steel screws?

I'm confused about either using steel or stainless steel with aluminum. I've read conflicting views on here. What's wrong with using one over the other with aluminum? Thanks

Almost all boat manufactures use stainless. We use stainless and have never had an issue.

I used stainless steel for every bolt or screw on my boat.

Stainless and aluminum together is fine as long as it is not used in salt water. It is normal non-stainless steel that corrodes faster due to dissimilar metals.

screwballl said:

Stainless and aluminum together is fine as long as it is not used in salt water.

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Whats wrong with stainless steel, aluminum and salt? I used stainless on my tin and plan to use it quite a bit in the salt. Everything I've read says to use stainless steel hardware.

lckstckn2smknbrls said:

I used stainless steel for every bolt or screw on my boat.

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+1

mtnwkr said:

screwballl said:

Stainless and aluminum together is fine as long as it is not used in salt water.

Click to expand...

Whats wrong with stainless steel, aluminum and salt? I used stainless on my tin and plan to use it quite a bit in the salt. Everything I've read says to use stainless steel hardware.

Click to expand...

Here is a copy and paste of one of my own posts from last year, in response to a thread debating conventional steel screws (most of which are going to be zinc coated) and stainless steel screws.

Isn't entirely relevant to the question, but it still has a few key points.


"I'm assuming by regular metal, that he is speaking of medium carbon steel screws and bolts (I'm talking grade 2 - grade 8 bolts and most screws sold today). These are all zinc coated. Now, ON PAPER, aluminum with zinc is a much better match than aluminum with stainless steel, which would be the case, IF the aluminum and ss quantities, or the aluminum and zinc quantities identical.

On the aluminum and stainless side of things, the stainless will be the cathode, and the aluminum the anode, due to stainless's lower reactivity. The cathode is the more noble metal, and the anode is the active metal, or the one you will see the corrosion on.

With aluminum v. zinc, the aluminum, having a lower reactivity, will be the cathode, and the zinc the anode.

Therefor, when you have Al plus SS, the Al will corrode, and when you have Al plus Zinc, the zinc will corrode. While it sounds as if you would want the fastener, not the boat to corrode, you have to look at quantities. On a hull, you have hundreds, often thousands of pounds of aluminum, whereas the fasteners used to attach the deck and accessories would equate to just a few pounds. Thus, the stainless fasteners aren't going to have much of an effect on the large mass of aluminum, but the large mass of aluminum will have a major effect on the small amount of zinc.

This is precisely why zinc is used as a sacrificial anode on aluminum boats and outboards, as OEM parts. The zinc is used, as it will corrode first, and thus keeps the natural galvanic corrosion from seawater from attacking the boat. It will favor the anode over the cathode any day of the week and twice on Sunday.

The is NO way to stop all corrosion on aluminum with usual methods. In fact, aluminum would be a virtually useless material if it didn't corrode. Instead, it rapidly oxidizes (as in almost instantaneously), which is why it must be welded on AC current, as it needs the alternating current to break up the oxide layer. Thus, you have to limit the corrosion. Ideally, matching alloy aluminum fasteners would be used, but they aren't practical, from a strength standpoint. Gold and platinum aren't practical from a cost standpoint. Stainless steel is the most commonly accepted medium between cost and function, which is why it is a standard in the marine industry.

If you don't like the way the stainless and aluminum co-mingle, weld them together, with a compatible alloy filler material. It is the best way to ward off corrosion by dissimilar fasteners, as no mechanical fasteners would be used."


I'll follow by saying the stainless steel bolt will slowly corrode the aluminum. I've personally owned boats that had heavy saltwater use in a previous life, and some of the SS fasteners did pit the aluminum a bit. However, had zinc coated steel fasteners been used, the zinc would have been eaten away very quickly, leaving the steel exposed, which too would have corroded quickly, more due to the saltwater than the dissimilar metals contact.

Without getting into more costly metals (nickel, platinum etc), stainless is the best bet. A good sealant (5200) will help isolate the metals to keep the aluminum from pitting, as would installing a zinc anode to the hull.