Zinc flake coating is a generic term for coatings and is used by several chemical providers globally. Zinc flake, by design, will lay and overlap on the products when coated. This allows for a blend of zinc flakes to formulate a uniform coating coverage. This specific coating is relatively thin (8-12 µm) and will produce a high level of corrosion protection for any part.
Don GeorgeZinc flake coatings generally are a mixture of zinc and aluminum flakes, which are bonded together by an inorganic matrix. These chemicals are applied to the product in a non-electrical process. This process consists of a dip, spin, and heat cured manner. Some zinc flake coatings are solvent-based and others are water-based and perform equally well.
Zinc flake coatings conform to several industry specifications, but the most recognized standard is the ISO 10683 for the transportation industry. Many customers utilize their own specifications as well for their zinc flake coating requirements.
What brought Zinc Flake Coatings to the Transportation and Other Industries?
Steve HlywaThe history, or background that brought the zinc flake technology into the transportation industry was primarily driven by three factors. All three of these factors will be examined in more detail below:
- Environmental conditions that require automotive vehicles to be “hexavalent chromium-free” for end of life cycle and processing.
- In the 1980s the finishes on fasteners (and other products) in the transportation industry were primarily a zinc chromate which is applied in an electroplating process. These finishes provided low levels of corrosion protection and contained “hexavalent chromium” which was an environmental concern in the electroplating processing and end of life vehicle disposal. The industry had to change!
- The need for better corrosion protection on all vehicles to improve customer satisfaction and at a good cost-benefit ratio.
- At the same time as the environment was getting more attention, customers were unhappy with rusty fasteners on their new vehicle. This also equated to difficulty in servicing the vehicles. Clearly, a better system was needed, but at a fair “cost-benefit ratio”. Automobiles were costing more and customers were expecting more.
- To eliminate the potential of “hydrogen embrittlement” in high strength bolts.
- Historically, there has been a concern with high strength fastener failure due to “hydrogen embrittlement” introduced into the parts during the electrolytically plating process. Even with safeguards and preventative measures, the opportunity was still there. High strength fasteners are used in several safety-critical applications and fastener failure (breaking) is just not an option.
How do Zinc Flake Coatings work?
Photo courtesy of Doerken USAZinc flake type coatings provide a barrier on the base metal that gives excellent protection from the elements that cause corrosion. In the diagram below you can see how the flakes lay on the base metal, and typically have the addition of a topcoat for friction control. This is very typical of zinc flake type coatings which are normally applied in a dip spin or rack (Dip, Drain, Spin) coating line. Pictured here, you can see how the zinc flakes lay and overlap on the part, which is very important for corrosion protection coverage. This method has provided excellent in-use performance for vehicles in real-life elements. Zinc flake coatings have performed great in salt spray testing, as well as cyclic corrosion testing (CCT).
Photo courtesy of Doerken USAZinc flake coatings have improved the corrosion resistance performance on Fasteners used in the harshest applications and are used by all original equipment manufacturers (OEMs). In the worlds of automotive, heavy truck, off-road equipment, and construction industries, zinc flake products are used extensively to provide the best corrosion protection for the OEMs.
Zinc flake coatings have now been used in the transportation industry globally for many years. They are still the preferred coating for the areas of the vehicle that sees the harshest environmental conditions.
What are the Benefits of Zinc Flake Coatings?
Zinc flake coatings have become one of the preferred coatings for fasteners in the transportation industry due to the benefits listed below:
- Excellent appearance in both silver and black colors
- Very good corrosion protection, over 2,000 hrs. of salt spray testing depending upon the coating thickness
- Excellent Cyclic Corrosion Testing results
- Good chemical resistance to exposure to all fluids used in the transportation industry
- Excellent resistance to extreme temperature
- Friendly to the environment
- Excellent friction control on fasteners with desired friction modifier top coatings
- No RISK of Hydrogen Embrittlement from the chemistry or application process
- Performs well in heat loosening tests
- Electrically conductive
- Very good “Cost-Benefit Ratio”
- And more
As the transportation industry has set newer and higher corrosion protection requirements, the zinc flake product has been able to meet (and exceed) the new challenges. Automotive and heavy truck use the zinc flake technology products in the harshest applications because it works.
Environmental Concerns are an ongoing industry issue
An additional benefit to the use of zinc flake coatings addresses the industry’s concern for the environment. The zinc flake coating chemistry and processing is very friendly to the environment. For processing, in use, and end of life disposal, zinc flake eliminates the concerns for OEM manufactures and it exceeds government requirements. This also applies to the welfare of the operators installing these fasteners in the assembly plants, as well.
What is the Future for Zinc Flake Coatings?
Like most good products, zinc flake coatings have been improved over the years to increase performance and meet the industry’s changing needs. The zinc flake product enhancements have taken corrosion resistance to new levels of performance, both on in-service vehicle usage and testing. The cyclic corrosion testing results have really made the industry take note, and there are more performance improvements coming.
The benefits of zinc flake coatings have been noticed by many companies looking to upgrade their corrosion resistance performance. Transportation and other industries are always looking to upgrade their products to improve customer satisfaction and gain more sales. Design engineers are tasked with upgrading their applications for longer and better in-service life and serviceability. The usage of zinc flake coatings has migrated to many other product components that were in need of corrosion upgrading. With the industry's demands to improve underbody and under hood corrosion protection, zinc flake coatings have answered the call. Due to its excellent corrosion characteristics, resistance to high temperatures, and in-service performance, zinc flake coatings are meeting the industry’s needs.
Chassis components such as subframes, larger stampings, a-arms, struts, suspension components, springs, u-bolts, fuel systems components and more are now reaping the benefits of the protection from zinc flake coatings. Testing has shown that 15 years underbody corrosion free life is achievable with zinc flake coatings on chassis parts.
Don George is Director of New Business and Steve Hlywa is Sales & Technical Support at Michigan Metal Coatings Company in Port Huron, MI. Visit www.michiganmetalcoatings.com
