Growth kinetics of intermediate phase layers in an early stage of hot dip galvanizing at 450 °C
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The hot dip galvanizing technique has been widely used as a surface treatment to prevent corrosion of steels [ 1]. Figure 1 shows the Fe–Zn binary phase diagram assessed by Burton and Perrot [ 2]. Four intermediate phases, ζ (FeZn 13), δ (FeZn 7–10), Γ 1 (Fe 11Zn 39), and Γ (Fe 3Zn 10), in the Zn-rich side are shown. After an adequate diffusion time below 530 °C, the formation of all these intermediate phase layers are predicted in the diffusion zone of the solid iron and liquid zinc couple (melting temperature of Zn is 419.6 °C). However, from the viewpoint of surface technology, the thick growth of intermediate phase layers sometimes leads to peeling off the layers because of their brittleness. Such problems were resolved through technical developments leading to industrial practices for galvanizing sheet steels. For example, the addition of small amount of aluminum to liquid zinc is effective in retarding the growth of intermediate layers. Recently, it has been recognized that the...
KeywordsSheet Steel Diffusion Time Layer Growth Diffusion Zone Diffusion Reaction
The authors thank Mrs. Kon for her assistance in the experiments.
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