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Delayed Blistering in Alkaline Zinc Electroplating

Q. We are having problems with delayed blisters in our zinc plated parts. The process is a rack operation with alkaline zinc, zinc content is 14-16 gr/lt and 120-140 NaOH. Client requires 15 to 35 microns and because of part configuration it is very difficult to plate, in order to achieve at least 15 microns in the lowest area, some areas are very close to 30-35 microns. We experienced delayed blisters 5 days after plating. 100% of parts where adhesion checked according to ASTM, tape test and were approved. Almost all the blisters have "popped" and we can see a black area underneath, but some blisters are "unpopped". What does the black area mean? We believe the pre-plating process is very thorough, parts are very clean. Base metal is Steel, hardened and tempered to 16-17 Rc, we don't consider this a hardened metal because of the low Rc value.

Some parts showed pitting in the finish; can these pits later develop into blisters?

We added agitation to the bath to improve efficiency and to renovate solution close to the plated parts.

Can bubbles from the anode be the culprit? There is a lot of gassing while plating is done. Plating at 4-5 Volts, 2 amp/sq. dm approx. for 60-70 minutes

Thank you for your help

Dargmar Jimenez
plating shop - Mexico
2005

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Q. Yesterday my shop ran a bar through our alkaline zinc-iron electroplater line. It is a part we have run hundreds of times with little problems. Today I got to work and discovered that the parts had blistered post-production. This is the first time I have encountered this problem. I am not sure what caused this to occur. Stresses in the plating was my first thought but I don't know what could cause this. The part ran through trivalent black chromate after being plated. We have a new black on our line so I'm not sure if this could be part of the problem but I doubt it. Any insight into this problem would be appreciated. Thank you.

-Steve

Steve Humphries
Plating Shop Chemist - Grand Rapids, Michigan US
November 21, 2008

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A. I doubt very much it's the chromate. Most often, this trouble is caused by organic contamination/too much brightener. Try running a Hull panel and see if you can reproduce the problem. Carbon filtering the plating solution might remove the contaminant, if that is indeed the trouble. Dave Wichern Consultant - The Bronx, New York November 21, 20082005 November 22, 20082005 A. Steve, There are many causes for blistering in plating (general) and alkaline non cyanide zinc (specific). In general, substrate preparation and/or solution contamination (i.e., hex chrome, etc.) are to blame. Frequently, latent blistering of alkaline non cyanide zinc deposits have been caused by excessive brightener (or high total organics). Some manufacturers claim that their products will not cause blistering to occur because they are polymer materials. Although I too am a supplier, I am still skeptical of these claims. In you case I would: a. Check cleaning (solution strength, age, ability to remove oils, temperature, electrical connections/rectifier on electroclean, etc.) b. Check rinsing. Lower temperature rinse water requires higher flows to be as effective (10 °F. rise in rinse temperature is the same as doubling the flow rate). When rinsing highly alkaline solutions (cleaners, zinc) low rinse temperatures will hamper rinsing. c. Check strength and cleanliness of acid pickle. d. Check chemistry of plating bath (zinc metal, hydroxide, carbonates). Correct as necessary. If possible test for metallic contamination. e. Check temperature of plating bath. One must remember the difference between room temperature and ambient temperature. Low temperature can cause blistering. f. If you can get blistering to occur on Hull Cell Panel, try carbon filtration to reduce total organics (including brightener). If this does not work and you cannot test for metallic contamination, dummy. If you determine that there is chrome contamination consult your vendor for the correct amount of sodium bisulfite (metabisulfite) they suggest as a reducer. g. Call your vendor! Gene Packman process supplier - Great Neck, New York A. Dear Mr.Steve, Delayed blisters may be due to poor cleaning or brightener overloaded. Carbon treat the bath (250 gm/1000 lit bath). Check oil level in the cleaner. If it requires go for fresh makeup for cleaner. P. Gurumoorthi electroplating process chemicals - Chennai, Tamilnadu, India November 24, 2008

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Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

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Alkaline Zinc Plating is blistering after two months

March 22, 2011

Q. DEAR ALL,

I'm Deepan. We currently face major blister issue, where the component is a plain sheet. The dimension of the component 300 mm length * 50 mm width & 3 mm thickness. The component is "s" shape. We are doing alkaline zinc plating; the variation in the regular plating is 1:2 where the component is fixed vertically;

In the month of December this material was plated, Major reason for blisters are IMPROPER PRECLEANING AND IMBALANCE IN ADDITIVES.

If improper cleaning may be the reason, the blister would form within 4 - 5 days, so we are suspecting an imbalance in brightener-booster additives.

If the addition level of Bri- booster level ratio changes, what would happen?

Pls help me to find the exact root cause for this issue.

Deepan M
plater - Chennai, Tamilnadu, India

Hi Mr.Praveen Kumar, Thank for your valuable Suggestion, You have mentioned about the excess brightener or booster ... If the brightener level is low & the booster level is moderate what would happen? Is there any other testing method for finding out the proportion of additives? Deepan M plater - Chennai, Tamilnadu, India April 9, 2011 Too much secondary brightener and too little base brightener Sara Sara Michaeli Tel-Aviv-Yafo, Israel April 10, 2011

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Q. Dear Mr.S.V. Aurobind,

This hot water quench I heard it before, can you please explain briefly how this could helps, sir.

Deepan M
plater - Chennai, Tamilnadu, India
June 30, 2011

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Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

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Q. The blisters are observed not on the complete surface but on particular areas that is different part to part. Is the problem of blisters due to organic contamination behaving in the same or will it occur all over surface of component?

Sharma Narinder Kumar
- Ludhiana, Punjab, India
May 7, 2013

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Q. We manufacture fasteners, and regularly sub-contract parts for zinc plating & yellow passivation to various British Standards.

We have recently had some parts rejected on us from our customer due to blistering & flaking, however we are confident that the parts did not leave us in this condition. This would suggest to me that we are experiencing the same delayed blistering as mentioned previously.

Due to our customers' demands, we have asked our platers to increase the time in the passivation stage in order to offer a brighter finish.

Is it likely that the blistering is caused by excessive time in this stage, or would it be that the concentration of the chemicals in the bath is incorrect?

Many Thanks,

James Adkin
- Chesterfield, Derbyshire, United Kingdom
June 27, 2017

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Ed. note: Peeling/blistering in alkaline zinc plating is a perennial problem. For more perspectives and experiences, readers may be interested in:
Letter 40868, "Zinc Plating with Trivalent Chromate is Blistering after Baking"