Question

A stainless steel manufacturer states, "Aluminum fastening should not be used with stainless steel." could you use stainless steel fastenings with aluminum? Explain.

Answer 1

Bimetallic corrosion can only occur when two dissimilar metals are in 'electrical' contact and are bridged by an electrically conductive liquid.

Aluminium and stainless steel together also appears to be a bi-metallic corrosion risk, from the 'nobility' table.
With this combination the affect of relative surface area on corrosion is important.

A large area of 'cathode' relative to 'anode' will accelerate the anodic corrosion. Although aluminium is anodic to stainless steel, large relative surface areas of aluminium to stainless steel can be acceptable, dependant on local conditions.
Stainless steel fasteners in aluminium plates or sheets are normally considered safe, whereas aluminium rivets or bolts holding stainless steel parts together is an unwise combination, as there is a practical risk of corrosion.

Always ensure that the aluminum part of the material is larger than the stainless steel screws to avoid it being eaten away. Aluminum which has an anodic nature will quickly disintegrate when it comes into contact with salty water, and will do the same when its surface area is less than that of stainless steel.

An example of the safe use of stainless steel and aluminium together is where stainless steel fasteners and hold down bolts are used to secure aluminium roadway or bridge parapet guards.
Even with no insulation between the metals, there should be little risk of corrosion.