Selected Cr(VI) replacement options for aluminum alloys: A literature survey

There is a significant move away from the use of hexavalent chromium, Cr(VI), which is a mature, trusted, and relatively inexpensive treatment that has been used for many years by industry to reduce corrosion. Although Cr(VI) is effective at reducing corrosion, it poses a substantial health hazard. While there is a need to define a process that will be able to replace Cr(VI), the process must be able to provide the same level of corrosion protection currently provided by hexavalent treatments. In addition, it needs to do this without the associated environmental problems. This paper focuses mainly, but not exclusively, on the trivalent chromium pretreatment (TCP) and its commercially available variants. The TCP was developed by the Naval Air Systems Command (NAVAIR) and is used by the US military. The rationale for the focus of this paper is that in the near term, the aeronautics industry needs to move away from Cr(VI) towards a more benign commercially available chemical treatment that can help protect the aluminum alloys used by that industry. TCPs are currently available commercially and have undergone numerous tests by multiple organizations to establish their effectiveness in reducing corrosion of both bare and painted aluminum alloys.