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Ask the Expert Question-and-Answer Archive

by Ron Joseph

March, 2006

Painting Magnesium

Q. I thank you in advance for all your help. What is the best thing to paint/spray on the internal part of engine cases completely made in magnesium? We are worried especially for the case that is in contact with the water of the cooling system because as you know the water is very, very bad for magnesium.

A. The most important issue concerns the surface preparation. There are various sophisticated methods for pretreating magnesium and one method that is presented by Resin Technology Group, LLC is:

1. Vapor degrease with stabilized Trichlorethylene.
2. Immerse in 10% Sodium Hydroxide for 10 minutes at 76-870oC.
3. Rinse 5 minutes in a cold water spray.
4. Immerse in a solution of 1 1/2 lbs. Chromic Acid, 1/4 lb. Sodium Nitrate in 1 gallon of water for 8 minutes at room temperature.
5. Rinse approximately 3 minutes.
6. Immerse in a 20% solution of Hydrofluoric Acid for 5 minutes at room temperature.
7. Rinse 1/2 - 1 minute.
9. Rinse 1-2 minutes.
10. Dry in hot air blast (71-98 degrees C) for 10 minutes.
11. Bond immediately or apply a Zinc primer for protection of freshly etched surfaces.

Since VERY corrosive and TOXIC chemicals are used in this process, I STRONGLY recommend that you find a contractor who already has such as process, or an alternative one in place.

There are several coating options, including, but not limited to liquid epoxy, liquid polyurethane and powder coatings. Your decision as to the best product for your application depends on the size and configuration of the parts, application equipment, availability of an oven, quality control and more.

Unfortunately I can't give you more details without asking you many, many more questions.

If you would like to work with me on a consulting, fee basis, I will be happy to assist you further by asking more detailed questions and then giving you a report that outlines your various options. For each option I will give you a list of advantages and disadvantages.
Regardless of the system you decide on, I strongly suggest that you first conduct experiments to determine that the final specification will perform to your satisfaction. I cannot sufficiently stress the need to test the final system under a variety of conditions before you go forward with the painting process.

Please contact me again if you would like to pursue this.

Best wishes,

Ron Joseph

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