Why don't we all reach some decisive conclusion in this thread and then
post it as a separate sticky thread?
Here's my version of this (rather long at that):
In typical watercooling setup consisting of mixed cooper/aluminum components
there are two distinct types of galvanic corrosion possible:
1) Galvanic corrosion as we usually understand it (aka "battery effect") -
two or more distinct parts of different types of material in contact with
electrolyte and connected electrically.
This problem in turn has several solutions:
(a) one of the most effective would be breaking electrical contact
between the cooper-aluminum parts. This means not connecting them
in any way with metals and also preventing them from being grounded.
So plastic hoses, plastic mounting screws, rubber pads and grommets etc.
(b) tempting way of solving this would imply removing the electrolyte
or effectively reducing the conductive properties of coolant. Now
pure water is not conductive, but that does not mean that putting DI
water would solve the problem. No matter what you put in the system
it will quickly become contaminated due to the large number of
foreign and often unknown substances involved. There are metals
themselves, metal oxides, hoses residue, organic residue, and god
knows what the insides of a typical radiator/heatercore looks like
but imho just the acid flux from soldering is enough. Partial way out
would be to flush the system with large quantities of DI water
initially but this would be really expensive and effective only to a
certain (unknown) extent.
Now the real reason to use DI water is that this way no additional
contaminants would be introduced into the system.
(c) using chemical treatments such as "water wetter" to inhibit
corrosion. Again just slows down the rate of the corrosion so by
itself is probably sufficient just for some lengths of time. On the
positive side improves thermal properties and keeps life out. So
adding it is a matter of "good housekeeping".
2) Pitting - most common type, usually mistaken for effect of #1 but has little
to do with it. It is in fact "micro"-galvanic corrosion occurring to
the aluminum parts of the setup. This is due to the use of alloy aluminum as
oppose to pure metal.
The galvanic corrosion occurs on the surface of
the material where foreign metals are clustering in high enough numbers to
disrupt the protective aluminum oxide surface film. The electrolyte
contacts the surface and galvanic reaction occurs between surrounding
aluminum and alloy metal with aluminum being consumed as an anode.
More details are available
here.
Typically not "life-threatening" and has only aesthetic effects
since formation of hydrofobic and insoluble aluminum hydroxide
clogs the pit. But in the presence of acid hydroxide reacts with it
thus making the pit open and allowing the corrosion process to continue.
Some acidcan be contained in the add-ons to coolants depending on the mixture
and some can be present in the system initially (water soluble acid flux?).
The solution would be to use pure aluminum, but due to availability,
price, and difficulties with machining this is a die-hard way.
Anodizing could help but may be cost prohibitive on a DIY level.
Using DI water is a definite must because it's the way to get rid of
any halogen ions ( F, Cl, Br, I) as they play most important part in
pitting.
The way out is the good olde all cooper system
if one wishes to commit to WC.
Additional points:
By DI i mean at the very least distilled, better home deionized, the overkill
is lab grade deionized water.
Use of sacrificial anode could help #1: a piece of Zn or Mg in contact
with both electrolyte and the Al part should do the trick.
Most often encountered in typical system is #2 and not #1 judging by
the kind of damage observed (cells or pits) ,but again both are
possible so the best way would be to design system keeping in mind
both kinds of problem.
weird formatting eh.
