銅含量及晶出物對鋁合金孔蝕影響之研究

Effects of Copper Content and Primary Precipitate on the Pitting Corrosion of 1050 Aluminum Alloy

鋁合金耐蝕性質受到合金元素、顯微組織及環境之影響。本文主要研究不同銅含量1050鋁合金，藉由不同製程處理，改變不同晶出物的組成、形態及布，分別探討在Cl-及SO42-環境中之抗孔蝕性質變化。結果發現：（1）當鋁合金Cu含量差異不大下，長期孔蝕成長與Cu含量之相關性不強，但短時間含Cu量較高的鋁合金，其蝕孔發生之速率會較快。（2）高Cl-環境有助於孔蝕之起始，而混合SO42-及Cl-溶液，則有助於蝕孔之成長。（3）浸泡試驗結果證實，研磨面之腐蝕現象較未研磨面輕微，顯示鋁材表面的異質體與鋁片孔蝕發生機率息息相關。（4）孔蝕起始位置即時觀察證實鋁合金表面的孔蝕起始位置為晶出物周圍，這些呈陰極的Al-Fe-Si或Al-Fe-Si-Cu晶出物，若為網狀連續結構或聚集密度較大時，孔蝕發生時間就愈短，而晶出物之種類並非鋁合金易腐蝕之主要原因。

Effects of copper content and primary precipitates of 1050 aluminum alloy on the pitting corrosion in Cl and SO42-2 solutions were investigated in this study. The results showed that copper assisted pitting initiation. However, the pitting growth rate of aluminum alloy was almost independent of the copper content below 0.112%. High Cl environment enhanced the initiation of pitting, and mixed solution of Cl and SO42- helped the propagation of pitting. Surface polishing improved the pitting corrosion resistance. This result implied that surface constituent particles had close relation with the pitting corrosion of aluminum alloy. In-situ observation test indicated that pitting initiated in the vicinity of primary precipitates. The primary precipitates like Al-Fe-Si and Al-Fe-Si-Cu were nobler than the Al matrix. If they were arranged with network or cluster, the time to bring out pitting corrosion would dramatically be shortened.