Zr,Co,Ni,V微合金化对含硅结构钢热浸镀锌性能的影响

研究了在锌池中依次添加0.1%Zr、0.1%Co、0.1%Ni、0.1%V微合金化元素对含硅结构钢热浸镀锌性能的影响,并结合扩散通道理论解释了合金元素及其协同作用对硅反应性抑制的机理。研究表明,锌池中添加0.1%Zr或0.1%Co+0.1%Zr时,会在ζ层外侧形成少量不连续的Zn-Fe-Zr或Zn-Co-Zr三元化合物,但其只减薄了Sandelin钢镀锌时的镀层厚度,而对抑制高硅钢的硅反应性基本没有贡献。继续添加0.1%Ni后,Ni会在纯锌层与ζ层的界面上富集,可抑制Q235钢的硅反应性,但不能抑制Q345钢中的硅反应性。直到锌池中添加了0.1%Zr-0.1%Co-0.1%Ni-0.1%V后,才能很好的抑制Q345钢中的硅反应性。此时,在自由锌层与ζ层的界面上形成了明显的Zn-Fe-Ni-V化合物。通过扩散通道模型可以很好地解释这些实验现象。     

热浸镀中硅反应性研究

根据对Zn-Fe-Si三元体系的热力学评估计算和实验研究,体系中Si的化学位随Zn含量的增加而迅速提高.通过高温镀锌实验分析了diffuse-△(δ相 锌液)区域形成的原因,阐述了热浸镀锌中硅反应性的机理.镀层中的Si有向Fe含量高的相(特别是δ/ζ相界附近的δ相)、δ/ζ相界及ζ相晶界富集的趋势.随时间推移,扩散通道向富Si端移动,切过ζ相与液相两相平衡的共轭线,导致ζ相晶界附近出现的液体容纳Si,形成液体通道,液相穿过ζ相并与外面的锌液连接.液体直接与δ相接触,导致微应力的出现,液体可以沿着微裂纹腐蚀δ相,形成破碎的diffuse-△区域,锌液直接侵蚀基体.镀层生长受界面反应控制,镀层的线性生长导致形成较厚的镀层.     

Control of Silicon Reactivity in General Galvanizing

In general galvanizing Si dissolved from steels destabilizes the Γ and Γ₁ phases in the alloy layer of the coating. It also alters the morphology of ζ crystallites in the alloy layer thereby exposing the δ layer to the melt. The incompatibility of the liquid phase and the δ phase cause the latter to disintegrate. These changes result in an excessive steel reactivity in general galvanizing. This reactivity can be easily controlled by alloying the Zn bath with metals, such as Ni, if the Si content of the steel does not exceed 0.20%. To combat a fully developed reactivity problem, one has to stabilize the Γ and δ sublayers in the coating. Alloying the bath with suitable metals can generate new equilibrium states to allow the co-existence of the liquid phase and the δ phase thereby preventing its disintegration; the Γ and Γ₁ phases can be stabilized through solid solution of the alloying elements in these phases. The introduction of Al to general galvanizing baths generates new equilibrium states thereby ushering a total new approach to Si reactivity control. Part of this paper was presented at the 7th Asia Pacific General Galvanizing Conference held in Beijing China, September 14-17, 2007.     

Synergistic effect of Cu and Si on hot-dipping galvalume coating

The coating microstructures and thicknesses of the iron panels galvanized in galvalume baths containing 0.0, 0.1, 0.5 and 1.0 wt.%Cu for 10 s, 30 s, 60 s, 180 s, 300 s and 600 s have been studied detailedly. The results indicate that Cu can effectively control the Fe–Al reactivity by the synergistic effect with Si. The addition of Cu makes Si be enriched in the reaction region during the hot-dipping. It promotes the formation of the τ₅ phase and hinders the growth of the Fe₂Al₅ phase. The diffusion path model was introduced to studying the effects of Cu and Si in the present study. The addition of 0.5–1.0 wt.%Cu in galvalume bath forms a stable diffusion path, iron substrate/Fe₂Al₅/FeAl₃/τ₅/overlay. The violent reaction between the iron substrate and the Al–Zn liquid is under control by the compact intermetallic layer, and it decreases the thickness of the intermetallic layer.     

钴对含硅钢镀锌层的组织和生长动力学的影响

利用扫描电镜及波谱,研究锌浴中的钴对Q235和Q345钢热浸镀锌层组织及其生长动力学的影响.结果表明:锌浴中含0.075%(质量分数)钴时,能完全抑制Q235镀层组织发生硅反应性;而对于Q345,则需要在锌浴中加入0.3%钴才能部分抑制硅反应性;在锌浴中加入少量的钴后,镀层组织中疏松ζ层转变成与液相直接接触的富钴ζ相和由消耗δ相生成的致密ζ相;致密的ζ相层阻止液相和δ相的直接接触;富钴ζ相可容纳大约0.25% Si,避免在固-液界面产生硅的富集,液相通道消失,从而抑制含硅钢热浸镀锌过程中硅反应性的产生.     

Microstructure of the coating and mechanical properties of galvanized chromium-rich martensitic steel

Protecting the modern high-strength steels against corrosion is a challenge because the coating technology must be compatible with forming and must preserve the mechanical performances. Batch galvanizing after hot stamping could provide a simple solution to this complex problem. A commercial high-strength martensitic steel containing 13 wt.% Cr, 0.35 wt.% Si, 0.3 wt.% Mn and 0.15 wt.% carbon has been galvanized with a commercial zinc alloy. Galvanizing produces a ~ 15 μm thick coating that is bright, continuous and metallurgically bonded. The intermetallic layer is made of ? crystals, which forms an open 3-dimensional structure. Tin, nickel and aluminium are found able to moderate the Sandelin effect. Comparison with other steels galvanized the same way indicates that chromium slows down the kinetics of the metallurgical reaction. Chromium distributes both in the ? and η phases, and follows a diffusion-like profile in the coating. The nickel from the alloy concentrates in the Fe-Zn intermetallic compound. Aluminium segregates at the surface and interface. It also provides a gettering effect that fixes silicon in sub-micron particles dispersed in the ? and η phases. Tensile experiments and fatigue tests demonstrate that the mechanical performances of the martensitic steel are preserved after coating. Comparison with similar experiments performed on a TRIP800 steel indicates that using galvanized martensitic steel is best worth in static applications.     

Technigalva and other developments in batch hot-dip galvanizing

The Technigalva process is a batch hot-dip galvanizing process developed over the past ten years that uses nickel additions for better control of coating structure, especially when galvanizing “reactive” steels containing around 0.1 wt.% Si. Optimization of the process relies on understanding of the role of nickel in the galvanizing reaction and formation of dross. Increasing demand for more environmentally friendly galvanizing processes has helped to lead to development work in batch hot-dip galvanizing on chromatefree passivation, alternative fluxes for using Zn-Al alloys, and process optimization.     

Wetting force and contact angle measurements to evaluate the influence of zinc bath metallurgy on the galvanizability of high-manganese-alloyed steel

The present investigation aimed to evaluate the influence of zinc bath metallurgy on the hotdip galvanizing of a high-manganese-alloyed steel (commercial grade X-IP 1000). Wetting force and contact angle measurements were carried out by the Wilhelmy plate methodology to assess zinc bath compositions. The Wilhelmy plate methodology was particularly suitable for both quantifying liquid zinc wetting and producing coated samples to be characterized. The aluminium content of the zinc bath varied between 0.05 and 1.10 wt % and manganese as well as silicon was additionally added to the bath composition. Best wetting occurred with aluminium contents which are typical for industrial galvanizing baths (0.12-0.22 wt %). But zinc wetting and wetting reactivity decreased with increasing aluminium content > 0.30 wt %. Hence, aluminothermic MnO reduction seems to be ineffective in the present case. Wetting results might be further improved by adding manganese or silicon to the zinc bath due to an improved wetting reaction. However, the formation of additional phases in the coating has to be considered with regard to technical use.     

Reactive wetting during hot-dip galvanizing of high manganese alloyed steel

The present study discusses reactive wetting during hot-dip galvanizing of high Mn alloyed steel (X-IP1000, 23 wt.% Mn) and is focused on investigating the influence of the metallic Mn concentration in the steel bulk composition on phase formation at the interface steel/coating. Samples were in-line bright annealed (1100 °C/ 60 s in N2-5%H2 at DP −50 °C) prior hot-dipping to avoid external MnO on the steel surface. This approach was applied to avoid influencing the wetting reaction by an aluminothermic MnO reduction, because this is considered to lead to an unwanted zeta-phase (FeZn13) formation in the coating by hot-dipping of Mn alloyed steels (< 5.0 wt.% Mn). The influence of hot-dipping parameters, which are contributing to the kinetics of the wetting reaction, was examined in terms of varying bath-Al content (0.17 and 0.22 wt.%), bath temperature (440-500 °C) and strip entry temperature (420-520 °C). The structure and chemical composition of both galvanized coating and interface steel/coating were characterized. While external MnO was verifiably avoided, brittle zeta-phase distinctively appeared at the interface steel coating together with the typical Fe₂Al₅ phase. This shows that the model of aluminothermic MnO reduction failed in the present case. This study suggests an alternative model explaining the appearance of zeta-phase with the removal of bath-Al by metallic Mn, which is dissolved out of the steel bulk into the Zn bath. The present investigation shows that alloying elements in the steel bulk may influence coating quality not only “indirectly” by external formation of nonwettable oxides, but also “directly” by influencing phase equilibria and kinetics of the wetting reaction. Understanding these phenomena will improve processing of (high) alloyed steel concepts as well as industrial Zn bath management.     

Die Feuerverzinkung siliziumhaltiger Stähle – Problem und Lösungsmöglichkeiten

Hot dip galvanizing of silicon containing steels – the problem and some attempts to its solution Hot dip galvanizing of silicon containing steels, which are increasingly used today, involves the danger of very thick, poorly adherent, unsightly zinc coatings forming on the steel surface. Quite a number of attempts have been made to prevent this drawback. Chemical surface treatments of the steels to be galvanized did not yield the desired success, whilst mechanical surface treatments by shot blasting gave positive results in certain cases only. Galvanizing in the upper temperature range of conventional working practice (475–485 °C) appears appropriate for steels containing 0.15–0.20% Si, whereas low-temperature galvanizing at 430–440 °C using conventional galvanizing baths should be universally applicable provided that suitable methods are found for pre-heating parts of larger dimensions. Galvanizing with inhibited attack of the zinc caused by small additions of aluminium (less than 0.2%) did not yield coating thicknesses independent of the Si content of the steel. High-temperature galvanizing at more than 530 °C gives satisfactory coatings irrespective of the Si content of the steel; saturation of the galvanizing bath with iron should, however, be avoided. Low-temperature galvanizing at less than 430 °C is possible on principle, provided that the melting point of the zinc is reduced by adding alloying elements such as tin (10–30%), magnesium (3%), or aluminium (4–5%). However, tin is expensive, magnesium deteriorates the wetting properties of the steel, and aluminium requires a very careful pre-treatment, the coatings obtained exhibiting low thicknesses and dependency on the Si content of the steel with iron-saturated baths. Galvanizing with reduced zinc concentrations in zinc-saturated lead baths gave zinc coatings independent of the Si content, while currentless galvanizing in zinc-saturated salt baths was not successful.     

An Experimental Study of the Liquid Domain of the Zn-Fe-Al-Mn Quaternary System at 460 °C

The liquid domain of the Zn-Fe-Al-Mn quaternary system at 460 °C was experimentally investigated. The nature of relevant intermetallic compounds was studied using scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS). A total of 12 Fe-oversaturated baths with various Mn additions was prepared for the study. When the Al addition was fixed at 0.14 wt.%, δ-FeZn₁₀ and δ-MnZn₉ were found to co-exist with the liquid phase at low Mn additions. Increasing Mn additions above 1.3 wt.% greatly stabilized δ-MnZn₉ so that it became the sole compound existing in the liquid phase. When the Al addition was fixed at either 0.16 or 0.27 wt.%, η-Fe₂Al₅ was found at low Mn additions but ceased to exist as Mn additions increased above 0.8 wt.%. The current study indicates that the addition of Mn to the bath promotes the formation of δ phases, thus shifting the invariant point of δ/η in the Zn-Fe-Al ternary system to a higher Al level. Based on experimental results, the liquidus surfaces in the Zn-rich corner of the quaternary system at 460 °C were schematically constructed, and implications for practical galvanizing operations were suggested.     

Electroless ternary Ni-W-P alloys containing micron size Al2O3 particles

In the present investigation electroless ternary NiWP-Al₂O₃ composite coatings were prepared using an electroless nickel bath. Second phase alumina particles (1 µm) were used to codeposit in the NiWP matrix. Nanocrystalline ternary NiWP alloys and composite coatings were obtained using an alkaline citrate based bath which was operated at pH 9 and temperature at 88 ± 2 °C. Mild steel was used as a substrate material and deposition was carried out for about 4 h to get a coating thickness of 25 ± 3 µm. Metallographic cross-sections were prepared to find out the coating thickness and also the uniform distribution of the aluminum oxide particles in NiWP matrix. Surface analysis carried out on both the coatings using scanning electron microscope (SEM) showed that particle incorporation in ternary NiWP matrix has increased the nodularity of composite coatings compared to fine nodular NiWP deposits. Elemental analysis of energy dispersive X-ray (EDX) results showed that codeposited P and W elements in plain NiWP deposit were 13 and 1.2 wt.%, respectively. There was a decrease in P content from 13 to 10 wt.% with a marginal variation in the incorporated W (1.01 wt.%) due to the codeposition of aluminum oxide particles in NiWP matrix. X-ray diffraction (XRD) studies carried out on as-plated deposits showed that both the deposits are X-ray amorphous with a grain size of around 3 nm. Phase transformation studies carried out on both the coatings showed that composite coatings exhibited better thermal stability compared to plain NiWP deposits. From the XRD studies it was found that metastable phases such as NiP and Ni₅P₂ present in the composite coatings heat treated at major exothermic peak temperature. Annealed composite coatings at various temperatures revealed higher microhardness values compared to plain NiWP deposits.     

Corrosion behavior of iron-based alloys in the LiBr + ethylene glycol + H2O mixture

The corrosion resistance of 1018 carbon steel, 304 and 316 type stainless steels in the LiBr (55 wt.%) + ethylene glycol + H₂O mixture at 25, 50 and 80 °C has been studied using electrochemical techniques which included potentiodynamic polarization curves, electrochemical noise and electrochemical impedance spectroscopy techniques. Results showed that, at all tested temperature, the three steels exhibited an active-passive behavior. Carbon steel showed the highest corrosion rate, since both the passive and corrosion current density values were between two and four orders of magnitude higher than those found for both stainless steels. Similarly, the most active pitting potential values was for 1018 carbon steel. For 1018 carbon steel, the corrosion process was under a mixed diffusion and charge transfer at 25 °C, whereas at 50 and 80 °C a pure diffusion controlled process could be observed. For 316 type stainless steel, at 25 and 50 °C a species adsorption controlled process was observed, whereas at 80 °C a diffusion controlled mechanism was present. Additionally, at 25 °C, the three steels were more susceptible to uniform type of corrosion, whereas at 50 and 80 °C they were very susceptible to localized type of corrosion.     

Synthesis of Ti3SiC2 bulks by infiltration method

T₃SiC₂ bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of solid TiC and Ti powders. Silicon pellets were placed at the bottom of the precursor pellets as the liquid source. The starting compositions can be represented by the formula 2TiC + Ti + xSi, where x = 1.0, 1.2, 1.5 and 1.8, respectively. The phase formation and microstructure of the bulks were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) system. The results demonstrated that the TiC/Ti precursor pellet could only react with Si completely when the x value is 1.8. Impurities SiC, Ti-Si binary compounds and Ti₈C₅ appeared along the silicon diffusion direction. It is found that the compositions of impurities strongly depended on the Si-concentration. Reaction mechanism of this Ti₃SiC₂ infiltration synthesis has also been discussed based on the Si-concentration changes on the diffusion path.     

The effect of Si additions on the high temperature oxidation of a ternary Ni-10Cr-4Al alloy in 1 atm O2 at 1100 °C

The oxidation of four Ni-10Cr-ySi-4Al alloys was studied at 1100 °C to examine the effects of Si additions (from 2 to 6 at.%) on the behavior of the alloy Ni-10Cr-4Al. Addition of 2 at.% Si prevented completely nickel oxidation, but could not form alumina scales. Larger Si additions produced alumina only over part of the alloy surface (about 20% with 4 at.% Si and 30% with 6 at.% Si), but could not prevent completely the internal oxidation of Al. The results are interpreted by extending to quaternary alloys the mechanism of the third-element effect already proposed for ternary alloys.     

Phase transformation behavior of nanocrystalline Ni-W-P alloys containing various W and P contents

In the present investigation, electroless (EL) ternary Ni-W-P coatings were prepared using hypophosphite based alkaline bath by varying sodium tungstate as tungsten source (5-80 g/L). Maximum amount of W incorporation (8.2 ± 1 wt.%) was obtained when the bath contained about 20 g/L of tungsten source. At very high concentrations of W source in the bath the deposit contained about 4 wt.% W and 2 wt.% P. All the as-deposited ternary coatings exhibited nodular surface morphology. X-ray diffractograms (XRD) obtained for as-deposited EL NiWP alloys indicated that crystallinity of the coatings increased with decrease in phosphorus content. Calculated grain size for the deposits varied from 1.2 to 12.7 nm when the tungsten source varied from 5 to 80 g/L in the bath. Higher crystallization temperatures were obtained due to W codeposition in NiP matrix. Presence of metastable phases such as Ni₅P₂ and NiP apart from stable Ni and Ni₃P was identified for the heat treated deposits (400 °C/1 h) containing lower amount of W and higher amount of P. Whereas other ternary deposits after the heat treatment predominantly revealed face centered cubic (f.c.c.) Ni (111) peak. Activation energy for the crystallization of all the alloys has been carried out by modified Kissinger method. Microhardness measurements were carried out on all the deposits isothermally heat treated at 600 °C for 1 h.     

The corrosion behavior of plasma sprayed Fe2Al5 coating in molten Zn

Aluminum coating was plasma sprayed on Fe-0.14-0.22 wt.% C steel substrate, and heat diffusion treatment at 923 °C for 4 h was preformed to the aluminum coating to form Fe₂Al₅ inter-metallic compound coating. The corrosion mechanism of the Fe₂Al₅ coating in molten zinc was investigated. SEM and EDS analysis results show that the corrosion process of the Fe₂Al₅ layer in molten zinc is as follows: Fe₂Al₅ → Fe₂Al₅Zn_x (η) → η + L(liquid phase) → L + η + δ(FeZn₇) → L + δ → L. The η phase and the eutectic structure (η + δ) prevent the diffusion of zinc atoms efficiently. Therefore the Fe₂Al₅ coating delays the reaction between the substrate and molten zinc, promoting the corrosion resistance of the substrate.     

Hot-dip galvanization with pulse-electrodeposited nickel pre-coatings

The galvanizing process whereby steel is electrodeposited with nickel using pulsed current waveforms and hot-dipped in a molten zinc bath at 450 °C is investigated here as a potential route to mitigate the coating overgrowth problem. The influences of processing parameters, including electroplating and galvanizing durations, on the evolutions of microstructure and phase structures, and polarization characteristics of galvanized steels are explored. The results from the polarization study and salt spray tests indicate that the galvanized coating prepared with a nickel pre-coating, comprising zinc–nickel intermetallic layers, exhibits significantly better corrosion resistance than the conventionally-galvanized steel.     

热浸镀锌合金技术的发展与应用

综述了国内外关于热浸镀锌合金技术的最新发展.研究表明,锌浴中同时加入Ni和Bi的热镀锌效果较常规锌浴及Zn-Ni合金浴更佳;锌浴中加入适量的Sn可抑制高含硅量(大于0.25%Si)的钢材镀层的异常生长,其抑制机理是由于Sn在Fe-Zn合金相层生长前沿会形成一层连续层,从而阻碍了Fe-Zn相层生长。文中还介绍了Zn-Sn-Ni-Bi、Zn-Sn-V(Ni)以及Al-Sn-Bi合金技术的实际应用情况.      

批量热浸镀锌工艺机理的研究现状

热浸镀锌是钢铁材料户外长效防护的最佳选择。传统的调整参数、试加合金等“试错法”难以满足现代制造业的发展,故全面、完整的热浸镀锌机理研究已迫在眉睫。针对我国批量热浸镀锌产量大、重经验轻理论、技术落后、污染严重等特点,从镀层的形成机理、镀层的合金化机理、锌浴液态特征等方面综述分析了批量热浸镀锌工艺理论的研究现状和不足,指出了基体和锌浴界面之间的相互作用、合金元素添加的可预测性、浸镀后表面粘附锌液层的结晶、锌浴液态特征等研究的重要性。建议从以下几个方面完善热浸镀锌机理：加强基材离开锌浴至冷却结晶结束这一阶段镀层组织结构的演变研究;在研究镀层合金化机理的同时,注重合金化镀层的应用推广,尤其是加强低合金高强钢的热浸镀锌研究;重视并加强锌浴表面张力、流动性、结晶特性的液态特征研究和数据积累;在形层机理研究的基础上,结合工艺参数进行镀层的预设计及镀层预控制研究。