Zinc plating adventures

Discussion in 'Castings, finishing/ repair/ and patina's' started by Mark's castings, Mar 2, 2019.

  1. So living near the sea in the tropics causes all sorts of corrosion problems in the workshop. After a lot of work I have a bright satin zinc plating process that works for a wide variety of base metals, doesn't contain cyanide and doesn't have any sugars like most of the Youtube recipes that go off and have growths floating in them in a week. The problem with zinc is that it usually has a chromate passivation applied afterwards to colour it yellow or silver blue. It used to be made with sodium dichromate which is hexavalent and leaves a hexavalent coating that has the best salt spray test results of any process. This has been replaced with safer trivalent chrome passivation that leaves a less toxic coating but which oxidises over time back to hexavalent chrome if any of the plating forums are to be believed.

    So once I had a nice plating bath sorted, I found an online paper about anodizing zinc to give a coating with up to 20 times the saltwater immersion corrosion resistance of freshly plated zinc. The first attempt had some mistakes with the formula which still worked but gave a black finish to the zinc. The second try with the correct formula made the bright polished zinc go a bit frosty and gave a coating that can be dyed to whatever colour you want. I can now anodize any metal object that will take a zinc plating, not to mention diecast zinc stuff like some carburetors.

    Zinc plating with anodize.jpg
    Last edited: Mar 3, 2019
    Tobho Mott, _Jason and Gippeto like this.
  2. oldironfarmer

    oldironfarmer Silver Banner Member

    Very cool!
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    Very cool!
  4. Beone

    Beone Lead

    Wow! We need tutorial on the process!!
  5. Gippeto

    Gippeto Copper

    I'd be interested in that as well. I played around with a sodium bisulfate process for anodizing aluminum with some success and did some zinc plating to thicken bearing shells (long story), good stuff to know for when you need it...and you never know you need it until...well...you do.;)

  6. I just had another try with a plated steel sample and no end of trouble trying to reproduce the results I had with the copper tube (blue). If the anodizing voltage is too high initially (30 Volts) it seems to actually etch/damage the zinc and make it go black in an ugly pattern. Further testing shows the black copper tube sample in the photo is just etched zinc and has no protection where the blue tube sample is hard to scratch and resists acids that would attack zinc immediately. You can read and download the paper here: https://www.researchgate.net/publication/267395560_Anodizing_of_Zinc_for_Improved_Surface_Properties

    I used the anodizing solution 'A' shown in the paper which is 0.75 molar sodium hydroxide and 0.2 molar borax. For the dyes, I used food colouring dyes which work well for aluminium anodizing too.
    Gippeto likes this.
  7. Gippeto

    Gippeto Copper

    Thanks, saved it for later.


Share This Page