AZ31鎂合金環保型含矽酸根鹼性陽極處理研究

Abstract

本研究藉由處理液成份與條件、皮膜微結構與成份、皮膜抗蝕性之間關係的建立探討環保型含矽酸根鹼性陽極處理系統處理液成份與條件的影響以及氟離子在此系統中的重要性。陽極氧化的製程使用了壓鑄型AZ31鎂合金。微結構觀察及皮膜特性分析方面使用了OM和SEM觀察試片表面，並製作橫截面試片，以TEM觀察皮膜厚度和結構。化學組成及結晶性則搭配GA-XRD、SAD、和XPS的分析結果。抗蝕性由極化曲線和鹽水浸泡來量測皮膜。結果發現氟離子，但不為獨氟離子，可促使微弧放電。電解液KOH的濃度則可以使皮膜的構成與結晶性改變，直接影響到腐蝕的行為與防腐蝕性能。最後在最佳防腐性能之標準試樣的TEM微結構分析得知介面阻障層(barrier layer)的生成與氟離子使其致密化的效應。

In this study, electrolyte parameters, coating microstructure, and corrosion behavior of AZ31 anodized in alkaline silicate solutions are established and the importance of fluoride is discussed. Microstructural characterization used optical microscope (OM) and scanning electron microscope (SEM) for surface morphology. Cross-sectional microstructures were observed with transmission electron microscope (TEM). In chemical analyses, glancing angle X-ray diffraction (GA-XRD), TEM paired selected area diffraction (SAD), and X-ray photoelectron spectroscopy (XPS) techniques were used. Finally, corrosion behaviors were evaluated with potential polarization curves and salt immersion tests (SIT). Results showed silicate alone, when added to KOH in sufficient amounts is capable of inducing sparks without addition of fluoride. The KOH concentration can alter the coating composition and crystallinity, directly affecting the corrosion behavior and protective properties of the anodic coating. On the cross-sectional observation of reference samples anodized in alkaline silicate solutions, fluoride was found to contribute to the densification of a critical dielectric barrier layer.