Metal Finishing Guide Book

2013

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Immersion Time (min) 2 Coating Weight (mg/ft2) 11.4 5 25.5 8 43.3 Table 2: Coating Weight of 2024 T-3 Alloy pretreatment is equal to or better than conventional trivalent chromates or hexavalent chromates. Results of 168 to 500 hours can be achieved in neutral salt spray testing (ASTM-B117), depending on the aluminum alloy tested. In short, this newly developed trivalent chromium chemistry offers an overall superior performance without any sealer or a topcoat. This novel trivalent chromium treatment has also been used to replace high- and mid-temperature anodizing seals. It has proven to be an environmentally friendly and efficient anodizing seal without any hazardous chemicals. RESULTS AND DISCUSSION Figure 3: EPA = enhanced performance additive. Figure 4 Most aluminum alloys were tested and able to achieve up to 500 hours of neutral salt spray (NSS) corrosion resistance. The concentration of trivalent chromium pretreatment material ranged from 15–25% by volume with various time cycles from 3–5 minutes at ambient temperatures. This new chemistry has been pursued due to its tremendous success in initial testing. It is a drop-in replacement for hexavalent chromate. As mentioned earlier, due to the low concentration and chemistry of non-hazardous substances, it can be operated in a manufacturing environment without any exhaust system requirements. The pretreatment of aluminum is important to achieve desired specifications. Alloys such as 6061 and 7075 are relatively easy to process and can work with most available detergent and activation agents, acids, or deoxidizers. On the other hand, 2024 alloy (with up to 5% copper content) is very susceptible to localized corrosion due to segregation of intermetallic particles along the grain boundaries, and it requires specific pretreatment. The nature of this alloy makes it sensitive to some etching cleaners and may require certain acids to activate the part surface. This patented trivalent chemistry by NAVAIR is simple to operate provided that you pay attention to the pretreatment and pH of the bath. The normal 345

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