Preventing corrosion when mounting camper to aluminum flatbed with bolts

[ReluctantTraveler]

A lot of flatbed campers (like the ones from Four Wheel Campers) are mounted with bolts to aluminum flatbeds.

All of the grade 5/8 bolts I'm seeing are made of steel. How do you avoid corrosion as that steel comes in contact with the aluminum bed?

 

[Hummelator]

You could sleeve them and add nylon washers on either side but I wouldn’t worry to much about doing that. I’d just switch out the mounting bolts periodically ( conditions dependant)

 

[ReluctantTraveler]

You could sleeve them and add nylon washers on either side but I wouldn’t worry to much about doing that. I’d just switch out the mounting bolts periodically ( conditions dependant)

Oh, is it just the steel that corrodes? I was under the impression the steel damaged the aluminum as well?

 

[NatersXJ6]

Look up galvanic series chart with enough details to show your specific steel and aluminum alloys. Even with the chart in mind, it can be really difficult to estimate without deep experience. In many fields, there is an entire career available just in corrosion engineering and corrosion prediction. You can split a lot of hairs there to no real value gain.

In real world conditions, not floating in seawater, there probably isn’t a huge difference over the life of the parts. Are you trying to build a 500 year camper, or one that lasts 20-30 years before an overhaul?

Personally, I would use thick attachment points and thick bolts. Maybe go so far as to use hot dipped galvanized bolts, torqued to minimize movement, and then go camping.

 

[ReluctantTraveler]

Look up galvanic series chart with enough details to show your specific steel and aluminum alloys. Even with the chart in mind, it can be really difficult to estimate without deep experience. In many fields, there is an entire career available just in corrosion engineering and corrosion prediction. You can split a lot of hairs there to no real value gain.

In real world conditions, not floating in seawater, there probably isn’t a huge difference over the life of the parts. Are you trying to build a 500 year camper, or one that lasts 20-30 years before an overhaul?

Personally, I would use thick attachment points and thick bolts. Maybe go so far as to use hot dipped galvanized bolts, torqued to minimize movement, and then go camping.

I'd love to get 20+ years out of it, for sure! But yea, my priority is to not have it fly off the flatbed because the bolts fail. ???

 

[NatersXJ6]

I'd love to get 20+ years out of it, for sure! But yea, my priority is to not have it fly off the flatbed because the bolts fail. ???

Yep, think about other things joined with dissimilar metals. Aluminum heads bolted to Iron blocks, or steel bolts holding aluminum brackets onto an engine… yes they can corrode and even fail, but the likelihood is low and there is usually a contributing cause, like an antifreeze leak or something similar that creates a bigger problem. The problem wasn’t the dissimilar metal bolts… that just looks like the problem… in reality it is elsewhere.

 

[jmmaxus]

I’m designing an aluminum trailer and I plan to use Zinc Aluminum coated bolts and nuts aka ultra coat or armor coat. They are steel but the coating should prevent corrosion.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

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[Alloy]

I’m designing an aluminum trailer and I plan to use Zinc Aluminum coated bolts and nuts aka ultra coat or armor coat. They are steel but the coating should prevent corrosion.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Sent from my iPhone using Tapatalk

These are medium grade so you could upsize and use stainless.

Add a layer of UHMW tape to the washers

Slippery (Low-Friction) Tape - Lee Valley Tools

www.leevalley.com

Make sure to use some Tef-Gel and you'll be good + be able to take it apart. A little (2 grams/bolt) goes a loooong way.

hmmm?? the system won't let me post the link to TG-01 syringes of Tef-Gel on Amazon

 

[ChasingOurTrunks]

A bit of Never-Seez on the bolts will deal with any issues you are likely to see between overhauls.

Never Seez Pure Nickel Special NSBT-16N (16 oz. Brush Top)

Never Seez NSBT-16N Pure Nickel Special contains a high-quality bearing grease with pure nickel, graphite and other additives found to enhance anti-seize performance.

neverseizeproducts.com

In my aluminum truck cap, I also only used stainless hardware but it was all small and it’s expensive. For big bolts the stuff above is good at preventing corrosion and wrecking of the threads from dissimilar metals.

 

[jmmaxus]

These are medium grade so you could upsize and use stainless.

Add a layer of UHMW tape to the washers

Slippery (Low-Friction) Tape - Lee Valley Tools

www.leevalley.com

Make sure to use some Tef-Gel and you'll be good + be able to take it apart. A little (2 grams/bolt) goes a loooong way.

hmmm?? the system won't let me post the link to TG-01 syringes of Tef-Gel on Amazon

There are Grade 8 bolts as well with the same coating available on that site


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[Hummelator]

Oh, is it just the steel that corrodes? I was under the impression the steel damaged the aluminum as well?

To be perfectly honest, my experience with galvanic corrosion/ corrosion in general in with the overhead doors you often see In the automatic car washes at gas stations and the like. The door panels are aluminum + polycarbonate and the fasteners are generally just standard galvanized.
the chemicals they use to wash car is surprisingly harsh and usually the panels hold up quite well and the fasteners are generally the first To deteriorate.

 

[Alloy]

just use your favourite galvanised fasteners

Consider using Anti-seize, its a good idea on most anything.

If there's road salt around I wouldn't put galvanized one bare aluminum. At the very least I'd use UHMW tape on the washers.

Ani-seize contains different metals and chemicals plus water so the opposite will happen.

 

[ReluctantTraveler]

I DO actually live in a coastal salt zone (best of both worlds for corrosion)!

 

[Natedog57]

Dissimilar metal corrosion or galvanic corrosion attacks the weaker metal first... although both metals will begin to degrade.

I am familiar with SS and aluminum in contact in marine (salt water) applications, and the aluminum sees the most damage when in contact with each other.

Spacing these metals apart via a nylon washer as mentioned above is about the best way to prevent this corrosion.

Since the OP is discussing using a Steel fastener, I would recommend using a special coated Grade 8 bolt such as: https://www.fastenal.com/product/details/11137295. The coating on this bolt should offer the best corrosion resistance available in a G8 fastener, arguably better than Hot Dipped Galv. many are familiar with, which isn't commonly available in G8 anyways.

Anti-seize on the threads of the bolt should help ensure you can remove the nut after a period of time, especially since there is the concern/possibility of the Steel bolt experiencing corrosion from coastal/road salt.

I think Nickle based anti seize is preferred over Copper when applied in contact to aluminum.

Simply keeping the undercarriage cleaned via regular fresh water rinsing would probably also meaningfully extend the life of all components.

 

[ReluctantTraveler]

Dissimilar metal corrosion or galvanic corrosion attacks the weaker metal first... although both metals will begin to degrade.

I am familiar with SS and aluminum in contact in marine (salt water) applications, and the aluminum sees the most damage when in contact with each other.

Spacing these metals apart via a nylon washer as mentioned above is about the best way to prevent this corrosion.

Since the OP is discussing using a Steel fastener, I would recommend using a special coated Grade 8 bolt such as: https://www.fastenal.com/product/details/11137295. The coating on this bolt should offer the best corrosion resistance available in a G8 fastener, arguably better than Hot Dipped Galv. many are familiar with, which isn't commonly available in G8 anyways.

Anti-seize on the threads of the bolt should help ensure you can remove the nut after a period of time, especially since there is the concern/possibility of the Steel bolt experiencing corrosion from coastal/road salt.

I think Nickle based anti seize is preferred over Copper when applied in contact to aluminum.

Simply keeping the undercarriage cleaned via regular fresh water rinsing would probably also meaningfully extend the life of all components.

Thank you so much for this! Exactly the kind of detail I needed. Much appreciated, friend!