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topic 5425

Alkaline EN Strike Failure


I am having difficulty with alkaline EN strikes. Our company has trialed two different products in the past month and the first operated successfully for one day and the second for just under two days before we started to experience massive adhesion problems.

We are plating on (mostly) 5052 and 5083 aluminium alloys. Our drag in is quite high due to the parts having in some cases hundreds of blind threaded holes. The process immediately before the alkaline EN is a non-cyanide zincate followed by a double air-agitated flowing rinse. We trialed the alkaline EN as a method to increase the acid EN bath life which currently is around 1.25 MTOs but obviously we can't have the alkaline EN failing at this rate.

The pH, temperature and metal/reducer concentrations have been maintained as specified in the TDS for the product. Is it possible that the drag-in could be causing the problem?

John Reid
plating shop - Brisbane, Qld, Australia

1 of 2 simultaneous responses(2000)

Rinsing after the zincate is critical. Although air agitation will help, I suggest spray rinsing will be more effective to remove the zincate residues from the holes. Besides this it is my opinion that the problem may be associated with the pretreatment. I suggest you contact Atotech to discuss this problem further.

Shakeel Akhtar
- B'ham, UK

2 of 2 simultaneous responses(2000)

You think that the drag in of the zincate is the problem. You must check this theory in order to prove whether it is true or not. The easiest way to do that is by analyzing the zinc content of the alkaline EN. This is done by atomic absorption. If you do not posses such a technical device I am sure that your supplier does. (He owes you this analysis). Double air agitated rinse might not be enough. Try three rinses or add eductors to improve rinsing.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel


I performed some research in the lab at the possibility of adding the Aluminum EN strike to our process. I found that we experienced adhesion problems after several days of using the bath. I found that after just one day of use, the pH of the bath was below the operating parameters and that it required additions of Ammonium Hydroxide.

If the adhesion problem is localized on the workpiece then it could be any number of things. But, if the adhesion is poor overall, try adjusting your pH to make sure the it is within the normal operating range.

Tony D'Amato
wastewater treatment - Chicopee, Massachusetts


Adjusting pH is a part of plating EN, whether it is a low pH one or a high pH EN. Tony, the fact that you had to adjust pH after one day of work is OK.

Sara Michaeli
Sara Michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel

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