Stainless Steel Fasteners and Auminum

[ReverenceEng]

Sample situation:

Aluminum angle ledgers attached to wall, wall sign with aluminum angle stringer to hang off ledger. What type of bolts are best to fasten along the length (exclude aluminum bolts)?

Steel manual and other sources show that a mechanically deposited or hot dipped bolt would be best, with stainless steel being a second best choice. All assuming exterior exposure, but not in a terribly corrosive environment or receiving salt spray. Couple this with aluminum and zinc being super close on galvanic series.


I am curious about this because I feel like literature says one thing, but I get comments back from plan checkers and other PE's from third party reviewers saying another thing..."people" aare frequently championing stainless steel "just because" of the name of it (I feel).

Can we field some comments please?

 

[Dhurjati Sen]

@ReverenceEng

Normally, Stainless Steel (passive) is at the topmost of a Galvanic Series and also farthest from Aluminium. SS bolts are also readily available.

 

[SwinnyGG]

I think for cosmetic applications, a lot of people prefer stainless steel because the head of the bolt itself won't produce white or red corrosion.

What materials make the lowest-potential galvanic couple doesn't always align with a) what people's expectations are or b) what will be best cosmetically.

 

[GGedge]

It is common on, for example, building facades and cladding system to join aluminium with stainless steel bolts and corrosion is not an issue, even on parts fully exposed to the atmosphere. Stainless may be preferred to galvanizing because the former do not require maintenance, whereas the latter may which is difficult if they are hidden. Galvanic series are not really helpful for atmospheric corrosion because they are usually for conditions of immersion in sea water. If you have access to or can find a copy of BS PD6484 that provides data based on exposure of couples in atmospheric exposure.