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I have an issue with chemical plating of Iron, the component is immersed in Methyl Ethyl Ketone for a time span and then Zinc galvanized plating starts to corrode. I am not understanding what measures should I take. I am not at all into chemical engineering I am embedded engineer and trying to sell my products to companies.enter image description here

My advisor said I should get them alkaline coated.

This effect takes place after 3 days and there are no immediate results to the test.

Thank you You guys are awesome.

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  • $\begingroup$ Your big challenge: Given your moving parts and usage, what portions would wear out a chemically resistant coating via physical damage? How strong would a material need to be in those regions? There are likely better ways, but it is likely possible to build a sealed semi-flexible case around the part, potting it where it transitions to materials that are not suffering and without hampering the purpose much. $\endgroup$
    – Abel
    Jan 22 at 12:56
  • $\begingroup$ TBH these are metal clamps for Drums used in industrial packaging. So we cannot really enclose them, the pieces are small 2 inches and weigh 32 grams. i have tried getting them galvanized till 35 microns and same things happen. Although I am getting the component Alkaline solution dipped now I am worried about the aftermath. Strength required is 1 Tons tensile not shear. And the component has passed that test. $\endgroup$ Jan 22 at 13:14
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    $\begingroup$ given the locations where your parts are expected to grind against one another, my reccomendation would be to swap the zinc galvanized for electroless nickel plating. doesn't help salvage your current part, but should work well for new ones. $\endgroup$
    – Abel
    Jan 22 at 13:31
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    $\begingroup$ There are different zinc-based galvanized coatings that are tuned to different environments. It may as simple as better prep and a slight modification to the coating. Or you may need to manage the cleaning solution better. $\endgroup$
    – Phil Sweet
    Jan 22 at 15:10
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    $\begingroup$ Run a test with acetone as the solvent instead and see if the same thing happens to your part. Acetone has a PH of 7. $\endgroup$
    – Phil Sweet
    Jan 22 at 15:18

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Ritmesh, just to be clear: are the iron parts cleaned in MEK before zinc coating, or are the zinc-coated iron parts corroding after being exposed to MEK during service as drum clamps? I ask because the the usual process for pre-zinc dip coating is an initial acid wash and rinse/dry, not an MEK cleaning dip.

Also please note 35μm of zinc is not very thick and may not be able to cover up all the pits & scratches in the iron.

Also I notice that the corrosion is pitting corrosion associated with the sheared edges of these parts which suggests pinholes in the zinc in the roughened zones. Two things to try: a tumble deburring of the parts before zinc coating to remove any sharp edges, and a thicker zinc coat.

Finally, if the problem is pinholing then you should be able to rapidly produce it by dipping the parts into a warm, well-oxygenated weak acid solution with a little salt in it and then watching closely for gas evolution at the zinc surface, where the pinholes are. You can also do the pinhole test by assembling an electrochemical cell where one electrode is copper and the other is your zinc-coated part and the solution is a weak acid. this will resolve pinholes in seconds if you do it right.

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