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Why does the Silver and Gold Plated Aluminum 6061T6 turn white while baked at 200 C

we plate aluminum 6061T6 with Silver and a thin film of gold. We used this plated components for high vacuum applications. These parts after plating are vacuum baked at 200 °C for 72 hours. This process is required to remove moisture from the plating process. The gold plated surface turns white. My question is; Is there diffusion of silver in Gold at this low temperature or is the Gold evaporating?. our vacuum level is 5.0 x 10-6 torr. I can not find any information on this subject, will appreciate any advice.

Victor Granados
Electronic application under vacuum - Santa Barbara, California, USA
July 15, 2009

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First of two simultaneous responses --

There is no way your the gold is evaporating. It is definitely due to diffusion. And because it appears the diffusion is occurring at relatively low temperatures, the gold is diffusing via grain boundaries.

Eric Lewandowski
- Massachussets
July 21, 2009

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Second of two simultaneous responses --

Silver will diffuse right thru gold at room temperature and instantly if heated, the hotter the faster.You must have a diffusion barrier of nickel or palladium

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

July 21, 2009

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July 27, 2009

Is the high temperature and time really required making the parts dry? Which parts are we talking about, geometrical form?

Which final application are the parts used finally? As well at high temperature?

Regards,

Dominik Michalek
- Mexico City, Mexico

We plated thousands of gold plated parts for high heat applications and experienced no diffusion to 700 F. with an underlying layer of nickel.

Robert Reiten
plating shop - Bend, Oregon, United States
July 30, 2009