2024鋁合金的孔蝕機構研究

Pitting Corrosion Mechanism of A 2024 Aluminum Alloy

本研究係以即時觀察和錄影方式記錄2024鋁合金的孔蝕起始和生長過程，並藉助於試驗後的正面和側面觀察以及以環氧樹脂複製孔蝕的型態觀察，來判斷孔蝕的發生和生長機構，並提出一個概念模型描述之。本研究證實2024鋁合金的孔蝕是由於晶出物／基地的伽凡尼效應所造成，晶出物相對於基地為陰極，因此促進基地的腐蝕溶解。蝕孔型態可分成大小兩類，小而獨立的腐蝕坑定義為一般孔蝕，是由單一的顆粒造成周圍基地的腐蝕所產生；大且深的腐蝕孔洞稱為嚴重孔蝕，是由於一般孔蝕暴露出次表面晶出物群體後引發連續腐蝕反應所造成。

The initiation site and process of pitting corrosion in a 2024-T3 aluminum alloy were observed and recorded by an in-situ monitoring method to help investigating pitting mechanism. Post corrosion examinations, which included observations from plane view, cross-sectional view, and epoxy replicas of pits were also adopted for the mechanism study. A conceptual model is proposed to explain the pitting process and mechanism. Pitting has been demonstrated to be caused by the galvanic effect induced by the constituent particle/matrix couples. Constituent particles in the alloy are relatively cathodic to their matrix and, therefore, cause the dissolution of matrix. Two groups of pit were identified: general pitting that is associated with interactions of the matrix with isolated surface particles; and severe pitting that results from the interactions with a cluster or clusters of subsurface cathodic particles.