# dissimilar metals - engineers pls help



## allthunbs (Jun 22, 2008)

I remember that stainless steel screws and steel don't mix in damp environments. However, I can't remember if aluminum and steel also suffer dissimilar metal characteristics. I'm trying to rebuild the bottom of my patio door and I need to refasten the tracks. The screws were completely gone.

Thanks for the help


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## RJM (Apr 11, 2010)

allthunbs said:


> I remember that stainless steel screws and steel don't mix in damp environments. However, I can't remember if aluminum and steel also suffer dissimilar metal characteristics. I'm trying to rebuild the bottom of my patio door and I need to refasten the tracks. The screws were completely gone.
> 
> Thanks for the help


Stainless steel screws in an aluminum frame should be fine. Aluminum is so active (anodically) that it will form a protective oxide coating in minutes. Stainless steel is also rendered realatively inactive through passivation. Stainless steel fasteners in aluminum is a commonly used system.


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## allthunbs (Jun 22, 2008)

Thanks very much RJM. Stainless in Aluminum it is then.


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## RStaron (Sep 25, 2009)

I agree with RJM60. Stainless fasteners in Alum. is the way to go.


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## Shortcut (Jan 25, 2010)

*Galvanic*

Hi Ron,
Galvanic bi metalic corrosion can occur between stainless steel and aluminium, ref nobility table.
On aircraft construction for instance a barrier is made between the two surfaces if disimilar metals are to be in contact.......
However as it's only the patio door it;s not likely to experience speeds of mach 2!!!!!
I wouldn't worry about it.


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## Thrifty Tool Guy (Aug 23, 2007)

allthunbs said:


> I remember that stainless steel screws and steel don't mix in damp environments. However, I can't remember if aluminum and steel also suffer dissimilar metal characteristics. I'm trying to rebuild the bottom of my patio door and I need to refasten the tracks. The screws were completely gone.
> 
> Thanks for the help


Try Brass screws


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