The only reason you would need to do that is for corrosion resistance in a steel radiator. If you use copper, you don't need to worry about corrosion as long as you use distilled water and acid-clean copper. If you can't do that, then use phosphor bronze instead of copper. Phosphor bronze should be more than adequate for corrosion resistance, even at modestly elevated temperatures.
Well im using aluminum everything. I considered switching to copper because its easier to seal by solder then aluminum by alumaweld. In which case I could move to higher pressure system to get that phase change going. But I would then have to rebuild my radiator, its aluminum.
I know you can't mix metals in a system, they will corrode eachother. And I want to use them to lower the surface tension in the water, it will help it stick to walls inside, fill in those microscopic scratches and better conduct heat. I kinda want this to be a sealed, no fluid change out every year.
Why do you want to use that complex heatsinks, when the current ones are good enough, and pretty cheap.
Well, you can experiment with that, but Hg can dissolve some metals, it is a bad idea to put galvanic metals together...
Why complicate when you already have a decent heatsink? If you need more heatsinking, make it bigger, or even labby-style.
Yes, mixed metals can corrode each other in a galvanic reaction, but that's not what I'm talking about when I warn you against mixing gallium and or mercury with aluminum. Within seconds, your aluminum will crumble to dust with the mercury. Within minutes, your aluminum will be as fragile as paper with the gallium. It's not mere corrosion, it's near-instant catastrophic destruction. With the mercury, it's obvious. With the gallium, everything will look fine until you poke it with your finger and it falls apart.
The other metal to avoid is tin, if you use active refrigerated cooling. The cold will cause a phase change in the tin, and it will crumble to dust too, right before your eyes. That's something to be aware of when you choose your solder, since most of them contain anything from pure tin to an alloy.
Also be aware that heating and cooling will cause whiskers to form in many metals. Those can cause an explosion in your batteries, or some other unpleasant effect. The size of some lithium batteries in use here is big enough to zip off fingers if they explode while you're gripping your device. Hopefully you're wearing eye protection so you don't need to worry too much about shrapnel.
I always use a face shield in addition to eye protection if I'm doing something that has even a small chance of going badly. It has save my face and my eyes more times than I can count.
and whiskers arent too much to worry about. granted i do have a phase change system in place, it wouldnt be very efficient and probably only cool a few degrees. and it would be like any other short, im using protected LiFe so they are a little more stable than other lithium chemistry batteries