Effect of Coarse Second-Phase Particles on Galvanic Corrosion of Anodized 6061 Aluminum Alloy Coupled with C1100 Copper

This study investigated the effect of second-phase particles on the galvanic corrosion of anodized 6061 aluminum alloys coupled with C1100 copper alloys. The AA6061 alloys were solution treated at 530-570 degrees C for 1 h, followed by water quenching or furnace cooling. Anodic coatings of thicknesses 1, 5, and 12 mu m were formed on AA6061-T6 after anodizing. The galvanic corrosion current of AA6061 coupled with C1100 copper was measured using a zero-resistance ammeter for 8 h in two solutions, namely 3.5 wt.% NaCl and 1.0 wt.% NaClO, at 25, 40, and 60 degrees C. Black Mg2Si particles measuring 3-5 mu m and white Al-Fe-Si-Cu particles measuring 3-8 mu m were observed in the furnace-cooled AA6061 specimens. The highest galvanic corrosion current density (1312 mu A/cm(2)) in a flowing NaClO electrolyte was observed at 60 degrees C for the free-anodized AA6061-T6 alloy coupled with C1100 copper. The lowest galvanic corrosion current density (15 mu A/cm(2)) was observed in a 12-mu m-thick anodic coating on AA6061-T6 alloy coupled with C1100 copper in a static 3.5 wt.% NaCl electrolyte at 25 degrees C. A severe corrosion attack was observed for a thin and nonuniform anodic coating on AA6061 alloy coupled with C1100 copper after the galvanic corrosion test because the coarse second-phase particles in the thin anodic coating on AA6061 caused perforations in the anodic coating. However, the thick anodic coating on AA6061 can effectively reduce the galvanic corrosion of AA6061-T6 coupled with C1100 copper in static or flowing electrolyte solutions.