How to stop corrosion on Magnesium

How do you stop and clean corrosion on Magnesium before painting. It is not serious yet but I dont whant it to continue.

I am not sure this is possible.
I have a few experiments running, as we speak.

1) Just ruffed it up and soaked in Diesel.
2) Sand blasted cleaned and painted.
3) Sanded cleaned and painted.
4) Just scraped of the loose stuff.
I will post the resoults here in 20 years.

You need to bolt on a sacrificial metal cathode ( anode? ) What metal would you use? If you read the hype of some of the after marked treatments for auto body corrosion their potions would make it last forever!

Magnesium has a bad habit of corroding from the inside out. If the part is not painted a squirt of wd-40 or another penetrating oil will stop the corrosion if done regularly.

In your case, just clean off the corrosion, prime and paint. I wouldnt be surprised if the more you clean the more corrosion you find.

You could have it annodized, however that is usually pretty pricey because it is a proprietary process owned by Dupont I think. They get a cut of every item annodized by someone using the process.

I would be inclined to prep it well and put a really durable paint on it.

zinc

Crofter said:

You need to bolt on a sacrificial metal cathode ( anode? ) What metal would you use? If you read the hype of some of the after marked treatments for auto body corrosion their potions would make it last forever!

Click to expand...

Zinc is used in the boating industry as an attempt to stop corrosion

I was making a joke of trying to prevent the corrosion by something bolted on that is sacrificial to Magnesium. That is its problem. It is very often used to protect other metals from corrosion by being the victim itself. In the saw it was only used for its light weight factor. If all of the saw were magnesium it would be ok. The iron on the other parts of the saw is what sets up the corrosion causing electrolosis. Special attempts are made in piping applications to break dissimilar metal connections. Teflon gaskets and teflon washers and sleeves at flanged connections make an attempt to stop electrolysis but it goes on to some extent anyway.

sandblast the snot out of it with medium silica sand, fill any pits with jb weld, sand smooth, prime and paint. if ya want a super duper job, use epoxy auto primer.

Look on page 4:
http://www.enviro-navair.navy.mil/data/pdf/factsheets/files/2004/Corrosion_Control_Factsheet.pdf

It is,in fact,an electrolysis thing,as has been stated.Both aluminum and mag are sacrificing metals,mag.more so.From my own little life of dealing with metals,both these metals will last longer if not stored on a concrete floor.Put them on a board or something non metallic.I would be inclined to think if they were stored,long term,without the bar attached,they would last longer.It is mainly on a 40 year old saw you see this phenomenon.Perhaps a small zinc plate would be helpful?Remember the good old J B weld Works for me.

JB Weld is nothing more than epoxy.

JB weld is MUCH more than just an epoxy, its like a welder for those of us who cant use regular welders. its like duct tape, but more permanent.

Corrosion:

Hello firebrick43. When I was in the Army, we had to do some modifications on the OH-23 helicopter main rotor heads. Had to replace some old studs with modified ones. Anyway the old studs were removed, the holes cleaned or tapped out and before installing the new studs we were required to spray the tapped, reworked holes with Zinc Chromemate (spelling ?) a sort of primer. I've used it on Aluminum and Mag. after cleaning away any corrosion. Clean up any obvious corrosion, make sure the surface has no oil, wax, etc on it, spray the surface with Zinc Chromemate, let dry, fill pits with red oxide primer, sand smooth, prime and paint. As AL said keep the saws off the concrete floor and I usually spray my saws with WD-40 if they are to sit for awhile. Removing bars is an option, but would recomend it for really long term storage, say for over 6 months. Just some thoughts on this corrosion thing. OK, my 2 cent worth. Take care. Lewis.

Zinc Chromate Used to be an additive in Marine Primers. (Don't know if the eco-freaks have changed that world ) Used to be available in most Marine oriented stores. When you paint a lower unit the best thing to do is get down to a clean surface & prime with the green colored primer loaded with Zinc Chromate & then finish with an marine epoxy paint. Problem with sacrificial anodes is they need to be in a solution (Like water) to really work well over a large surface.

Keep it in a climate controlled house

Water:

I had an old 55 hp Johnson (50 Anniveraary Version) that was on a boat that camae up from Florida. Needless to say that the thing had a lot of salt water corrosion on it. I removed the lower unit and removed every bit of scale, corrosion, etc.I could see. Made sure she was clean and I primed the lower unit with some green colored Zinc Chromate (2 good coats, well covered). I then used some spray paint that matched the original color I got from NAPA. The boat was out of water, more than it was in, but didn't notice any more problems with corrosion while I had it. Which was over 5 years. Take care. Lewis.

I paint on mag all of the time in my work (aircraft painting) so I think I have something to offer on this subject. Paint adhesion and corrosion prevention are really one and the same thing. Any metal corrodes. Some, like the 'light' metals, aluminum, mag beryllium, zinc, etc., corrode much more readily than other familiars like iron and copper. To get paint to stick really well to any metal, you have to stop the corrosion process. Otherwise your paint is riding on a layer of oxide which is constantly ablating away and falling off. This is done by passivating the metal with an ion exchange. Remember that metal is corroding all of the time. As soon as you make it bare, it is corroded a little tiny bit by exposure to the air. This is not such a big deal with iron and steel, but with aluminum, for instance, you get a few minutes of bare time after grinding or sandblasting where you can get pretty good adhesion without treatment. After that the paint won't stick. So not only do you have to get off all the corrosion, you have to keep the metal from re-oxidizing long enough to get it painted.

So then the procedure is to remove the new (invisible) corrosion, usually with an acid bath, then immediately apply a conversion treatment. For aluminum the standard product is something called Alodine 1201. It 'converts' the surface of clean, corrosion-free aluminum to an aluminum chromate substance, which does not corrode at all. Then the paint will stick like mad and no more corrosion happens.

There WAS a similar treatment system for mag from the same company, Henkel , Alodine 1001, but is no longer in their product catalog since Henkel took over the Alodine line from Parker Amchem. More recently I have been buying mine from Eldorado Chemical under the name Mag Kote. Quarts of Alodine 1201(for aluminum only) can stll be bought with the DuPont label from your local auto paint jobber as 226S. This is re-badged Alodine 1201 straight from Henkel. Unfortunately the mag version was never available in the DuPont label to my knowledge. Unfortunately again, Eldorado makes you buy 4 gallons minimum, which is more than you will ever need.

Mag is very sensitive to acids, so acid washing is usually not used. Either the freshly ground/sandblasted mag is treated immediately with the conversion treatment, or a mild alkaline wash is used. I successfully used plain ammonia detergent from the grocery store diluted about 3:1. Then the Mag Kote is applied by spray or dip.The treatment causes an immediate visible change in the surface color of the metal, which indicates that the treatment is effective.

Once treated, you can apply the primer/paint system of your choice. Zinc or strontium chromate/epoxy primers are best. I like the mil-p-23377 yellow primer. Without paint, the surface treatment is easily scratched off as it is only a few molecules thick. The treatment stops further corrosion and gets the paint to stick and the paint in turn protects the surface treatment fom damage.

All of this stuff is really toxic, containing several different toxic heavy metals and cyanide salts, so you should handle it carefully and follow directions.

Jimbo

My experience is not as detailed as the one posted by Jimbo but I have had a little experience with painting aluminum. When I worked for the USCEC we built many things from aluminum. As the grunt I always got the job as priming and painting them. I used a clear/blue primer that stunk like heck. I then painted as usual. I would imagine many of my paint jobs are still there.

Bill

A excellent thread!

Bumping an old thread. Some good tech here.