Dissimilar metal question

[Jim and Chris Neuman]

Coming from the sailing world I am a touch sensitive about corrosion brought on by dissimilar metals in close contact.

Has anyone seen any issues arising from use of the Anderson system where the steel brackets come in contact with the aluminum frame?

 

[Frank C]

44 minutes ago, Neuman's said:

Coming from the sailing world I am a touch sensitive about corrosion brought on by dissimilar metals in close contact.

Has anyone seen any issues arising from use of the Anderson system where the steel brackets come in contact with the aluminum frame?

 

I haven’t seen any issues with the Andersen steel frame brackets or with the Oliver galvanized steel subframe for the suspension causing any problems with the Oliver aluminum frame (yet).  Steel, zinc and aluminum are all pretty close to each other on the galvanic series chart, which means minimal galvanic reaction (but not zero).  This is from my good old metals handbook.  The farther apart two metals are on the chart, the greater the galvanic corrosion reaction.  This is seawater exposure so pretty much a worst case, but road salt & moisture would be just as bad.  The order can change a little depending on the exact environment.   As an example, 316 stainless against aluminum is very bad.   And the lower number metal becomes the sacrificial material in the pair.   It’s why zinc is used as a sacrificial anode in a lot of systems with dissimilar metals and water, like boats and water heaters.  A dielectric material barrier between the metals helps, even a layer of paint.  And if the aluminum is anodized, that helps as well. 
 

Edited March 15, 2021 by FrankC

[John E Davies]

Where would aluminum 6061T6 fall on that chart? I think this could be a real problem if you tow in winter over salt or mag chloride treated roads. Oliver uses plenty of 304 stainless fasteners like self tapping screws all over the frame and I have never seen any issues. I also haven’t seen any degradation of the anodes. OTH I neither tow on wet roads (except when it is unavoidable) nor in winter. I think it would be a good topic for long term monitoring from those owners who use their rigs year round, for skiing especially. But IMHO those units will be suffering from far more extensive damage to the frame, running gear and exterior steel fittings than a little localized dissimilar metal corrosion. I have only seen underneath one such (admittedly neglected) Ollie, and frankly it was a disgusting mess. I don’t think the factory would offer a five year frame warranty if they felt it was not durable, but maybe they would consider prolonged caustic chemical exposure to be abuse...

John Davies

Spokane WA

Edited March 15, 2021 by John E Davies

[Frank C]

6 minutes ago, John E Davies said:

Where would aluminum 6061T6 fall on that chart?

I'll have to dig a little deeper but most of the galvanic charts just lump all "aluminum alloys" together, so 6061 probably isn't much different, close to steel and zinc.   The use of a stainless screw threaded directly into the aluminum frame could be a long term issue if towing on salted roads in the winter.

Edited March 15, 2021 by FrankC

[John E Davies]

One more comment, if you do bolt on an aluminum part to the Ollie steel subframe, use a good bedding/ barrier sealer. While it may not be 100% necessary, it could help a lot.

John Davies

Spokane WA

Edited March 15, 2021 by John E Davies

[Jim and Chris Neuman]

Good point on the bedding compound.   

Masts, booms, whisker poles & other common high-load components in sailboats typically use 6061 T-6 alloy.  Fasteners used to attach hardware is typically 18-8 stainless.  An anti-sieze compound such as lanolin applied to the threads can go a long way toward keeping bolts free and preventing snapping off of fastener heads ...  a stainless fastener can become extremely difficult to impossible to remove if installed dry into aluminum with no anti-sieze.

[Frank C]

2 hours ago, Neuman's said:

Good point on the bedding compound.   

Masts, booms, whisker poles & other common high-load components in sailboats typically use 6061 T-6 alloy.  Fasteners used to attach hardware is typically 18-8 stainless.  An anti-sieze compound such as lanolin applied to the threads can go a long way toward keeping bolts free and preventing snapping off of fastener heads ...  a stainless fastener can become extremely difficult to impossible to remove if installed dry into aluminum with no anti-sieze.

18-8 is a good choice for that environment, and any anti-seize or thread-locker will help to interrupt the conductive path that causes the galvanic reaction.  You mentioned lanolin, and like every other subject on the internet, you can find pro and con arguments about lanolin as a anti-seize/corrosion inhibitor.   Here's an example from the sailorsolutions.com website, for anti-seize products.  One brand (teflon based) of course mentions that the use of lanolin in a competitor product is not ideal:

"Tef-Gel® is a US Navy specified non-lanolin synthetic formulation.  Lanolin, (an extract of wool) used as the base for the popular anti-seize product can absorb small amounts of moisture which will allow for corrosions and seize your stainless steel to aluminum joint after a few years. The paint will blister in the surrounding area.'

But lanolin has a lot of history to back up its use, and the marine world is a good example to follow with the Oliver.  The Ollie is built more like a boat than a typical sticks and staples SOB trailer.

Edited March 15, 2021 by FrankC