電鍍鋅鎳合金及精進三價鉻鈍化製程

Electrodeposited Zn-Ni Coating and Associated Trivalent Chromium Passivation Process

本研究藉由鋼板電鍍鋅鎳合金再進行三價鉻基礎配方進行化成處理，開發三價鉻皮膜，並期望有優異的阻抗及耐蝕性。電鍍液採用鹼性鋅鎳合金製程，鍍液溫度25 oC，電流密度為1.0-3.0 A/dm2；三價鉻鈍化液（pH < 2）主要成分有硝酸鈉、硝酸鉻、硝酸鈷，而鈍化時間分別有10、30、60秒三種不同製程。實驗結果，鋅鎳合金鍍層厚度約3μm，鎳含量15-18wt. %。經XRD分析繞射峰以（330）為主及（600）、（444）、（552）、（741）、（660）。以動態極化電位測量，隨三價鉻鈍化改變進行腐蝕極化，其中以鈍化時間30秒耐腐蝕性最佳。經XPS分析三價鉻皮膜主要為Cr2O3、ZnO和NiO所組成。透過TEM觀察鋅鎳合金鍍層為γ相之柱狀結構且有單一方向性（330）。經三價鉻鈍化處理，皮膜厚度約250 nm，厚度均勻，有更佳的耐腐蝕能力。

A protective coating on steel substrate was prepared by electrodepositing Zn-Ni alloy and subsequent passivation with trivalent chromium conversion treatment. This trivalent chromium coating is believed to have superior electrochemical impedance and resistance to corrosion. Zn-Ni alloy coating was first electrodeposited in an alkaline bath at 25 ℃ and 1.0 ~ 3.0 A/dm2. Subsequently, trivalent chromium passivation was performed in acidic (pH < 2) conversion solution containing chromium nitrate and cobalt nitrate. Three different conversion durations, 10, 30, and 60 s, were investigated. Experimental results showed that the Zn-Ni coating was about 3 μm in thickness and consisted of 15 ~ 18 wt. % of nickel. Moreover, the Zn-Ni coating exhibited columnar grains with, through XRD measurement, (330) preferred orientation and other diffraction peaks in (600), (444), (552), (741) and (660). The result of dynamic polarization measurements on the passivated coating revealed that the one with 30 s treatment demonstrated the best corrosion resistance. Further analysis using XPS showed the trivalent chromium coating mainly consisted of Cr2O3, ZnO and NiO. In TEM examination of the Zn-Ni coating, the conversion coating had a thickness of 250 nm and fine porous structure. This uniform coating demonstrated good corrosion resistance.