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apposing metals and corrosion??

A

Anonymous-0

Well-known Member
pretty much talked myself outta the oxy/acetyline or propane torch for now. Just can't justify the price. Still need to patch my fenders tho... Just saw some aluminum step plating (diamond plate??) that is just the ticket as far as the width I need. Just have to cut it to length and bend a right angle on one end. Thought I'd just cut/clean the rusted area, prime it, then undercoat the area of the patch and pop rivet it in place. See any problems? Not supporting anything, just cosmetic and getting rid of some snags.

I know the best thing is to weld in a patch of sheetmetal, but getting it is not real convenient. I can get the aluminum, stainless, and galvanized sheet metal at the BB store on the way home.
 
Ya know you can weld up cracks in fenders with 7018 3/32, I have done it lots and I aint a welder. but your idea is OK to iffin yous a redneck...lol
 
Sounds like a plan there dave, yeppers two dissimilar metals creates a battery via galvanic action which leads to corrosion and property changes...... That aluminum diamond plate sure looks good at least until oxidation dulls it grrrrrrrrr At some RV shows they have some expensive but very effective cleaner/polish that shines that aluminum back up but I cant get the first wife to cooperate lol

John T
 
never thought of the corrosion on the surface... Was thinking more of in between the two surfaces... Guess I'll rethink it a little. Saw the neighbor throwing out some car fenders this morning, if they are still there when I get home, I'll snag a couple and practice welding on them with the stick welder..... then just do the job right....

Thanks
 
Despite galvanic action which sure does exist, I dont see it as all that much of a worry, its NOT like things will rust and oxidize away and fall part at that aluminum/steel junction in the next few weeks lol. Also, rusting or corrosion requires oxygen (Oxidation DUH) so if oxygen is kept away (or two metals arent in actual contact) with coatings or silicone etc etc it may take several weeks before them fenders fall off lol

That bright shiny aluminum diamond tread plate is so purdyyyyyyyyyy go ahead n use it n send us pictures !!!!!!!!! (Its so fun to be compassionate with and spend other peoples money money lol heck that makes me a abundant grrrrrrrrr)

Take care dave

John T
 
lyle,

A redneck would cover the crack with duct tape.

A redneck may use screws instead of pop rivets.

I should know, I lived with rednecks for 10 years and have a degree from RT, Redneck Teck.

I wouldn't worry about electrolysis between iron and aluminum. Cover it with horse poo and forget about the rust.

George
 
Could you flaten out the bad areas and paint some bedliner on it using the stuff you roll on. This stuff can be rolled on and you can make it whatever thickness you want, just don't get it on you as it is there for a while.
 
(quoted from post at 13:04:12 11/02/12) lyle,

A redneck would cover the crack with duct tape.

A redneck may use screws instead of pop rivets.

I should know, I lived with rednecks for 10 years and have a degree from RT, Redneck Teck.

I wouldn't worry about electrolysis between iron and aluminum. Cover it with horse poo and forget about the rust.

George
Click to expand...
m thinkin I gots the same degree, you should see some of the chit I do...lol
 
(quoted from post at 05:06:33 11/02/12) Could you flaten out the bad areas and paint some bedliner on it using the stuff you roll on. This stuff can be rolled on and you can make it whatever thickness you want, just don't get it on you as it is there for a while.
Click to expand...

Yes, but don't know if it's available over here. Don't think I could get it in the mail. Can you tell me of one (brand)you think is best so I can look into it. Maybe find something here compareable. I would do the whole fenders with it and my foot boards/step.

Thanks.
 
Aluminum alloys vary greatly in their resistance to corrosion. Most hardware store aluminum is 6061, which has reasonably good corrosion resistance.

It's a very common practice in aircraft construction to rivet aluminum and steel sheet metal together. The main thing is to bond the "fretting surfaces" so water can't get between them. Typically the surfaces are primed with zinc chromate or epoxy primer and assembled wet. You can also use a polysulfide or polyurethane sealant for the same purpose. (Silicone is no good because paint won't stick to it.)
 
The <a href="http://en.wikipedia.org/wiki/Metal_reactivity">table</a> in the link shows the relative reactivity of metals. The lower on the table the more stable. If you attach a higher element (like aluminum or zinc when something is galvanized) to a lower one (like iron) the higher one will corrode and protect the lower one. So an aluminum patch will corrode away, but it should prevent any steel that is next to from corroding.

As a side note, the sacrificial anodes that I specify for offshore oil and gas installation are usually some sort of aluminum alloy.
 
Actually it's "faying surface". You don't get fretting unless you have relative motion (or micro-motion) between surfaces.
 
Dave, you can use a suitable material to create a "bond-break" to effectively, separate contact between the 2 dissimilar materials, thus preventing galvanic action. I used to deal with it all the time on high rise construction especially structural connections between exterior metal and glass components and the superstructure, its actually a very important detail to get right in those conditions. Pipe fitters will install Dielectric Unions when making a transition from say copper to galvanized or any similar combination.
 
Dave, as a suggestion, clean both top and bottom with lacquer thinner cleaner, apply J.B.Weld top and bottom . Sand,Prime then rivet the diamond tred plate reprime rivets, repaint heads or apply J.B weld to underneath fender where rivet heads are exposed. Should be good to go for years. JMO. LOU.
 
The problem is not in the metals themselves, it is
in the CONTACT between dissimilar metals. Toss in a
conductive environment (saltwater, mud, ect....),
and let the corrosion begin. Yes, the aircraft
industry will rivet dissimilar metals together, but
when they are destined to be in a "conductive
environment" (such as Navy/Marine aircraft), they
put a break between the two. A good substance for
this is a good sealant like butyl rubber. A GOOD
paint also works.
 
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