸盐电解液体系,在AZ91D镁合金表面制备微弧氧化膜,研究不同浓度K2ZrF6对微弧氧化膜抗点燃性能的影响.采用扫描电镜观察燃烧前微弧氧化膜的微观结构变化,结合XRD分析涂层的相组成,并借助抗点燃性能测试装置,考察微弧氧化膜的起燃时间.结果 添加K2ZrF6制备的微弧氧化膜主要由MgO、Mg2SiO4、MgF2和ZrO2组成.随着K2ZrF6含量的增加,膜层中大尺寸缺陷减少,致密性和厚度显著提高,表面粗糙度先增加、后降低.添加0～10 g/L K2ZrF6的微弧氧化膜的致密性较差,这类微弧氧化层在火焰的作用下,会形成大量的烧蚀孔洞和纵向扩展裂纹;添加15、20 g/L K2ZrF6的微弧氧化膜,具有更为致密的内层,这类微弧氧化膜直到基体完全熔化变形,才会出现横向扩展裂纹,导致涂层失效.AZ91D镁合金经过含15 g/L K2ZrF6的电解液微弧氧化处理后,起燃时间最长,抗点燃性最好.结论 K2ZrF6浓度对微弧氧化膜抗点燃性的影响主要体现在对其致密性的影响上,内层的致密结构能够减少在高温火焰作用下形成的烧蚀孔洞,以及延缓裂纹的产生,从而阻碍熔融的液态镁和镁蒸气向外扩散,减缓氧化反应的程度,提高涂层的抗点燃性.     

Preparation of MgO coatings on magnesium alloys for corrosion protection

MgO coating is formed on magnesium alloy by anodic electrodeposition in 6 M KOH solution, whereas Mg(OH)₂ coating is produced by anodization in 10 M KOH solution, which could be successively converted to MgO by calcination in air at 450 °C. The evolution of morphology, structure and composition of anodic film obtained on Mg alloy is investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and X-ray diffraction (XRD). Potentiodynamic polarization measurements show that the as-grown MgO protective coatings are very effective in improving the corrosion resistance of magnesium alloy compared to bare metallic magnesium.     

电解质对AZ91D镁合金微弧氧化的影响

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。     

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro‐arc oxidization technique

With increasing applied voltage, three types of anodic coatings, passive film, micro‐spark ceramic coating and spark ceramic coating were made by micro‐arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali‐silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro‐spark ceramic coating, prepared in the voltage range of 170~220V exhibits compact, homogeneous structure and highest corrosion‐resistance.     

纯钛表面载骨碎补提取物涂层的制备与性能

为了提高纯Ti的生物活性和抗感染性,采用微弧氧化(UMAO)制备多孔涂层,并以植酸(PA)偶联骨碎补提取物(ERD),并分析涂层结构、形貌及性能。结果表明,随着ERD浓度的提高,纳米颗粒增多,有PO43-,P2O74-和O=P-O-生成;载药12.5g/L的膜层摩擦磨损系数低,膜层结合力较高,为亲水涂层,膜层的电位提高了0.32V,自腐蚀电流降低一个数量级,模拟体液浸泡有羟基磷灰石(HA)生成。纯钛表面通过超声微弧氧化,植酸偶联载药的耐蚀性,结合力,生物活性均有提高。     

Effects of Voltage on Microstructure and Corrosion Resistance of Micro-arc Oxidation Ceramic Coatings Formed on KBM10 Magnesium Alloy

Micro-arc oxidation (MAO) coatings on KBM10 magnesium alloy were prepared in an electrolyte system with sodium silicate, potassium hydroxide, sodium tungstate, and citric acid. The effects of voltage on the microstructure and corrosion resistance of MAO coatings were studied using stereoscopic microscopy, scanning electron microscopy, x-ray diffraction, scratch tests, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results showed that the roughness of the MAO coatings, diameter, and number of pores increase with the increase in voltage. The coating formed at the voltage of 350 V exhibited the best adhesive strength when evaluated by the automatic scratch tester. The coatings were mainly composed of MgO, MgWO₄, and Mg₂SiO₄, and the content of Mg₂SiO₄ increased with the increase in voltage. The corrosion resistance of MAO coatings could be improved by changing the applied voltage, and the best corrosion resistance of MAO coating was observed at the voltage of 350 V.     

基于配方均匀试验优化微弧氧化电解液浓度配比

目的 研究电解液中各电解质不同浓度配比下微弧氧化膜层的制备、微观结构及耐蚀性能,以确定最优配方.方法 基于配方均匀试验方法,在硅酸盐系电解液中对AM60B镁合金进行微弧氧化处理.引入微弧氧化反应的可行性和微弧氧化膜层的成膜性两个试验指标,分别评判本研究中某电解液配方是否具有实际应用价值,以及评价在某个电解液配方下所制得膜层的合格程度.利用涡流测厚仪、扫描电镜(SEM)、X射线衍射(XRD)、电子探针(EPMA)、硝酸点滴实验以及电化学实验等方法,分别表征膜层的厚度、微观结构、物相组成、元素成分及耐蚀性能.结果 当电解液中NaOH的质量浓度小于10 g/L时,方能获得表观完整且色泽均匀的微弧氧化膜层.当NaOH和KF的浓度配比接近,且两者之和约为Na2SiO3所占配比时,即Na2SiO3为19.24 g/L、NaOH为8.80 g/L、KF为11.96 g/L时,膜层中孔径的尺寸小,缺陷少,致密度最高,此时膜层的耐蚀性最好,与基体相比,该膜层的硝酸点滴耐蚀性提高了39倍,电化学耐蚀性提高了3个数量级.膜层主要由MgO、Mg2SiO4及少量的MgF2、MgAl2O4组成,但含量有差别.结论 实验设计方法的选择是保证本研究结果有效性的核心和关键.电解液中NaOH的浓度高低是决定某电解液配方是否具有实用价值的首要因素.只有Na2SiO3、NaOH和KF三者间具备适当的配比时,才能降低膜层中的微孔尺寸,减少微裂纹,提高其致密度,并能够在膜层中沉积更多的优质物相,这些是增强膜层耐蚀性的前提和保障.     

NH4F浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响

目的 考察乙二醇-氟化铵电解液中氟化铵浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响,提高镁合金氟化物膜层的耐腐蚀性能。方法 在含不同浓度NH4F的EG-NH4F电解液中,采用微弧氧化的方法制备氟化物膜层,NH4F质量浓度分别为40、60、80、100、120 g/L。通过扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)和X射线衍射仪(XRD),对膜层表面微观形貌和成分组成进行分析,并通过电化学测试表征了膜层的腐蚀防护性能,通过盐雾试验评估了膜层长效防腐蚀行为,通过SEM和EDS表征了腐蚀形貌和腐蚀产物。结果 在EG-NH4F中制备膜层的物相组成主要是MgF2。随着NH4F浓度的提高,微弧氧化的起弧电压与工作电压均逐渐减小,膜层中氟含量逐渐增加,膜层的孔径减小,孔数量分布更加均匀,膜层表面粗糙度降低。质量浓度为100 g/L NH4F的膜层自腐蚀电流密度(Jcorr)为2.226×10^‒7 A/cm²,较镁合金基材降低了1个数量级,极化电阻Rp增大到90.156 kΩ.cm²,其阻抗模量|Z|f=0.01 Hz=8.55×10⁵ Ω.cm²,与镁合金基材的阻抗模量|Z|f=0.01 Hz=8.86×10² Ω.cm²相比,提高了3个数量级。结论 微弧氧化处理能够显著改善AZ31镁合金的腐蚀防护性能。NH4F浓度的增加有利于提高膜层的耐腐蚀性能,质量浓度为100 g/L NH4F的膜层耐腐蚀性能最优。     

磷酸盐浓度对5083铝合金微弧氧化膜组织与耐腐蚀性能的影响

为研究电解液浓度对微弧氧化的影响规律,在磷酸钠电解液中采用恒压模式对5083铝合金进行微弧氧化,采用场发射扫描电镜、划痕仪以及电化学工作站等研究了电解质浓度对膜层生长速率、组织成分、膜基结合强度以及耐腐蚀性能的影响。结果表明:随着磷酸钠浓度的增大,氧化膜厚度线性增加,膜层表面的"火山堆积"状形貌特征愈发明显,但浓度过大时氧化膜出现局部不均匀堆积及较大孔洞,其对氧化膜成分影响不明显;氧化膜与基体结合良好,且随着浓度增加结合强度出现先增后减的趋势。当磷酸钠浓度为10 g/L时,氧化膜的自腐蚀电流最低,为2.96×10~(–8) A/cm~2,比铝合金基体降低了1个数量级,表现出良好的耐腐蚀性能。     

Growth characteristics and corrosion resistance of micro-arc oxidation coating on pure magnesium for biomedical applications

Protective micro-arc oxidation (MAO) coating was prepared on pure magnesium in aqueous solution without toxic components under a constant current density. The whole anodizing process can be divided into four stages based on the differences in voltage, sparking behaviour and oxygen evolution. SEM micrographs show that a thick and dense coating can be obtained after anodizing for adequate time. The corrosion resistance of the samples with anodic coatings was evaluated by drop experiments and potentiodynamic polarization tests. The results confirm that the thick and dense coating can efficiently protect the magnesium substrate from corrosion in aggressive environments.     

Effect of silicate anion distribution in sodium silicate solution on silicate conversion coatings of hot-dip galvanized steels

Silicate conversion coatings are prepared by immersing hot-dip galvanized (HDG) steel sheets in sodium silicate solutions with 5 wt.% SiO₂ and SiO₂:Na₂O molar ratio in the range of 1.00 to 4.00. The coating with better corrosion resistance is usually obtained in silicate solution with higher molar ratio (3.00-4.00). In this article, the distribution of types of silicate anion in solutions is investigated by transmission infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (²⁹Si NMR), and the surface of the silicate coating is analyzed using reflection infrared spectroscopy (RA-IR). Results indicate that the anion distribution is mainly monomer, linear and less cyclic anions at low molar ratios in very alkaline solutions. With increase in the molar ratio, small anions decrease, two- and three-dimensional anions increase. Accordingly, the silicate coating prepared in the solution with high molar ratio (≥ 3.00) contains a higher number of large silicate anions, and Si-O-Zn and Si-O-Si bonds of the coating increase, leading to the formation of more dense silicate coating and better corrosion resistance of the coating. Based on the above results and the potential-pH diagram of zinc, probable causes for differences in structure and compactness of silicate coatings, prepared by immersing HDG steels in sodium silicate solutions with different SiO₂:Na₂O molar ratio, are discussed.     

Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing

To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) sheets were post-sealed with sodium silicate (water glass) solutions. The morphology and chemical composition of the composite coatings was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of sodium silicate post-sealing treatment on the corrosion behaviors of phosphate coatings was investigated by neutral spray salt (NSS) tests and electrochemical measurements. The results show that after the silicate post-treatment the pores among zinc phosphate crystals are sealed with the films containing Si, P, O and Zn, leading to the formation of the continuous composite coatings on the surface of HDG steel. The corrosion resistance of the composite coatings depending on concentration of sodium silicate and post-sealing time is greatly improved by the silicate post-treatment. The optimum concentration of silicate and post-sealing time are 5 g/L and 10 min, respectively. Both the anodic and cathodic processes of zinc corrosion on the samples are suppressed conspicuously, and the synergistic protection effect of the single phosphate coatings and the single silicate films is evident. Moreover, the low frequency inductive loop in electrochemical impedance spectroscopy (EIS) is disappeared and the electrochemical impedance values are increased for more than one order of magnitude. The corrosion protection of the composite coatings is comparable to that provided by the chromic acid post-treatment.     

铝合金表面钼酸盐改进植酸转化膜的耐蚀性能

目的通过钼酸钠(SM)添加剂、SM前处理、SM后处理三种方案对铝合金表面植酸转化膜进行改进研究,以进一步提高其耐蚀性。方法通过动电位极化测试研究改进后铝合金在3.5%(质量分数)Na Cl溶液中的耐蚀性。结果随着SM添加剂浓度的增加,铝合金表面植酸转化膜的耐蚀性先增强再减弱,SM质量浓度为30 g/L时的腐蚀保护效率Pe最大,达95.5%,而不含SM时的Pe仅为86.8%。p H值太大(p H=8.0)或太小(p H=3.0)都不利于形成耐蚀性更好的膜层,p H值为6.0时的Pe达98.6%。SM后处理会严重影响植酸转化膜的耐蚀性,腐蚀电流密度Jcorr大幅增大;SM前处理可提高植酸转化膜的耐蚀性,Pe达98.2%;SM前处理与添加剂同时应用时,植酸转化膜耐蚀性提高幅度更显著,Jcorr仅为0.042μA/cm2,极化电阻Rp达222 kΩ·cm2,Pe达99.5%。结论 SM添加剂和SM前处理均可明显提高铝合金表面植酸转化膜的耐蚀性,且复合作用时的效果更显著,而SM后处理不能提高铝合金表面植酸转化膜的耐蚀性。     

植酸修饰改性对TC4钛合金微弧氧化膜层性能的影响

通过向电解液中添加有机酸植酸,提升了TC4钛合金微弧氧化涂层的耐腐蚀性能和热稳定性。通过扫描电子显微镜、X射线衍射仪、X射线光电子能谱仪和热冲击实验等技术手段,分析了植酸对涂层形成、形貌和性能的影响。结果显示,植酸的添加使放电微孔更加细小,提高了涂层的形成效率并优化了相结构。通过动电位极化测试,发现添加植酸显著提高了微弧氧化涂层的耐腐蚀性能。将电解液中的植酸浓度调整为12 mL/L（最佳植酸浓度）后,腐蚀电流密度由8.406×10^-5 A·cm^-2降低至2.580×10^-6 A·cm^-2。循环高温氧化试验结果表明,TC4钛合金的耐热冲击性能和高温抗氧化性能得到了改善。