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Do Copper Braze Joints Present an Adhesion Problem for Alkaline Zinc?

2001

Do copper braze joints present an adhesion problem for an alkaline zinc line? The parts are processed as follows,

Machined from low carbon steel tubing
Brazed to an adapter (SAE 1015)
Bent and packed for plater
Plated Zinc with yellow chromate
Powder Coated

After powder coat we are having blistering and poor adhesion only in the areas of braze flash or overrun. Our braze is 92% Cu and 8% Sn.

Any help, opinion, or feedback would be appreciated.

Kevin Davis
- Versailles, Kentucky, USA

We plate parts that have copper braze with alkaline zinc all the time, so it can be done. Sloppy brazing will be a problem, however. We do not powdercoat after the zinc yellow, so I don't have specific knowledge about that. However, you should monitor your zinc bath and chromate bath for copper (and iron) contamination. You can do this with atomic adsorption (AA) equipment.

Tim Neveau
Rochester Hills, Michigan
2001

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