Does galvanized steel react with other metals?

Galvanized steelcan be combined with a variety of other metals. In certain construction and fabrication scenarios, it may come into contact with stainless steel, aluminum, copper, or other weather-resistant steel.

When galvanized steel is paired with different metals, it can lead to galvanic corrosion. This process is similar to how zinc protects iron from rust by creating small electrical currents between the zinc and iron in the steel. However, when zinc comes into contact with other metals, it can also generate electrical currents with them. In some metal pairings, this contact diverts zinc's protective action to the other metals.

The issue of galvanic corrosion is particularly influenced by the relative sizes of the metal surfaces in contact. It’s problematic from an engineering perspective to have a small anode surface in contact with a large cathode surface. For example, using a small galvanized rivet, which is coated in zinc, on a large untreated steel sheet can cause the rivet to fail over time. The difference in electrical potential draws electrons from the zinc coating on the rivet, eventually depleting its ability to protect the steel.

Conversely, when a large anode surface is paired with a small cathode surface, stability is maintained. For instance, a stainless steel rivet attached to a zinc plate will remain durable for decades. This is because the majority of the rivet’s surface is in contact with zinc, which offers protection.

Now, let's explore the challenges and advantages of some common metal combinations with galvanized steel.

Copper and Brass

When galvanized steel comes into contact with copper or brass, it can lead to rapid corrosion, especially in humid environments. Even having galvanized steel near copper or brass is risky; water runoff, particularly in areas with acid rain, can carry enough copper to damage the zinc coating on the galvanized steel.

If avoiding contact between brass or copper and galvanized steel is not possible, it is essential to insulate the two metals to prevent electrical contact. Non-conductive gaskets can protect joint faces, and insulated grommet-style fasteners should be used for connections. Designers must also ensure that water from rain, melted snow, or other sources flows from the galvanized surface toward the copper or brass surface, not the reverse.

Stainless Steel and Aluminum

In environments with low to moderate humidity, galvanized steel does not have conductivity problems when paired with stainless steel or aluminum. However, in marine settings or areas with consistently high humidity, it becomes crucial to insulate galvanized components from aluminum or stainless steel to prevent issues.

Weathering Steel

Using galvanized bolts in unprotected steel is generally not an issue. The galvanized bolt will develop a rust layer that shields it from further corrosion.

The location where the steel is used significantly impacts the severity of issues caused by metal-to-metal contact. In rural areas, most metals do not cause erosion to galvanized steel. However,in saltwater environments, nearly all metals, including austenitic cast iron, chromium, gold, gunmetals, nickel, nickel-copper alloys, nickel-chromium-iron alloys, nickel-chromium-molybdenum alloys,nickel silver, platinum, rhodium, silver, hard (but not soft) solders, tin, and titanium, can erode galvanized steel.