Alclad Aluminum

mhorowit wrote:
For the folks who use Alclad Aluminum. Am I corrrect in that if you
don't intend to paint it, it needs no additional coating? - Mike

Monsieur Horowitz, you should alodine it and paint it. That gives you
a triple whammy against corrosion. I've seen the cladding corroded
through on alclad aluminum and the surface underneath, which was 2024,
corroded all to hell.

Where are you using it?

I'm presently working on an airframe with a lot of 6061 in it. It's
from the 50's and very corroded, although the talk on 6061 is that it's
corrosion-resistant. Well, if you saw this you would say it ain't.

So where the aluminum is stilll usable, I clean, apply phosphoric acid,
clean again, and etch with chromic acid, i. e., I alodine. Then prime
and paint.

With the steel parts, I remove corrosion and if the part is still
usable, i. e., not too pitted, I bead-blast it, paint it with an acid
etch 2-part epoxy primer, then with a good organic paint before
reinstalling it in the aircraft. This would include parts like strut
attach fittings, drag wires*, pulley brackets, aileron and flap hinge
brackets, wingtip bow attach fittings, wing tank hardware, and butt
hinge fittings. If it were legal, I'd do a lot of powder-coating, and
I notice a lot of companies who manufacture PMA parts powder-coat their
parts. I just received a rudder which was beautifully powder-coated.
I doubt that damn thing will corrode any time soon.

Treat scrupulously against corrosion. You owe it to the next
generations who will appreciate your old airplane and cherish it as you
do.

I just watched a video by respected ragwing Piper specialist, Paul
Babcock, restoring a Super Cub. He says that because of a recent Piper
mandatory service bulletin, most of the Super Cubs in the USA are
required to have their fabric ripped away and the metal parts repaired
or replaced and treated against corrosion and painted. Having seen
the hidden condition of a few of these older PA-18's inside the wings,
I think I agree with Piper and Babcock. Some of them are scary.


*The newer drag wires are CRS, so no corrosion protection needed.

jls wrote:


Where are you using it?


The leading edge of the ailerons is thin alluminum sheet. I put a lot
of effort into physically removing corrosion on the left aileron and if
the right was in the same shape, I was thinking it would be easier to
simply make new parts. Someone pointed out that alodining chemicals
could be brushed on (rather than having to build tanks) and cost was
very reasonable, so I think I'll stick with my original approach. The
sheetmetal will be covered by fabric.

By the way... There is a metal prep that is used for cleaning prior to
alodining. It is a phosphoric solution. Is that also used for
chemically removing corrosion, or simply preping the surface for the
chromic coating? - Mike

mhorowit wrote:
jls wrote:


Where are you using it?


The leading edge of the ailerons is thin alluminum sheet. I put a lot
of effort into physically removing corrosion on the left aileron and if
the right was in the same shape, I was thinking it would be easier to
simply make new parts. Someone pointed out that alodining chemicals
could be brushed on (rather than having to build tanks) and cost was
very reasonable, so I think I'll stick with my original approach. The
sheetmetal will be covered by fabric.

You don't need tanks for alodining. You brush it on, let it sit
awhile, then wash it off. Use phosphoric acid solution first, then
wash off, then chromic acid solution. Then wash off, leaving a little
tannish, bluish color behind on the aluminum surface.

You can use a little scotchbrite to get off the oxide powder before
using phosphoric acid.

I have restored several sets of ailerons on Taylorcrafts from the 40's
and the aluminum in most cases is restorable. After you've alodined
you can prime with Polyfiber's proprietary primer which won't dissolve
when you glue on the fabric to the leading edge.

By the way... There is a metal prep that is used for cleaning prior to
alodining. It is a phosphoric solution. Is that also used for
chemically removing corrosion, or simply preping the surface for the
chromic coating? - Mike

The phosphoric acid prepares for chromic acid coating,as well as
removing some corrosion. Use scotchbrite if the corrosion is thick and
powdery.

mhorowit wrote:
jls wrote:


Where are you using it?


The leading edge of the ailerons is thin alluminum sheet. I put a lot
of effort into physically removing corrosion on the left aileron and if
the right was in the same shape, I was thinking it would be easier to
simply make new parts. Someone pointed out that alodining chemicals
could be brushed on (rather than having to build tanks) and cost was
very reasonable, so I think I'll stick with my original approach. The
sheetmetal will be covered by fabric.

You don't need tanks for alodining. You brush it on, let it sit
awhile, then wash it off. Use phosphoric acid solution first, then
wash off, then chromic acid solution. Then wash off, leaving a little
tannish, bluish color behind on the aluminum surface.

You can use a little scotchbrite to get off the oxide powder before
using phosphoric acid.

I have restored several sets of ailerons on Taylorcrafts from the 40's
and the aluminum in most cases is restorable. After you've alodined
you can prime with Polyfiber's proprietary primer which won't dissolve
when you glue on the fabric to the leading edge.

By the way... There is a metal prep that is used for cleaning prior to
alodining. It is a phosphoric solution. Is that also used for
chemically removing corrosion, or simply preping the surface for the
chromic coating? - Mike

The phosphoric acid prepares for chromic acid coating,as well as
removing some corrosion. Use scotchbrite if the corrosion is thick and
powdery.

mhorowit wrote:
jls wrote:


Where are you using it?


The leading edge of the ailerons is thin alluminum sheet. I put a lot
of effort into physically removing corrosion on the left aileron and if
the right was in the same shape, I was thinking it would be easier to
simply make new parts. Someone pointed out that alodining chemicals
could be brushed on (rather than having to build tanks) and cost was
very reasonable, so I think I'll stick with my original approach. The
sheetmetal will be covered by fabric.

You don't need tanks for alodining. You brush it on, let it sit
awhile, then wash it off. Use phosphoric acid solution first, then
wash off, then chromic acid solution. Then wash off, leaving a little
tannish, bluish color behind on the aluminum surface.

You can use a little scotchbrite to get off the oxide powder before
using phosphoric acid.

I have restored several sets of ailerons on Taylorcrafts from the 40's
and the aluminum in most cases is restorable. After you've alodined
you can prime with Polyfiber's proprietary primer which won't dissolve
when you glue on the fabric to the leading edge.

By the way... There is a metal prep that is used for cleaning prior to
alodining. It is a phosphoric solution. Is that also used for
chemically removing corrosion, or simply preping the surface for the
chromic coating? - Mike

The phosphoric acid prepares for chromic acid coating,as well as
removing some corrosion. Use scotchbrite if the corrosion is thick and
powdery.

mhorowit wrote:
jls wrote:


Where are you using it?


The leading edge of the ailerons is thin alluminum sheet. I put a lot
of effort into physically removing corrosion on the left aileron and if
the right was in the same shape, I was thinking it would be easier to
simply make new parts. Someone pointed out that alodining chemicals
could be brushed on (rather than having to build tanks) and cost was
very reasonable, so I think I'll stick with my original approach. The
sheetmetal will be covered by fabric.

You don't need tanks for alodining. You brush it on, let it sit
awhile, then wash it off. Use phosphoric acid solution first, then
wash off, then chromic acid solution. Then wash off, leaving a little
tannish, bluish color behind on the aluminum surface.

You can use a little scotchbrite to get off the oxide powder before
using phosphoric acid.

I have restored several sets of ailerons on Taylorcrafts from the 40's
and the aluminum in most cases is restorable. After you've alodined
you can prime with Polyfiber's proprietary primer which won't dissolve
when you glue on the fabric to the leading edge.

By the way... There is a metal prep that is used for cleaning prior to
alodining. It is a phosphoric solution. Is that also used for
chemically removing corrosion, or simply preping the surface for the
chromic coating? - Mike

The phosphoric acid prepares for chromic acid coating,as well as
removing some corrosion. Use scotchbrite if the corrosion is thick and
powdery.