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Mike Switzer
02-25-2015, 08:14 PM
Just wondering if anyone has a recommendation for chemical paint removal on a magnesium part? I don't want to use any kind of media blast as the unpainted portions are supposed to be semi polished.
Thanks

Bill Berson
02-25-2015, 09:50 PM
I don't have a recommendation. My experience is that most paint strippers tend to etch or oxidize magnesium. It looks dull grey after stripped.

Mike Switzer
02-26-2015, 12:15 AM
That is what I was afraid of. I know some of the "Aircraft" paint strippers are safe for aluminum but not so much for magnesium. From what I have seen though, any kind of blasting media is worse. I may be in for a lot of hours & some elbow grease.

martymayes
02-26-2015, 08:36 AM
Any alkaline based chemical paint stripper should be safe to use. Turco 6813 is one of the better performing alkaline strippers and depending on type of coating being removed, may take slightly more patience than methylene chloride strippers. Also somewhat more expensive than methylene chloride strippers. Another option is hydrogen peroxide based chemical paint strippers. Acid based paint strippers may etch the surface but paint shops use it all the time.

Mike Switzer
02-26-2015, 08:56 AM
Thanks Marty. Restoring magnesium parts is a new one for me. One thing I know - I will try it on a spot that won't show when assembled first.

Bob H
02-26-2015, 07:03 PM
I'd avoid chemical treatments unless you are sure they won't induce any tendency for stress corrosion cracking. I'd go with a blast process using a soft medium like walnut shell and then clean blasted surface with acetone.

Mike Switzer
02-27-2015, 12:32 AM
Bob, do you think walnut shells would not pit the magnesium? I have seen some indy car mag wheels that were soda blasted & they looked terrible afterwards, that was why I was leaning toward chemical stripping.

Bill Berson
02-27-2015, 09:12 AM
What are you working on?

Mike Switzer
02-27-2015, 10:10 AM
Well, it isn't entirely aviation related (although any profits will support my homebuilding efforts) - It is a set of original rims off a Jensen Healey. Not real common & I sure don't want to ruin them.

krw920
02-27-2015, 01:10 PM
Bob, do you think walnut shells would not pit the magnesium? I have seen some indy car mag wheels that were soda blasted & they looked terrible afterwards, that was why I was leaning toward chemical stripping.


Google to the rescue.

http://stevekouracos.com/restoration/tips-and-tricks/aluminum-magnesium-wheel-restoration/

Mike Switzer
02-27-2015, 04:16 PM
Thanks for that link - very helpful. I just got off the phone with TP tools, (I have one of their blast cabinets) they have a plastic media that they say will take off any paint, dirt, or corrosion and will leave the surface smooth as original.

Bill Berson
02-27-2015, 04:37 PM
I wouldn't alodine and then use self etching primer.
Self etching primer is for raw metal.

Mike Switzer
02-27-2015, 05:04 PM
I wouldn't alodine and then use self etching primer.
Self etching primer is for raw metal.

I don't know that I will do all that, this one is getting restored as a nice driver, not a show car. As near as I can tell, originally they didnt prime them, they just masked off the bits they didn't want paint on & shot a coat of black enamel on everything else, front back & inside. Gonna do a bit more research into the coating options.

martymayes
02-28-2015, 08:29 AM
A chemical stripper or blasting media that is not supposed to damage the substrate will remove the shine from a polished surface but it can be buffed back to shine like new. It's just a matter of expending the elbow grease.

Bob H
02-28-2015, 04:44 PM
Magnesium is galvanically reactive so that if you clean the surface and expose fresh material, it will oxidize quickly with a dull finish. That oxide can react with moisture to produce undesirable intergranular corrosion which will induce cracking under stress. You want to generate a protective coating on the metal which is why Dow Chemical came up with Dow 7 as a coating to be applied immediately after machining.
The Dow 7 makes a protective oxide that resists the corrosion and keeps the mag from developing those cracks. It's similar to Alodine. If you blast the surface, have the proper coating available for quick application.

Bill Berson
02-28-2015, 06:18 PM
I know they called them Mag wheels. But aren't they usually actually aluminum or a mixed alloy?

Mike Switzer
03-01-2015, 06:19 AM
Magnesium is galvanically reactive so that if you clean the surface and expose fresh material, it will oxidize quickly with a dull finish. That oxide can react with moisture to produce undesirable intergranular corrosion which will induce cracking under stress. You want to generate a protective coating on the metal which is why Dow Chemical came up with Dow 7 as a coating to be applied immediately after machining.
The Dow 7 makes a protective oxide that resists the corrosion and keeps the mag from developing those cracks. It's similar to Alodine. If you blast the surface, have the proper coating available for quick application.

Thanks - I will look into that

Mike Switzer
03-01-2015, 06:22 AM
I know they called them Mag wheels. But aren't they usually actually aluminum or a mixed alloy?


Most of the aftermarket pieces are aluminum, but some OEMs used magnesium thru the early to mid 70s.

Bob H
03-01-2015, 10:51 AM
The term "alloy wheels" means they are an aluminum casting. "Mag wheels" refers to cast magnesium. You stated that wheels were magnesium which is what all the discussion was about.
If wheels are actually aluminum, no sensitivity to cracking and no special Dow 7 conversion treatment required.

Mike Switzer
03-01-2015, 09:36 PM
These are original magnesium wheels, which was why I started the thread as I have no experience removing paint from magnesium. Sorry for the confusion, my previous post was in reference to Bill's question. Most alloy wheels are aluminum, but some of the the British manufacturers continued to use magnesium thru the early 70s.