環保無鉻化鋅鐵合金產品開發

Characterization and Application of Eco-friendly Chromium-free Galvannealed Steel Sheet

因應環保趨勢，鍍鋅類鋼片的後處理製程逐漸朝向無三價鉻或六價鉻之表面處理。本文以熱浸鍍鋅鐵合金鋼片為基材，研究新開發的無鉻皮膜及鉻酸皮膜樣品的性能差異，並藉三維光學顯微鏡、掃描式電子顯微鏡、原子力顯微鏡及電化學等方法探討表面特徵、耐蝕性及烤漆等特性。結果歸納為：（1）從巨觀至微觀的解析過程，清楚掌握材料的表面特徵，確認粗糙度受鍍層形貌及皮膜厚度雙重影響；此外，採優化製程製備之無鉻A樣品的皮膜緻密性較其他樣品更佳；（2）動電位極化曲線及電化學交流阻抗結果顯示無鉻A樣品具最低腐蝕電流（1.48μA/cm2）及最高阻抗（7,261Ω·cm2），電化學與鹽霧測試結果一致，證實緻密性佳的無鉻皮膜同樣具最佳耐蝕性；（3）烤漆樣品的循環腐蝕測試則顯示各個樣品符合烤漆耐蝕要求；此外，微觀解析佐證刮痕區域旁的漆層起泡或剝離主要來自金屬陽極溶蝕作用所貢獻。

In response to the environmental issue, the post-treatment of galvanized steel is gradually toward the surface treatment without trivalent nor hexavalent chromium. In this study, the hot-dip galvannealed steel sheet was used as the substrate to study the performance among chromium-free and commercial chromate samples. Surface characteristics, corrosion resistance, painting application were investigated by 3-dimension optical profiler, scanning electron microscope, atomic force microscope, and electrochemical methods. Results were summarized as follows: (1) From macroscopic to microscopic analyses, surface characteristics was clearly studied, and it’s indicated that the overall roughness was affected by the surfece texture of alloy layer and the thickness of the coating. In addition, the chromium-free A coating manufactured by the modified coating process also showed the better coverage than the other samples. (2) Polarization curve and Nyquist results showed that the chromium-free A sample had the lowest corrosion current (1.48 μA/cm2) and the highest low-frequency impedance (7,261 Ω·cm2), indicating that its corrosion resistance was better than that of other samples. (3) Cyclic corrosion test of painted samples showed that chromium-free samples met requirements. Besides, microstructure analysis confirmed that anodic undermining was the main cause of the blistering.