The focus of this project was to validate use of zirconium-based pretreatments as an alternative to those currently approved for use on military vehicles. For steel substrates, the incumbent pretreatment technology is zinc phosphate, as described in TT-C-490 Type I, including di- and tri-cation versions. Zinc phosphate provides a crystal structure to which organic coatings such as paints and powder coatings can adhere. A chrome sealer or rinse provides improved corrosion resistance but increases waste disposal costs and introduces additional Environmental Health and Safety concerns. Chromium-based pretreatments are more commonly employed for aluminum substrates; these include hexavalent (MIL-DTL-5541 Type I) and trivalent (MIL-DTL -5541 Type II) chromium products. The overall goal of this project was to process and field test coupons or small components that demonstrated the corrosion resistance capabilities of a MIL-DTL-53072 finish, replacing the typical pretreating step (whether ferrous/zinc-phosphate or nonferrous/chrome-functional) with a zirconium oxide pretreatment film.
This demonstration project built on the findings from WP-1676 and demonstrated the performance capabilities of zirconium pretreatment for protection of reconditioned material at U.S. Army and U.S. Marine Corps depots. X-Bond 4000, a commercial pretreatment, was selected for this demonstration and is commonly used with a variety of metal substrates and industrial finishes. WP-1676 provided the initial evaluation of zirconium immersion pretreatments intended for Original Equipment Manufacturer (OEM) application over cold rolled steel and aluminum with water-borne and solvent-borne Mil-Spec primers.
Results in corrosion performance were similar to the chrome (VI) and zinc phosphate pretreatment controls. In conjunction with the U.S. Army Combat Capabilities Development Command Army Research Laboratory, modified versions of the commercial zirconium pretreatment showed corrosion resistance equal to or better than zinc phosphate in both spray-applied and immersion-applied processes. Accordingly, the work showed that the current commercial zirconium pretreatment technology, with some modifications, is suited for use in Department of Defense (DoD) OEM processes. Visits to Marine Corps Logistics Base Albany, Albany, Georgia, and Letterkenny Army Depot, Chambersburg, Pennsylvania, suggested that development of an immersion zirconium pretreatment process would be of utility for DoD repair depots as well.
PPG Industries, Inc.’s zirconium-based pretreatment technology provides the initial layer of corrosion protection and enhances adhesion to both steel and aluminum substrates. This reduces pretreatment line complexity and costs over incumbent materials. The replacement offers several other advantages over present pretreatments, including the elimination of toxic metals such as nickel used in zinc phosphate and chromium. The zirconium pretreatments developed have been in commercial use on automotive and industrial paint lines for over 15 years and represent a mature technology for transition to military use.