预镀镍对活性钢热镀锌的影响

Effect of Electrodeposited Ni Layer on the Galvanized Coatings of Reactive Steels

研究了四种含硅钢板预镀镍后热浸锌时镀层的生长动力学,以及镀层中合金相的形成和生长规律,探讨了预镀镍对活性钢热浸锌镀层生长的抑制机理。实验结果表明:预镀镍法可以显著降低活性钢镀锌层的快速生长,获得厚度适宜、表面光亮,粘附性好的镀层。预镀镍钢板热浸锌时首先形成一系列的Ni-Zn合金γ′,γ和δ2相,随着进一步的扩散和反应,γ′,γ和δ2相逐渐消失,生成了Fe-Zn-Ni三元金属间化合物Γ2和Fe-Zn金属间化合物Γ和δ;随后Γ2相消失,在δ相和液相Zn间生成块状的ζ晶粒,并逐渐变成稳定致密的连续ζ层。钢板预镀镍后热镀锌时完全改变了Fe-Zn相的生长顺序,明显延缓了ζ相的生长,显著抑制了活性钢热浸镀锌层的异常生长。

Four types of steels containing 0.04%, 0.09%, 0.14% and 0.36%Si were electrodeposited 3μm nickel layer and then galvanized in molten Zn at 450℃ for various periods of time respectively. Formation and growth of intermetallic compound layers on the surface of the specimens were investigated. The results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with proper thickness, bright appearance and good adherence. EDS results show that a series of Ni-Zn alloys γ＇ ,γ and δ2 were first formed on the surface of the samples. With prolonged immersion time, the Γ2-Fe-Zn-Ni and δ-Fe-Zn were formed accompanied by the gradual disappearance of γ＇, γ and δ2 layer. After longer immersion time, the lumpy ζ- Fe-Zn occurred between δ and liquid Zn and the Γ- Fe-Zn did between steel substrate and ＆ Subsequently, ζ was in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changed the formation of Fe-Zn intermetallic compounds. The growth of ζ was greatly delayed, therefore the abnormal growth of the galvanized coating of reactive steels was eliminated.