Formation mechanism of Zr-based conversion coating on 6061-T6 Al and C1100 Cu galvanic couple
Journal
Corrosion Science
Journal Volume
256
Start Page
113188
ISSN
0010-938X
Date Issued
2025-11
Author(s)
Abstract
Friction stir welding is a solid-state method for joining similar or dissimilar metals. Dissimilar weldments are susceptible to galvanic corrosion, signifying the need for surface treatment. The feasibility of forming a continuous ZrO2 conversion coating on 6061-T6 Al/C1100 Cu dissimilar weldments in a ZrF62- solution was studied, focusing on the macro-galvanic coupling effect. C1100 Cu did not undergo a conversion coating reaction in the ZrF62- solution at pH 4. However, the conversion reaction proceeded when coupled to 6061-T6 Al. In contrast, the conversion coating reactions prevailed on 6061-T6 Al with and without coupling to C1100 Cu. The microstructure of the stir zone of 6061-T6 Al/C1100 Cu dissimilar weldments is highly heterogeneous. Micro-galvanic corrosion prevailed in the ZrF62- solution, and the resulting ZrO2 conversion coating contained many cracks. In contrast, a sound conversion coating formed on the 6061-T6 Al/C1100 Cu dissimilar weldments because the macro-galvanic coupling between 6061-T6 Al and C1100 Cu base metals compensated the micro-galvanic effect in the stir zone. These results corroborate that a rise in pH is necessary to trigger the dissociation of ZrF62-. Thus, Zr conversion coating is feasible for Al and Cu dissimilar weldments.
Subjects
Aluminum
Conversion coating
Copper
Friction stir welding
Galvanic couple
Publisher
Elsevier BV
Type
journal article