Removing zinc plating from aluminum screws

num pergola I'm building

obably anodize the screws). I Googled it and found a couple tutorials aroun d using citric acid and another using another type of acid. However, when I went to the hardware store, they had nothing of the sort.

ng enough acid) ? Thanks!

Tractor Supply Co sells Citric acid. It is used by farmers to clean milkin g machines and such.

But why remove the zinc plating. It is there to reduce galvanic corrosion.

Dan

I'd like to remove the zinc plating to reduce galvanic corrosion (I'll probably anodize the screws). I Googled it and found a couple tutorials around using citric acid and another using another type of acid. However, when I went to the hardware store, they had nothing of the sort.

Any suggestions for the best way to go about this (or where to get a strong enough acid) ? Thanks!

I think you have a bigger problem. I don't think you have aluminum screws. I have never heard of aluminum lag screws (it seems like an extremely poor application for aluminum) and can see no good reason why they would be zinc plated (I am not sure it is even possible). I can see a good reason why normal steel lag screws would be zinc plated. When I search for the part number, sku, or upc code, it comes up as Zinc Plated Steel Grade 2 everywhere except the amazon page.

I think someone goofed when they were writing the specs. If you look a bit farther down the page:

"Product description

Zinc Plated Steel Grade 2 - Manufacturer: Hodell-Natco Industries."

I've got some small aluminum wood screws that were used to fasten my storm windows to the trim. They are maybe a #8 and 1/2 inch long. It doesn't take a lot of torque to twist the head off with a slotted screwdriver...

I would use some Anti-seize like:

generously on the threads or a thick grease, like wheel bearing. I've had good results through the years using either of them...

Yeah, if that screw is aluminum, it looks like it would twist right off. Something isn't right there.

FWIW, though, galvanized platings are sometimes used to protect aluminum. The galvanic potential of the two metals is close but the zinc would still corrode preferentially. It is used in some marine environments.

Stripping it off would be a mistake in any case. Any galvanic corrosion would attack the zinc and protect the aluminum. Ordinary muriatic acid (dilute hydrochloric) is what I use to strip galvanizing off of steel EMT tubing for brazing or welding, but it will also attack aluminum.

num pergola I'm building

obably anodize the screws). I Googled it and found a couple tutorials aroun d using citric acid and another using another type of acid. However, when I went to the hardware store, they had nothing of the sort.

ng enough acid) ? Thanks!

Thanks for the input, everyone.

Any idea what people use, then? I know pergolas (and other structures) made from aluminum are quite common. Surely they have some mechanism for attach ing the aluminum to the ground, wall, or in my case parapet wall.

I don't mind just using these screws, assuming they're zinc-plated steel. I just was worried about galvanic corrosion over time.

Thanks for the input, everyone.

Any idea what people use, then? I know pergolas (and other structures) made from aluminum are quite common. Surely they have some mechanism for attaching the aluminum to the ground, wall, or in my case parapet wall.

I don't mind just using these screws, assuming they're zinc-plated steel. I just was worried about galvanic corrosion over time.

You could electrically isolate the bolts by using a plastic sleeve and washer to keep the steel screw from actually touching the aluminum.

Right. Unless you isolate them like that, either the fastener or the abluminum being fastened is going to corrode eventually. In the case of common steel fasteners, they'll corrode first -- and it's generally simple oxidation of the steel, not galvanic corrosion in the presence of aluminum in a galvanic "cell." Theoretically, the aluminum should protect the steel but it usually does not.

Google "fasteners for aluminum" and read a few of the explanations. You'll see what's used in industry, and why, with plenty of examples.