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Zinc-plate appearance problems (white, powdery, rough surface)

A discussion started in 2005 and continuing through 2017 . . .


Q. Came across parts after batch zinc-plating in acid-chloride that exhibit a white, powdery, streaky appearance (Parts are flat ~16 x 16 w/ moderate forming). When compared to "good" batches, "bad" batches seem rougher in texture (along with a overall lower reflectivity). Subsequent rubbing of the finished part surface with your hand exaggerates the powdery condition and leaves a white residue. You can clean off an area of a "bad" part with an acetone-soaked rag which removes the white residue and the zinc coating remains in tact.   

It's questionable whether the substrate and/or plating process contains the key variables for this problem.  Batch process utilizes two rounds of cleaning w/ de-ionized water and finally plating in a acid-chloride bath. Parts and finally a clear chromate conversion coating to passivate. 

Anyone ever see this condition and have any ideas? Thought maybe surface roughness of the substrate and/or clear chromate was the culprit.

Thanks for the help.

Chris Tobin
metallurgist - Baltimore, Maryland


A. Hello Chris. You say you 'came across' these, which leaves us with the questions of whether they are new or old and whether you are working in the plating shop or these parts were shipped to you, etc. My first guess is it's boric acid. Some plating shops (low tech, non-spec work) will on occasion hang a bag of boric acid in a plating tank and almost immediately start plating, with result that crystals or powder form on the plated parts.

My second guess equals your first guess that it's a clear chromate problem.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. Ted, thank you for the quick response. To help clarify my original inquiry, we are currently supplying low-carbon 1006/1008 CRSH to a customer who stamps parts and uses their own plater. Our customer and their plater are quite frustrated and I can understand they would want to question the substrate properties (ladle chem., rust-preventative oil, etc..). They've requested we be a main player in the analysis. I've begun working with their plater (via phone) to help them resolve and to this point have only received "good" and "bad" parts along with substrate ID(yet to do SEM/EDS on the powder). Info. gathered thus far leads me to believe there are more problems to worry about than the substrate.

Info gathered:

Zinc Plating
by Geduld

-All supplied substrate is confirmed to be supplied with the same rust-preventative oil (Quaker Ferrocote 61).

-Supplied substrate is Al-killed 1006/1008 w/ very low residual Si and similar chemistry, however a few shipments had higher levels of Cu (.11% vs .05%). Would higher Cu levels in the steel makeup be an issue?

-Supplied substrate had surface profilometer values measured in microinches of ~30-50 which is seen as typical for most mills at the same gauge (.040"-.050"). Maybe higher surface roughness holds excess solutions/oils through cleaning/plating/chromating?

-Plater uses alkaline cleaning solution w/ two rounds of rinses and plates out a .0002 - .0005 flash zinc in acid chloride w/ a final trivalent coat(clear chromate).

-Plater reports that they will run a batch of parts that will exhibit this condition IMMEDIATELY AFTER THE PLATING PROCESS (apparently within seconds) and run another soon after, apparently under the same conditions with another batch of similar steel (same grade, etc..) without issues (nice bright, uniform zinc). Keep in mind I haven't determined if "immediately" means as soon as it comes out of the acid chloride tank or right after the chromate is applied (which I will obviously need to investigate). Could you help me understand the steps between plating and chromating and between chromating and finished product?

-There's apparently no handling involved, as the plater uses a circular rack which can hold ~80 of these parts at one time.

-The condition seen on these parts is strikingly similar to the bottom left photo of letter 18213, however, the entire surface seems to be very very light white in color (powdery and streaky with a rougher surface). It becomes even more exaggerated though when touched or rubbed with any applied pressure.

-The plater has been relying on what has been referred to as a "time-saver" which we are told is a belt-sander that is used on the steel prior to plating. This works well for them and is a large part why they are questioning substrate.

Being more process metallurgy oriented with only some electroplating knowledge (and knowing not to overstep my bounds), I'm looking for help from the finishing community to direct the right questions to the plater and help set up experiments to determine root cause.

Thanks again for the input

Chris Tobin (returning)
metallurgist - Baltimore, Maryland










ajay raina
Ajay Raina
Ludhiana, Punjab, India

February 12, 2013

Q. Hi All experts,

I'm facing blur and rough surface problem on my rack plating (some okay but most have blur and roughness problem).
I've checked the ph between 5 - 5.5 and the temperature is around 29 °C.

rough surface on rack plating

Please advise, Lovely thanks.

Tim Horng
- Malaysia

July 5, 2013

Q. Good day,
I have a current customer complaint due to a surface finish on one of our part numbers that they define as "rusty". Before we ship the parts to our customer this condition is not present. Parts normal transportation is by sea (I go ignore if that is a factor for this "rust" to appear) but the customer claims that not all the parts have this condition so we would like to know what to look for at with our supplier that plates the part and focus on the factors that could produce these "physical appearance or rust". I appreciate your help.

rusty surface finish

Monica Bustamante
- Tijuana, BC, Mexico

July 12, 2013

A. Dear Monica,

You must focus on your plating supplier and the packing of your parts. You must seal the parts (by putting them in bags, covering them in nylon films, etc) to assure that the transportation is not an issue. If this was done properly, then you must see if the plating process was done well... When I see this photograph I see two problems:

- Plate peeling (bad adhesion of the zinc plate)
- Dull plating (not bright plate, this means almost certainly that the corrosion resistance is not good)

I suggest you attack the problem (if it is) of the packing first, as it is the easiest. Then, you should talk to your plating supplier to improve the plating quality (you may do well if you inspect the parts that you have to ship, and if you see any defects, take photographs and take the parts to show them to your supplier).

Hope this is clear enough, best regards and good luck!

Daniel Montanes
- Cañuelas, Buenos Aires, Argentina

July 12, 2013

A. Monica,
The customer could be correct. You might try putting some parts out on the roof for a week or two and see what happens and leave some in salty water, tests like that. You can also heat some up and rub some and check to be sure the parts don't look like the customer is reporting. If you can or cannot duplicate the results, the first thing to do would be to check the work instructions and be sure the process is being followed and that the equipment is in fine condition. If the equipment is in very bad shape and there are no instructions then I would start there. Assuming you have really nice equipment and people following instructions, you can try tweaking your process a little bit by running fewer parts, adding more process time and other tricks to make a thicker coating. It could be that you're a little flaca. Buena suerte.

blake kneedler
Blake Kneedler
Feather Hollow Eng.
Stockton, California

July 15, 2013

thumbs up signThank you very much!! I already started questioning this. I appreciate the feedback.

Monica Bustamante
- Tijuana B.C. Mexico

May 29, 2014


I am a buyer and receiver. I don't have direct experience in plating. I order our parts to be plated with the following description: Zinc Chloride Clear Rack Lacquer .0002" meeting plating spec ASTM B633 - Type III Fe/Zn 5.

We have regular problems with white rust, streaking and drip marks that are visible when received from plater. See picture for most recent quality problem.

34107-3  34107-4

Is this a prep issue or a plating issue? Or chromate coating not done properly?

Paul Braden
- Rockwood, Ontario, Canada

May 2014

A. Hi Paul. I'd categorize it as a vendor issue because parts that look like this should not be shipped to you :-)

I realize the temptation to want to understand the issue and your desire to explain to the vendor what they are doing wrong, but it's very difficult and probably not productive because they probably know a lot better than you and I what the problem is :-(

My guess is that improper drying or lack of drying is involved, based mostly on the second picture where we see marks that look like what you would get if the pipes were set down wet on cardboard or newspaper to dry (what we are seeing as the top would be the bottom as they dry). Although I'm reasonably confident that this is one problem, and that it can cause the white rust shown on the first photo, I'm far from confident that it is the only problem.

I would suggest that you decide what constitutes unacceptable appearance vs. what are acceptable minor cosmetic flaws, then agree with your plater about it, and even build "sample boards" of good & bad parts if necessary. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

May 16, 2015

Q. Dear experts,

We are doing zinc plating (barrel plating) with trivalent white, hexavalent yellow passivation for our machined parts. After plating, these parts are packed in polythene bags and put inside cartons in a closed atmosphere. Some parts are not sold immediately were kept at our warehouse for one year. These parts were re inspected after one year and found passivation fade out and white patches. Please help to resolve the issue.

Dinesh Babu
- Chennai, Tamilnadu, India

March 2017

Hi Dinesh. They probably weren't dry.


pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

March 29, 2017

Q. We are using zinc plated on ms steel cover in a timer switch in automobile industry. After few operations some of the cases white residue starts formation inside the cover and moisture formed due to operational condition (heat raised around 60 °C in closed environment).
What's the problems in the zinc plating.
Please provide solution.

Subhrashekhar Mukherjee
switches - Jharkhand,India

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