Because it is one of the lightest and strongest metals available, the use of magnesium is growing in many industries including aerospace, automotive, electrical and military. It has good fatigue strength, excellent strength-to-weight ratio, is non-magnetic and has relatively high thermal and electrical conductivities. The disadvantages of magnesium is that is has poor corrosion resistance properties which can lead to structural or mechanical failure and has inadequate adhesion qualities for paint.
Like most metals, magnesium will oxidize when exposed to the atmosphere and exposure to water or high humidity causes it to corrode even more rapidly. To ensure safe and reliable performance, magnesium components must have some form of protective treatment.
Protective coatings are applied to magnesium parts to slow corrosion and ensure long term structural integrity. PTI offers three types of magnesium coatings:
- Dow 17 Anodizing
- Dow 7 Chemical Conversion
- Dow 19 Chromic Acid.
Dow 17 Magnesium Anodize
This anodic chemical treatment is applied using an electrical current and is suitable for any magnesium alloy. The most robust of the three treatments, Dow 17 penetrates the surface and has a dimensional build up of between .0006 – .0012” depending on the thickness of the coating. The Dow 17 process results in a light green to dark green surface finish. It provides increased abrasion and corrosion resistance and is an excellent base for paint or any other post treatments.
Dow 7 Chemical Conversion Coatings
Dow 7 is a chemical conversion coating that is ideal for both new and overhauled parts that possess dissimilar materials such as inserts. The chemicals will react only to the bare magnesium converting the outer layer of the magnesium to a protective coating. This treatment has no appreciable dimensional change making it a good choice for parts with no coating tolerance. Dow 7 results in a brassy or dark brown finish depending on the type of magnesium alloy as well as the age and condition of the component.
Dow 19 Chromic Acid Coating
Dow 19 is used on magnesium parts that need a spot touch-up for minor damage repair or a temporary coating for corrosion prevention between production processes. This chromic acid coating is applied by manual application or immersion in a tank. Parts will be a light, brassy brown color varying slightly based on the type of alloy. Dow 19 also offers no appreciable change in dimension to the component.
PTI has been helping manufacturers with their magnesium components for over 30 years. Our dedicated and experienced technicians can help you determine which magnesium coating method is right for your components.