Cadmium plating blistering/adhesion issues

A. Dear Dave,

I have experienced this same problem years ago when Chloride Zincs were first on the market, it seemed at the time that the "Blistering" was not a blister as such more an Exfoliation, the Zinc used to "grow" and just flake off, but never to the base steel always to a Zinc base, I thought that the problem was caused by high concentrations of the Wetter component of the Brightener system, any way we seemed to be able to overcome the problem by lessening the wetter component from about 3% by volume to about 2.2 - 2.5 % maximum with a corresponding drop in the brightener component, from memory the add rate of the brightener was down to 70 % of that recommended by the supplier.

I know there have been improvements in the systems in the meantime but it is worth a try anyway, if it fixes your problem let us know

regards

A. DAVID,

THE HARDNESS OF THE BASE METAL PLAYS AN INTEGRAL PART IN WHETHER THE ZINC PLATE STAYS ON OR BLISTERS. ANY STEEL PART WITH A HARDNESS OF 38 ROCKWELL C OR GREATER, SHOULD NOT BE ZINC ELECTROPLATED. HYDROGEN EMBRITTLEMENT IS THE CULPRIT. MECHANICAL PLATING WHICH DOES NOT IMPART HYDROGEN INTO THE BASE METAL IS REALLY THE CHOICE OF PLATING.

IN N.A. FORD, GENERAL MOTORS, AND CHRYSLER ALL HAVE MECHANICAL PLATING SPECIFICATIONS JUST FOR THIS PURPOSE. CHECK WITH TERRY CLARKE OF Macdermid G.B. FOR MORE INFORMATION

I KNOW OF SOME PLATERS, BECAUSE I USED TO BE ON THE CHEMICAL SUPPLY SIDE, DO GET AWAY WITH THIS BLISTERING BY REWORKING THE PARTS. GUARANTEED - THEY WILL BE FINE THE SECOND TIME THROUGH. MAKE SURE YOU ADJUST YOUR PRICE ACCORDINGLY.

FINALLY, THE TYPE OF SOLUTION ie. CYANIDE/CHLORIDE/ALKALINE AND THE THICKNESS OF THE DEPOSIT WILL CAUSE BLISTERING

• CHLORIDES HAVE A HIGH ORGANIC INCLUSION IN THE DEPOSIT WHICH WILL EXPAND UPON HEATING EG.BLISTERS
• ALKALINES ARE PRONE TO "POST DELAYED BLISTERING" DUE TO STRESS
• CYANIDES ALTHOUGH THEY DO NOT COMMONLY BLISTER CAN IF OVERLOADED WITH ORGANICS
• ANY ELECTROPLATED ZINC DEPOSIT, AS IT APPROACHES 1.0 MILS IN THICKNESS, WILL TEND TO BLISTER.

REGARDS
RAY

A. I have experienced similar problems with Zinc plating blistering prior to painting when the paint was forced cured, or powder coated. I also believe it is a problem with entrained brighteners,or brightener levels. However, interestingly enough, the main prevention step was determined to be controlling the plate thickness. When the thickness was controlled to .2-.3 mils the problem went away.When the plate thickness was above .4 mils it blistered when heated.

A. While probably stating the obvious, the embrittlement of high-strength (i.e. high-carbon) steels is due to entrapment of atomic hydrogen in the steel.

My experience with this problem was when having high-strength carbon steel parts plated with zinc chromate in a batch plating process. The only solution we found was baking of the plated parts at 350-375 °F for 1-3 hours (depends on thickness of part). This theoretically removed quantities of entrapped hydrogen from the steel and coating. This completely eliminated the problem without changing the plating process itself. These parts were AISI 4140 /4150 steels which were heat-treated prior to plating with tensile strength in the 150 ksi range. The baking requirements for your steels might be somewhat different. If we did not bake these products we encountered periodic embrittlement failures in service. The metallurgical condition of the steel to be treated also influences the embrittlement potential.

It is probable that hardened parts require consideration of a different cleaning method to reduce the potential for hydrogen embrittlement. Blast-cleaning or alkaline cleaning pretreatment may reduce the potential for hydrogen embrittlement for high-carbon, high-strength steels when compared to other methods which evolve hydrogen as a by-product. Those more knowledgeable about plating process might know other plating process controls which could achieve reduction in hydrogen entrapment.

A. Hi Dale. The goal for plating is perfect adhesion, meaning that either the substrate or the coating will tear--separation will not occur at the interface. I'm not personally aware of a reason to expect less in this case.

However, what I would be much more concerned about would be absorption of plating solution into any porosity in the sintered powdered metal. I think you may want to investigate vacuum impregnation to seal the powdered metal parts before plating. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

What is the composition and history of the base metal?

A. Hi David. I think perhaps this calls for Hull Cell testing. I think you could use a hanging Hull Cell in each tank in this case, which would further reduce the variables to narrow it down to whether the plating solution itself is the problem. Good luck.

A. Has chromic acid from chromate carryover from ragged racks entered the tank?
Have you mixed in titanium anode baskets, which alternately anodize and do not pass current causing voltage increase and then strip when the current is turned off?
Surface Prep? Are you plating onto leaded steel or 4000 high strength steel?
Switch the rectifier leads to opposite tanks and see what happens.
Dip out solution into a 5 gallon bucket, hang over an anode basket, add 4 oz/gal Sodium Cyanide, plate and see what happens.

A. Hi. I would agree that plating adhesion does not require "tooth" and is not dependent upon a rough or smooth surface.

Regards,

A. You should not use titanium baskets in a cyanide solution. When the current is turned on the titanium "anodizes" and becomes less conductive, the voltage goes up (if automatic) and the current goes down. Recommend a change to steel baskets now.

A dip in HCl on 4000 is seldom enough activation, try a Nickel Chloride Strike: 2 Pounds per gallon Nickel Chloride with one quart per gallon HCl, cathodic. Do not use the S-rounds - use Rolled Depolarized Anodes and take then out when not in use.

A. ASTM B201-80, 'Standard Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces,' describes rubbing with a soft gum eraser to determine the adhesion of chromate coatings.

ASTM B766, 'Standard Specification for Electrodeposited Coatings of Cadmium,' describes several destructive-type abrasion tests but also refers to ASTM B571, 'Standard Practice for Qualitative Adhesion Testing of Metallic Coatings' for additional methods. The burnishing test (rubbing with a rounded end steel rod) given there is relatively non-destructive.

I am not familiar with your base metal. I do know that in high carbon steels like 4340 that you can over-clean or over-etch it and get millions of tiny blisters. If you get blisters that are over 1/8", then you probably are not cleaning or etching adequately.
You might have to go to a nickel strike to prevent it.

Like James, I am not familiar with 8740, but according to my ASM alloy book it contains in % carbon .38-.43, Manganese .75 to 1.00, Phosphorus .04, sulfur .04, Silicon .2 - .35 . . . and these next three which are your problem: Nickel.4 - .7, Chromium .4 - .6, Molybdenum .2 - .3.

Because of the nickel, chromium and moly, you must use some sort of drastic activation. Start with a nickel chloride strike as James suggested; 1.5 pounds/gal nickel chloride and 1 quart/gal Hydrochloric Acid, rolled Depolarized Bagged Nickel Anodes (S-rounds will not work after the first day due to their rapid solubility), room temperature, about 2 or 3 minutes. If it works, then remove the anodes between loads to prevent the metal increase. If this does not work, then contact: "The Nickel Development Institute" ; get the address from Ted Mooney of finishing.com.

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November 4, 2008

Hi. The Nickel Development Institute is at www.nidi.org

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Can't use a nickel strike. AMSQQP416 requires cadmium directly on base metal for steel parts. Your problem is probably not cleaning. The material is usually heat treated to a high strength level (HRc 40-50). Treat it like a high strength steel. Make sure the heat treat scale is off. Try a stress relief (375 °F for 5 hrs.) before plating. Then run a DOE using various cleaning and acid dip times. I run different parts using 8740 and need to use different processes to avoid blisters. So try your DOE separately across different types of parts. 8740 is a pain (been there, done that)!

A. Hi Jonathan,

We too are experiencing blisters in cad plate lately . The problem most likely originates from surface preparation. In our case improper grit blasting appears to cause the problems. We do not use brighteners by the way.

best regards

Jeroen

A. What is the metal and alloy that you are trying to plate cadmium onto?

A. Had the same problem many years ago on the same base metal.
Turned out to be over cleaning and / or over etching.

We cut both times in half, checked for water break and plated. Problem went away.

A. Is it "leaded" steel ?

A. Hi Surya. I can suggest that the first step is to find out clearly what is not adhering to what. Is the cadmium peeling off of the nickel plating, which remains completely intact? If so you may need to do the cadmium plating immediately after the nickel plating and/or add a nickel strike to reactivate the nickel. If the nickel is peeling off of the aluminum you must look into what is between them: cyanide copper plating, electroless nickel plating, etc., because your nickel plating may be peeling from them, or the zincating may be defective and everything is coming off. Good luck.

Regards,

A. Hi cousin Keerthi. You can carbon treat the bath to remove organic contamination. What organics do you suggest and why? What has Hull Cell testing told you?

Personally I'd be surprised if that was actually the cause of the problem --although it's possible. Is this a cyanide bath or acid bath, rack or barrel? What is the substrate, mild steel?

Heaven helps those who help themselves -- people would like to help you, but as you can see from the dozens of previous entries on this thread regarding blistering of cadmium plating, plus many other threads about cadmium plating on this site, and from the 3-page table on troubleshooting cadmium plating baths in the Canning Handbook, there can be many interrelated causes. To make progress, we'll probably need to know what you learned, not just that you have a problem :-)

Luck and Regards,

A. Hi Keerthi,

As per your above question 1.Patches 2.Blister and 3.Contamination .

1.Patches : Patches occur due to contamination of foreign metals such as Copper, lead, Tin, Iron and other metals and decomposition of organic brighteners into the cadmium plating solution.

2.Blister : Your question is not clear which substrate you getting blister, whether plating or under coat or zincating. Insufficient activation or neutralising and poor cleaning causes the blister or detachment of plating.

3.Contamination : Contaminated foreign metals (organic Impurities) in the bath should be removed by activated carbon treatment and filtration.

I hope your problem will solve and helpful to you

Regards,

A. Hi Miron Lev,
Maybe these 2 things can help you:

- do you have an activator tank before the Chromate passivation?
- the PH in the chromate solution have a big role in the outcome of the color.

This is a problem that I faced in the past too,