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.     

热镀锌层上磷酸锌转化膜的生长与耐蚀性

热镀锌钢板在pH3.0、45℃的磷酸锌溶液中磷化2～600s,用扫描电镜、能谱仪和X射线衍射仪分析磷化膜的组织形貌和成分,并探讨膜层的生长行为。结果表明:磷酸锌晶体在锌晶粒内及晶界处均可成核,开始是以接近平行的片状生长,并逐渐向多方向生长成扇骨状的晶片。随着磷酸锌晶体的成核和生长,磷化膜的覆盖率增加,但晶体之间的孔隙难以完全消除;长大的磷酸锌晶片容易折断脱落,导致磷化后期膜层的质量增量减小;磷化膜主要由Zn3(PO4)2.4H2O组成。热镀锌钢板经磷化处理后,耐蚀性显著提高,磷化膜的耐蚀性随磷化时间和膜层覆盖率的增加而提高。     

Crystallographic research of spangle on hot dip galvanized steel sheets

The spangles on hot dip galvanized steel sheet were investigated on an X-ray diffraction(XRD) meter by the rotating crystal method. The correlations between the crystallographic orientations of spangles and their morphologies were analyzed. The results show that the correlation can be classified into three types: β=0°, 0°<β<90° and β=90° by β. Crystallographic model of single spangle under the ideal condition was established based on the experimental results. The correlation between α and β can be deduced by their geometric relation as an equation.     

Growth and corrosion behavior of molybdate passivation film on hot dip galvanized steel

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An atomic emission spectroelectrochemical study of passive film formation and dissolution on galvanized steel treated with silicate conversion coatings

The effect of a silicate conversion coating, which was applied on electrogalvanized steel (EG) and hot dip galvanized steel (HDG), on zinc passivation and dissolution is investigated by atomic emission spectroelectrochemistry (AESEC) using anodic/cathodic cycles in a neutral borate buffer solution. We are able to decompose the total zinc oxidation rate into a soluble (dissolution) and insoluble (passivation) component. It is found that the silicate conversion coating reduces the soluble component with no measurable effect on the insoluble component. The results imply that zinc passive film formation occurs unhindered underneath the silicate film but the film effectively blocks zinc dissolution.     

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.     

退火工艺对980 MPa级热镀锌双相钢组织及性能的影响

利用奥钢联热模拟试验机模拟980 MPa级双相钢连续退火镀锌过程,利用拉伸试验机、光学显微镜和扫描电镜研究连续镀锌工艺中均热温度和快冷出口温度对双相钢组织及力学性能的影响。结果表明,经热镀锌退火后,980 MPa级双相钢的微观组织为铁素体+马氏体,组织中有Nb,Ti碳氮化物析出。随着均热温度的升高,马氏体体积分数呈逐渐增加的趋势,屈服强度和屈强比不断升高。快冷出口温度从340 ℃升高到430 ℃,马氏体发生回火分解,降低了试验钢的屈服强度,同时改善了伸长率。快冷出口温度为400 ℃时,强塑积达到最大值13.9 GPa·%。当均热温度为840 ℃,快冷出口温度为460~480 ℃时,可以获得抗拉强度在980 MPa级以上的双相钢。     

Molybdenum-phosphorus compounds based passivator to control corrosion of hot dip galvanized coated rebars exposed in simulated concrete pore solution

Hot dip galvanized (HDG) coating passivated with molybdenum-phosphorus compounds based passivator exhibits high degree of corrosion protection exposed in chloride contaminated simulated concrete pore solution (SPS). The coating develops very stable corrosion products and its corrosion potential gets greatly ennobled due to the formation of a complex passive layer. This composite layer has been identified as hydrozincite (HZ) embedded with several other compounds. The studies reveal that the presence of passive films on HDG makes the HZ layer more impervious and less soluble in the test electrolyte. The layer also helps in faster development of hydrozincite film on HDG surface. A faster healing of defects in hydrozincite layer takes place for passivated than the unpassivated surface. Electrochemical impedance spectroscopy (EIS), Raman Spectroscopy, Scanning Electron Microscopy (SEM), energy dispersive X-ray analysis (EDXA), and X-ray diffraction (XRD) studies etc. have been performed to study the kinetics and understand the mechanism of formation of hydrozincite at the corroding interface. These studies are expected to provide a new area in development of lesser polluting protective passive layer on galvanized coatings.     

热镀锌影响因素综述

论述了热镀锌原板化学成分、带钢表面状态、锌液成分、锌液温度和带钢入锌锅温度对热镀锌钢板镀层性能及表面状态的影响。     

热浸Zn-Ti合金镀层的耐腐蚀性能

为了抑制热镀锌过程中因含硅活性钢引起的镀层超厚生长,采用在纯锌浴中加Ti的方法,研究了热浸Zn-Ti合金镀层的耐蚀性能.采用浸泡腐蚀、电化学极化、交流阻抗以及X射线光电子能谱等方法,研究了热浸Zn-Ti合金镀层的耐蚀性能.结果表明:Zn-Ti舍金镀层在5%NaCl溶液中的自发腐蚀倾向小于Zn镀层,其极化电阻和交流阻抗增大,腐蚀电流密度减小,耐蚀性能提高.Zn-Ti镀层表面形成的氧化膜由ZnO和TiO2组成.Zn-Ti合金镀层的耐腐蚀性能优于纯锌镀层是由于在镀层表面形成了更加稳定的TiO2膜.     

我国超宽幅汽车板热镀锌生产线的分析

介绍了国内武钢、邯宝和京唐2 080 mm超宽幅汽车板热镀锌机组的产品方案、主要技术参数、机组特点、以及主要工艺装备,并针对未来汽车用钢的发展趋势,对今后国内新建宽幅汽车板热镀锌机组的建设和发展进行了展望。     

热镀锌机组立式钝化辊涂机的改造

针对某厂从国外引进的立式钝化辊涂机存在涂料辊寿命短、涂头角度偏大及移动调整机构繁琐等问题,进行了设备改造,使整体结构简化并成功用于实际生产中。改进后的辊涂机运行稳定,减少了钝化液的浪费,取得了良好的效果。     

Cerium chemical conversion coatings for corrosion protection of stainless steels in hot seawater environments

In order to replace the hazardous chromate‐based surface treatment, a new cerium chemical conversion coating was developed on 316L stainless steel through a mixed solution of hydrated cerium nitrate, citric acid, and hydrogen peroxide. The chemical composition was characterized by energy‐dispersive spectroscopy, X‐ray photoelectron spectroscopy and atomic force microscope. The dense conversion coating is composed of CeO₂ with a small amount of Ce₂O₃ and has small grain size lower than 50 nm. Its thickness is about 47.4 nm as determined by spectroscopic ellipsometry analysis. Potentiodynamic polarization was used to study the corrosion behavior of the coatings in the concentrated artificial seawater at 72 °C. In comparison with the conventional nitric acid‐chromate passivated specimens, the cerium conversion coatings show much higher pitting potentials. It is suggested that the cerium conversion treatment is more effective than the nitric acid‐chromate passivation to improve the pitting resistance of 316L stainless steel used in the hot seawater environments.     

退火工艺对冷轧低碳热镀锌钢板组织均匀性的影响

通过模拟退火试验及工业试制,研究了退火工艺对冷轧低碳热镀锌钢板组织均匀性的影响,探讨了钢板出现混晶组织的原因,并制定了解决方案。结果表明:加热速率偏低是造成混晶组织的主要原因,随着加热速率的升高,组织细化且均匀性改善;在较低加热速率下,延长均热时间和提高退火温度在一定程度上加剧了组织的不均匀性。针对镀锌机组降速生产引起混晶的问题,结合模拟退火试验结果,降低退火温度可以改善降速导致的混晶问题,制定了降速生产的退火工艺并应用于实际生产。     

浅析热镀锌机组停启机操作工艺方法

针对本溪钢铁公司冷轧热镀锌机组停启机时产生大量废品的问题,摸索出一套切实可行的操作工艺和方法,从而可合理控制退火炉气氛,达到了减少废品的目的。     

表面渗钛的镀锌钢板点焊电极寿命试验研究

对Cr-Zr-Cu合金的镀锌钢板点焊电极进行了表面渗钛处理，通过点焊电极寿命试验观测了表面渗钛处理前后镀锌钢板点焊的表面质量和电极端面状况。试验结果表明，采用表面渗钛可以提高镀锌钢板点焊电极的耐磨性和热稳定性，从而延长了电极的寿命。     

42CrMo钢六角头螺栓热镀锌裂纹分析

42CrMo钢六角头螺栓在热镀锌工艺完成后的磁粉探伤时发现部分螺栓的圆角处存在裂纹。采用光学显微镜、扫描电镜和能谱仪等对螺栓进行了断口、显微组织和成分分析。结果表明,开裂螺栓经破断后的断口符合氢脆断口特征,断口附近氢元素的质量分数偏高,达4×10^-6。裂纹形貌特征和氢脆裂纹特征吻合,裂纹两侧组织为正常的调质组织且裂纹内还发现有锌液残余,可以排除裂纹是由于组织异常或在淬火时产生的。因此,可以推断42CrMo钢六角头螺栓开裂类型为氢致开裂,氢致开裂发生在热镀锌过程中。     

热镀锌带钢清洗工艺探讨

基于对清洗工艺的探讨 ,分析了各因素对带钢清洗效果、清洗控制、清洗运行稳定性的影响 ,以及如何进行清洗净化度检验和清洗设备选择。