West Systems 860 Aluminum Etch Kit
A two-part treatment for preparation of aluminum surfaces for bonding
with epoxy. Our research shows adhesion to aluminum is significantly
improved with this process. Also improves paint adhesion.
860-8 Two 1/4 pint bottles (treats about 50 sq. ft.)
860 Two 1-pint bottles (treats about 200 sq. ft.).

http://www.westsystem.com/

I didn't know aluminum oxidized within minutes so I did a test.

Part of a piece of aluminum was scraped removing any oxidation and making
the scraped part bright and shiny. Two hours later the scraped part was
still just as bright and shiny. Eighteen hours later the scraped part was
not as bright and shiny. Part of the surface which had been scraped the
day before was rescraped and the difference was noticeable, the newly
scraped surface was brighter than the surface scraped the day before, but
both scraped surfaces were still a lot brighter than the part of the
surface which had not been scraped at all.

I would conclude that there is some oxidation in the first 24 hours.



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On 15 Oct 2005 14:53:26 GMT, (William R.
Watt) wrote:


I didn't know aluminum oxidized within minutes so I did a test.

Part of a piece of aluminum was scraped removing any oxidation and making
the scraped part bright and shiny. Two hours later the scraped part was
still just as bright and shiny. Eighteen hours later the scraped part was
not as bright and shiny. Part of the surface which had been scraped the
day before was rescraped and the difference was noticeable, the newly
scraped surface was brighter than the surface scraped the day before, but
both scraped surfaces were still a lot brighter than the part of the
surface which had not been scraped at all.

I would conclude that there is some oxidation in the first 24 hours.


If you can't see the film, doesn't mean it's not there.
Astro mirrors are aluminized, these days.
In a vacuum chamber, a small aluminum sample is vaporized off a
filament onto the glass.
Then they let the air back in. That mirror surface looks good for
years. And if they hard coat it, it lasts even longer.

Brian W

William R. Watt wrote:
I didn't know aluminum oxidized within minutes so I did a test.

Part of a piece of aluminum was scraped removing any oxidation and making
the scraped part bright and shiny. Two hours later the scraped part was
still just as bright and shiny. Eighteen hours later the scraped part was
not as bright and shiny. Part of the surface which had been scraped the
day before was rescraped and the difference was noticeable, the newly
scraped surface was brighter than the surface scraped the day before, but
both scraped surfaces were still a lot brighter than the part of the
surface which had not been scraped at all.

I would conclude that there is some oxidation in the first 24 hours.



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William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
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THe thin layer of oxide that forms in the first seconds is nearly
transparent. Try again, this time using a white piece of cloth. Polish
until the area seems as "bright and shiny" as you want. Notice the
black stuff on the cloth. That is aluminum oxide. Wait 30 seconds and
use a clean portion of the rag to polish the "bright and shiny" part you
just polished. Notice the black stuff? That is more aluminum oxide.

Aluminum is like silver. It oxidizes almost instantaneously.

It is this thin layer that fails when gluing parts. The adhesive bonds
to the oxide layer and the oxide fails, not the glue.



--
“The darkest places in hell are reserved for those who maintain their
neutrality in times of moral crisis.”

dazed and confuzzed wrote:


Aluminum is like silver. It oxidizes almost instantaneously.

It is this thin layer that fails when gluing parts. The adhesive bonds
to the oxide layer and the oxide fails, not the glue.

I wonder how the Lotus Elise stays together then? It has an aluminium
tub-chassis, constructed from aluminium extrusions bonded together with
epoxy resin.

--

Geoff

Regarding the corrosion of aluminum in bonding with epoxy..one of the
homebuilt aircraft was put together using the method of sanding the surface
through the still "wet" epoxy. The theory was the epoxy on the sanding
surface would minimize the corrosion.

some of the homebuilt aircraft groups may be able to help. I know of one
company that designs and builds reduction gears for the homebuilt market and
they use a glue along with mechanical fasteners (bolts). I believe that
they use a locktite product.

Brian

On Sun, 16 Oct 2005 07:53:43 -0700, "patrick mitchel"
wrote:

Regarding the corrosion of aluminum in bonding with epoxy..one of the
homebuilt aircraft was put together using the method of sanding the surface
through the still "wet" epoxy. The theory was the epoxy on the sanding
surface would minimize the corrosion.



Reminds me of a sure fire stunt to pull on electronics technicians.

You ask them to bet you can't solder some aluminum alloy sheet strips
together with regular solder. They think it's a sure thing.

You prepare two strips, and scrape the surface with your pen-knife,

Then you place a blob of hot solder on the strip. (Of course it
doesn't tin) Then you scrape the strip through the melted solder.
It tins under the scrape, if its hot enough.
Soon you've scraped a good length of tinning on the strip, and you
prepare the other strip the same.

At that point, you sweat the two tinned strips together in the usual
way. Try pulling them apart. They will break away from the sweated
lap joint.

Brian Whatcott Altus OK

On Sun, 16 Oct 2005 13:35:55 +0200, GeoffC wrote:

dazed and confuzzed wrote:


Aluminum is like silver. It oxidizes almost instantaneously.

It is this thin layer that fails when gluing parts. The adhesive bonds
to the oxide layer and the oxide fails, not the glue.

I wonder how the Lotus Elise stays together then? It has an aluminium
tub-chassis, constructed from aluminium extrusions bonded together with
epoxy resin.

It's not that you can't epoxy aluminum. Of course you can. You just have
to do good surface preparation first.

There are products designed for this. Someone mentioned an etch sold by
West Systems or something like that. I think there is something called
Marine Tex that bonds well to aluminum.

But in the OP's case, I would just use JB-weld to stick the piece back in,
then put a single layer of fiberglass/epoxy over the outside of the broken
piece, then paint. I would sand the area in the immediate vicinity of the
break down to bare metal and clean with acetone or alcohol prior to
applying the epoxy.

Surface preparation is EVERYTHING in bonding applications.

--Mac