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High-Corrosion Resistant Trivalent Chrome Conversion Coating

05/08/2009
 

Nontoxic, High-Corrosion Resistant Trivalent Chrome Conversion Coating Helps Eliminate Hexavalent Chrome Use

Saporito Finishing Company now offers a high-corrosion trivalent chrome conversion coating for aluminum, magnesium and zinc die castings that will help eliminate the need for toxic hexavalent chrome use. The conversion coating is a clear blue finish similar to standard clear chromate and meets or exceeds MIL C 5541 high-corrosion resistance requirements, as tested per ASTM B117.

The coating was originally developed by the U.S. Department of the Navy and licensed to several manufacturers. Saporito Finishing worked with the Navy and its licensees to test the products ability to meet the requirements of industry standards, as well as corporate and global directives to eliminate use of toxic hexavalent chrome including RoHS and ELV.

Extensive comparison testing showed that the new trivalent chrome conversion coating performed as well as or better than conventional hexavalent chromate conversion coating. Results of 168-hour, side-by-side neutral salt-spray tests, as specified by MIL C 5541 and ASTM B117, include:

  • No difference in corrosion resistance of wrought 2024 and 6061 panels.
  • Better performance by trivalent chrome conversion coating on A380 die cast panels.
  • Higher corrosion resistance yielded by trivalent chrome conversion coating on castings.

In further testing, A380 die castings were coated with the trivalent chrome conversion coating, painted, and subjected to cross hatch adhesion testing. The panels showed excellent bonding capability with no compromise of the bond strength, as compared to the conventional hexavalent chromate.

The trivalent chrome conversion coating is also superior to hexavalent chromate conversion coating because it is not affected by baking or exposure to heats associated with curing processes typical in paints, powder coats, and rubber molding, as well as service conditions. While traditional hexavalent chromates dehydrate when exposed to temperatures higher than 150 degree Fahrenheit cracking and exposing the substrate underneath, which then corrodes and fails completely trivalent chromates can be baked at temperatures up to 400 degrees Fahrenheit with minimal degradation of their corrosion resistance. That makes trivalent chromates excellent bases for paints and rubber bonding, markedly superior to hexavalent finishes.

"We are thrilled to offer this new trivalent chrome conversion coating that eliminates the environmental concerns associated with hexavalent chrome" said Jeffrey Logan, Saporitos Operations Manager.

"The mandate to eliminate hexavalent chrome, which has found its way out of the automotive industry and into the electronics sector, will also impact customers in the medical sector this year, and other sectors of manufacturing are sure to follow. Its exciting to offer our customers a product that can replace hexavalent chromate coating, while offering equal or better performance."

Saporito Finishing Company, located in the Chicago suburb of Cicero, IL, is an ISO certified company with more than 60 years of plating, anodizing, finishing and metal treatment knowledge, as well as tumbling and deburring capabilities. The company offers more than 135,000 square feet of processing area, supplemented by full-service chemical laboratories meeting the needs of customers in the electronic, aerospace, aircraft and commercial industries.

Saporito Finishing is your single source for anodizing and metal finishing processes. Magnesium anodizing, metal plating, mechanical finishes and aluminum treatments.

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