熱浸鍍鋅鋼板鐵鋁障蔽層微結構分析

Microstructural Characterization of Fe-Al Inhibition Layer in Hot-Dip Galvanized Sheet Steel

陳志凱(Chih-Kai Chen)

指導教授 ： 林招松

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.10301

摘要

熱浸純鋅和鐵鋅合金鋼板因具有優異抗蝕性，廣泛應用於汽車車體和相關零組件，熱浸純鋅鋼板同時大量應用於建築、家電與五金工業。在最佳化熱浸鍍鋅製程開發時，必須同時建立有效且快速鑑定熱浸純鋅鍍層微結構的方法。
本研究即在建立一有效熱浸鋅鍍層微結構分析技術，藉以探討鋅浴鋁含量與溫度、鋼板入溫、熱浸時間對熱浸鋅鋼板界面微結構的影響。實驗結果顯示，在化學腐蝕後橫截面OM試片能觀察到Fe-Zn合金相，由鍍鋅層往內依序為ζ相和δ相，受限於解析力，OM下並無法觀察到Γ和Fe-Al相。然而，藉由橫截面TEM以及擇區電子繞射和低掠角XRD分析證實單一Fe2Al5相存在鋼板和純鋅之間，同時TEM/EDAX分析顯示在界面處鋁含量較高，Fe2Al5的形貌有顆粒狀和層狀兩種形式。另外，開路電位作為一個快速分析鐵鋁層是否存在的方法，除此之外，從開路電位曲線也可了解整個腐蝕過程並非均勻。另外，利用開路電位方法將熱浸鍍鋅上的各層用4% 鹽酸剝離後，可用SEM觀察其表面形貌和對各鍍層做低掠角XRD分析。
綜合以上實驗結果，在低鋅浴鋁含量下(0.12wt%)，當鋅浴溫度、鋼帶入溫和熱浸時間三者值愈大，Fe-Al相轉換成Fe-Zn相程度愈大。在中、高鋅浴鋁含量 (0.16wt%、0.20wt%)，Fe-Al障蔽層尚未合金化成Fe-Zn相下，鋅浴溫度或鋼帶入溫愈高，界面Fe-Al障蔽層厚度愈厚。

關鍵字

鐵鋁障蔽層 ； 鐵鋅合金相 ； 熱浸鍍鋅 ； 開路電位 ； 化學腐蝕

並列摘要

Hot-dip galvanized and galvanealed steel sheets have excellent corrosion resistance, and can be found in body panels and related components in the automobile industry. Large amounts of hot-dip galvanized steel plates are also used in structure, home appliances, and tool applications. To optimize the hot-hot dip galvanize process, it is essential to develop a quick and effective microstructural evaluation method.
In this study, an effective technique to determine the effect of aluminum content in the zinc bath, bath temperature, strip entry temperature, and dip-time on the interface microstructure has been established. Results showed that Fe-Zn intermetallic compound can be observed in chemically color etched cross-sectional OM samples: ζ and δ were observed from the zinc coating towards the steel substrate. However, Γ and Fe-Al phases were not observed under OM due to its limited resolving power. In contrast, via cross-sectional TEM, selected area diffraction, EDAX, and GA-XRD analyses, higher aluminum content can be found at the zinc-steel interface in the form of granular and lamellar Fe2Al5 intermetallics. Also, open circuit potential can be a time-saving technique to analyze the presence of Fe-Al phase. Furthermore, the non-uniform corrosion behavior can be observed in the open circuit potential curve. Selective layer on the coating can be removed while performing open circuit potential in 4wt% HCl to observe each layer morphology and crystallinity in SEM and GA-XRD.
In summary, when bath temperature, strip entry temperature, and hot-dip time increase, the extent of transformation from Fe-Al to Fe-Zn phases increases, in low aluminum content zinc bath (0.12 wt%). In mid-to-high aluminum content zinc bath (0.16 wt%, 0.20 wt%), in the condition that Fe-Al inhibition layer have not transformed to Fe-Zn intermetallics, the higher the bath or strip entry temperature, the higher thickness in the Fe-Al inhibition layer.

並列關鍵字

Fe-Al inhibition layer ； Fe-Zn intermetallics ； hot-dip galvanized ； open circuit potential ； chemically color etched

參考文獻

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