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
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