Corrosion behaviour of Zn–Al–Mg coated steel sheet in sodium chloride-containing environment

Conventional hot-dip galvanised zinc coated (Z) and novel hot-dip galvanised Zn–Al–Mg alloy coated (ZM) steel sheet samples with a coating thickness of 7 μm each were exposed to standardised salt spray test and cross-sections of the corrosion samples were analysed by using SEM and EDS. On Z corrosion proceeds very fast and the steel substrate is attacked even after 100 h of exposure. ZM samples showed a different behaviour. The entire metallic ZM coating is converted into a stable, adherent aluminium-rich oxide layer, which protects the steel substrate against corrosive attacks. This layer is the main reason for the enhanced corrosion resistance of the ZM coating in sodium chloride-containing environment.     

The influence of pre-straining on the corrosion fatigue performance of two hot-dip galvanised steels

The corrosion fatigue behaviour of a hot-dip galvanised ferritic pearlitic steel and of a hot-dip galvanised Ti-alloyed high-strength interstitial free steel was investigated. The testing mode was constant displacement, fully reversed plane bending. Both materials were tested as received and 10% uniaxially pre-strained. The effect of pre-straining on the zinc coating was investigated using polarisation resistance measurements and the scanning reference electrode technique (SRET). It was found that pre-straining is detrimental to the corrosion fatigue behaviour of both steels, due to damage to the zinc coating, leading to increased localised corrosion and in general higher corrosion rates.     

Ra 及 Rpc 对无铬耐指纹热镀锌板表面性能的影响

目的研究热镀锌板表面平均粗糙度Ra和峰值数Rpc对无铬耐指纹热镀锌板表面耐指纹性、耐腐蚀性和涂装性的影响。方法将Ra=0.6~1.1μm和Rpc=55~100的热镀锌板制成耐指纹板,采用X射线光电子能谱仪分析其组成,采用分光光度仪分析其耐指纹性,采用硫酸铜混合溶液滴定和盐雾试验方法检测其耐腐蚀性,采用涂漆和冲击实验检测其涂装性。结果耐指纹膜和锌层表面形成Si—O—Zn金属键,耐指纹膜除了物理结合,还通过化学键合的方式与锌层表面结合。在充分交联固化和化学键合的情况下,无铬耐指纹热镀锌板耐指纹性不受热镀锌板Ra和Rpc的影响;热镀锌板Ra值越低,耐腐蚀性越好;耐指纹膜单位质量为1.1 g/m2,Ra≤1.1μm时,耐指纹板72 h盐雾试验白锈面积不大于5%;热镀锌板Rpc值越高,无铬耐指纹热镀锌板涂装性越好,Rpc≥80时,耐指纹热镀锌板涂漆冲压后,漆膜完好。结论 Ra和Rpc对热镀锌板耐指纹性影响不大,对耐磨蚀性和涂装性影响显著。     

稀土La对热镀锌层耐蚀性能的影响

向热镀锌（GI）（Zn-0．2％Al）锌池中加入微量单质稀土La,采用热镀锌模拟机制备含La的锌镀层。采用盐雾腐蚀试验、全浸腐蚀失重试验和线性极化试验,研究了单质稀土La元素对镀层耐蚀性能的影响。结果表明,不同的腐蚀试验结果具有很好的一致性;相对Gl镀层而言,含La镀层中的La并未明显抑制白锈的产生,但明显抑制了红锈的...     

对比研究热浸镀55%Al-Zn镀层与Zn镀层在盐水中的腐蚀机理

用盐雾腐蚀和浸泡腐蚀两种方法对比研究了热浸镀55%Al-Zn镀层和Zn镀层在盐水环境中的腐蚀行为。用光学显微镜和扫描电子显微镜观察了清除腐蚀产物后镀层表面组织和横截面形貌特征。热浸镀55%Al-Zn镀层在盐雾腐蚀288h时的失重率约为Zn镀层的1/2,说明55%Al-Zn镀层具有更好的耐蚀性。用电化学阻抗谱方法分析镀层的腐蚀机理,认为55%Al-Zn镀层腐蚀前期由扩散控制,后期由于极化电阻的减小,电荷转移增多;而Zn镀层腐蚀前期是由于极化电阻减小,电极表面以电荷转移过程为主,后期表现出扩散特征。     

Effect of silicate pretreatment, post-sealing and additives on corrosion resistance of phosphated galvanized steel

Sodium silicate （water glass） pretreatment before phosphating, silicate post-sealing after phosphating and adding silicate to a traditional phosphating solution were respectively carried out to obtain the improved phosphate coatings with high corrosion resistance and coverage on hot-dip galvanized（HDG） steel. The corrosion resistance, morphology and chemical composition of the coatings were investigated using neutral salt spray（NSS） tests, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results show that pretreatment HDG steel with silicate solutions, phosphate coatings with finer crystals and higher coverage are formed and the corrosion resistance is enhanced. Adding silicate to a traditional phosphating solution, the surface morphology of the coatings is nearly unchanged. The corrosion resistance of the coatings is mainly dependent on phosphating time. Phosphating for a longer time （such as 5 min）, the corrosion resistance, increasing with concentration of silicate, is improved significantly. Post-sealing the phosphated HDG steel with silicate solutions, the pores among the zinc phosphate crystals are sealed with the films containing Si, P, O and Zn and the continuous composite coatings are formed. The corrosion resistance of the composite coatings, related to the pH value, contents of hydrated gel of silica and Si2O^2- 5 and post-sealing time, is increased markedly. The improved coatings with optimal corrosion resistance are obtained for phosphating 5 min and post-sealing with 5 g/L silicate solution for 10 min.     

硝酸铈处理对磷化膜组织和耐蚀性的影响

为了发挥磷化膜和铈盐膜的优势,采用硝酸铈前处理或硝酸铈后处理对热镀锌层上的磷化膜进行改进,通过SEM,EDS,NSS和Tafel极化研究了硝酸铈改进磷化膜的显微组织和耐蚀性,并与铬酸盐钝化膜进行了比较。结果表明:硝酸铈前处理或后处理改进磷化膜均为含P,O,Ce和Zn化合物的复合膜,基本上克服了单一膜层的缺陷,使得复合膜的耐蚀性明显增强;硝酸铈后处理改进复合膜的耐蚀性优于铬酸盐钝化膜,有望成为高毒性铬酸盐钝化膜的替代品。     

Incorporation graphene into sprayed epoxy–polyamide coating on carbon steel: corrosion resistance properties

In this study, the graphene incorporated into epoxy–polyamide coatings were successfully obtained on carbon steel substrates by spraying process. The corrosion resistance properties of the coatings were investigated, including salt spray corrosion, sea water corrosion and electrochemical corrosion resistance. The results show that the addition of graphene could improve the corrosion resistance properties of the epoxy–polyamide coatings. The coatings in the presence of graphene had better salt spray corrosion than that in the absence of graphene. The surface of the epoxy–polyamide coating exhibited lots of pitting corrosion. The coatings with the addition of graphene showed better sea water corrosion than the coating without graphene. After drying, the epoxy–polyamide coating in the absence of graphene was broken and failed. The coating with 1?wt-% graphene exhibited the best anticorrosion capability as evidenced by the highest corrosion potential and the lowest corrosion current density. The graphene incorporated into epoxy–polyamide coatings were shown to effectively protect carbon steel against corrosion because the graphene nanosheets could be acted as the good chloride ions, oxygen and water molecules barrier.     

钢板热镀55%Al-Zn层的耐盐水腐蚀性能

采用全浸、半浸和盐雾等试验方法研究了钢板热镀55 %Al-Zn合金镀层在3%NaCl的盐水溶液中的腐蚀行为.观察分析了镀层的组织结构和在盐水中 腐蚀后的表面形貌及腐蚀产物,阐述了镀层在盐水中的腐蚀过程和机理.结果表明55%Al-Zn 合金镀层比Zn镀层更耐蚀,并同样具有Zn镀层对钢基体的保护能力.     

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.     

Effect of molybdate post-sealing on the corrosion resistance of zinc phosphate coatings on hot-dip galvanized steel

The technique of post-sealing the phosphated hot-dip galvanized (HDG) steel with molybdate solution was addressed. The composition and corrosion resistance of the improved phosphate coatings were investigated by SEM, EDS, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements, and neutral salt spray (NSS) test. The results showed that molybdate films were formed in the pores of phosphate coatings, and the compact and complete composite coatings composed of phosphate coatings and molybdate films were formed on the zinc surface, resulting in that both the anodic and cathodic processes of zinc corrosion were inhibited remarkably; the corrosion protection efficiency values were increased; and the electrochemical impedance values were enhanced at least one order of magnitude. The low frequency impedance values for the composite coatings were increased at the initial stages of immersion in 5% sodium chloride solution, indicating the self-repairing activity of the composite coatings.     

Preparation and characterisation of acrylic–polyurethane-based waterborne anticorrosion coating on galvanised steel

Four water-based organic composite coating solutions were prepared and applied on galvanised sheet samples producing a transparent film of about 5-µm thickness. Their corrosion performances were examined by Tafel polarisation, EIS, salt spray and cyclic corrosion tests. The primary coating formulation contained an acrylic emulsion and polyurethane dispersion mixture together with additives. The corrosion resistance properties of the primary formulation were enhanced by adding nano-ZnO particles, and further improved by adding corrosion inhibitors such as zinc phosphate and sodium phosphate. The final formulation on galvanised samples showed 720?h of salt spray resistance and 90 cycles of cyclic corrosion resistance, SAE J2334. The Tafel and EIS studies indicate that the coating possesses barrier protection properties. The electrolyte penetrates through the coating within 24?h but progress of corrosion depends upon the coating adhesion and its compactness, that is improved significantly by adding nano-ZnO and corrosion inhibitor to the coating formulation.     

热镀锌板双硅烷无铬钝化膜性能的研究

目的为进一步提高热镀锌板无铬钝化膜的耐腐蚀性能。方法以偏钒酸铵和氟钛酸作为无机组分,添加主要成膜物质苯丙乳液,通过硅烷偶联剂KH-560和KH-570将两者紧密连接,在热镀锌板表面获得一层耐腐蚀性较强的双硅烷无铬钝化膜。采用中性盐雾试验、电化学试验、扫描电镜(SEM)、傅里叶红外光谱(FTIR)等表征钝化膜的耐腐蚀性能。结果热镀锌板-双硅烷无铬钝化膜经96 h中性盐雾试验,腐蚀面积在2%~4%,腐蚀电流密度比热镀锌板基体降低一个数量等级,这表明双硅烷无铬钝化膜能提供良好的耐腐蚀能力。SEM分析表明在热镀锌板表面生成了一层均匀、连续、致密的钝化薄膜,钝化膜的厚度大约在3μm。FTIR分析表明,双硅烷无铬钝化膜中存在—(CH_2)_n—、C=O、Si—O、Si—O—Si、Si—O—Zn键。结论在热镀锌板表面生成了一层均匀、致密的钝化膜,使热镀锌板呈现良好的耐腐蚀性能,且满足工业应用标准。     

Chemistry of corrosion products on Zn-Al-Mg alloy coated steel

Zn-Al-Mg alloy (ZM) coating provides a decisively enhanced corrosion resistance in a salt spray test according to DIN EN ISO 9227 (NSS) compared to conventional hot-dip galvanised zinc (Z) coating because of its ability to form a very stable, well adherent protecting layer of zinc aluminium carbonate hydroxide, Zn₆Al₂(CO₃)(OH)₁₆·4H₂O on the steel substrate. This protecting layer is the main reason for the enhanced corrosion resistance of the ZM coating. Surface corrosion products on ZM coated steel consist mainly of Zn₅(OH)₆(CO₃)₂, ZnCO₃ and Zn(OH)₂ with additions of Zn₅(OH)₈Cl₂ · H₂O and a carbonate-containing magnesium species.     

Effects of rare earth elements on corrosion behaviors of low-carbon steels and weathering steels

The effects of rare earth elements on the corrosion properties of low-carbon steel and weathering steel were investigated. To elucidate the roles of rare earth elements (Ce and La) and the corrosion behavior of steels, salt spray tests, electrochemical techniques, X-ray diffractometer, scanning electron microscopy, Electron Probe Micro Analysis (EPMA), and Auger Electron Spectroscopy (AES) were conducted. The results showed that the addition of rare earth elements enhances the corrosion resistance of both low-carbon steels and weathering steels, indicated by lower corrosion current density and salt spray corrosion rate after rare earth alloying. On the one hand, rare earth elements modify the morphology of inclusions and thus slow down the micro-area electrochemical corrosion, which improves the electrochemical corrosion resistance of these two steels. On the other hand, rare earth atoms tend to segregate toward the interface between the rust layer and the matrix. Hence, salt spray corrosion resistance is improved due to the enhancement of adhesion and compactness of the rust by the addition of rare earth elements.     

钼酸盐后处理提高热镀锌上磷化膜耐蚀性的探讨

将磷化后的热镀锌钢板用钼酸盐后处理,以提高磷化膜的耐蚀性。用SEM、EDS、电化学极化测量和盐雾试验研究了钼酸盐后处理对磷化膜组成和耐蚀性的影响。结果表明,经钼酸盐处理后,磷化膜上磷酸锌晶体间的孔隙被钼酸盐膜填补,从而在锌层表面形成了由磷化膜和钼酸盐膜构成的连续完整致密的复合膜;复合膜的极化电阻Rp显著增大,腐蚀电流密度显著减小,耐蚀性大大增强。磷化300s、后处理50s时复合膜的耐蚀性最优,Rp比单磷化膜的增加了一个数量级。     

模拟酸雨大气环境镀锌钢的室内加速腐蚀行为和机理

目的 采用室内加速试验方法研究热浸镀锌钢在模拟酸雨大气环境中的腐蚀行为和机理。方法 主要采用失重法对试样的腐蚀动力学进行研究,采用EDS、XRD和XPS对试样进行腐蚀产物成分分析,通过SEM和共聚焦显微镜观测试样表面形貌,采用EIS对试样表面涂层的保护性能进行检测。结果 在模拟酸雨大气环境中,厚度损失与时间呈幂函数关系,腐蚀大致是一个减速过程但在104 d后加速,在120 d后试样表面出现红锈和密集、深而窄的点蚀坑。主要腐蚀产物有ZnO、Zn4SO4(OH)6及可溶性产物ZnSO4.xH2O和Na2ZnSO4.4H2O,并且由截面形貌可知,镀层在酸雨环境中易被破坏。结论 在模拟酸雨大气环境中,热浸镀锌本身的耐蚀性很快失效,腐蚀速度加快直至生成的腐蚀产物在缺陷处形成较为完整的产物膜,对镀层的腐蚀具有一定抑制作用。但是酸雨环境中腐蚀产物膜较薄,易被破坏,这种溶解会使镀层失去保护,进一步腐蚀。     

Enhanced corrosion protection by powder coatings on hot rolled steel (HRS) for high-temperature applications

Hot rolled steel (HRS) has long been a major product to the motor industry for bodywork, as galvanised steel (zinc coatings), and it is widely used in building and as tinplate (including tin and chrome oxide coatings) for food, etc. can-making. Among more specialist uses its moderate production costs makes it suitable for the manufacturing process. In this study, newly developed corrosion protection enhanced silicone based powder coating was evaluated on hot rolled steel (HRS). The powder coating in this study was developed to withstand high temperatures up to 550°C without any degradation. In the study silicone resin was incorporated with fillers, corrosion inhibitors and fibres at various compositions to achieve maximum heat resistance and improved corrosion resistance. Protective behaviours of the differently formulated powder paints were investigated before and after heat exposure. The developed paint system was evaluated using various test methods such as heat resistance, salt spray, Electrochemical Impedance Spectroscopy (EIS), adhesion test and microstructure study using SEM. The evaluation of test results revealed that powder coating combining zinc dust particles and mineral fibres have better performance due to better corrosion and adhesion stability in the corrosive environment before and after heat exposure up to 550°C.     

电弧喷涂Ti6Al4V涂层的组织与耐蚀性能研究

采用电弧喷涂技术在Q235钢基体上喷涂Ti6Al4V涂层,并对涂层进行封孔处理.表征了涂层的物相组成和微观形貌,通过盐水浸泡实验和极化曲线测试对比分析了Q235钢基体、未封孔涂层和封孔涂层的耐腐蚀性能.结果表明:涂层呈典型的层状特征,物相组成为TiN,TiO和少量的Ti;未封孔涂层与封孔涂层均具有较宽的钝化电位区间,封...     

Q235钢表面热镀铝微弧氧化陶瓷层的性能

通过热浸镀铝后进行微弧氧化的方法在Q235钢表面获得一层陶瓷层,测定了微弧氧化陶瓷层的耐蚀性、耐磨性及硬度。结果表明无论是在NaCl溶液还是在海水中,陶瓷层的耐蚀性均优于热浸镀铝层。热浸镀铝层与陶瓷层都在10%NaCl溶液中的耐蚀性最差。陶瓷层的耐磨性显著优于经840℃淬火 150℃回火的45#钢,当摩擦延长米为70m时,陶瓷层的耐磨性提高了2倍多。陶瓷层的硬度比基体提高了约10倍。