Magnesium, stopping corrosion and powder coating

[sdold]

I have a problem with some parts I did a while back, and I have a few questions. If anyone can help I'd appreciate it big time.

A year or so ago I powder coated a couple of magnesium airplane control yokes. I prepped them by blasting with aluminum oxide and washing down with acetone. I recently got them back because they had a problem; the powder coating is deteriorating in spots that seem to have corrosion pitting underneath. They are mostly in the areas where the pilot holds the yoke, but are also in a few other areas.

I'm not too familiar with the chemistry here. If there is corrosion pitting in the magnesium, should I treat it with something, besides just blasting with Aluminum Oxide?

Is there a special powder I should use instead of plain polyester? I used a black glossy polyester powder before.

I have a can of zinc primer powder. Where is this usually used, and is it of any benefit on magnesium?

Thanks in advance for any advice anyone has. I'm already aware of the fire hazards of magnesium, I'll be careful

Steve

[FiReBReTHa]

joining thread to learn.

[Banditperformance]

Interested too, because I have a few Magnesium rims to do, C5 Vette. Could be a BIG future

[Popeye]

Steve,
We do a lot of control yokes and never had a problem. We strip them with aluminum oxide, epoxy fill and sand any heavy pitting, dust off with compressed air and then off gas 1 hour at 425f. Usually spray them hot.
Several out there 4 yo and look like the day we did them..
The acetone may be your problem IMO

[sdold]

What kind of epoxy do you use? And what kind of powder? I wondered about the acetone. I wish I had paid more attention in chemistry.

[Banditperformance]

I found that I had bubbling if I didnt' pre-bake after wiping down with Acetone

[CarWiz]

You might try Iridite or Alodine pretreatment. These are chromate conversions for aluminum but I've heard they work on magnesium too. You'll want Class 1A compounds and an alkaline clean pre-rinse.

[Popeye]

Steve,
We use fix-it epoxy, easy to work and takes the heat no problem. Most yokes we use a standard TGIC outdoor satin black. If you do a gloss make sure and use the additive or you'll get pinholes.

[sdold]

Thanks! I've never heard of using an additive with gloss black, or pinholes. I'll go search the catalog and threads and see if I can find anything.

I have been using Caswell Black Cat Urethane on outdoor things like car bike carriers, maybe I should try that on Yokes too. It's slightly satin-like.

Carwiz: Thanks, I do have some Alodine, I'll look into that.

Banditperformance: I've noticed that wiping with Acetone leaves a film on my parts. I'm not sure if I'm buying crappy acetone, or if it's from my rags, or what, but lately I'm having better luck just washing with simple green detergent and drying in the sun. It's certainly cheaper After using it I don't see any residue.

[twisted0650]

Originally Posted by CarWiz

You might try Iridite or Alodine pretreatment. These are chromate conversions for aluminum but I've heard they work on magnesium too. You'll want Class 1A compounds and an alkaline clean pre-rinse.

Sorry for this late bit of wisdom, probably not relevant to the situation now, but just come across this site today and felt that I had to comment on this.
You don't really want to use alodine. There is a treatment called magnadine specifically made for magnesium. We get ours from Aircraft Spruce and Specialty, I know its available elsewhere also. You need to be really careful with magnesium, and especially magnesium aircraft parts, due to the high susceptability of corrossion. I am an aircraft mechanic, 16+ years now, and have seen a good many magnesium parts scrapped due to incorrect processes and procedures. Mainly wheels, but other items as well. One more thing, just a word of warning, anyone dealing with aircraft parts, be careful. If something happens, and it somehow can be traced back to something you did/applied, whatever, you can be held liable.