合金化时间对热镀锌IF钢板镀层相结构的影响

通过模拟合金化镀锌试验,研究了IF钢合金化镀层结构随着合金化时间的演变规律。结果表明:在520℃合金化时,随着合金化时间的延长,镀层中铁含量快速增加,而当铁含量超过12%时,增长缓慢。合金化7 s时,镀层从表面到基板依次是纯锌η相、柱状ζ相(Fe Zn13)以及栅状δ1P相;随着时间增加,基体Fe继续向镀层扩散,纯锌η相、柱状ζ相消失,栅状δ1P相逐渐转变为致密的δ1k相,同时在基板处生产了齿状的Γ相,在合金化17 s后,镀层相结构最终稳定为δ1k相和基板处少量的Γ相。     

扩散处理工艺对镀锌层组织和性能的影响

研究了扩散处理工艺对要进行热冲压成形的钢板含0.17%Al(质量分数)的镀锌层组织和性能的影响。结果表明,随着扩散处理温度的提高和保温时间的延长,镀锌层组织和性能发生了明显的变化,在520℃扩散处理20 s后镀锌层表面的ζ相消失。随着扩散处理温度的升高,镀锌层与钢基体界面处的Γ相增厚,在500~520℃时增厚尤为明显。当镀层由ζ相和疏松的δ相或者由疏松的δ相和Γ相构成时,镀层塑性较好。而致密的δ相会明显降低镀层的塑性。     

低碳钢在锌液中的界面反应动力学及机理研究

研究了低碳钢短时间浸入锌液后铁、锌之间的反应过程。结果表明,低碳钢与锌液的反应层产物主要包括靠近内侧呈柱状晶生长的紧凑、致密δ-Fe Zn10相和外侧较为疏松的ζ-Fe Zn13相,稳定生长阶段疏松的ζ-Fe Zn13相生长占据主导地位。铁、锌的反应产物生长过程符合抛物线生长规律,生长初期主要受界面反应控制,而在稳定生长阶段,主要受液锌原子扩散控制。铁、锌产物层从钢基体到表面依次为过饱和α-Fe、Γ1-Fe5Zn21、δ-Fe Zn10、ζ-Fe Zn13和表层的η-Zn。     

添加Ti和Al对热浸镀锌层组织结构的影响

制备了Ti、Al含量不同的热浸镀锌层,利用扫描电子显微镜(SEM)和能谱仪(EDS)观察分析了镀层的组织结构.结果表明:Ti能有效抑制镀层中ζ相的生长,降低合金相层的厚度.60 s浸镀,添加0.04％ Ti时消除了镀层中ζ相分层现象;添加0.07％ Ti时在ζ/η相界生成细小颗粒状T相;240 s浸镀,在ζ/η界面及η相中生成了颗粒状T相,甚至形成连续分布的T相小岛.锌浴中同时添加Ti和Al对Fe-Zn合金相生长的抑制作用加剧,短时间浸镀时就促使含铝T相在η相中生成.     

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.     

镀锌工艺对高强IF钢热镀锌层显微组织的影响

以含Ti高强IF钢为基体进行热镀锌试验,借助SEM、XRD研究了镀锌温度和保温时间对热镀锌层的影响规律,分析了镀层的形成过程与机理。结果表明,ζ相急剧增长,镀锌层发生了圣德林效应,低温镀锌时ζ相为粒状或针状,高温时为柱状。δ相的生长受到抑制,始终为栅状。当镀锌温度和保温时间均较高时,ζ相和δ相中间会形成粒状的混合区域。镀层在低温时由内到外依次为δ相、ζ相、η相,较高温度时由内到外依次为δ相、粒状混合相、ζ相、η相。     

Ni 含量对热浸 Zn-Al-Ni 合金镀层组织和耐腐蚀性能的影响

为了提高热浸镀锌层的耐腐蚀性能,向Zn-0.01%Al镀浴中添加少量Ni,在Q235钢表面获得Zn-Al-Ni热浸镀锌合金层,并用光学显微镜观察了镀层的组织,通过全浸腐蚀实验表征了镀层的耐腐蚀性能。结果表明:随着镀浴中Ni含量的增加,Zn-Al-Ni镀层的腐蚀速率先减小,后增大,当Ni含量为0.05%时,镀层的耐腐蚀性能最好;可以通过降低ζ相层的厚度以及增大δ相层的厚度,来提高镀层的耐腐蚀性能。     

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.     

镀锌层重量对其生长规律的影响

采用场发射扫描电镜(SEM)、能谱分析仪(EDS)分析了不同镀锌层重量下镀锌层微观组织及相分布情况。结果表明,镀锌层重量为80、120 g/m²,镀锌层中的δ相呈栅栏状,ζ相从疏松状变为致密状;而镀锌层重量为275 g/m²时,镀锌层中的δ相呈致密状,ζ相呈疏松状。3种镀锌层重量下的δ相厚度占总厚度的比例最少,且各相厚度与镀锌层重量呈正比关系。当镀锌层重量较小时,锌层表面疏松多孔,有类似晶界的沟槽;随着镀锌层重量的增加,镀锌层表面变得致密平整,沟槽深度明显变浅变少。因此镀锌层重量影响其微观组织结构,进而影响锌铁合金的相结构。     

无铵助镀剂中铁盐对热浸镀锌镀层性能的影响

为探究热浸镀锌无铵助镀剂中铁盐对镀层的影响,选取无铁盐的无铵助镀剂及含铁盐的无铵助镀剂。采用SEM和EDS对比分析不同助镀剂所获得的镀层的组织结构和成分。结果表明:无铵助镀剂中的二价铁盐浓度为10~30 g/L有助于提高镀层表面质量;不含二价铁盐的无铵助镀剂镀层的合金相层由Г、δ、ζ和η相组成,并且界限较明显。含二价铁盐的无铵助镀剂镀层的整个合金相层排列整齐致密,Г相几乎不存在,其中δ相和ζ相的界限不明显,并且塑性相δ相在合金相所占的比例较大,经成分分析,由无铵助镀剂带入的部分铁离子被还原成铁原子后,有促进镀层中δ相的形成,抑制ζ相生长的作用。     

Characterisation of industrially produced galvannealed coating by open circuit potential (OCP) measurement technique

An attempt has been made to characterise the industrially produced galvannealed coating by the open circuit potential (OCP) measurement technique. It confirms that the industrially produced galvannealed coating consists of four iron–zinc intermetallic phases, Fe3Zn10, Fe5Zn21, FeZn10 and FeZn13, in layers on the steel substrate. The OCP results are compared with other characterisation techniques such as galvanostatic scan EIS and glow discharge optical emission spectroscopy (GDOES). The additional advantage of this technique is not only to confirm different iron–zinc intermetallic phases in the coating but also to identify the stability of all these phases in an aggressive chloride environment. It was established that the dissolution rate of the Fe3Zn10 phase which contains the maximum amount of iron is the slowest whereas the dissolution rate of the FeZn13 phase which contains the minimum amount of iron is the fastest. This can be explained by the fact that the phase containing more of the more active metal (zinc) is dissolved faster than the phase containing more of the less active metal (iron).     

Crack initiation and propagation of galvanized coatings hot-dipped at 450 °C under bending loads

Crack initiation and propagation behaviors in the intermetallic layers of galvanized coatings subjected to bending loads are characterized and numerically simulated. Coating structure of galvanized steel prepared by hot dipping at 450 °C is a laminate composite consisting of δ, ζ, and η phases, with an infinitesimal layer between the coating and steel article speculatively representing a Γ phase. The specimens were deformed in a four-point bending configuration, and the evolution of cracks was investigated as a function of bending angles. Through-cracks were found to develop in the δ layer of the coatings after thermal cooling due to thermal stresses and propagate toward the outer surface under increments of bending loads. Finite element simulations of galvanized steels were subsequently developed with an initial crack tip located in the δ layer to determine the controlling parameters of the crack propagation and to assess the coatings' fracture parameter, critical far field stress, and stress distributions. The analysis highlights the enhancement of fracture resistance of the galvanized coatings owing to the presence of the ζ layer.     

稀土Ce对热浸渗铝扩散层生长和组织的影响

研究了稀土Ce对15CrMo钢热浸渗铝扩散层生长的影响;采用OM、SEM和EDS分析了扩散层的组织、成分和相结构。结果表明,扩散层由η相(Fe2Al5)、ξ相(FeAl2)、β2相(FeAl)、β1相(Fe3Al)和α相组成,其中η相和ξ相是主要相;添加稀土Ce将减少扩散层中的孔洞,细化晶粒,并明显减少η相;稀土Ce对扩散层的生长起一定的阻碍作用,这种作用的大小与Ce的添加量密切有关。     

INFLUENCE OF SILICON IN STEELS ON GALVANIZED COATINGS

After steel sheets （0.37wt%Si） pre-electroplated with a thin layer of pure Fe were immersed in molten zinc for various time, the change in the microstructure of the galvanized coating on the steel and the change of α-Fe/Г interface were studied. The EDS （energy dispersive sepectroscopy） resuits show that excessive silicon accumulates on the surface of the steel substrate due to the low solubility of silicon in the Г layer after the Fe layer is depleted by the increasing growth of the compound layers. With the movement of α-Fe/Г interface towards the substrate by the Fe/Zn reaction, silicon-rich α-Fe peels off from the substrate and breaks into particles. The particles, much like an inert marker in a Kirkendall effect experiment, move towards the δ layer through the Г layer because silicon-rich α-Fe can not be adsorbed in the Г layer. On reaching the 8/F interface, the particles quickly dissolve in the δ layer, and accelerate its growth, resulting in the gradual disappearance of the Г layer. At the same time, the normal coating is quickly changed into coatings typical of reactive steels as silicon dissolved in the δ layer soon diffuses toward the ζ layer. A similar process may happen in the initial stage of galvanizing reactive steels on a small scale, although it is hard to be observed.     

Mg-(11-13)Gd-1Zn变形镁合金的组织和力学性能

制备了3种成分的Mg-Gd-Zn三元合金,并对其显微组织和力学性能进行了较系统的研究.结果表明,Mg-（11-13）Gd-1Zn（质量分数,%）三元合金的铸态组织由α-Mg,（Mg,Zn）₃Gd和具有14H结构的长周期堆垛有序相（14H-LPSO）组成;（Mg,Zn）₃Gd呈现典型的网状共晶形貌,其体积分数随Gd含量的增加而增大.热挤压过程中（Mg,Zn）₃Gd相破碎,其颗粒沿挤压方向排列,而14H-LPSO相则分布于条状分布的（Mg,Zn）₃Gd颗粒之间.铸态和挤压态合金在高温固溶处理后,14H-LPSO相的体积分数增加,大部分（Mg,Zn）₃Gd相溶入基体.挤压态合金经固溶和时效（T6）处理后,显微组织中14H-LPSO相的体积分数大幅度增加,而且出现了β′和β₁沉淀颗粒.对挤压后的合金直接进行时效处理（T5）过程中也形成了β′和β₁沉淀,但14H-LPSO相没有显著增加.3种合金中Mg-11Gd-1Zn合金在T6态的性能最好,抗拉强度高达416 MPa.     

IF钢合金化镀层相结构及60° V弯粉化性能研究

基于工业化生产的连续热镀锌产线，以无间隙原子钢（IF钢）合金化镀层板为研究对象，采用扫描电镜（SEM）、X射线衍射仪（XRD）、电感耦合等离子光谱仪（ICP）及60° V弯设备，研究了合金化温度对IF钢合金化镀层相结构、镀层Fe含量以及镀层抗粉化性能的影响规律。结果表明:在合金化温度为485~545 ℃时，随着温度的增加，镀层中η、ζ相依次消失，δ、Γ相含量逐渐增加，镀层Fe的质量分数由7%增加到12%，粉化宽度由2.45 mm增加到4.23 mm；在合金化温度为515~530 ℃时，镀层相结构主要为δ相，Fe含量约为10%，粉化宽度＜4 mm，镀层具有良好的综合性能。因此，可通过控制合金化温度来控制IF钢合金化镀层的相结构并获得相应的抗粉化对策，为大批量生产提供技术支撑。     

Mg-3.0Nd-0.2Zn-0.4Zr镁合金表面电沉积Cu镀层及其耐腐蚀性能

研究Mg-3.0Nd-0.2Zn-0.4Zr（NZ30K）镁合金上电沉积Cu镀层的前处理过程及耐腐蚀行为。研究结果表明：活化膜和浸锌层均优先在Mg12Nd共晶相表面沉积。Cu镀层能够为镁基体提供长达60 h的防护作用,这主要归因于其致密的镀层结构及浸泡过程中形成较稳定的钝化膜。热震试验证明镀层具有良好的结合力。     

Al-Zn-Mg-Cu合金在时效过程中η相沿小角晶界的析出序列

采用高分辨透射电子显微镜和高角环形暗场扫描透射电子显微镜结合X射线能谱仪,研究Al-Zn-Mg-Cu合金叩相沿小角晶界的析出序列。试样在135℃分别时效5min到6h。结果表明,η相在小角晶界的析出序列是：SSS→VRC→GPⅡ区→η’→η。基于非平衡晶界偏析和非平衡晶界共偏析理论,在Al-Zn-Mg-Cu合金时效过程中,通过溶质一空位对的扩散,大量的沉淀形成元素偏析到晶界。这种晶界偏析在VRC、GPⅡ区、η’相和η相的形核和生长中起重要作用。     

Substitution of Cu and/or Al in η phase (MgZn2) and the implications for precipitation in Al–Zn–Mg–(Cu) alloys

The effects of Cu and Al substituting for Zn within bulk samples of η phase (nominally MgZn₂) have been studied by laboratory X-ray powder diffraction and nuclear magnetic resonance. Increasing Al concentration causes both of the η phase lattice parameters to increase linearly, while increasing Cu concentration causes both parameters to decrease linearly. These effects also appear to combine in a linear fashion if both Al and Cu are substituted into the MgZn₂ structure, particularly in the case of the a lattice parameter. Al was found to substitute evenly onto both Zn sites, while Cu substitutes preferentially onto the 6(h) site at low Cu concentrations, before causing significant disruptions to the structure at concentrations above 1.1 at.%, leading to the transition to long period stacking phases at the expense of η. High-resolution synchrotron powder diffraction from a commercial Al–Zn–Mg–(Cu) alloy revealed that the η phase precipitates with lattice parameters that are substantially smaller than for pure MgZn₂, indicating Cu concentrations of at least 8.9 at.% and probably higher. It is likely that the Al matrix provides a mechanical constraint on the formation of any long period stacking phases and allows the η phase to exist in these alloys with such high Cu concentrations.     

Role of silicon in steels on galvanized coatings

In this article, five kinds of silicon-containing steel sheets have been electrodeposited, and then immersed in a pure molten zinc bath at 450 ℃ for various periods of time. The results by scanning electron microscopy (SEM) show that the coating of the sam-ple (0.09 wt pct Si) with iron-electrodeposited pretreatment eliminates the reactive zones which are found in the coating without iron-electrodeposited pretreatment. The galvanized sample (0.28 wt pct Si) with iron-electrodeposited pretreatment exhibits a compact and coherent coating. The coating of the sample (0.37 wt pct Si) with the iron-electrodeposited pretreatment experiences a transition from a compact and coherent coating to a reactive one. The energy dispersive spectrum (EDS) results reveal that for the galvanized samples with iron-electrodeposited pretreatment, ex-cessive silicon accumulates on the surface of the substrate due to the low solubility of silicon in the F, after the iron layer is depleted by the increasing growth of the Fe-Zn intermetallics. With the movement of the substrate/F interface toward the substrate, silicon-enriched α-Fe peels off from the substrate and breaks into the particles. The particles move toward the δ layer through the Γ layer because silicon-enriched α-Fe cannot be absorbed in the Γ layer. When the particles reach the δ/Γ interface, they are dissolved in the δ layer, making the Γ layer thin or even vanish.