[Artie F. Emm]

A friend asked me to modify a steel bolt in a particular way, and I later learned he wants to use it on an anodized aluminum truck rack. I told him he may run into galvanic corrosion, with dissimilar metals in contact.

Depending on how he wants to go, I may suggest we work up a part using aluminum, but the aluminum stock I have is not anodized. Does galvanic corrosion occur between anodized aluminum and non-anodized / raw aluminum?

[Poland308]

Any two metals that are discimilar in any way will have some sort of galvanic corrosion. However unless it will see flowing liquid or flowing electricity. I.E. Grounding for lighting on a car. Then the corrosion will probably be irrelevant. Exposure to salt brine / or ice melt will also make things more susceptible to this type of corrosion. But then again salt water corrodes almost anything.

[Arno]

Galvanic corrosion is always an issue but especially on fasteners/bolts it's often not possible to go to alumiunium as the strength is much less.

It's fairly easy to prevent most of the galvanic reaction by adding some sort of insulation between them. This can be various things.. Eg.:

• (if suitable for the loads) Using nylon or other plastic washers between any steel washers that will contact the ali
• Painting/coating the surfaces that get into contact so there's little to no metal-on-metal contact
• Use an active galvanic inhibitor on contact-surfaces between the materials like Tef-Gel, Duralac or similar

The key is to break any current path between the parts and keep moisture out that will create the actual electrolytic 'cell' between them.

Once you do that then the galvanic reaction will be very manageable.

Maritime users are of course constantly battling this with dis-similar metals on various ships and vessels (eg. steel hull, stainless railings, aluminium masts/cranes, etc. and add in a nice dose of salt water..) and they have developed at lot of things to combat it.

Bye, Arno.

[Artie F. Emm]

Thanks for your response, Josh. We started to look into the fixturing for this, and all (or most) of the commercial T-slot nuts are steel, so we figured the problem couldn't be that bad. And even tho the nuts are $3 each at McMaster.com we spent a few minutes welding one up out of a nut and some washers.

[Oilman]

If you are really concerned about the bolts/nuts consider painting them with a thinned coat of aluminized paint. It may tighten up the threads but this may just function like a thread locker. The auto industry uses aluminized steel for heat shields. This is a process similar to hot dipped galvanizing but with aluminum being the majority of the dip bath.

Besides the rack might look nicer with bright bolts. Of course if the anodized rack is of a different color then you might simple find a paint that is similar. Another thought is to spray on a thin clear coat to act as a conductive/corrosion barrier.

[Artie F. Emm]

Good ideas, I'll run them by my friend. He's impressed with the selection at McMaster and has other t-slot applications on his woodworking equipment so I think he's planning to buy from there. A shot of clear coat sounds like a smart move.