A Note About Aluminum Fasteners

When choosing which type of accessories to attach to your Framing Tech aluminum fabrications, the first concern should be the strength, stability, and durability of the fasteners used. After all, depending on the type, size, weight, and material of the accessory you are attaching, these fasteners are likely to be exposed to considerable stress over time, undergo regular wear and tear, risk exposure to corrosive substances, and experience challenging weather events such as wind, rain, snow, extreme cold, and extreme heat. While our extruded aluminum profiles are up to the task in all these eventualities, the same cannot be said of aluminum fasteners.

As you browse through our selection of aluminum fastener nuts, bolts, and screws, you will notice in the product specifications that none of them are actually made of aluminum. Strong as it is, aluminum is rarely a suitable material for any kind of nut. For one thing, the yield strength is too low. Moreover, a ductile metal like aluminum is highly prone to galling (or adhesive wear), where the aluminum nut under compressive force adheres to an aluminum surface, making later removal very difficult. Similarly, aluminum bolts and screws are simply not suited for heavy-duty use, as they have low shearing resistance compared to steel and other metals commonly used as fasteners. For that reason, most of our fasteners are made of steel or stainless steel for maximum strength.

Those familiar with materials science and engineering will quickly recognize that this solution introduces its own set of problems—namely, galvanic corrosion. When aluminum and steel come in contact with one another in the presence of an electrolyte such as humidity or rainwater, they act as a kind of battery. Aluminum (the anode) will transfer electrons to the steel (cathode), weakening the aluminum over time.

Of course, a key factor in the reaction between aluminum and steel is the surface area involved. Since the surface area of a steel nut or bolt is relatively small, one can expect the corrosion rate to be correspondingly small.

Yet, to minimize even further the risk of deterioration to the aluminum in this situation, we provide many of our steel and stainless steel fasteners with either a zinc or black oxide coating. The low electric potential difference between these types of coatings and aluminum acts as a barrier between the steel fastener and the aluminum surface, thereby minimizing or preventing any significant galvanic corrosion.