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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:
http://www.resintechgroup.com/tables/surface.html#mag
MAGNESIUM AND ITS ALLOYS
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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