stainless steel bolts on aluminum structure

[rj1939]

I am wanting to build a weather resistant structure, out of aluminum, but what I read, stainless fasteners aren't compatible with aluminum....................how much of a problem is this in the real world? Is there a way to make it work?

 

[Ries]

Depends what you are doing.
I built a bench, in 1978, in a public place, all aluminum structure, Stainless bolts. It was outside, in Seattle weather for close to 20 years. I ended up rebuilding it, in about 2002, and when I took it apart, zero galvanic corrosion between the bolts and the aluminum flat bar. Some aluminum oxide on the aluminum, but thats normal.
This was about 4 miles from the Salt Water.

Is this a situation where failure will cause injury or death?
Is this a situation where you must warranty this, and, if anything happens, you are on the hook for big bucks?
Is this a situation where you will never be able to check up on it?
Is this on a seagoing boat, or in a chlorine heavy environment like an indoor pool?

If no to all of the above, I wouldnt worry about it.

 

[gustafson]

Outside of salt water simply not an issue

Now if you wanted to use aluminum bolts on a stainless structure that could be a problem

It is not just galvanic corrosion, it is the direction of the material loss

Pop rivets in a stainless sheet might[or might not] disappear

Pretty much everyone who rants about galvanic corrosion in situations that are not constantly immersed are just quoting theory and not experience.

 

[plastikdreams]

Tell that to my magnesium ocean-going sailboat with the carbon keel...

[Stored near the seashore, came back and it was gone]

More seriously, I've seen bare Al attacked when used on the underside of cars in the salt belt.

Really though...what metal doesn't get attacked in the salt belt on cars lol.

 

[john.k]

In fact ,plain steel bolts work OK with ally in the weather.....reason being ,its like attaching a giant sacrificial anode to each bolt......Galvanized bolts also work with ally structures,Zn and Al seem to get along together quite well......The problem with austenitic stainless steel ,is its very susceptible to hydrogen embrittlement ....which mild steel is not ..........and austenitic stainless is costly .

 

[gustafson]

Tell that to my magnesium ocean-going sailboat with the carbon keel...

[Stored near the seashore, came back and it was gone]

More seriously, I've seen bare Al attacked when used on the underside of cars in the salt belt.

well, you should have checked the scrapyards


salt eating aluminum on cars is less than salt eating steel, and doesn't stop them from using it.

 

[Trboatworks]

I am wanting to build a weather resistant structure, out of aluminum, but what I read, stainless fasteners aren't compatible with aluminum....................how much of a problem is this in the real world? Is there a way to make it work?

Just use Lanocote or an equivalent on threads.

This stuff stands up with stainless fasteners into aluminum for marine applications:

Amazon.com: Lanocote Corrosion Control 4 Oz. : Automotive

 

[BT Fabrication]

I am wanting to build a weather resistant structure, out of aluminum, but what I read, stainless fasteners aren't compatible with aluminum....................how much of a problem is this in the real world? Is there a way to make it work?

I build with stainless and aluminum all the time, zero issues. you just dont want aluminum and mild steel or aluminum and copper or brass.

 

[greif1]

If you want to hedge your bets a bit, fasteners made from 316 or 316L have improved corrosion resistance.


Some of what has been said already, but a bit less antidotal ;

Stainless Steel & Aluminum: Why You Shouldn't Use Them Together and Proper Precautions To Take If You Do - Albany County Fasteners
The other situation in which these materials can be used together with little impact on rust prevention is if the cathode area is very small when compared to the anode area. For example, if the base material is a large sheet of aluminum, then using very small stainless steel screws will not dramatically decrease the life. Conversely, if you use aluminum to attach a large sheet of stainless steel, the aluminum life will be dramatically shortened.

 

[triumph406]

I did a project where we put a brass fastener into aluminum, then into a bucket of Pacific seawater. Didin't take long to get really ugly

Then tried Ti, the 6061 part and the Ti part have been in the same seawater bucket (covered to prevent evaporation) for 10+ years, not a hint of corrosion.

Ti good, Brass bad, that's all I can offer.

There are plenty of galvanic tables that will tell you compatibility between materials.

----------------------------

If your structure isn't immersed in a bucket of seawater, or less than 2 miles from the ocean you'll be ok

 

[Bondo]

Really though...what metal doesn't get attacked in the salt belt on cars lol.

The cat doesnt corrode because it's already been cut off and scrapped


I build quite a fee things in good facilities with alum frames and SS 304 hardware, never had a problem. But those people usually use CO2 for washdown

 

[gustafson]

I did a project where we put a brass fastener into aluminum, then into a bucket of Pacific seawater. Didin't take long to get really ugly

Then tried Ti, the 6061 part and the Ti part have been in the same seawater bucket (covered to prevent evaporation) for 10+ years, not a hint of corrosion.

Ti good, Brass bad, that's all I can offer.

There are plenty of galvanic tables that will tell you compatibility between materials.

----------------------------

If your structure isn't immersed in a bucket of seawater, or less than 2 miles from the ocean you'll be ok

Galvanic tables are the start of the problem. They tell you something but not really everything. Lots of people[here] act like having a galvanic potential is going to be a problem, well, it can be, but frequently isn't

Again, outside of immersion in salt water, stainless bolts in an aluminum object are not a problem.

Galvy bolts are such junk and always have been, that I use stainless for everything outdoors, non structural items on the car, everywhere.

I replaced all the small exterior hardware on a car that I bought in 1984 with SS, you know those little screws that hold tail light lenses on that clean right the fook off when you look at them? Come right out

38 years later.

 

[rcoope]

There is also the example of dinghy and yacht rigging. There are literally hundreds of thousands of extruded and anodized aluminum spars with stainless shroud connection plates and rivets, stored outside in all kinds of weather and all over the world with no routine corrosion problems. What I don't know is what alloys are involved. "Marine grade" hardware is super expensive but is that yacht industry markup or is it because these parts are all 316LVM and if so, what would happen if they were 304?

 

[gustafson]

There is also the example of dinghy and yacht rigging. There are literally hundreds of thousands of extruded and anodized aluminum spars with stainless shroud connection plates and rivets, stored outside in all kinds of weather and all over the world with no routine corrosion problems. What I don't know is what alloys are involved. "Marine grade" hardware is super expensive but is that yacht industry markup or is it because these parts are all 316LVM and if so, what would happen if they were 304?

My neighbor at work has a center console boat with aluminum super structure.

held on with ss hardware

15 years old


still perfect


has never, in its existence, been more the 500 yards from salt water

sits in salt water from May to October


I took a pic this afternoon but am too lazy right now to post it



galvanic corrosion is a problem with objects submerged in an electrolyte.

everything else is just corrosion, and yes galvanic can be contributing, but not the primary driver

 

[Trboatworks]

Years back we were preparing for a modest voyage and I decided that my responsibilities as skipper required I take a cursory glance into the bilges.
It was a bit of a shock as I found the nuts on the keel bolts were totally gone- corroded to heaps of dust in the bit of water there.
I think one half crescent of nut remained but that was it.
The keel bolts were spotless.

Well I ran out and bought a new set of washers and nuts and we carried on.

Those were the good old days when we still got out on the boat….

 

[Strostkovy]

We see the aluminum oxidize under the washers on some of our products. Structurally it's no issue.

I find zinc plating to be more compatible with aluminum in terms of visible corrosion, but you only have that thin layer of zinc protecting the steel bolt so it's not for all applications.

I would guess that black oxide stainless would be a good option but I have little more than anecdotal experience with those.