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Heat Treat for Resistance

I have a question regarding heat treating. I have beryllium copper strips that are being nickel plated 0.00127 - 0.00254 with a gold flash selective plate over the contact area. I need a resistance of less than 99 milliohms. We are having the parts heat treated after plating. I'm not sure if it is to lower the resistance, or for some other reason. I recently had some parts that sat for 9 months between the plating and heat treat process, and the resistance is measuring as high as 1000 milliohms.

My questions are: Do you think the heat treat is to keep the resistance down, or is it just a coincidence? How long do you have after the plating process to have parts heat treated? A day? A month? Unlimited?

Thank you! Sandy Mundis
- Middletown, Pennsylvania, USA
 

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Hello Sandy!

The heat treatment of beryllium copper is aging at either around 600F for the high strength alloys, or 900F for the high conductivity alloys, for about 2 to 3 hours. In both cases the electrical conductivity increases with the aging, and is even better if the material is overaged. The purpose of the aging is not for increased electrical conductivity, however: it is to increase the strength and fatigue resistance. Otherwise you wouldn't use expensive and strong beryllium copper now, would you?

Beryllium copper is supplied by the mill in the solution treated condition, and is aged by the customer after forming or machining into the desired shape. While I don't have empirical evidence, it will likely age by itself after a few hundred years. You'll likely want to have the heat treating done before then. :) Hydrogen embrittlement due to plating is NOT an issue here, as it is for high strength steels.

Both Brush-Wellman and NGK Metals, the suppliers of beryllium copper, have technical support folks who I have always found helpful. I'd certainly recommend contacting them should you have any questions.

Lee Gearhart
metallurgist - E. Aurora, New York