Car manufacturers using aluminium for outer body parts have different demands concerning the permitted amount of copper to reduce filiform corrosion. Japanese and European automobile manufacturers both use alloy AA6016, however the Japanese demands are more rigorous (< 0.01% Cu) than the European demands (<0.2% Cu). The demands in the United States are even less than in Europe. US manufacturers use alloy AA6111 with a copper content up to 0.9%. This difference in requirement is based on dissimilar experiences. To gain more knowledge about the influence of copper on filiform corrosion, the authors have investigated alloy AA6016 with different copper contents (<0.01% and 0.07% Cu) and alloy AA6111 (0.7% Cu) in different laboratory and outside exposure tests for several process and product variables (sanding, pre-pickling, phosphate quality, chrome-free rinsing, lead-free electrocoat). The tests confirm that copper is detrimental although both alloys AA6016 meet the filiform corrosion demands. However AA6016 (<0.01% Cu) clearly shows the best results. The level of 0.2% Cu allowed in Europe is disputable. It is better to use lower amounts (<0.1% Cu). Higher amounts of copper as in alloy AA6111 cause more filiform corrosion. This is even more pronounced in case of an incomplete phosphate quality although chrome-free rinsing strongly reduces this negative effect. Type of paint system also seem to influence filiform corrosion. Optimised paint systems may enable the use of higher copper contents. The use of a lead-free electrocoat has only a marginal effect and pre-pickling has no effect. Sanding only has an effect in outside exposure testing which shows that laboratory tests are not sufficient to get a clear picture of filiform corrosion.
Filiform corrosion of painted aluminium automotive body sheet with special attention to the alloying element copper
2000
10 Seiten, 20 Bilder, 2 Tabellen, 18 Quellen
Conference paper
Storage medium
English
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