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?
--
73, Cecil http://www.w5dxp.com

On Nov 7, 2:36*pm, Cecil Moore 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?
--
73, Cecil *http://www.w5dxp.com

Cecil, there are plenty of connectors ( Bronze? ) on the market that
accept copper/alluminum
combinations. On the other hand I understand that if the joint is free
from the atmosphere
i.e. a tight interface the problem is not all that bad, G.E proved in
court during the 50's that if the connection
is tight or embedded an increase in resistance does not occur, I
believe that analysis still stands.
Co defendants that could not provide a similar defence got hammered
because their joints did
not provide a virgin interface thus existing corrosion was trapped
thus it could grow.to a sizable resistance
Art

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!

Cecil Moore 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?

The problems are mostly the different thermal coefficients of expansion
and surface oxidation of Al. Galvanic corrosion can also be an issue.

For more than you probably want to know:

http://www.inspect-ny.com/aluminum/aluminum.htm

If you are talking about your house wiring, the above link will get
you to stuff that addresses the problem.

If you are talking about home brew stuff, the general solution is to
clean, apply anti-oxide grease, and connect under compression, i.e.
something with a tightening screw.


--
Jim Pennino

Remove .spam.sux to reply.

"Cecil Moore" wrote in message
...
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?
--
73, Cecil http://www.w5dxp.com

Hello Cecil,



This is the kind of stuff you need.

http://www.niled.fr/Gamme_Niled/PDF/B/PageB06.pdf



You can also connect directly copper and aluminum if you apply (and
maintain) a fair amount of Penetrox P8A (Burndy) all over the joint.



Kind regards,



Philo

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

"Cecil Moore" wrote in message
...
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?
--
73, Cecil http://www.w5dxp.com

As others have mentioned, there are two issues involved: differing
coefficients of thermal expansion and galvanic corrosion. Placing the joint
under strong compression is the method of choice for eliminating the thermal
expansion problem. Galvanic corrosion is not so simple to solve, however.

Galvanic corrosion, often misnamed "electrolysis", occurs when two (or more)
dissimilar metals are brought into electrical contact in the presence of
water. When the junction, known as a galvanic couple, forms, one of the
metals in the couple becomes the anode (which corrodes faster than it would
if the other metal was not present), while the other becomes the cathode
(which corrodes slower than it would without the other metal being present).
When contact between the dissimilar metals is made, the anode will corrode
faster while the corrosion of the cathode will decelerate or even stop. If
the terms anode and cathode sound familiar to terms used to describe the
electrodes in batteries, they are one and the same. A battery is nothing
more than two dissimilar electrodes immersed in a chemically conductive
solution. If an external circuit is connected to the anode and cathode of a
battery, when the circuit draws current, the anode corrodes. The battery is
depleted when the anode is fully corroded away.
We can use a galvanic series of metals to predict which metal will
preferentially corrode with respect to the other. Usually presented in a
table, the metals are listed in order of most corroded to least corroded.
I am including one such table with this post, courtesy of the McNally
Institute, 1637 Sand Key Estates Ct., Clearwater, Fl 33767. Note that
aluminum is located near the top of the table while copper is near the
center. This shows that the aluminum is anodic and will preferentially
corrode with respect to copper. There are two major factors that increase
the degree of corrosion in any dissimilar metal couple: (1) how far apart
the two metals are in the galvanic series. and (2) the ratio of the exposed
areas of the cathode metal to the exposed area of the anode metal. The
further apart the metals are, and the larger the exposed cathode metal area
to the exposed anode area, the faster the anode will corrode. An aluminum
rivet in a copper sheet will quickly corrode away, while a copper rivet in
an aluminum sheet will show far less corrosion (the corroded aluminum is
spread out over a larger area).

One method of corrosion protection is to use metals close to each other in
the galvanic series. The other method is to protect the junction between
the metals from moisture. One reader suggested the use of a grease such as
Penetrox or Noalox. These compounds, which are carried by most electrical
supply houses, are merely fine, irregular-shaped zinc particles in a water
resistant grease. When used between aluminum and copper joints, the zinc
particles pierce the oxide coatings of both the copper and the aluminum when
the joint is placed in compression. The grease keeps moisture out and zinc
is very compatible with aluminum; however, the grease and zinc particles do
not provide galvanic corrosion protection. These greases are best used in
aluminum to aluminum joints. Coating the copper with lead, tin, or lead/tin
solder before the joint is made will also provide some degree of protection
as these metals or alloy are located between copper and aluminum in the
galvanic series. An alloy terminal block that transitions gradually from
one alloy to another sounds like a great idea, but it is virtually
impossible to make such an alloy. As an example copper aluminum alloys
cannot contain more than a few percent copper before the copper precipitates
out. Welding, machining, or placing a high copper aluminum alloy under
strain can cause microscopic particles of copper to form in the alloy.
Localized corrosion will occur around these particles.

As amateur radio operators who encounter aluminum antennas connected to
copper feedlines, about the best we can do is use good mechanical contact
combined with a protective paint to keep moisture out of a joint. I usually
use an acrylic paint as it has superior ultraviolet resistance which is
needed if the joint is outdoors. My personal favorite is clear Krylon spray
for this use. It lets you seen the joint and any corrosion that is formed.
Some joints have held up for more than 15 years in my experience.

73, Barry WA4VZQ

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~

GALVANIC SERIES OF METALS AND ALLOYS
-----------------------------------------------------------

CORRODED END ( ANODIC OR LEAST NOBLE)

MAGNESIUM
MAGNESIUM ALLOYS
ZINC
ALUMINUM 5052, 3004, 3003, 1100, 6053
CADMIUM
ALUMINUM 2117, 2017, 2024
MILD STEEL (1018), WROUGHT IRON
CAST IRON, LOW ALLOY HIGH STRENGTH STEEL
CHROME IRON (ACTIVE)
STAINLESS STEEL, 430 SERIES (ACTIVE)
302, 303, 321, 347, 410,416, STAINLESS STEEL (ACTIVE)
NI - RESIST
316, 317, STAINLESS STEEL (ACTIVE)
CARPENTER 20CB-3 STAINLESS (ACTIVE)
ALUMINUM BRONZE (CA 687)
HASTELLOY C (ACTIVE) INCONEL 625 (ACTIVE) TITANIUM (ACTIVE)
LEAD - TIN SOLDERS
LEAD
TIN
INCONEL 600 (ACTIVE)
NICKEL (ACTIVE)
60 NI-15 CR (ACTIVE)
80 NI-20 CR (ACTIVE)
HASTELLOY B (ACTIVE)
BRASSES
COPPER (CA102)
MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905)
SILICONE BRONZE
NICKEL SILVER
COPPER - NICKEL ALLOY 90-10
COPPER - NICKEL ALLOY 80-20
430 STAINLESS STEEL
NICKEL, ALUMINUM, BRONZE (CA 630, 632)
MONEL 400, K500
SILVER SOLDER
NICKEL (PASSIVE)
60 NI- 15 CR (PASSIVE)
INCONEL 600 (PASSIVE)
80 NI- 20 CR (PASSIVE)
CHROME IRON (PASSIVE)
302, 303, 304, 321, 347, STAINLESS STEEL (PASSIVE)
316, 317, STAINLESS STEEL (PASSIVE)
CARPENTER 20 CB-3 STAINLESS (PASSIVE), INCOLOY 825NICKEL - MOLYBDEUM -
CHROMIUM - IRON ALLOY (PASSIVE)
SILVER
TITANIUM (PASS.) HASTELLOY C & C276 (PASSIVE), INCONEL 625(PASS.)
GRAPHITE
ZIRCONIUM
GOLD
PLATINUM

PROTECTED END (CATHODIC OR MOST NOBLE)

"Cecil Moore" wrote in message
...
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?

1. I encountered dissimilar metal parts which had been joined by what was
termed "explosive welding" and/or "explosive bonding" both of which terms
show up nicely in Google.

In my case, the parts were cylindrical sleeves, the top of each being
stainless steel and the bottom being aluminum. I only saw one (out of
thousands) with the bond fractured and I don't know what hit it to break it.
They seem quite strong.

Perhaps a vendor of such products has something you can use.

2. I see a lot of brass and darn little corrosion. Would a transition
piece of brass be acceptable?

"Sal"

On Fri, 07 Nov 2008 14:36:58 -0600, Cecil Moore
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?

Methinks this might be worth reading:
http://yarchive.net/electr/galvanic_corrosion.html
It's a collection of postings about glavanic corrosion with lots of
good info.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

----- Original Message -----
From: "Sal M. Onella"
Newsgroups: rec.radio.amateur.antenna
Sent: Friday, November 07, 2008 11:20 PM
Subject: Aluminum to Copper interface



"Cecil Moore" wrote in message
...
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?

1. I encountered dissimilar metal parts which had been joined by what was
termed "explosive welding" and/or "explosive bonding" both of which terms
show up nicely in Google.

In my case, the parts were cylindrical sleeves, the top of each being
stainless steel and the bottom being aluminum. I only saw one (out of
thousands) with the bond fractured and I don't know what hit it to break
it.
They seem quite strong.

Perhaps a vendor of such products has something you can use.

2. I see a lot of brass and darn little corrosion. Would a transition
piece of brass be acceptable?

"Sal"

Red, yellow, and naval brass as well as aluminum bronze alloys are
marginally anodic with respect to copper so these alloys would provide
minimal corrosion protection. I know it might not be obvious, but steel
would make a better intermediate metal.

This will make sense if the actual voltages are included in the galvanic
series. These voltages are in sea water and with respect to a standard
calomel electrode.

Zinc -0.98 to -1.03
volts
Aluminum -0.70 to -0.90 "
Cast Iron -0.60 to -0.72
"
Steel -0.60 to -0.70
"
Red Brass, Yellow Brass, Naval Bross,
Aluminum Bronze -0.30 to -0.40 "
Copper -0.28 to -0.36
"


73, Barry WA4VZQ