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08-16-2023, 07:07 PM
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#1
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Junior Member
Join Date: Aug 2023
Posts: 5
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Why steel screws shouldn't be used in aluminum
My antenna was leaking two of the screws were still threaded in to the frame the rest rusted away corroding the aluminum roof.
I don't understand why RV manufacturers continue to do this to us?
This is what's left of the roof.
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08-16-2023, 07:14 PM
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#2
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Junior Member
Join Date: Aug 2023
Posts: 5
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My fix
Aluminum roof, aluminum flashing, aluminum pop rivets lexel sealant.
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08-16-2023, 07:14 PM
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#3
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Senior Member
Join Date: Mar 2012
Location: Florida panhandle
Posts: 1,305
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steel into aluminum is fine if sealed correctly……every year
__________________
2018 Adventurer 19RD 19’ 11”
Ford E350 V10 Cutaway Chassis Class C
#10050 GVWR, #18500 GCWR Smoke that!
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08-16-2023, 08:58 PM
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#4
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Senior Member
Join Date: Feb 2020
Posts: 821
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Steel and aluminum form a galvanic couple. To get galvanic corrosion moisture and an electric current. The moisture in the air and static electricity is enough. You shouldn't have steel and aluminum in contact. The best thing you can do is seal the contact areas to keep the moisture out. Usually this means dipping the screw in something before installing it. I used lithium grease on an umbrella fitting I made that sat outside for 7 years. I took it a part and it had zero corrosion. Other thread sealers should work, you have to remember to coat under the head as well. If you install a steel part on an aluminum part you need to prevent the contact and seal the surfaces as well. Paint works well. On the other hand, I had a garden hose with an aluminum end fitting that screwed on to a hose bib. After a few months, I went to take them a part and the hose bid tried to unscrew from the wall. I had to use a pipe wrench on the hose bib and channel locks on the hose. The moisture was from an obvious source the electricity from static from the water flowing through the hose.
Iron Pipe and Copper pipe are also a no no. You are supposed to have a dielectric union between them.
__________________
Tom
2017 RAM 1500 4x4 5.7 HEMI
2015 PCW ECON 18RBS
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08-17-2023, 08:29 AM
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#5
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Senior Member
Join Date: Jul 2017
Posts: 985
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hope you plan on sealing those rivits and edge of that sheet
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08-17-2023, 10:39 AM
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#6
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Senior Member
Join Date: Nov 2018
Location: Beaver Dam, Wisconsin
Posts: 5,902
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I suspect some of the statements above are factually incorrect. The situation is more complicated than they state.
Proper steel hardware holding on aluminum aircraft wings are standard. See instructions for assembling Vans Aircraft kit planes.
Zinc plated screws will fail sooner or later with or without contact with aluminum. Once screws have begun to failed, constant wet conditions will take out aluminum as well as many other materials.
Joint vibration in wet environments removes the protective oxide from the bare aluminum. Chemicals in near by particle board can also corrode aluminum.
Zinc plated hardware in automotive environments are cheap, but bound to fail soon.
Some aluminum alloys are more resistant to wet corrosion than others.
The conditions shown should have been evident well before failure occurred. Remove and replace rusting plated hardware. I usually replace with stainless steel in situations like those shown above.
On new zinc plated hardware under a travel trailer, I prime and paint heads and protruding threads well before corrosion starts. The paint also serves to seal in many cases.
__________________
Paul Bristol
Kodiak Cub 176RD
Nissan Pathfinder 2015
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08-17-2023, 04:47 PM
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#7
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Senior Member
Join Date: Feb 2020
Posts: 821
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This is a good write up about galvanic corrosion.
link
There is also a NASA Marshall Space Flight Center document out there that talks about Stress Corrosion Cracking, which is a different phenomena and how different aluminum alloys, tempers, and forms are resistant to SCC.
__________________
Tom
2017 RAM 1500 4x4 5.7 HEMI
2015 PCW ECON 18RBS
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08-21-2023, 08:26 AM
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#8
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Senior Member
Join Date: Jan 2021
Location: Independent Republic of Horry
Posts: 565
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Simple rule: do not mix magnetic and non magnetic.
__________________
2018 Ram 1500, 2020 Cougar 22RBS
Just the 2 of us and 2 Jacks on the roam.
Meet us at Olympus Mons. Gone Traveling.
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08-21-2023, 11:25 AM
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#9
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Moderator Emeritus
Ford Super Duty Owner
Join Date: Aug 2000
Location: Bryan, TX when not traveling.
Posts: 22,975
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Here are some write up on galvanic actions on dissimilar metals'
Galvanic action
Ken
__________________
Amateur Radio Operator (KE5DFR)|No Longer Full-Time! - 2023 Cougar 22MLS toted by 2022 F150, 3.5L EcoBoost Tow Max FX4 Lariat Travel with one Standard Schnauzer and one small Timneh African Gray Parrot, retired mechanical engineer
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