A Basic Guide to the Corrosion Resistance of Common Fastener Alloys* 

Grade	Corrosion Resistance
Carbon and alloy steels	Rust in moist air but coating or plating can be used for protection.
Stainless steels	Good resistance in mild environments without coatings. Pitting is a problem when chlorides are present.
Specialty alloys	Excellent resistance to specific environments.

Recommended Fastener Alloys for Joining Metal in Mild Environments*

Metals Joined	Recommended Fastener Alloys
Steel to steel	Carbon & alloy steels Stainless steels A286 Alloy 718
Steel to stainless	Carbon & alloy steels (coated) Stainless steels A286 Alloy 718
Stainless to stainless	Stainless steels (300 series) A286 Alloy 718 Specialty alloys Titanium
Steel to aluminum	Carbon & alloy steels Stainless steels (300 series) A286 Alloy 718 Titanium
Aluminum to aluminum	Aluminum Stainless steels (300 series) A286 Alloy 718 Titanium

*Note: Corrosion is basically an electro-chemical reaction between the fastener metal and its environment. An example of this is unprotected steel becoming rusty. The iron in the steel combines with available oxygen to form iron oxide. Moisture acts as an electrolyte that will influence the rate of this reaction.

The rate or speed of the corroding process can be accelerated by increased temperature, increased quantities of the electrolyte and contact with other metals.

Therefore, when selecting a metal for fastener use, its total environment, including the materials the fastener will be holding together, must be considered.

Sources of Information - IFI Fastener Standards, 6th Edition and Corrosion Engineering by Mars G. Fontana, McGraw-Hill Book Company, Copyright 1986.