Wu, Yi-TingYi-TingWuChen, Siao-YingSiao-YingChenYang, Zong-SyunZong-SyunYangHuang, Han-ShengHan-ShengHuangI-Chung ChengCHAO-SUNG LIN2025-08-142025-08-142025-110010938Xhttps://www.scopus.com/record/display.uri?eid=2-s2.0-105011047695&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/731387Friction 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.falseAluminumConversion coatingCopperFriction stir weldingGalvanic couplejournal article10.1016/j.corsci.2025.1131882-s2.0-105011047695