Has anyone had there mags shot peened ? Did it turn out good or bad ? I need to get my g***er wheels cleaned up............Thanks
i bead blasted a pair. came out looking like cast aluminum. six months later they were back to looking dark gray.
Blasting magnesium with anything, including gl***, imparts contaminants into the surface that will ultimately cause more corrosion than if the part was never blasted. Cleaning with sulfuric acid is best for magnesium. Unfortunately, depending on the alloy, that may darken the color. Since acid cleaning removes corrosion promoting contaminants, blasting is ok if the part is acid cleaned after..
CutawayAl do you spray the acid on them or submerge it in a tank???Also how long do you let them soak for???
We were having a lot of trouble with magnesium parts in the mechanical exhibits we built. The magnesium division of DOW was one of my shop's customers. What I know about this was learned from a chemist there and the literature they provided to me. We eventually ended up on a help list others could call for advise. I had a plastic tank of acid large enough to dip everything we needed to do. Sometimes half of the part at a time. I don't remember the submersion time. With a high concentration of acid I'm pretty sure it wasn't more than about 30 seconds with a previously cleaned/blasted part. When you can see the entire surface of the part fizzing, that's enough. Immediately rinse with clean water. I used city water with no problem. I think you could do a decent job by constantly brushing the part with fresh acid. Obviously you want to avoid the fumes or getting it on you. After acid cleaning we applied a yellow/gold zinc-chromate coating(another tank). After drying that was followed by zinc-chromate epoxy primer. Any paint is ok, we used polyurethane. Following this procedure we had no further corrosion problems. Recnetly I saw a part that we did over 15 years ago and it still looked fine. That part was high purity magnesium. The alloy your wheels are made of probably wouldn't hold up as long. What we used was the most effective process for our needs. There are other processes that leave a clean silver finish. I have never used one of those processes and unfortunately don't remember anything about what's involved with them. Another option for your wheels would be blasting with zinc media. This doesn't require a follow-up acid cleaning. On a chart of galvanic compatibility zinc is close to magnesium. So unlike steel shot, sand, aluminum oxide, carbide, slag, or even the minerals gl*** contains, the tendence for zinc to promote corrosion is low. I have done a few parts this way. They were left unpainted and held up pretty well. But understand, everywhere the part is touched will eventually result in a discoloration. Zinc blasting media is expensive and hard to fund. I bough it from a guy whop made specialty wire and welding rods. He had a way to cut zinc wire into thin discs. My reclaim-type siphon blast cabinet handled the media pretty well, but I had to throttle down the reclaim a little to avoid loosing too much good media. Hopefully some of this is helpful.
I'm sure your wheels look fine. The problem is; the steel shot coated the wheels with a thin layer of steel, as though they were marked all over with a steel crayon. Magnesium is so prone to corrosion that even that little bit of contamination will significantly promote corrosion. And unfortunately, in the battle between steel and magnesium, magnesium loses. What you have now will corrode way faster than the bare uncontaminated metal would. If you want to shot blast your wheels that's completely fine with me, but you need to do it with an understanding the pros and cons. Also be careful when blasting(especially shot blasting) thin areas as the stress induced can actually crack the metal.
Have you tried Magnesium polish and one of those foam sponges that you can put in a drill? Mothers or Flitz both work well for me.
I shot peened a set over 2 years ago, which removed all surface oxidation. I've kept them coated, clean and dry and they look the same as they did then.
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