What's the best plating material for interconnects plugs ?

Most small RF connectors are beryllium copper, tellurium copper, or brass with a gold plating for corrosion resistance. Same for audio connectors. While gold is not the ideal conductor, it's better in the long run than other materials that decay and corrode. 

Just to clarify where several posters have stated that silver oxide is a good conductor

@ljgerens Thank you for the correction. Ironically, I read that misinformation on Audiogon.

In my experience it's down to how good the contact is and whether it gets disturbed. If it's clamped tightly and rarely moved then copper or sliver are fine, if it's a press fit (like RCA, XLR or banana) then gold on gold eliminates worries about corrosion and the softness of the material ensures a good contact surface area. There is no benefit from using rhodium outside of a caustic environment. 

@ssg308 -  one approach to connector selection is to consider the conductivity of the metals being used

Please see this link that shows the IACS conductivity rating of various metals
IACS of Metals, Alloys and Solder (avoutlet.com)

1. Silver 106%
2. Copper 100%
3. Gold 76%
4. Rhodium 39%
5. Nickel 24  %

However - when plating - for the plating material to "Stick" to the actual metal of the pins of a connector, many times requires a substrate plating that has an even lower IACS rating

This generally means the connector will not provide the best possible performance

However - Silver Plating onto Pure Copper requires no substrate and therefore provides the best combination from a conductivity perspective

But beware - some "silver plated copper" connectors are actually made from some type of copper alloy, like Beryllium copper, which is not as conductive as pure copper, but it is more robust

What about the black tarnish? - Some people regard the black tarnish that often develops on silver (plated) connectors to be a problem. But in reality, the tarnish is only microns in thickness and can be removed simply by reseating the connector. The tarnish is regarded as a "semi conductor", so it will conduct electricity, but not quite as well as silver.

Unfortunately it is also not as simple as selecting the best IACS ratings for the various materials

My current RCA plugs are silver plated copper and they outperform many solid silver connectors. So metals are not the whole story either.

I have found the best connector uses pure copper as the base material and silver for the plating and all my connectors on all my cables are created in this manner

Gold and Rhodium has a certain "image", but they both pale in comparison to a good silver plated copper connector when it comes to sound quality.

Just another opinion - Steve :-)


 

If the base metal is garbage, it doesn't matter what exotic metal is plated on it. Throw in plastic for the insulating/molding parts and the problem is compounded even worse. One gets what one buys...