Application of CeH–V/ sol–gel composite coating for corrosion protection of AM60B magnesium alloy

Application of a composite coating on AM60B magnesium alloy consisting of cerium–vanadium conversion coating and a hybrid sol–gel layer was investigated. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses revealed a cracked nodular structure for the cerium–vanadium conversion coating which was mainly composed of O, Ce, V, and Mg atoms. All the cracks in the conversion coating were completely sealed by a thin, compact and defect-free hybrid sol–gel film. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments in Harrison's solution showed that the cerium–vanadium conversion coating provides minimal protection against corrosion while the composite coating significantly increases the corrosion resistance of the magnesium alloy. Sol–gel film provides protection against corrosion by sealing cracks in the cerium–vanadium conversion coating and acting as a barrier. Scanning electron microscopy analyses after polarization tests confirmed the results obtained by the electrochemical tests.     

油酸钠在乙二醇-水溶液中对AM60镁合金的缓蚀作用

采用电化学方法和扫描电子显微镜研究了油酸钠对AM60镁合金在50%(体积分数)乙二醇-水溶液中的缓蚀作用。结果表明:油酸钠能抑制AM60镁合金在乙二醇-水溶液中的腐蚀,是一种阳极型缓蚀剂,随着油酸钠量的增加,缓蚀率逐渐增大;油酸钠在常温和高温下对AM60镁合金在乙二醇-水溶液中均有较好的缓蚀作用,且常温下油酸钠的缓蚀效果更好;油酸钠在AM60镁合金表面的吸附为自发过程,且符合Temkin吸附等温方程。     

Influence of molybdate species on the tartaric acid/sulphuric acid anodic films grown on AA2024 T3 aerospace alloy

AA2024 T3 alloy specimens have been anodised in tartaric acid/sulphuric media and tartaric acid/sulphuric media containing sodium molybdate; molybdate species were added to the anodising bath to enhance further the protection provided by the porous anodic film developed over the macroscopic alloy surface. Morphological characterisation of the anodic films formed in both electrolytes was undertaken using scanning electron and transmission electron microscopies; the chemical compositions of the films were determined by Rutherford backscattering spectroscopy that was complemented by elemental depth profiling using rf-glow discharge optical emission spectrometry. The electrochemical behaviour was evaluated using potentiodynamic polarisations and electrochemical impedance spectroscopy; the corrosion performance was examined after salt spray testing. The porous anodic film morphology was little influenced by the addition of molybdate salt, although thinner films were generated in its presence. Chemical composition of the anodic film was roughly similar; however, addition of sodium molybdate in the anodizing bath resulted in residues of molybdate species in the porous skeleton and improved corrosion resistance measured by electrochemical techniques that was confirmed by salt spray testing.     

Elektrochemische Rauschmessungen zum Nachweis der Wirksamkeit von neuen Korrosionsschutzschichten auf Aluminium und Magnesium

Electrochemical noise measurements for the determination of the effectiveness of new corrosion protection layers on aluminium and magnesium The corrosion behaviour of the aluminium alloy AlMg1 and of the magnesium alloy AM60 have been investigated by electrochemical noise measurements in chloride and sulfate solutions. It should be proved, whether protecting layers based on self assembling molecules, which have been adsorbed on the samples before the electrochemical noise measurements, could inhibit pitting corrosion. The measurements do show, that several systems have an inhibitive effect, others not. Potentiostatic tests in combination with the measuements of the current noise are useful for a quick determination of the break through potential.     

环氧涂层中锌铬黄颜料对镁合金的防蚀机理

采用电化学阻抗、动电位极化、开路电位监测和X射线光电子能谱(XPS)等手段,研究了环氧涂层中锌铬黄颜料对镁合金的腐蚀防护作用,并分析了其防蚀机理。结果表明,锌铬黄防锈颜料均匀分散在涂层中,增强了涂层的屏蔽性能以及涂层与镁合金基体的结合力;在3%NaCl水溶液中,锌铬黄是一种阳极型缓蚀剂,它依靠铬酸根离子的阳极钝化作用形成钝化膜,阻滞了阳极腐蚀过程,造成涂层试样开路电位正移,使涂层试样的阳极极化增大。     

镍基固溶体增韧Cr_(13)Ni_5Si_2合金在含Cl~-溶液中的腐蚀行为

采用极化曲线,Tafel阿和电化学限抗谱(EIS)技术,研究了镍基固溶体增韧Cr_(13)Ni_5Si_2金属硅化物合金在不同Cl~-浓度Na_2SO_4+NaCl溶液中的电化学腐蚀行为,并对其表面钝化膜进行了X射线光电子能谱(XPS)分析.结果表明:由于超高的Cr含量易于在表面形成以Cr_2O_3为主的稳定钝化膜以及组成相Cr_(13)Ni_5Si_2和Cr3Ni5Si2高的化学稳定性,合金在不同Cl~-浓度溶液中均具有良好的耐蚀性;合金的开路电位,破裂电位和腐蚀电流密度等几乎不随Cl~-浓度的增加而改变,即合金对Cl~-浓度不敏感,在中性含Cl~-介质中耐蚀性优异.     

Corrosion characterization of Mg-8Li alloy in NaCl solution

The corrosion mechanism of Mg-8Li alloy in NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion resistance of Mg-8Li alloy in 0.1 M NaCl solution gradually deteriorated with increasing of immersion time expect for 2 h immersion, which was consistent with the SEM observation of corrosion morphology. Mg-8Li alloy exhibited filiform type of attack under significant anodic control of magnesium solution reaction. The cathodic reaction was driven by hydrogen evolution reaction. The presence of filiform corrosion also proved a resistant oxide film naturally formed on the surface of Mg-8Li alloy.     

Electrochemical behavior of anodized Mg alloy AZ91D in chloride containing aqueous solution

Electrochemical behavior in aerated 3.5 wt.% NaCl solution of Mg alloy AZ91D anodized or not has been investigated by using electrochemical impedance spectroscopy, potentiodynamic polarization and E_corr-t curve. Their microstructures before and after corrosion have been examined under scanning electron microscope. Testing results from E_corr-t and polarization curves indicate that the corrosion behavior of Mg alloy makes significant, characteristic changes due to anodization. Impedance spectra obtained show a regular evolution with exposure time revealing the development of corrosion damage. SEM micrographs confirm that there are pores, defects and microcracks in anodic film which determine the existence of film-vulnerable regions. Electrochemical data are combined with micrographs to explain protection mechanism of anodic film and corrosion mechanism of Mg alloy.     

Effect of the electrolytic solution composition on the performance of micro-arc anodic oxidation films formed on AM60B magnesium alloy

Anodic oxidation in the micro-arc regime is one of the most investigated techniques used to coat magnesium alloys with ceramic coatings for protection from corrosion and wear. The composition of the electrolytic solution affects the anodic oxide layer morphology and composition and its behaviour in aggressive environments. In this paper the influence of the composition of the electrolytic solution on the anodic oxidation process of AM60B magnesium alloy and oxide properties is discussed. Scanning electron microscopy and x-ray diffraction were employed to assess morphology, crystallographic structure and composition of the anodic oxide. Electrochemical polarization tests were performed to evaluate the corrosion resistance behaviour of the coated magnesium alloys.     

磷酸钠在NaCl溶液中对AZ31镁合金的缓蚀作用

采用电化学阻抗法、动电位极化曲线法、全浸泡失重法和扫描电镜,研究了在3.5%(质量分数)Na Cl溶液中磷酸钠(Na3PO4)对AZ31镁合金腐蚀的抑制作用。结果表明:Na3PO4对3.5%Na Cl溶液中的AZ31镁合金具有缓蚀作用,其缓蚀率随着Na3PO4含量增大逐渐提高,当Na3PO4质量浓度为1.0 g/L时,缓蚀率达到81.5%。结合扫描电镜分析表明,Na3PO4在镁合金表面形成含有Mg(OH)2和Mg3(PO4)2的保护层,这层致密的膜减少了基体与Cl-接触,抑制了镁合金的阳极反应。     

镁合金在大气环境中电偶腐蚀行为及规律的研究

在北京大气环境下，研究AM60镁合金和不同金属材料（碳钢、不锈钢、黄铜和铝合金）偶接的电偶腐蚀行为规律。研究表明，镁合金作为阳极发生不同程度的电偶腐蚀，通过1a的北京大气环境下的暴露试验后，AM60镁合金的电偶腐蚀效应由强到弱的顺序为：碳钢、黄铜、不锈钢和铝合金，其中镁合金与LY12铝合金偶接的电偶腐蚀效应最小。通过与其它地区室外暴晒的镁合金电偶腐蚀效应的对比，表明环境因素影响着镁合金的电偶腐蚀效应。同时阴极材料、试验时间、试样尺寸（偶接面积）和试验环境都会对镁合金电偶腐蚀效应产生影响。经1a曝晒的AM60镁合金形成了具有保护性的腐蚀产物层阻碍了腐蚀发展。北京地区高自然降尘量导致金属表面湿润时间加大，从而加速了AM60镁合金的电偶腐蚀。采用XRD方法分析表面的腐蚀产物，用金相显微镜和扫描电镜（SEM）观察试样腐蚀后的表面形貌特征和腐蚀产物的结构，并用与之相连的能谱仪分析腐蚀产物中的元素组成。     

SP700 钛合金的热处理 / 阳极氧化工艺研究

目的采用电化学阳极氧化法,在SP700钛合金的表面制备多孔结构的氧化膜。方法利用Autolab PGSTAT30型电化学工作站,采用三电极体系,辅助阴极为石墨电极,参比电极为饱和甘汞电极,工作电极为试样,测定试样的动态极化曲线和阳极氧化I-t曲线。利用扫描电子显微镜观察阳极氧化表面多孔氧化膜的微观形貌,分析热处理工艺、阳极氧化电压、电解液成分等参数对SP700钛合金阳极氧化行为的影响规律。结果钛合金材料经固溶时效处理后,α相和β相的相对含量发生了变化,从而使氧离子对电化学反应界面的内应力发生变化,使得表层氧化膜更加平整,耐腐蚀性提高。F-是阳极氧化膜上纳米孔形成的必要条件,随着F-浓度的增加,阳极氧化膜表面纳米孔的密集程度增加,孔径减小,氧化膜厚度增加。在一定范围内,随着阳极氧化电压的增大,氧化膜增厚,但电压过高会破坏氧化膜的稳定性。结论用电化学阳极氧化法处理钛合金表面,得到了多孔结构的氧化膜,获得了理想的耐腐蚀性能。固溶时效处理后,钛合金的耐腐蚀性提高。     

8-羟基喹啉修饰Fe-W非晶镀层及其耐蚀性

采用电化学方法，研究了8—羟基喹啉修饰Fe—W非晶镀层工艺及其耐蚀性．通过恒压阳极氧化，在Fe—W非晶合金表面形成8—羟基喹啉修饰膜，但膜层耐蚀性较差．在修饰液中加入乙二胺和溶纤剂等助剂，可在电极表面形成一层稳定的彩色修饰膜，铬酸盐封闭处理能增强修饰电极的抗蚀效果．极化曲线测试结果表明，抗蚀层阻滞了氧的阴极还原反应及阳极反应，提高了Fe—W合金镀层在中性NaCl介质中的耐蚀性．     

烧结钕铁硼电镀锌铁合金工艺与耐蚀性能

采用弱酸性氯化物镀液在钕铁硼基体上制备了高耐蚀性的锌铁合金镀层,讨论主要工艺参数对镀层铁含量的影响,优化工艺条件。采用盐雾试验(NSS)、SEM和电化学方法研究镀层的耐蚀性能和耐蚀机理。结果表明,优化工艺条件后合金镀层含铁质量分数为0.92%,钝化后在质量分数3.5%的Na Cl溶液中出白锈时间达到196 h。合金镀层对钕铁硼基体起到阳极保护的作用,镀层结晶致密,填补了钕铁硼基体的固有缺陷,同时又为获得致密的钝化膜创造了条件,减少了镀层表面的缺陷,使镀层整体具有极高的电阻,提高了其耐蚀性能。     

Baking treatment effect on materials characteristics and electrochemical behavior of anodic film formed on AZ91D magnesium alloy

The composition and microstructure of the anodic films formed on AZ91D Mg alloy, with or without baking, were investigated. The associated corrosion behavior of the anodized alloy in 3.5 wt% NaCl solution was also examined using electrochemical impedance spectroscopy (EIS). The results show that MgO was the main component in the anodic film which also contained some Mg(OH)₂, Al₂O₃, Al(OH)₃, and MgAl₂O₄. Both the amorphous and crystalline forms of anodic film were identified. The degree of crystallinity depended on baking temperature, which increased with increasing temperature in the range of 50-250 °C. The amounts of MgO and Al₂O₃ increased as a result of a dehydration reaction. The polarization resistance of anodized Mg alloy was improved significantly by increasing the oxide content in the anodic film. An optimum value of polarization resistance of anodic film was obtained for the alloy baked at 150 °C for 2 h followed by air cooling.     

铝阳极氧化膜的硫酸钇脉冲封闭

研究了硫酸钇脉冲封闭对工业纯铝阳极氧化膜受热开裂行为及电化学行为的影响.利用扫描电子显微镜(SEM)观察了沸水封闭和钇盐脉冲封闭后阳极氧化膜的表面和截面形貌.利用电化学交流阻抗谱(EIS)和极化曲线研究了两种封闭方法的电化学腐蚀行为.结果表明,通过硫酸钇脉冲封闭,可以将钇元素引入到氧化膜中.与沸水封闭氧化膜加热后表面出现了宽度达1 μm的粗大的裂纹相比,硫酸钇封闭的氧化膜表层更加致密,其多孔层孔壁的加粗、孔隙减小,氧化膜显微硬度明显提高,使得氧化膜在加热后仅出现一些细小的微裂纹.从交流阻抗结果可以看出,硫酸钇封闭氧化膜的Rp值是沸水封闭氧化膜的1.43倍,极化曲线结果表明,经过钇盐封闭后,氧化膜的自腐蚀电位比沸水封闭的试样正移约280 mV,自腐蚀电流密度降低为沸水封闭试样的0.41.钇盐封闭的氧化膜在NaCl溶液中的耐蚀性能也有显著提高.     

Effect of erbium addition on the corrosion behaviour of Mg–Al alloys

The corrosion behaviour of two Mg–Al–Er alloys with increasing content of erbium (Mg₉₅Al₃Er₂ and Mg₉₅Al₂Er₃) has been evaluated in borate buffer solution and compared with that of the commercial AM60 alloy (Mg–6.0Al–0.13Mn, at%) employed in the automotive industry. Scanning electron microscopy and quantitative electron probe microanalysis were used to characterize the samples, prior and after the electrochemical tests. The experiments were carried out in 0.05 M H₃BO₃+0.075 M Na₂B₄O₇ solution with pH=8.4. Anodic polarization curves were recorded, potentiostatic current decay transients were obtained at anodic potentials and the polarization resistance was determined. The alloys show similar microstructures characterized by a Mg-based solid solution, surrounded by a very small amount of a secondary phase. The alloys investigated exhibit enhanced corrosion resistance with respect to AM60 alloy. Electrochemical investigations reveal that the surface layers formed on the erbium-containing alloys provide a better protective effectiveness than the magnesium hydroxide or aluminium hydroxide layer formed on AM60 in borate buffer solution. Based on preliminary analysis, the incorporation of erbium in the Mg(OH)₂ lattice is believed to be responsible for the improved corrosion behaviour of the Mg–Al–Er alloys.     

非恒温电解液中AA5083Al-Mg合金阳极氧化膜的制备及其耐蚀性

采用硼酸-硫酸-草酸电解液在铝合金表面制备有序多孔层,研究阳极氧化过程中电流随时间的变化,分析界面反应并计算膜层的生长效率。采用扫描电子显微镜、交流阻抗和动电位极化曲线研究膜层的微结构及其在不同温度环境下的耐蚀性。结果表明：在氧化层界面双离子层浓度的增大有利于提高膜层的生长效率。所制备的阳极氧化膜厚度为8-9μm,孔径为10-14 nm,膜层的微观形貌受金属基体组织结构的影响较大。在沸水封闭后膜层为分层结构,表面呈细片状。氧化膜层封闭后能够明显降低试样的自腐蚀电流密度,且耐蚀性随着环境温度的升高而具有更好的稳定性。     

Triazole and thiazole derivatives as corrosion inhibitors for AA2024 aluminium alloy

The 1,2,4-triazole, 3-amino-1,2,4-triazole, benzotriazole and 2-mercaptobenzothiazole were evaluated in the present work as corrosion inhibitors for protection of the 2024 aluminium alloy in neutral chloride solutions. The corrosion protection performance was investigated by means of DC polarization and electrochemical impedance spectroscopy (EIS). Scanning Kelvin probe force microscopy (SKPFM) and atomic force microscopy (AFM) were used to study the evolution of the Volta potential distribution and the surface topography during corrosion tests.The results show that all inhibitors under study confer corrosion protection to the AA2024 alloy forming a thin organic layer on the substrate surface. Benzotriazole and 2-mercaptobenzothiazole offer better corrosion protection in comparison with the other two. The inhibitors studied act decreasing the rate of both the anodic and cathodic processes. In the latter case the dealloying of the copper-reach particles is hindered, slowing down the oxygen reduction.     

Electrochemical behavior of Cu-Zn-Al shape memory alloy after surface modification by electroless plated Ni-P

The electrochemical behavior of Cu-Zn-Al shape memory alloy (SMA) with and without electroless plated Ni-P was investigated by electrochemical methods in artificial Tyrode‘s solution. The results showed that Cu-Zn-Al SMA engendered dezincification corrosion in Tyrode‘s solution. The anodic active current densities as well as electrochemical dissolution sensitivity of the electroless plated Ni-P Cu-Zn-Al SMA increased with NaC1 concentration rising, pH of solution decreasing and environmental temperature uprising. X-ray diffraction analysis indicated that after surface modification by electroless plated Ni-P, an amorphous plated film formed on the surface of Cu-Zn-Al SMA. This film can effectively isolate matrix metal from corrosion media and significantly improve the electrochemical property of Cu-Zn-Al SMA in artificial Tyrode‘s solution.