Abstract:

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 interm etallic 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 10μm 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 of 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 Γ layer till to a disappearance of the G layer.Moreover.the iron-electrodeposited pretreat.ment 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-electrode-posited layer.

Key words: hot-dipped galvanizing, reactive steel, Fe electr0dep0siti0n