無裂紋三價鉻電鍍製程開發及研究

Abstract

本研究旨在甲酸銨與尿素雙錯合系統中，藉由高電流密度的施加與硫代水楊酸的添加，開發出鍍液穩定、沉積速率高、無裂紋的三價鉻電鍍製程。研究中藉由哈氏槽檢視鍍液的電流密度操作窗口，並利用掃描式電子顯微鏡觀察鍍層的表面形貌、橫截面，為了檢視鍍層的結晶性，利用X光繞射分析儀進行分析，並使用電子微探儀進行鍍層中碳、硫的定量，另外，透過硬度測試以探討鍍層性質與電鍍條件之間的影響。 研究結果顯示，尿素的添加可提升鍍液穩定性與使用週期，在3.72M甲酸銨與3.72M尿素的雙錯合系統中，鍍液穩定性佳且有較寬的電流密度操作範圍。利用此鍍液在高電流密度條件下仍能獲得光亮鍍層的特性，添加硫代水楊酸後，施加高電流密度(80ASD)可獲得沉積速率0.33μm/min、厚度20μm的無裂紋三價鉻鍍層

Trivalent chromium electrodeposition process has some problems such as instability of the electrolyte, difficulty to obtain thick coating and cracks penetrating through the deposition. In this study, a wide operating range in applicable current density had been obtained by adjusting concentration of the complexing agent in trivalent chromium bath. Hull-cell test had been operated in this study to examine the range in applicable current density. The surface morphology and cross-section of the deposited coatings were observed by SEM. The crystallinity of the deposition was examined by X-ray diffraction. In addition, hardness test had been operated to make more discussion about the relation between properties of the chromium coating and the parameters of electrodeposition process. The study reveals that adding urea would solve the problems of current efficiency decades with deposition time during trivalent chromium electrodeposition process. It is shown that the widest range in applicable current density is obtained from the bath containing 3.72M ammonium formate and 3.72M urea. After adding the thiosalicylic acid to the trivalent chromium bath, a thickness of 20μm, bright and crack-free coating can be obtained at a deposition rate of 0.33μm/min by applying current density of 80ASD.