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  for Metal Finishing since 1989
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Blistering Problem for EN on Zinc Casting

 

We are encountering blistering problem on Zinc ZL2 casting. The soft blisters seem to appear right after the EN process. We tried to prolong the alkaline soaking time but without much improvement. Some of us suspect the Zinc material is contaminated, or the casting is porous. As we are not plating experts, we really need help to resolve the blistering issue.

Appreciate your inputs on :

1. Material 'pureness' effect on plating

2. Causes of blistering for EN on zinc castings.

3. What can be done to eliminate blistering.

Thank you very much.

BP Tan
- Singapore

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1. What is the preplating cycle that you use? Did your process work OK in the past?

2. Zincate- try double zincate and for difficult zinc castings you should try triple zincate.

3. Use two types of EN. The first should be an alkaline EN (PH 9-10) followed by an ordinary EN with PH 4.7-4.9.

4. Give more info about your process and then it will be easier to assist you.

Sara Michaeli
Tel-Aviv-Yafo, Israel

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We had never done EN plating on zinc before.

Our vendor uses :

1. Solvent cleaner QEM 183 for 2 mins.
2. Alkaline cleaner NG-30 for 10 mins max.
3. Electro degreasing Max cleen BG-3200 for 2 mins.
4. Acid activation FKS 101 for 1 min.
5. Copper plating KCU and CUCN for 3-5 um.
6. EN Kizai SB for 30 mins.

Soft blisters appear to be due to non-adhesion as the base metal can be seen after breaking the blister.

My rationale is that if base metal can be seen, then the copper strike must be the problem.

Another saying is that zinc component casted from re-cycled scrap which were plated, causes EN plating problem due to contamination of the base material. Please advice.

Is Zinc 2 more difficult to EN plate than, say zinc 3 or 5?

Thank you. Please advice.

BP Tan
- Singapore

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Dear BP Tan:

I noticed that you didn't mention any strike or step between cyanide copper and EN. How do you start the EN reaction? Copper, if free from pores to the base zinc, will not be catalytic to reaction and would have to be started somehow. If it starts without any help it probably means that it is too thin and porous. Then you have problems because the EN will attack zinc before it covers the surface. Please give more information to help better.

Guillermo Marrufo
Monterrey, NL, Mexico

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Please disregard my previous reply, I was referring to plating on Aluminum not to zinc casting. Anyhow, Gulliermo is right, copper is not autocatalytic to EN and you need an activation between the copper and the EN in order to ensure good adhesion.

There are a few possibilities to activate copper prior to EN:

1. Palladium ( too expensive!)
2. Nickel strike
3. Electrolytic activation in the EN solution.

Regarding your preplating activation, I am not familiar with the proprietary cleaners that you use, just make sure that they are designed for zinc casting meaning not too alkaline and the activation is not too acidic.

Sara Michaeli
Tel-Aviv-Yafo, Israel