Carbon steel and Aluminum
Carbon steel and Aluminum
(OP)
Hello, I have a situation where an aluminum track will be fastened to an existing structure with grade 5 bolts. The contractor installing the bolts said he will use a copper anti corrosion inhibitor between the steel and aluminum. The aluminum track is being used to clean windows on a high rise. I've done some research into how these metals react with each other, but chemistry has never been my strong point. I'm just looking for some disussion on how these metals react and what is typically used to prevent corrosion. Thanks in advance for the help.





RE: Carbon steel and Aluminum
"Painted on" materials will probably wash away after a few years - I would think.
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
This would not be the first such structure, find out how other people have solved it. Google?
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
Definitely something that needs to be engineered, not left to the installation contractor to slather on some goop. And yes, copper is a horrible choice here.
The aluminum is probably anodized.
The galvanic potential of aluminum varies quite a bit with grade, and so far we don't know the grade.
The bolts are probably plated, and the plating is probably zinc.
Since this is a window washing track there will be chemicals involved. Those chemicals will most likely be alkaline, and if intended to be mixed with water will be mixed at a much higher concentration than instructed on the bottle.
When the probably zinc plated bolts are tightened down on the probably anodized unknown grade aluminum the anodized film will probably crack locally, causing potential sites for highly localized galvanic corrosion to occur.
The probably zinc will corrode preferentially to the aluminum, which is probably the preferred situation. However eventually enough thickness may be lost to allow the bolt preload to go away, which is probably not a really desirable failure mode.
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
I would also wet install the fasteners with sealant (look for a sealant that contains chromates like PS 870 from pro seal).
If someone's life depends on this joint then you want to ensure inspections occur (remove bolts and inspect for cracks and corrosion).
RE: Carbon steel and Aluminum
RE: Carbon steel and Aluminum
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Carbon steel and Aluminum
Teflon washers might help but it seems to me that you will still have moisture enter the joint. Note that teflon is a bad choice if you have a structural joint. The washers will deform over time and let in moisture. High rise, window cleaning, and teflon washers are words I wouldn't want to mix together.
I would definetly wet install with sealant. Further, you can coat the heads and nuts with sealant. If you want to add even more protection to the joint you can coat with corrosion protection compound.