WE43-T5鎂合金在氯化鈉和硫酸鈉水溶液之腐蝕行為

Abstract

鎂合金因具低密度和高比強度，為理想的高強度輕量化材料，且具有生物相容性，能夠被廣泛應用在航太、生醫、汽車等領域。由於鎂活性高，於製程中增加稀土元素可有效提升其強度、抗蝕性與高溫抗潛變能力。為促進鎂合金在產業中的進一步應用，了解其腐蝕機制和抗蝕行為相當重要。 本研究使用含有富Y與富Zr微米級二次相的WE43-T5鎂合金，分別浸泡於0.5 M NaCl和0.5 M Na2SO4水溶液中24小時，探討不同陰離子對其基地與二次相所產生之腐蝕行為。 根據即時攝影，發現WE43在兩種溶液浸泡24小時內並未觀察到腐蝕產物有breakdown的現象，且從析氫測試、重量損失測試、光學顯微鏡與電子顯微鏡的結果可知，兩種二次相皆會導致伽凡尼腐蝕發生，另試片於0.5 M NaCl水溶液中較多局部腐蝕，而浸泡在0.5 M Na2SO4的試片則局部腐蝕的數量較少、尺寸較大，主要以基地的大範圍腐蝕為主，且整體的腐蝕程度更為嚴重，有違一般所認為之氯離子較具有攻擊性以致腐蝕行為較強的印象。透過電化學測試，亦印證在0.5 M Na2SO4中生成之腐蝕產物層其保護性較差。 為探討硫酸根離子所造成之影響，本研究提出了離子對形成以及陰離子吸附改變Mg(OH)2排列方式的可能機制。研究結果有助於了解氯離子和硫酸根離子對於WE43-T5合金的腐蝕產物結構與保護性差異，並可作為未來防蝕設計之參考依據。

In this study, WE43-T5 magnesium alloy containing Y-rich and Zr-rich secondary phases was immersed in 0.5 M NaCl and 0.5 M Na2SO4 solutions for 24 h to investigate the corrosion behavior of the matrix and secondary phases. Real-time imaging revealed no obvious breakdown during 24 h immersion in either solution. Results from hydrogen evolution, weight loss measurements, OM, and SEM indicated that both types of secondary phases induced galvanic corrosion. More localized corrosion sites were observed in NaCl solution, whereas fewer but larger localized corrosion spots, along with widespread matrix corrosion, were found in Na2SO4 solution. The overall corrosion severity was greater in the sulfate solution. Electrochemical tests further confirmed that the corrosion product layer formed in Na2SO4 provided inferior protection compared to that in NaCl. To explore the underlying mechanisms, this study proposes that the presence of sulfate ions influences corrosion behavior through ion-pair formation and anion adsorption, which alter the crystallographic orientation of Mg(OH)2. These findings contribute to a better understanding of how chloride and sulfate ions affect the structure and protectiveness of corrosion products on WE43-T5 alloy.