【作者】 彭浩平；

【导师】 苏旭平；

【作者基本信息】 湘潭大学 ， 材料学， 2012， 博士

【摘要】 热浸镀锌广泛应用于提高钢材的耐蚀性，Zn-55%Al、Zn-5%等锌铝镀层的耐蚀性能要优于单一的锌、铝镀层。由于锌铝熔池中铝的存在，导致钢基与熔池之间发生激烈的放热反应，同时镀层金属间化合物层快速增厚、熔池中产生大量的锌铝渣。为控制钢基与熔池之间的快速反应，在熔池中加入硅和铜等合金元素，针对铁、锌、铝和硅之间的相互反应，测定了相应的相关系，研究了合金元素对镀层的影响，明确热浸镀锌铝中的界面反应和熔池中锌铝渣的形成机理，以利于改善镀层的组织结构。试验测定了Zn-Fe-Cu三元体系450°C、620°C和800°C等温截面，在该体系中未发现三元化合物。450°C等温截面中存在8个三相区，试验结果表明铜在Γ和δ_Fe相中的溶解度分别为17.9at.%and15.2at.%，而在液相和ζ相中的溶解度很低。这个结论证明了在热浸镀锌熔池中加入的铜含量达到1.0at.%时，将促使Γ和δ_Fe相的形成，同时抑制ζ相生长。在该体系620°C和800°C等温截面中分别存在4个三相区和3个三相区。620°C时γ和Γ相形成连续固溶体，该连续固溶体在本研究中被命名为γ/Γ相。620°C等温截面中δ_Fe和δ_Cu相伸入相图内部，所形成的(γ/Γ+δ_Fe+δ_Cu)三相区成分范围狭小。在Zn-Al-Ni三元体系600°C等温截面中存在8个三相区，在该体系中同样未发现三元化合物。镍在液相中的溶解度非常低，最大值未超过0.8at.%。共存在该体系中的二元相AlNi和NiZn伸入相图内部，可以清晰的判断三相区(NiZn+AlNi+Ni₃Zn₁₄)和（AlNi₃+AlNi+NiZn）存在于该等温截面中，同时在本研究中确定了AlNi,Al₃Ni₅和AlNi₃相的三相平衡关系。根据实验研究结果显而易见，当少量的镍加入到锌铝熔池中时，熔池成分将无法维持在液相区域，而是进入到两相区或者三相区，从而导致锌铝熔池中形成大量的化合物。在热浸镀锌铝中提出了扩散通道的改变对镀层中金属见化合物层形成的控制机理，在热浸镀（扩散偶）化合物层开始形成阶段，扩散通道沿熔池成分与对应的铁铝二元化合物形成的两相区共轭线穿过该相区，对应层状的铁铝二元化合物在铁基上连续形成。随着热浸镀（扩散）时间的延长，扩散通开始向两扩散原始组元的连线移动，一旦扩散通道移动到切割液相和其对应铁铝化合物组成的两相区共轭线时，优先形成在钢基上的铁铝二元化合物层将失稳破裂，同时液相通道在化合物层中形成，将导致熔池液相直接接触钢基而发生界面反应控制的反应过程，镀层金属间化合物层的厚度将显著增厚。在锌铝熔池中添加铜能有效的抑制其铁铝之间的反应，铜的加入能促使τ₅的形成，同时控制Fe₂Al₅层的快速增厚。当0.5¹.0wt.%的铜加入到锌铝熔池时，铜能够促使硅在界面反应区域富集，该区域之前熔池液相与FeAl₃相的平衡被液相与τ₅之间的平衡关系所取代，此时界面反应扩散通道为（钢基/Fe₂Al₅/FeAl₃/τ₅/锌铝熔池），镀层金属间化合物外层形成致密的τ₅相层，这种现象避免了熔池液相直接腐蚀钢基，从而控制了钢基与熔池之间的反应，镀层的金属间化合物层厚度明显减薄，Fe₂Al₅相层减薄程度尤为明显。试验研究了硅含量在1.0～3.0wt.%范围内，温度580～610°C时熔池中锌铝渣相的形成机理，熔池中所形成的锌铝渣相被鉴别为FeAl₃相和含锌的τ₅相。同时在580～610°C温度范围内建立了Zn-Fe-Al–Si四元体系中(Al_0.55Zn_0.45)_1-x-yFe_xSi_y截面富锌铝侧相平衡关系，可以直观的看出随熔池硅含量和温度的变化，熔池中所含锌铝渣的种类。当硅含量不超过1.3at.%时，熔池中锌铝渣相仅为FeAl₃相，在1.0～1.6wt.%硅含量锌铝池中所形成的FeAl₃相中最大的硅含量为1.93wt.%。当硅含量达到2.0wt.%时，熔池中仅含有τ₅锌铝渣相。在本研究工作中，580～610°C温度范围内1.6wt.%硅含量熔池中均出现FeAl₃相和τ₅相共存的现象。更多还原

【Abstract】 Hot dip galvanizing is widely used to improve the atmospheric corrosion resistanceof the steel sheet. The corrosion resistance of the hot-dipping Zn-Al coating （for exampleZn-55%Al, Zn-5%Al coating et al.） is superior to a single coating （Zn, Al coating）.Because of the presence of aluminum, resulting in the strong and rapid exothermicreaction between the steel matrix and the A1-Zn bath, rapid growth of alloy layer, andlarge amounts of Zn-Al dross forming in the bath. To control the violent reaction occursbetween the iron substrate and bath, the alloying elements, such as Si and Cu, will beadded in the A1-Zn bath. Focusing on the interaction between Fe, Zn, Al and Si, therelated phase diagrams were determined and the effect of alloying elements on coatingswere carried out. The interfacial reaction and forming of intermetallic dross phases inhot-dipping Zn-Al bath have been studied, which is important to control themicrostructure of Zn-Al coating.The450°C、620°C and800°C isothermal section of the Zn-Fe-Cu ternary systemwas experimentally determined. No new ternary compound was found in the system.Eight three-phase regions exist in the450°C isothermal section. isothermal section.Experimental results indicated that the solubility of Cu in the Γ （Fe3Zn10） and the δ_Fephase reaches as high as17.9at.%and15.2at.%, respectively, and the solubility of Cu inliquid and ζ phase is lower. The results confirm, in galvanizing, the addition of Cu in bathup to1.0at.%would favor the formation of the Γ phase and δ_Fephases, the other wayround, it inhibits the development of the ζ phase. Four three-phase regions have beenidentified in the Zn-Fe-Cu ternary system at620°C, and three three-phase regions havebeen confirmed in the800°C. The γ （Cu5Zn8） and Γ phases form a continuous solidsolution at620°C, which is designated as the γ/Γ phase. Binary phases δ_Feand δ_Cuextendinto the ternary system at620°C, the three-phase triangle of (γ/Γ+δ_Fe+δ_Cu) is small andnarrow.Eight three-phase regions have been identified in the Al-Ni-Zn ternary system at600°C. No new ternary compound was found in the system. The solubility of Ni in theLiq. phase is low, which is no more than0.8at.%. Binary phases AlNi and NiZn extendinto the ternary system, and they co-exist in the Al-Ni-Zn ternary system at600°C. Thethree-phase triangles of (NiZn+AlNi+Ni₃Zn₁₄) and （AlNi₃+AlNi+NiZn） are constructedin this ternary system. As is shown in this research result, the three-phase equilibriumrelationship of the phases AlNi, Al3Ni₅and AlNi₃has been confirmed in the present study.According to this result, when a proper amount of Ni is added into the Al-Zn bath, thebath composition does not remain at Al-Zn liquid region, but enter two-phase orthree-phase region. Consequently, a great many intermetallic compounds in Al-Zn bath reduce the fluidity of melt.The interface reaction process between the iron-base and different baths was studied.The controlled mechanism of alloy layer formation by the diffusion path change ingalvanizing was proposed. In the beginning of the alloy layer formation in galvanizing（diffusion layer）, the diffusion path crosses the two-phase region of melting bath andrelevant Fe-Al compound following a tie-line. A corresponding continuous lamellarFe-Al compound forms firstly on the iron-based surface. with the immersion（diffusion）time increases, the diffusion path trends to move gradually to the line connecting withtwo diffusion component points. Once the diffusion path cuts the tie-line of the two-phaseregion of melting bath and the relevant Fe-Al compound, the preferential forming Fe-Alcompound layer is steadiness losing and breaking. At the same time, the liquid channelsforms in the alloy layer （diffusion layer） as the diffusion path cut the tie-line, whichleaded Zn-Al liquid to connect with iron-base directly, the reaction is controlled byinterfacial reaction, which brings the thickness of coating alloy layer （diffusion layer）increased rapidly.Cu is an effective bath additive for controlling the Fe-Al reactivity in Galvalumeprocess. The addition of Cu in the Galvalume baths promotes the formation of the τ₅phase and hinders the Fe₂Al₅phase. When0.5¹.0wt.%Cu is added in Galvalume baths,the presence of Cu makes Si be enriched in the reaction region during the hot-dipping.The liquid phase becomes in equilibrium with the τ₅phase, initially in equilibrium withFeAl3as the enrichment of Si in the coating. the diffusion path is ironsubstrate/Fe₂Al₅/FeAl3/τ₅/overlay. The compact τ₅will form on the outer intermetalliclayer, this phenomenon of the liquid phase eroding the α-Fe phase directly will beavoided. As a result, the intermetallic layer thickness greatly reduces, and the Fe₂Al₅phase layer becomes very thin.The intermetallic dross phases in galvalume baths containing1.0～3.0wt.%Si inthe temperature range of580～610°C have been studied detailedly. The intermetallicdross phases are considered to be the FeAl3phase and the τ₅phase containing Zn. TheAl-Zn-rich corners of (Al_0.55Zn_0.45)_1-x-yFe_xSi_ysection in the Al-Fe-Si-Zn system at580～610°C have been constructed. It is intuitionistic for prediction of the change in the natureof the intermetallic dross phases present in galvalume baths for variations of Si contentand temperature. For Si content dose not exceed1.3wt.%, the dross is the FeAl3phasesolely, and the most Si content in the FeAl3phase is1.93wt.%for1.0～1.6wt.%Si inbaths. When Si content up to2.0wt.%, the intermetallic dross phase is τ₅phase solely. Inour study, FeAl3and τ₅can co-exist when Si content is about1.6wt.%in baths at thetemperature range of580～610°C.更多还原