AZ31B鎂合金與6N01鋁合金摩擦攪拌焊接異質接合經微弧氧化表面處理的腐蝕行為研究

Corrosion Behavior of Friction Stir Welding 6N01 and AZ31B With Micro-Arc Oxidation Surface Treatment

林友瑞(Yu-Jui Lin)

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/博士(2021年)

https://doi.org/10.6342/NTU202100360

摘要

摩擦攪拌焊接為近代新發展出的固態焊接技術，雖然有需要施加夾具加壓、工件形狀無法太複雜等限制，但仍然為鋁、鎂、鈦等金屬提供一個快速且高品質的焊接方法。但近期相關研究多著重於焊接後的機械性質的探討，抑或是同系統合金腐蝕速率的研究，鮮少有探討異質金屬焊接的腐蝕行為和腐蝕機制的建立。本研究探討兩種輕金屬AZ31B鎂合金與6N01鋁合金經摩擦攪拌焊接異質金屬接合後的腐蝕速率，並從其腐蝕行為建立其腐蝕機制的模型。同時為了改善其腐蝕抗性耐腐蝕性，對焊接件施加微弧氧化表面處理。本研究中將摩擦攪拌焊接件分為三區:鋁母材區(BM-6N01)、鎂母材區(BM-AZ31B)和攪拌區(SZ)。藉由分析整塊焊接件和各區的析氫實驗、動電位極化曲線和電化學交流阻抗分析可得知未經微弧氧化表面處理的焊接工件中各區的腐蝕速率由大到小為 SZ > BM-AZ31B > BM-6N01。因為異質金屬焊接造成的伽凡尼腐蝕，在陽極的富鎂相形成嚴重的腐蝕，但同時也觀察到陰極的富鋁相亦受腐蝕。從腐蝕樣貌和電化學測量結果推定是因為陽極的富鎂相劇烈腐蝕氧化、造成局部酸鹼值快速上升，而鹼性環境又使得陰極的富鋁相的保護層Al2O3/Al(OH)3轉化成不具保護性的AlO2-，最終造成富鋁相的嚴重腐蝕。矽酸鹽系統的微弧氧化表面處理可同時在攪拌焊接件的三區形成白色陶瓷氧化層，微結構分析顯示兩種母材區上的氧化層均為上層疏鬆、下層緻密的雙層結構，而鹽霧試驗結果證實此雙層陶瓷氧化層可大幅提升抗蝕性。然而，攪拌區的微弧氧化層仍是最易受到腐蝕，顯示因為巨觀與微觀組織與成分的不均勻性，擦攪拌焊接異質金屬焊件的表面處理仍是一大挑戰。

關鍵字

鋁合金 ； 鎂合金 ； 摩擦攪拌焊接 ； 微弧氧化 ； 析氫實驗 ； 電化學交流阻抗分析

並列摘要

Frictional stir welding (FSW), which was developed in 1990, is a novel solid-state welding technology and suitable for welding Al, Mg, and Ti alloys despite the requirement of fixture and applied pressure and the limitations for complex-shaped articles. The mechanical properties of dissimilar FSW joints have been extensively studied and the corrosion rates of similar FSW joints have also received many attentions. However, the corrosion behavior and mechanism of dissimilar FSW joints are less studied. In this work, the corrosion rate and behavior of FSW dissimilar joints of AZ31B magnesium alloy and 6N01 aluminum alloy with and without micro-arc oxidation (MAO) surface treatment have been evaluated. The weld joint is divided into three regions; Al base metal (BM-6N01), Mg base metal (BM-AZ31B) and stir zone (SZ), and each region has perform potentiodynamic polarization, EIS, and hydrogen evolution tests. The tests results show the corrosion rate of non-MAO treated is, in order, SZ > BM-AZ31B > BM-6N01. The corrosive microstructure indicates that galvanic effect between Mg phase and other phases induce both anodic BM-AZ31B region and cathodic BM-6N01 region suffer severe corrosion. The intensify corrosion at anodic site BM-AZ31B raised the pH value to a level where protective layer Al2O3/Al(OH)3 at cathodic site BM-6N01 has turn into non protective AlO2-, therefor severe corrosion occur. The silicate-based micro-arc oxidation (MAO) surface treatment can simultaneously generate oxide layer on both 6N01 and AZ31B substrate, SEM images show the oxide layers are combined with an inner dense layer and an outer loose layer. SST results show that the oxide layer can provide good corrosion protection. Nevertheless, the SZ with an MAO layer is still the most vulnerable part to corrosion, signifying the surface modification of Mg-Al FSW dissimilar joints remains to be challenging due to the presence of both macroscopic and microscopic heterogeneities of Mg-Al FSW dissimilar joints.

並列關鍵字

Aluminum alloy ； Magnesium alloy ； Friction stir welding ； Micro-arc oxidation ； Hydrogen evolution ； Electrical impedance spectroscopy

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