Corrosion at Aluminum/Steel Junction [Archive]

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Front Office

June 19th 06, 07:34 PM

I need to build a dozen outdoor canopies for an office building.
I want to use structural aluminum channel, bolted with steel bolts.

Where might expect corrosion to arise over the years, and would
it be mainly in the aluminum or in the steel bolts?

Thanks for any help.

Please post here or email me at grayscale[AT]verizon.net

Ralph

Jack Linthicum

June 19th 06, 08:54 PM

Front Office wrote:
> I need to build a dozen outdoor canopies for an office building.
> I want to use structural aluminum channel, bolted with steel bolts.
>
> Where might expect corrosion to arise over the years, and would
> it be mainly in the aluminum or in the steel bolts?
>
> Thanks for any help.
>
> Please post here or email me at grayscale[AT]verizon.net
>
> Ralph

I would think stainless steel bolts or some form of fiber or plastic
(lucite) washer would provide the rigidity and separation. Not that
that view is universal:

http://www.eng-tips.com/viewthread.cfm?qid=154321&page=1

mattmlm (Structural)
9 May 06 10:21
I've got a project where Aluminum columns (and base plates) are being
anchored to a concrete pier/footing. The contractor used your everyday
common steel threaded anchor rods. In less than two weeks they are
completely rusted over. The contract documents called for hot-dipped
galvanized anchor bolts. (before judging, we did not provide the design
or specifications, simply consulting on a separate portion of the
larger project)

I'm thinking of having the contractor cut off and drill-in epoxy grout
anchors.

Will the galvanized anchor bolts react to the aluminum? Should I use
aluminum anchor bolts? If alum, what affect would the anchors have in
steel reinforced concrete?

Thank you,

MLM

Start your own Eng-Tips Group! Click Here!
Goahead (Aerospace)
9 May 06 11:10
Galvanized steel anchor bolts should be OK with aluminum.
As an extra precaution the contact areas could be painted with
insulating paint.

http://www.welding-advisers.com/
TVP (Materials)
9 May 06 11:30
Al bolts are unlikely to be strong enough if they were not specifically
incorporated into the design. Zinc is the most compatible coating for
steel bolts that is also relatively cost effective.
Heckler (Mechanical)
9 May 06 12:09
Aluminum and Zinc are really close together on my Galvanic Corrosion
Potential Chart.
mattmlm (Structural)
9 May 06 12:24
Is that good thing or a bad thing?

MLM
theonlynamenottaken (Structural)
9 May 06 13:17
Its a good thing... the farther apart two metals are on the galvanic
series the greater potential between them, hence more aggressive
attack.

Aluminum embedded in and in direct contact with concrete is not
acceptable. A chemical reaction occurs and the concrete literally self
destructs from the expansion (product of the reaction, just like rust
on carbon steel that is allowed to corrode in concrete). I don't know
about epoxy grouted aluminum in concrete but I've seen slabs with
aluminum cast into it break themselves apart.
UcfSE (Structural)
9 May 06 13:23
I have a question to go along with this. I have noticed in the past
with aluminum panels that the manufacturer of the panels has
recommended stainless steel screws with some kind of special washer
between the steel and the aluminum. Does that line of thinking work
also in this case, say with using stainless steel anchor bolts or epoxy
bolts with an aluminum base plate?
mattmlm (Structural)
9 May 06 13:40
How good is stainless in direct contact with Aluminum? When this issue
first came up, the only thing that I thought of was stainless. Then
came the comments about the specs calling for hot-dipped galvanized.
I've always assumed that stainless was preferred, if not required. Is
that assumption correct?

MLM

Also, thanks for the input.
Heckler (Mechanical)
9 May 06 14:35
ASTM A-153 or ISO 1461 covers hot-dip galvanizing. I think it's more
of a cost factor when considering Stainless verses galvanized steel.
Goahead (Aerospace)
10 May 06 12:04
Stainless should not be in contact with aluminum. Stainless fasteners
should be Cadmium or Zinc plated before
being inserted in aluminum bodies. Usual anodizing or conversion
coating are not protective enough at the contact place.

http://www.welding-advisers.com/
IFRs (Petroleum)
26 May 06 16:21
In my experience (27 years in the petrochemical industry), aluminum and
stainless fasteners are acceptable in most environments. Althought
they are far apart on the galvanic scale, the typically much larger
area of the aluminum part compared to the fastener reduces to nearly
nil the tendency of the aluminum to corrode. However, in this case,
I'd definitly use galvanized anchors - they were specified, are
compatible, are probably more available not to mention less costly.
Note that the environment is a critical issue - If this is on the
seashore, or exposed to wet atmosphere, or under water, or vibrating
from machinery, etc then corrosion needs to be re-evaluated.

larry

June 19th 06, 10:25 PM

"Front Office" > wrote in message
. ..
> I need to build a dozen outdoor canopies for an office building.
> I want to use structural aluminum channel, bolted with steel bolts.
>
> Where might expect corrosion to arise over the years, and would
> it be mainly in the aluminum or in the steel bolts?
>
> Thanks for any help.
>
> Please post here or email me at grayscale[AT]verizon.net
>
> Ralph

Ralph,
I'm 'going through' my 11 year old aluminum boat trailer right now which was
bolted together with galvanized bolts. I don't see the aluminum pitting I
would have expected around the bolt holes. I do have a few rusty bolts which
are easily replaced. I recommend you use this method. If you go with S/S
bolts you WILL have pitting around the aluminum holes (as the least noble
metal gets the damage) and it will not be easily repaired in the future.

Larry

My turbine powered boat project;
http://www.turbinefun.com

Vaughn Simon

June 19th 06, 11:38 PM

"Front Office" > wrote in message
. ..
> Where might expect corrosion to arise over the years, and would
> it be mainly in the aluminum or in the steel bolts?

I suggest you take this question to rec.crafts.metalworking.

Vaughn

Mark Andrew Spence

June 20th 06, 12:04 PM

Stealth Pilot

June 20th 06, 03:05 PM

On Mon, 19 Jun 2006 18:34:46 +0000, Front Office
> wrote:

>I need to build a dozen outdoor canopies for an office building.
>I want to use structural aluminum channel, bolted with steel bolts.
>
>Where might expect corrosion to arise over the years, and would
>it be mainly in the aluminum or in the steel bolts?
>
>Thanks for any help.
>
>Please post here or email me at grayscale[AT]verizon.net
>
>Ralph

a product called Duralac is designed to prevent the electrolytic
corrosion between dissimilar metals.
it is an aviation product made in england. comes in a white and yellow
tube.
it is a toothpaste consistency yellow fluid containing zinc chromate.
it dries slowly to a rubber consistency.

the stuff is used for pop rivets with great benefit in corrosion
control. you just dip them in it prior to setting the pop in a wing
skin.

it is good stuff. two tubes in my aviation tool box.
Stealth Pilot

Martin Evans

June 21st 06, 12:41 AM

On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot
> wrote:

>a product called Duralac is designed to prevent the electrolytic
>corrosion between dissimilar metals.
>it is an aviation product made in england. comes in a white and yellow
>tube.
>it is a toothpaste consistency yellow fluid containing zinc chromate.
>it dries slowly to a rubber consistency.

Minor point, it only contains Barium Chromate and White Spirit.

You can also buy bigger tins of it, It's used in a lot of marine
applications as well as aviation.

--

Stealth Pilot

June 21st 06, 02:32 PM

On Wed, 21 Jun 2006 00:41:07 +0100, Martin Evans
> wrote:

>On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot
> wrote:
>
>>a product called Duralac is designed to prevent the electrolytic
>>corrosion between dissimilar metals.
>>it is an aviation product made in england. comes in a white and yellow
>>tube.
>>it is a toothpaste consistency yellow fluid containing zinc chromate.
>>it dries slowly to a rubber consistency.
>
>Minor point, it only contains Barium Chromate and White Spirit.
>
>You can also buy bigger tins of it, It's used in a lot of marine
>applications as well as aviation.

had to drag out my tube.
that's true.

Stealth Pilot

[email protected]

June 22nd 06, 03:21 PM

Stealth Pilot wrote:
> On Wed, 21 Jun 2006 00:41:07 +0100, Martin Evans
> > wrote:
>
> >On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot
> > wrote:
> >
> >>a product called Duralac is designed to prevent the electrolytic
> >>corrosion between dissimilar metals.
> >>it is an aviation product made in england. comes in a white and yellow
> >>tube.
> >>it is a toothpaste consistency yellow fluid containing zinc chromate.
> >>it dries slowly to a rubber consistency.
> >
> >Minor point, it only contains Barium Chromate and White Spirit.
> >
> >You can also buy bigger tins of it, It's used in a lot of marine
> >applications as well as aviation.
>
> had to drag out my tube.
> that's true.
>
> Stealth Pilot

Hard to get zinc chromate in the average consumer product
anymore. It's been linked to cancer. Zinc *oxide* is often seen in
those green aerosol primers now. I can still get Endura epoxy zinc
chromate, clearly labelled "for industrial use only."

Dan

george

June 22nd 06, 10:10 PM

wrote:
> Stealth Pilot wrote:
> > On Wed, 21 Jun 2006 00:41:07 +0100, Martin Evans
> > > wrote:
> >
> > >On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot
> > > wrote:
> > >
> > >>a product called Duralac is designed to prevent the electrolytic
> > >>corrosion between dissimilar metals.
> > >>it is an aviation product made in england. comes in a white and yellow
> > >>tube.
> > >>it is a toothpaste consistency yellow fluid containing zinc chromate.
> > >>it dries slowly to a rubber consistency.
> > >
> > >Minor point, it only contains Barium Chromate and White Spirit.
> > >
> > >You can also buy bigger tins of it, It's used in a lot of marine
> > >applications as well as aviation.
> >
> > had to drag out my tube.
> > that's true.
> >
> > Stealth Pilot
>
> Hard to get zinc chromate in the average consumer product
> anymore. It's been linked to cancer. Zinc *oxide* is often seen in
> those green aerosol primers now. I can still get Endura epoxy zinc
> chromate, clearly labelled "for industrial use only."
>
Either go talk to a window maker or for information as to
bolts/connectors compatable with aluminium go to
http://www.everything-stainless-steel.info/stainless-steel-fasteners/

......... :-\)\)

June 24th 06, 01:43 PM

Normal mild steel or alloy steel is very close to alumnium on the galvanic
table (-0.7 cf -0.75 V) so galvanic corrosion is unlikely ... however you
need to make sure the steel is protected from surface corrosion which is a
separate issue.

To use stainless steel bolts in aluminium is risky. Stainless steel will
have a potential of approx -0.2 V and so you have a -0.5 V potential which
is on the limits of acceptability. Is the interface was protected with a
product such as the Duralac recommended by Stealth Pilot then you might get
away with it. Otherwise pitting of the the aluminium around the strainless
fasteners might occur if moisture is present.

Stainless bolts in aluminium structure are not as bad as putting aluminium
bolts in stainless but still risky business if outdoors. An absolute no no
if in a salt atmosphere.

"george" > wrote in message
oups.com...
>
> Front Office wrote:
> > I need to build a dozen outdoor canopies for an office building.
> > I want to use structural aluminum channel, bolted with steel bolts.
> >
> > Where might expect corrosion to arise over the years, and would
> > it be mainly in the aluminum or in the steel bolts?
> >
> > Thanks for any help.
> >
> > Please post here or email me at grayscale[AT]verizon.net
> >
> Use only stainless steel.
>

Morgans

June 25th 06, 12:22 AM

"Mark Andrew Spence" > wrote

> The TICONDROGA and SPRUANCE class ships had aluminum superstructures which
> were welded to a "fusion bar" which consisted of a piece of very clean and
> smoothly-machined piece of aluminum FLAT BAR joined to a very clean piece
> and smoothly machined piece of steel flat bar via explosive charges.

What was the purpose of the explosive charges? (besides, to go "bang" <g>)
--
Jim in NC

......... :-\)\)

June 25th 06, 01:19 AM

It is difficult to argue with someone who simply says '********' with no
explanation. However:

1. There are really several issues here. First we need to make the
assumption that both the aluminium and steel are adequately protected
against general surface corrosion. Lets assume that this is the case. As I
understood the original question, the issue was really "is steel and
aluminium going to cause any problems from the point of view of dissimilar
metal corrosion" (i.e. galvanic corrosion).

2. The answer, as per my previous post is, no. Following is some further
explanation:

3. In a case of galvanic corrosion you have two metals with different
voltage potentials. In this case say carbon steel bolts at -0.76 and
aluminium at -0.8 V (the actual numbers vary a little depending on where you
get them from). Stainless steel would be approx -0.2 V. Now in the presence
of a conductive media (i.e. moisture) a current flows from the more anodic
(aluminium in this case) to the more cathodic (steel) and the anode
(aluminium) will be eaten away.

4. Normally most corrosion control standards would say that a difference in
potential of 0.25V or less is acceptable. Clearly this is the case with
carbon steel and aluminium (difference is only 0.04 V). Thus the interface
is acceptable.

5. It is essential that the anodic material be the larger mass of metal
(which is the case awning under discussion). The smaller fasteners should
always be more cathodic. If it was the otherway around and we had aluminium
bolts in a steel frame then the bolts would certainly be consumed. Whilst
stainless steel fasteners have a voltage difference of 0.5+ V you can get
away with small stainless fasteners in aluminium because of the relative
mass of the two metals (see below in 7)

6. In any dissimilar metal situation is is advisable to put some form of
surface protection between the metals. Paint, sealant etc. If you can
exclude moisture you can generally get away with all sorts of sins ...
however the problems arise when the paint cracks and you get moisture
ingression so best not to rely on paint.

7. I refer you to MIL-STD-889 "Dissimilar Metals" and I quote "Generally the
closer one metal is to another the more compatible they will be" and another
"A small anodic area relative to the cathode area should be avoided. The
same metal or more cathodic metal should be utilised for small fasteners,
and bolts. The larger the relative anode area, the lower the galvanic
current density on the anode, the lesser the attack"

8. I also refer you to USAF T.O. 1-1-2 "You can with proper protection use
steel rivets in aluminium but you can never use aluminium rivets in steel"

9. I also refer you to AvP 970 which shows carbon steel and aluminium in the
same group indicating that they are safe for use together. (in MIL-STD-889
they are in adjacent groups but would still be considered OK ...
particularly when considering the leatives mass of the two metals).

Finally a practical illustration of what I am saying. I have, on the windows
of my house, flyscreens with aluminium frames. These are in a salt
environment 1/2 mile from the beach. They have stainless steel clips riveted
to them that are a simple angle of sheet stainless. They also have normal
carbon steel bolts through the frames in a nearby area. There is zero
evidence of corrosion between the steel bolts and the anodised alumnium
frame. The aluminium frame is completely and totally eaten away underneath
the stainless steel clips in a 1/2 x 1/2" area. Outside this region there is
no corrosion.

"Jim Watt" > wrote in message
...
> On Sat, 24 Jun 2006 22:43:45 +1000, "......... :-\)\)"
> > wrote:
>
> >Normal mild steel or alloy steel is very close to alumnium on the
galvanic
> >table (-0.7 cf -0.75 V) so galvanic corrosion is unlikely ...
>
> B O L L O C K S
>
>
> --
> Jim Watt
> http://www.gibnet.com

Robert

June 25th 06, 05:48 AM

"Morgans" > wrote in message
...
>
> "Mark Andrew Spence" > wrote
>
>> The TICONDROGA and SPRUANCE class ships had aluminum superstructures
>> which were welded to a "fusion bar" which consisted of a piece of very
>> clean and smoothly-machined piece of aluminum FLAT BAR joined to a very
>> clean piece and smoothly machined piece of steel flat bar via explosive
>> charges.
>
> What was the purpose of the explosive charges? (besides, to go "bang"
> <g>)
> --
> Jim in NC

To make a compression weld.

Since steel and aluminum melt at different temps you can't heat weld them
like you would with normal steel-steel or heliarc(sp?) (heat weld in a
controlled atmosphere) like you would aluminum-aluminum.

June 25th 06, 09:30 AM

I am now more or less "trespassing" here but I would like to give an
explanation to this question.

The very smooth metal surfaces (bars), aluminum and steel are placed one on
top of an other and the explosive charge is placed, I guess above the
aluminum bar? Does this process take place in some kind of a purpose built
explosion chamber or are the materials simply buried underground (the weight
of e.g. a thick layer of sand would give enough resistance) to be fused, who
knows?

The idea is, that the detonation creates shock waves so intense, that the
metal atoms of the contact surface (layer) area are a sort of mixed
(knocked) together, hence the term fused. The process is probably called as
explosion welding? The created bond is very strong and there is no room for
any moisture to get in. That is why the corrosion can't take place between
the dissimilar materials. At least I figure this to be the case. The Mark
Andrew Spence may give more accurate explanation.

JP

"Morgans" > wrote in
...
>
> "Mark Andrew Spence" > wrote
>
>> The TICONDROGA and SPRUANCE class ships had aluminum superstructures
>> which were welded to a "fusion bar" which consisted of a piece of very
>> clean and smoothly-machined piece of aluminum FLAT BAR joined to a very
>> clean piece and smoothly machined piece of steel flat bar via explosive
>> charges.
>
> What was the purpose of the explosive charges? (besides, to go "bang"
> <g>)
> --
> Jim in NC
>

Fred J. McCall

June 25th 06, 12:36 PM

"Morgans" > wrote:

:
:"Mark Andrew Spence" > wrote
:
:> The TICONDROGA and SPRUANCE class ships had aluminum superstructures which
:> were welded to a "fusion bar" which consisted of a piece of very clean and
:> smoothly-machined piece of aluminum FLAT BAR joined to a very clean piece
:> and smoothly machined piece of steel flat bar via explosive charges.
:
:What was the purpose of the explosive charges? (besides, to go "bang" <g>)

It's a method of driving two different metals together in such a way
that they sort of blend into each other rather than having to be
welded, bolted, or some such.

The same process came to be used for coins when we switched from
silver to copper-cored coins.

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

Paul J. Adam

June 25th 06, 11:16 PM

In message . com>,
writes
> Hard to get zinc chromate in the average consumer product
>anymore. It's been linked to cancer.

Milspec products a decade ago used to use strontium chromate in a grease
base, but even then the search was on for a less unfriendly replacement.

--
Paul J. Adam

Morgans

June 26th 06, 01:12 AM

"JP" > wrote in message
...
> Here's some links giving more precise explanation. The process is called
> explosion welding (EXW).
>
> http://www.key-to-nonferrous.com/Articles/Article51.htm
>
> The following link is an excellent one
>
> http://www.highenergymetals.com/Engineering%20and%20Design%20Basics%20Web%20Page.p df

Who says you cant learn anything on usenet? <g>

Thanks. I had never heard of explosive welding, until now.
--
Jim in NC