On Nov 7, 4:33*pm, (Dave Platt) wrote:
I'm no metallurgist so forgive my ignorance. Most of
us have had the problem of interfacing copper to
aluminum. Is there some sort of alloy terminal block
that will accomplish that feat? Seems simple enough
to create an alloy that gradually transitions from
copper to aluminum but what do I know?

As I understand it, the problem with these connections results from
at least two factors:

- *Different galvanic potential. *When these metals are in contact,
* *and there's also an electrolyte present (e.g. moisture plus almost
* *any sort of salt), one of the metals will take on the role of an
* *anode, and will start corroding away.

- *Different thermal coefficients of expansion... repeated heating and
* *cooling puts mechanical stress on the junction of the two wires and
* *can cause the joint to loosen, which increases the resistance,
* *which increases heating when current flows through the joint, which
* *increases thermal stress...

In order to use an alloy intermediary to reduce the problem, you'd
need one which is midway between aluminum and copper in both galvanic
potential, and thermal coefficient of expansion. *I tend to doubt
whether using a single, monolithic piece of alloy would eliminate the
fundamental problem... it'd just spread it out into two separate
junctions with lesser but still-nonzero mechanical and galvanic
incompatibilities.

A tapered alloy as you suggest may well be possible but I suspect that
it'd be expensive to make, and might have other problems. *Aluminum
can be alloyed with copper, but the resulting alloy might be just what
you don't want for electrical junctions... the 2000 (or 2xx.x)
aluminum/copper alloys are said to be extremely hard but prone to
stress corrosion cracking.

The approved methods for joining copper and aluminum seem to involve
either using high-pressure crimps which create a cold weld, or special
pressure connectors plus an antioxidant paste or cream which blocks
out moisture and thus prevents galvanic corrosion.

I gather it's possible to solder or braze the two metals together, but
I don't know what sort of strength the resulting bond will have.

--
Dave Platt * * * * * * * * * * * * * * * * * AE6EO
Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior
* I do _not_ wish to receive unsolicited commercial email, and I will
* * *boycott any company which has the gall to send me such ads!

Sound like David that the rules have been changed and aluminum wiring
has now been banned
because of the things you say are inevitable for failure! I was
unaware that things had got to that point.
Has aluminum been baned for all electrical parts in Industry now,? I
have been out of touch since retiring
but I would have thought that a common connection was a common heat
sink which would alleviate some of the things you point to.
In the court case I refered to it was accepted that if one material
was imbedded into the other such that there was a virgin interface
ther was no problem.
With respect to house wiring I would not have faith in the workman
ship
Art