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Thread: Magnesium Coating

  1. #1
    Senior Member
    Join Date
    Aug 2007
    Phila Pa. area

    Magnesium Coating

    A recent thread talked about corrosion of Magnesium parts, and using Gibbs and such to control it. Is there a procedure you can do at home if you want to strip a Magnesium part ( glass bead ), conversion coating,primer, and then top coat. I think you can use any good primer and top coat, but what about the conversion coating?
    Last edited by mike curnow; 12-07-2010 at 05:52 AM.

  2. #2
    Senior Member Jim Garfield's Avatar
    Join Date
    Oct 2003
    Rhode Island
    There are a number of DOW dichromate processes to seal and protect Mg. I think the one used by Porsche to seal engine casings and parts that turned the Mg blackish brown might have been No.7. I remember seeing a booklet put out by Dow years ago that described the different processes, it might be worth your while to check Ebay or Amazon to see if there are any copies still floating around. I'm not sure if these techniques can be used in a one off diy situation, or if they are only for industrial use.
    '74 leichtbau
    R Grp 246
    S Reg 823

  3. #3
    Senior Member
    Join Date
    Oct 2008
    Burford, ON, Canada
    Porsche Historian, contact for Kardex & CoA-type Reports
    Addicted since 1975, ESR mbr# 2200 to 2024 03
    Researching Paint codes and Engine Build numbers

  4. #4
    Hi Mike,

    I did a DOW7 coating on my 68 magnesium fan and housing. The darkness of the coating depends on the makeup of the magnesium alloy. Some come out with a dark brown finish and some result in a almost black finish.

    There are number of Dow coatings, such as DOW7, DOW9, etc. My guess is the different specifications are a result of how long the magnesium is left in the dichromate bath. I looked at doing my own DOW7 process, but the chromate chemical is so toxic it is no longer sol in the do it yourself kits. There are plenty of plating shops that can do this coating. Lots of aircraft parts require it.

    Best regards,

    Attached Images Attached Images    
    Brad Davis
    RGruppe #691
    Early 911S #1547

  5. #5
    Try here:

    There is a company in the UK called Indestructable paints and they make really high quality paints and finishes used for painting Military Helicopter Gearbox casings - always magnesium. I have 'begged' some of their paint as it has a huge cost and it is excellent. There must be some US based equivalents that supply Bell etc.

  6. #6

    Brad is right (great pics BTW), the final finish does depend on the magnesium. We used several sample mixes and also adjusted the dipping time, but even under the same solution and times different fans resulted in a different finish. We have also used the same process on engine cases, chain housings/covers etc. We have also done gear box cases eg here is a 915 box from an RS. Completely stripped of all and any steel


    Parts plated

    Then the cases were chromated, leaving a light grey finish and then box rebuilt.

  7. #7
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Portland, Oregon

    dow 9

    Dow 9 is dark gray when dry and almost black when oil is applied. Gordon
    Attached Images Attached Images  

  8. #8

    Henkel makes a pretty expensive "magnesium treatment kit" which can be used to provide a chromate base, over the top of which you would use a primer and final paint. I would glass bead, being aware that mag usually has corrosion so it's not unreasonable to expect a lot of pits and loss of material-- then bake the part in a hot oven for a while to remove any residual hydrocarbons, then hit it with the mag treatment kit.

    The thing comes in a paint can all sealed up, it's HAZMAT so has to go by ground. Probably five bucks worth of chemicals and the rest is product liability insurance. I bought one, what the hell.
    1966 911 #304065 Irischgruen

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