Epoxy Bonding to Aluminum and Magnesium

"smjmitchell" wrote in message [...] 5.
Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!


Interesting comment but the rear case on many A-65 Continentals, and on most
C-85's, is magnesium bolted to an aluminum alloy crankcase. The bolts, of
course, are cad-plated steel and there's a fat gasket between the cases.
Whenever I rebuild one of these engines I always use magnedyne to passivate
the magnesium and alodine for the aluminum case. Magnesium doesn't need
any contact with another metal to corrode like crazy, but it sure does make
a nice lightweight accessory case, including good bearing pockets for the
oil pump and its shafts. So you magnedyne it and paint it, and of course
paint the crankcase too after passivating it, just like the Continental
overhaul manual advises.

Aileron hinges on the later Taylorcrafts are magnesium, and so are the
yokes, and so are the wheels. Beautiful castings but they must be treated
and preserved with great care.

(Bill Hale) wrote in message . com...
Where can U get Belzona products in the US? Bill Hale

Depends on your location. Contact the Belzona website for your local
distributor or consultant. Sometimes you can find it at a Caterpillar
dealer but some of them mark it up a bunch.

The following is from the Belzona website:
With Belzona Distributors operating in over 120 countries, you are
never far away from Belzona products and service. Please contact the
appropriate Belzona Headquarters based on your geographic location and
the lead will be forwarded to your local Belzona Distributor.


To fill out an inquiry form for Belzona in North America, Latin
America and Asia:- Click Here
Belzona Inc.
2000 N.W. 88th Court
Miami, Florida U.S.A. 33172

Toll-Free 1-800-238-3280
Telephone: +1 (305) 594-4994
Facsimile: +1 (305) 599-1140

Sure, it works in practice. But does it work in theory?

"Blueskies" wrote in message m...
I was thinking ProSeal or similar for the interface...

I was too, until I looked at the temperature resistance of
polysulfides (ProSeal being that). It's pretty low, it releases
pretty completely at about 250 deg F, whereas the cheapest RTV starts
from there, and they have readily available compounds that go up to
700 deg F or higher.

I've always looked down my nose at RTV, and I've seen many jobs
bodgered up using it, but in this case, I'm beginning to believe it's
the right goop for the deal.

5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!

Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
cars, with WATER running through their engines, have cast iron blocks
and aluminum heads. In this situation, there is no ready source of
electrolyte. I don't see this as a huge concern. I'm more bothered
by oil leaks.

Auto engines have head gaskets between the electro different metals,
plus if you don't run an inhibitor is a mutli-metal water cooled engine
you will corrode the aluminum away, period.

Yours
Vern

You are right but there is one other very important issue here ... age is
also a big factor in bond line strength. If you test your three samples in
three years time you will see different results. Some of the effects of poor
surface preparation don't show up for years. In other words you can prepare
samples in different ways now and test them and get similar shear and peel
strengths. If you test those same samples in three years you could see that
one has lost a lot of its strength and the other has retained most if not
all.

A very complex issue and no something that can be encapsulated in a simple
posting. Best to follow established process specifications. Companies like
Locktite (who now sell Hysol adhesives) have data sheets on their web sites
that you can download. Just get them and follow them with a lot of care.


"Ron Webb" wrote in message
...

2. Next there is the issue of surface preparation. If the plans say
prepare
by running with 80 grid paper then it is fairly clear that the guy who
wrote
the plans knows little about what he is doing ! Epoxy metal bonding is
reliable if the surfaces are prepared properly but from what you have
said
I
doubt that is the case.

I recently did some testing with West Systems and aluminum. I used 3 test
strips, side by side. 1" wide fiberglass tape, 3 inches of bonding
surface
on 6061.

The first strip was applied with no surface impression at all.
The second strip was applied after sanding with 80 Grit
The third was sanded and etched with an etch (Duramix 4925)

The first strip came off with maybe a pound of force, pulling on the end
of
the fiberglass tape.
The second strip (sanded) took maybe twice that - it still came right off
The third (etched) strip never did come off, I tore the fiberglass tape It
stood up to at least 30 pounds in shear!

Surface preparation makes a BIG difference!.

See below for data as requested:

Also see MIL-STD-899 for further info (you can download that from the web)
at http://stinet.dtic.mil/str/index.html


Metal Potential
Magnesium and its alloys -1.60
Zinc die-casting alloy -1.10
Zinc plating on steel -1.10
Zinc plating on steel, chromate passivated -1.05
Galvanised iron -1.05
Tin/Zinc (80/20) plating in steel -1.05
Cadmium-Zinc solder -1.05
Wrought Al-clad Al Alloys -0.90
Cadmium plating on steel -0.80
Aluminium alloy castings -0.75
Wrought aluminium -0.75
Non-stainless steel & grey cast iron -0.70
Duralumin type un-clad alloys -0.60
Lead -0.55
Lead-silver solder -0.50
Tin-lead solder -0.50
Tinned Steel -0.50
Cr plating (0.0005") on steel -0.50
Stainless 12% Cr -0.45
Tin plating on steel -0.45
Cr plating (0.00003") on plating steel -0.45
Chromium (99%) -0.45
Stainless High Cr (18/2) -0.35
Copper and its alloys (Brass, bronze, etc) -0.25
Nickel-Copper alloys -0.25
Stainless, Austenitic (18/8) -0.20
Silver solder -0.20
Monel metal -0.15
Nickel plating on steel Titanium -0.15
Titanium -0.15
Silver and silver plating on copper 0
Rhodium plating on silver plated Copper +0.05
Carbon +0.10
Platinum +0.15
Gold +0.15

Condition Max. Potential Difference
Marine and outdoor environment 0.3 Volts
Indoor environment 0.5 Volts
Interior assemblies, hermetically sealed No restriction




"Greg Reid" wrote in message
om...
"smjmitchell" wrote in message
. au...

5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V
on
the galvanic table. That is a big different. You definitely need
something
to separate the two or the magnesium is going to get gobbled up !!


Interesting. Where might I information like this for making decisions
on what metals can be safely bolted together w/r/t galvanic corrosion?
At issue right now is whether it'll be OK to thread my brass
fuel-system finger strainers and fuel drains into aluminum blocks, but
other such questions will certainly come up in future.

Thanks,
Greg

Yes I would definitely alodine aluminium before bonding. Magnesium is a very
active (anodic) metal.

Of course the environment in which dissimilar metals interfaces operate has
a big influence on the likelihood and severity of corrosion. If the metals
interface is dry and sealed then you can get away with a lot ... if exposed
to moisture and or a salty atmosphere then you are in much bigger trouble !



" jls" wrote in message
. ..

"smjmitchell" wrote in message [...] 5.
Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need
something
to separate the two or the magnesium is going to get gobbled up !!


Interesting comment but the rear case on many A-65 Continentals, and on
most
C-85's, is magnesium bolted to an aluminum alloy crankcase. The bolts,
of
course, are cad-plated steel and there's a fat gasket between the cases.
Whenever I rebuild one of these engines I always use magnedyne to
passivate
the magnesium and alodine for the aluminum case. Magnesium doesn't need
any contact with another metal to corrode like crazy, but it sure does
make
a nice lightweight accessory case, including good bearing pockets for the
oil pump and its shafts. So you magnedyne it and paint it, and of course
paint the crankcase too after passivating it, just like the Continental
overhaul manual advises.

Aileron hinges on the later Taylorcrafts are magnesium, and so are the
yokes, and so are the wheels. Beautiful castings but they must be
treated
and preserved with great care.

Vernon Klukas wrote in message .. .
5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!

Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
cars, with WATER running through their engines, have cast iron blocks
and aluminum heads. In this situation, there is no ready source of
electrolyte. I don't see this as a huge concern. I'm more bothered
by oil leaks.

Auto engines have head gaskets between the electro different metals,
plus if you don't run an inhibitor is a mutli-metal water cooled engine
you will corrode the aluminum away, period.

Yours
Vern

Vern is 100% correct. I have repaired several automotive engines where
this has been a problem. I used Belzona Super Metal (1111) to repair
the problem. Also have used it to fix a multitude of diesel engines.
These were do to electroylisis and cavitation. This is caused because
the owners did not change or maintain the proper chemical balance of
the antifreeze.
Toyota engines require the Toyota antifreeze. Dexcool is not approved
and according to a Toyota engineer, it will eventually damage the
engine. He also told me not to mix Dexcool with glycol antifreeze.
To make a long story short, follow the engine manufactures
recommendations.

(Leon McAtee) wrote


It's probably not carrying any loads. A basic tenet of structural
design is that the stiffest load path carries the load, and the bolts
through the angle and into the case (secured with nuts and washers
inside the sump, before the engine is assembled) seem a bunch stiffer
that the epoxy.

Been there, done that.

Oooh, that's what I like! Experience...

The epoxy is more of a feel good thing. File
the sides of the sump flat, spot face the inside surface and bolt the
thing together with the bolt heads inside (no washers). Use some blue
Locktight on the heads and torque to the normal specs for the
fastener used and it won't leak.......at least that's been my
experience. A bit of Ultra Grey silicone doesn't seem to
hurt, as long as you get things torqued before it sets. You want good
metal to metal contact so things don't move around.

Why no washers? The little bit of radius at the root of the shank of
the bolt needs somewhere to go, yes? And may I assume you're putting
these bolts in a reamed hole?

That got me to thinking. Taper pins.

http://assist.daps.dla.mil/docimages...3/28/54217.PD4

Threads on the outside. I'll have to run the reamer in from the sump
side, through the aluminum angle and control the depth pretty
carefully.

I need to measure the thickness of the case walls to get the grip
length right, but I'm thinking an AN-386-2-9A from AS&S should do the
job. http://www.aircraftspruce.com/nsearch.php?s=taper

Another way to make the metal carry the load would be with locator
pins in reamed holes (called Shuffle pins when they're used on the
split line) to take the shear loads. I think with the tools and
tooling I have, the taper pins will be easier.

As for the corrosion issue, I haven't had any problems and I've
adapted this method to my ground bound VW's for attaching home brew
block heaters to the side since the old style oil sump things are so
hard or impossible to find anymore. If the corrosion isn't a real
problem driving on salted roads it shouldn't be a problem on an
aircraft.


All the above based on my personal experience only
==========================
Leon McAtee
Still looking for Aeronca C-2/3 factory drawings