Effects of lanthanum addition on corrosion resistance of hot-dipped galvalume coating

Effects of La addition on corrosion resistance of hot-dipped galvalume coating steel wire were investigated.The corrosion resistance of Zn-Al-Si-La alloy coatings containing 0, 0.02wt.%, 0.05wt.%, 0.1wt.% and 0.2wt.% La were evaluated by various tests such as copper-accelerated acetic acid salt spray testing（CASS）, immersion test in 3.5% NaCl solution, electrochemical tests including weak polarization curves and electrochemical impedance spectroscopy（EIS） tests, scanning electron microscope（SEM） test and X-ray diffraction（XRD） test.It was found that the corrosion resistance of galvalume coating could be improved by adding proper amounts of La.Meanwhile, the mechanism of the improvement of corrosion resistance by La addition was discussed.

Effects of cooling rate on microstructure and microhardness of directionally solidified Galvalume alloy

The influences of cooling rate on the phase constitution,microstructural length scale,and microhardness of directionally solidified Galvalume(Zn-55Al-1.6Si)alloy were investigated by directional solidification experiments at different withdrawal speeds(5,10,20,50,100,200,and 400μm·s^(-1)).The results show that the microstructure of directionally solidified Galvalume alloys is composed of primary Al dendrites,Si-rich phase and(Zn-Al-Si)ternary eutectics at the withdrawal speed ranging from 5 to 400μm·s^(-1).As the withdrawal speed increases,the segregation of Si element intensifies,resulting in an increase in the area fraction of the Si-rich phase.In addition,the primary Al dendrites show significant refinement with an increase in the withdrawal speed.The relationship between the primary dendrite arm spacing(λ_(1))and the thermal parameters of solidification is obtained:λ_(1)=127.3V^(-0.31).Moreover,as the withdrawal speed increases from 5 to 400μm·s^(-1),the microhardness of the alloy increases from 90 HV to 151 HV.This is a combined effect of grain refinement and second-phase strengthening.

Galvalume在不同介质中腐蚀产物的形貌和成分分析对比及其对耐蚀性能的影响

利用二次电子成像技术分析了Galvalume镀层在NaCl,Na2SO4以及NaCl+Na2SO4介质中腐蚀产物的形貌,并用X射线衍射技术分析了各种腐蚀产物的化学组成。结果表明,在NaCl介质中的腐蚀产物主要为结构疏松的晶态物质,对镀层基本无保护作用;而在Na2SO4以及NaCl+Na2SO4介质中的腐蚀产物主要为结构致密的非晶态物质,对镀层具有较强的保护作用,说明SO2-4的存在是形成致密非晶产物的根本原因。

Mg对Galvalume镀层微观结构、耐蚀性和成形性的影响

利用扫描电镜、X射线衍射仪、电化学测试和杯突试验研究了Mg(质量分数1.5%)对Galvalume(Zn-55Al-1.6Si)镀层微观结构、耐蚀性和成形性的影响.扫描电镜和X射线衍射仪检测结果显示,添加Mg后在Zn-55Al-1.6Si-1.5Mg镀层的枝晶间区出现了MgZn2相;腐蚀产物的微观形貌显示Mg能减少镀层腐蚀产物中的裂纹,并提高其致密性.电化学检测结果显示,Zn-55Al-1.6Si-1.5Mg镀层的腐蚀速度仅为Galvalume的34.1%,因此Mg能显著地提高Galvalume镀层的耐蚀性;MgZn2作为强化相,强化了镀层的枝晶间区,减少了成形杯弯曲外表面的微裂纹,显著地提高了Galvalume镀层的成形性.

Galvalume镀层钢在青岛海域海水中的耐蚀性能

采用极化曲线测试和交流阻抗技术研究了Galvalume镀层钢在青岛海域海水中的耐蚀性能,利用电子扫描电镜对镀层表面的腐蚀产物形貌进行了分析,详细探讨了海水温度和溶解氧浓度对Galvalume镀层钢电化学腐蚀行为的影响。结果表明:温度升高,破坏了保护性腐蚀产物膜在镀层表面的吸附,促进了阳极活化反应过程。低浓度的溶解氧抑制了阴极反应,镀层的耐蚀性能提高。

V对Galvalume熔池锌渣形成的影响

为研究V对Galvalume熔池中锌渣相形成的影响,采用扫描电镜及能谱仪,对不同V含量(0.02%、0.05%、0.10%、0.20%)的Galvalume熔池中产生的金属间化合物进行形貌、大小、分布及成分分析。结果表明:当V含量为0.02%时,Galvalume熔池中析出少量多边形锌渣相,尺寸为60~80μm;随着V含量的增加,析出的锌渣相尺寸变大,随着V含量的增加,锌渣相长大、增多,出现长条状锌渣、粗大多边形锌渣。当V含量不大于0.1%时,锌渣主要为FeAl3金属间化合物构成;当V含量为0.2%时,生成了FeAl3、Al2 3V4-Zn9.8和Al21V2-Zn6.8锌渣。

暂态线性极化技术研究Galfan与Galvalume的耐蚀性能

利用暂态线性极化技术测定了Zn镀层以及Galfan、Galvalume镀层在不同腐蚀介质中、不同pH下的极化电阻R_p值,以及R_p随时间的变化规律。结果表明,腐蚀刚开始时,在pH=5和pH=7的1mol/L NaCl、0.5mol/LNa_2SO_4、0.5mol/L NaCl+0.25 mol/L Na_2SO_4腐蚀介质中,Galfan的R_p均约为Zn镀层的2倍,Galvalume的R_p均约为Zn镀层的3倍。腐蚀一定时间后,Zn镀层和Galfan的R_p均逐渐降低,而Galvalume的R_p除在1mol/L NaCl腐蚀介质中外皆不断升高。表明Galvalume的腐蚀产物对镀层有保护作用,使其耐蚀性进一步提高。

热浸镀Galvalume合金工艺性能研究

用正交试验法研究了还原法热浸镀中合金主要成分铝、硅含量,浸镀温度、保温时间、钢带入水温度等对镀层附着强度、微观组织、表面质量、浸镀效果(漏镀情况)的影响,得出获取良好镀层质量的工艺条件和参数选择.

热浸镀Galvalume合金工艺性能研究

用正交试验法研究了还原法热浸镀中合金主要成分铝、硅含量,浸镀温度、保温时间、钢带入水温度等对镀层附着强度、微观组织、表面质量、浸镀效果(漏镀情况)的影响,得出获取良好镀层质量的最佳工艺条件和参数。

唐钢3^#生产线Galvalume无液相急冷工艺开发

在分析Galvalume生产工艺特点的基础上,通过进行实验室Galvalume浸镀工艺的模拟研究,实现了Galvalume产品的无液相急冷工艺,并在唐钢3~#生产线进行试生产,取得了良好的效果。

热浸镀Galvalume熔池流动与传热的数值模拟

根据热浸镀Galvalume熔池的几何结构及工艺参数,建立了Galvalume熔池的数学模型,对不同速度、宽度和入池温度带钢热浸镀Galvalume过程中的熔池进行了数值模拟。结果表明:熔池内锌液流速与带钢速度成正比,随着带钢速度加快,熔池低速流动区域减少;带钢宽度影响熔池整体的流动形态,熔池内低温区域随着带钢宽度变大明显增多;带钢入池温度升高使得熔池内温度分布更均匀。

常见结构材料在热浸镀Galvalume合金熔体中的腐蚀与防护研究现状

伴随着热浸镀钢材的大量应用,热浸镀设备在液态金属中的腐蚀问题及引起的钢材表面质量降低问题逐渐凸显,制约了热浸镀行业的发展。概述了在热浸镀熔融Galvalume合金(Zn-55Al-1.6Si%)中,铁基、钴基及其他合金的腐蚀行为。合金及腐蚀产物的溶解,腐蚀层中的元素互扩散,腐蚀产物生长的应力集中,是造成合金基体失效的主要原因。通过金属合金化或施加防护涂层,提高了材料对液态锌铝合金的耐蚀性。综述了引入不同合金元素对合金腐蚀行为的影响,并评估了陶瓷涂层、金属陶瓷复合涂层及搪瓷涂层在此环境中的防护效果。合金基体或防护涂层中引入硼化物,可有效降低液态锌铝合金的侵蚀。提高材料在液态金属环境中的不润湿性是改善其耐蚀性的关键。最后,展望并总结了熔融Galvaleme合金中的高性能防护涂层、合金设计原则及其腐蚀失效特性。

合金元素Sb对Galvalume镀层的影响及机理研究

向55%Al-Zn-1.6%Si熔池中加入0.1%Sb、0.3%Sb和0.5%Sb,在600℃进行热浸镀实验,对镀层组织进行扫描电镜和能谱分析,并对镀层金属间化合物的生长动力学进行了分析研究。研究结果表明:熔池中加入0.1%Sb即能对镀层金属间化合物层的生长起到抑制作用,随后进一步提高Sb的量,对金属间化合物层的生长的抑制作用没有明显变化。

Investigation and improvement of tiny spot defects on hot-dip galvanized automotive steel sheets

The causes of tiny spot defects on the surface of hot-dip galvanized automotive steel sheets were studied using scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS),and effective control measures were introduced.The results show that rubbing against the top roller after galvanizing is easy due to the local thickness of tiny spot defect location coating;therefore,the surface morphology is different from the normal part.Three kinds of defects,namely zinc slag,small slivers,and pitting,are likely to cause local thickening of the coating after galvanizing,leading to the formation of tiny spots.Therefore,resolving the three types of defects can effectively control the generation of tiny spot defects.Among them,due to the hereditary nature of the small sliver defect,focusing on its control and supervision is necessary.

Effect of hot-dip galvanizing processes on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel

A C–Mn dual-phase steel was soaked at 800°C for 90 s and then either rapidly cooled to 450°C and held for 30 s(process A) or rapidly cooled to 350°C and then reheated to 450°C(process B) to simulate the hot-dip galvanizing process. The influence of the hot-dip galvanizing process on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel(DP600) was investigated using optical microscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and tensile tests. The results showed that, in the case of process A, the microstructure of DP600 was composed of ferrite, martensite, and a small amount of bainite. The granular bainite was formed in the hot-dip galvanizing stage, and martensite islands were formed in the final cooling stage after hot-dip galvanizing. By contrast, in the case of process B, the microstructure of the DP600 was composed of ferrite, martensite, bainite, and cementite. In addition, compared with the yield strength(YS) of the DP600 annealed by process A, that for the DP600 annealed by process B increased by approximately 50 MPa because of the tempering of the martensite formed during rapid cooling. The work-hardening coefficient(n value) of the DP600 steel annealed by process B clearly decreased because the increase of the YS affected the computation result for the n value. However, the ultimate tensile strength(UTS) and elongation(A80) of the DP600 annealed by process B exhibited less variation compared with those of the DP600 annealed by process A. Therefore, DP600 with excellent comprehensive mechanical properties(YS = 362 MPa, UTS = 638 MPa, A_(80) = 24.3%, n = 0.17) was obtained via process A.

Surface modification of die casting mold steel by a composite technique of hot-dipping and plasma electrolytic oxidation

The hot dipping process of pure aluminum on H13 steel substrates followed by plasma electrolytic oxidation(PEO) was studied to form alumina ceramic coatings for protective purpose.H13 steel bars were first dipped in pure aluminum melts,and then,a reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate.The reactive layer was mainly composed of intermetallic Fe-Al(Fe_2Al_5);the thickness of aluminum layer and Fe-Al intermetallic layer were mainly influenced by dipping time(1.5～12.0 min) and dipping temperature(710～760 ℃).After PEO process,uniform Al_2O_3 ceramic coatings were deposited on the surface of aluminized steel.The element distribution,phase composition and morphology of the aluminized layer,and the ceramic coatings were characterized by SEM/EDS and XRD.The distribution of hardness across the composite coating is demonstrated,and the maximum value reaches 1864 HV.The thermal shock resistance of the coated sample is also well improved.

The Influence of Al on the Surface Properties of the Hot-dip Galvanized Melt

Wettability of Zn-Al alloy melt on the pure iron substrate at 450℃was studied.The effect of Al content(Zn,Zn-1Al,Zn-2Al,Zn-3Al,Zn-4Al,and Zn-5Al)on the wetting behavior and interfacial reaction was investigated by high-temperature contact angle measuring device and scanning electron microscope(SEM).The results show that,with the increase of Al content,the initial contact angle of the molten alloy on the substrate decreases gradually and the wettability increases gradually.Compared with the initial contact angle,the final contact angle is slightly reduced,because the Fe-Al inhibition layer is preferentially formed at the interface when adding Al to the alloy.The presence of Al will promote the occurrence of the reactive wetting,leading to an insignificant wetting spreading process,and the final contact angle negligibly differs from the initial contact angle.The adhesion work and charge density distributions of interface systems were calculated based on the first-principles.The results show that the adhesion work of the Fe/Zn and Fe/(Zn-Al)interface model is 2.0171 J/m^(2)and 13.7944 J/m^(2),respectively.The addition of Al greatly increases the adhesion work between alloy melt and iron substrate.Compared with the Zn-Fe and Al-Fe interface models,it can be seen that a significant charge migration phenomenon occurs between the interfaces.The amount of charge migration in the Al-Fe interface model is much larger than that in the Zn-Fe interface model,indicating that the bonding between Al-Fe atoms can occur more easily and the interaction between Al-Fe interfaces is stronger.This is also the reason why the addition of Al increases the adhesion work between interfaces.

Hot-Dip Coating of Lead-free Aluminum on Steel Substrates with Ultrasonic Vibration

Hot-dip coating has been practically employed in manufacturing zinc alloy coated steel sheets.However,it is difficult to coat aluminum alloy on a bulky steel substrate without sufficient preheating,because a rapidly solidified layer containing gas babbles is formed on a substrate surface.A variety of iron-aluminides are also formed at the interface of a steel and aluminum hot-dip coating system,which is the main difficulty in joining of steel with aluminum.Ultrasonic vibration was applied to a steel substrate during hot-dip coating of aluminum alloy to control a rapidly solidified layer and a brittle reaction layer.Hot dipping of columnar steel substrates into molten aluminum alloy （Al-2.7 mass fraction Si-4.6 mass fraction Sn） was carried out through the use of a Langevin oscillator with resonant frequency of 19.5 kHz.The application of ultrasonic vibration is quite effective to control a rapidly solidified layer and a surface oxide layer from a substrate surface by the sonocapillary effect based on a cavitation phenomenon,so that the intimate contact is achieved at the beginning of hot-dip coating.The application of ultrasonic vibration to hot-dipping is effective to control a reaction layer with less than 5 #m in thickness.An impact test exhibits that the good adhesive strength is approved in hot-dipped aluminum coatings with a thin reaction layer of approximately 5μm.

Hot-Dip Galvanized Sheet Production and Application

Hot-dip galvanized sheet is wildly used in construction,household appliances,ship,vehicle and vessel building and machinery,etc.In last ten years,with the development of automobile industry,the anti-eorrosion requirements for car body are increasingly strict,by which the rapid development in technology has been promoted.The application of hot-dip galvanized sheet,technological progress in production and some Chinese large units were introduced.

Preparation and hot-dip galvanizing application of CeO_2/Zn nanocomposite

CeO2/Zn nanocomposite was fabricated by high-energy ball milling and subsequent hot-press sintering under vacuum. The produced nanocomposite powders and bulks were characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM） and scanning electron microscopy （SEM） with an energy dispersive X-ray spectrum （EDS）. The as-fabricated nanocomposite bulks were added successfully into the hot-dip galvanizing bath to improve the corrosion resistance of coatings. The results show that after milling for 120min, nano-sized CeO2 particles are distributed homogeneously on the surface of fine Zn particles to form spherical-like nanocomposite powder with narrow grain size distribution. The subsequent sintering does not lead to a dramatic grain growth, and the distribution of CeO2 nanoparticles in the composite bulk is also homogeneous. With the addition of as-prepared bulks, the corrosion resistance of the galvanized coatings is improved obviously. It provides a feasible route for adding CeO2 nanoparticles into the hot-dip galvanized coating.