Aluminum with Steel screws 2

[JonathanDube]

We have 1/16" Aluminum sheeting screwed with steel self taping screws. The product gets heated 160°C maximum in a 50-70 % humidity environment. We are wondering how long (very approx.) could the thread hold the screw in place without being all "eaten up" by corrosion.

Thank you
Jonathan Dubé physics tech.

 

[KENAT]

You say steel screws.

Do you mean steel presumably zinc plated, or stainless steel.



KENAT, probably the least qualified checker you'll ever meet...

 

[0707]

In that aluminium thickness why don´t you use aluminium alloy rivets?

 

[JonathanDube]

Yes...sorry, I meant Zinc screws. I was about to change all the screws for Aluminium screws because of the corrosion (Zinc+Aluminium) But first, I need some advice about how fast corrosion can deteriorate the screw thread... I heard that there was no problem for about 2 years. On the other side, some told me that the chemical reaction Aluminium+Zinc would deteriorate threads pretty quicly and cause a nice little mess on the product.

 

[KENAT]

We used to avoid stainless fasteners into aluminium in Aerospace/Defense.

In fact we rarely threaded into aluminum at all, usually helicoil or similar.

On at least one design I remember using zinc plated steel pins in aluminium because of concerns over using stainless.

They lasted pretty well in a salt spray test, both with plain and anodized aluminium.

Of course this isn't threads where there are more traps etc so I guess I don't really know.

Sorry

KENAT, probably the least qualified checker you'll ever meet...

 

[israelkk]

The zinc coating will go first. It will sacrifice itself to protect the aluminum because it touches bare aluminum when it self tapping the aluminum sheet. So, nothing will happen to the aluminum thread as long as there is zinc on the screws. How long it will take this is a different question. In the aerospace business when aluminum sheet is riveted to the aircraft structure the instructions are to dip the rivets in a wet zinc chromate primer just before instaling the rivets.

 

[KENAT]

When I said they lasted pretty well I meant they were strcuturally sound. They looked like #%@#$^@#.

If Aesthetics is a concern then in your environment zinc plated may be a concern.

KENAT, probably the least qualified checker you'll ever meet...