预电镀铁对活性钢热镀锌层的影响

Influence of Fe-Electrodeposited Pretreatment on Galvanized Coatings of Reactive Steels

研究了5种含硅钢板(含硅量分别为0.04%,0.09%,0.14%,0.28%和0.36%)预电镀铁后热浸锌时镀层中合金相的形成和生长规律.结果表明:预电镀铁能够显著抑制活性钢镀锌合金层的快速生长.对于Sandelin钢、薄的过Sandelin钢和含硅量较低(约0.28%)的过Sandelin钢,可在其表面预电镀厚度不超过10μm的铁层再热镀锌,以解决其镀层超厚问题.电子探针显微分析(EPMA)结果表明:钢中的硅会在钢基表面富集;随着钢基/镀层界面向钢基方向移动,富硅的α-Fe破碎成粒子或絮状物,以类似克根达尔效应中惰性标记物的方式穿过Γ层进入δ层,从而促进δ层向钢基方向生长并吞并附近的Γ层,令Γ层逐渐消失.含硅钢预电镀铁后延缓并减弱了硅对热镀锌合金相的影响,故能在一定浸锌时间内抑制活性钢热浸镀锌层的快速生长,抑制时间随预电镀铁层厚度的增加而增加.

Five kinds of steels respectively with the Si contents of 0.04%, 0.09%, 0.14%, 0.28% and 0.36% were electrodeposited with iron layer and were then galvanized in molten Zn. The corresponding formation and growth of the Fe-Zn intermetallic compound layer were investigated. The results show that the Fe-electrodeposited pretreatment can obviously restrain the quick growth of the galvanized coating of reactive steel, and that eligible coatings can be obtained when such reactive steels as Sandelin steel, thin hyper-Sandelin steel and Sandelin steel with a Si content about 0.28% are electroplated with an iron layer less than 10 μm before being immersed in zinc bath. EPMA（Electron Prob Micro Analysis） results show that （1） excessive silicon in the steel accumulates on the surface of the steel substrate; and （2） with the movement of the steel/galvanized coating interface towards the steel substrate, the silicon-rich a-Fe peels off from the substrate and breaks into particles. The particles, much like the inert marker in Kirkendall effect experiment, enter the δ layer through the G layer, thus accelerating the growth of the δ layer towards the Г layer till to a disappearance of the G layer. Moreover, the iron-electrodeposited pretreatment postpones and weakens the influence of silicon on the galvanized coating, so that the quick growth of the galvanized coating can be inhibited in a certain galvanizing time that increases with the thickness of the iron-electrodeposited layer.