Corrosion develops when two dissimilar materials are combined in a corrosive electrolyte. This can occur when certain materials (such as aluminum) are in contact with stainless steel.
The most common solution to prevent galvanic corrosion is to select metals that are close together in the galvanic series. Separating the metals that are incompatible reduces the risk of these cells deteriorating. According to the levels of galvanic corrosion, stainless steel that comes into contact with materials such as copper is less likely to be a risk than when it is in contact with aluminum.
Although aluminum reacts negatively to stainless steel, large surface areas of aluminum to stainless steel can be acceptable depending on local environmental conditions. Severe corrosion is likely to take place in a marine environment. However, there are methods that can be used to reduce this effect. A good way to reduce corrosion is to use an isolating coating or paint on the aluminum and the steel to isolate them electrically. Insulating washers are also effective in isolating the two dissimilar materials and creating a relatively safe surface area.
Along with corrosion, discoloration of stainless steel may occur when combined with aluminum. This is also called ‘tea staining’. Discoloration can be prevented by the use of insulation and regular maintenance. Passivation can also be used to create the passive film on the fastener for better corrosion resistance.
As a leading stainless steel fastener specialist; and partnered with manufacturers and suppliers of the full range of stainless steel and aluminum use across all industries; Marsh Fasteners can help you ensure that you use the best products with the highest anti-corrosion qualities.
Customers often ask whether it’s possible or advisable to use stainless steel fasteners with aluminum. It’s well known that bringing the two metals into contact can cause corrosion. Corrosion develops when two dissimilar materials are combined in a corrosive electrolyte. This can occur when certain materials (such as aluminum) are in contact with stainless steel. However, there are ways to use stainless steel and aluminum together while preventing corrosion.
The most common solution to prevent galvanic corrosion is to select metals that are close together in the galvanic series. Separating the metals that are incompatible reduces the risk of these cells deteriorating. According to the levels of galvanic corrosion, stainless steel that comes into contact with materials such as copper is less likely to be a risk than when it is in contact with aluminum.
Steel and aluminum reaction
Although aluminum reacts negatively to stainless steel, large surface areas of aluminum to stainless steel can be acceptable depending on local environmental conditions. An example of the safe use of stainless steel fasteners with aluminum would be where stainless steel bolts are used to secure aluminum roadway parapet guards. In this case, the surface area of the aluminum is so large relative to the surface area of the stainless steel bolts that, there is a very low risk of major corrosion.
Severe corrosion is likely to take place in a marine environment. However, there are methods that can be used to reduce this effect. A good way to reduce corrosion is to use an isolating coating or paint on the aluminum and the steel to isolate them electrically. Insulating washers are also effective in isolating the two dissimilar materials and creating a relatively safe surface area.
How to tell the difference between aluminum and stainless steel
Not sure what materials you’re dealing with? It’s usually possible to till the difference between aluminum and stainless by sight, as the former has a duller appearance. Aluminum is also much lighter and softer than steel. However, it isn’t always so obvious; it depends on the alloys in question. Different manufacturing processes can create different appearances and finishes.
One way to be sure is to use the key test. Take a key and drag it along a flat surface. If the surface is aluminum, it will scratch quite deeply without too much pressure, since aluminum is much softer than steel. The steel will not scratch at all or only superficially.
What to put between steel and aluminum
When using stainless steel fasteners with aluminum surfaces, you can prevent corrosion by placing something between the two metals. Plastic or rubber washers or gaskets are good suggestions.
Along with corrosion, discoloration of stainless steel may occur when combined with aluminum. This is also called ‘tea staining’. Discoloration can be prevented by the use of insulation and regular maintenance. Passivation can also be used to create the passive film on the fastener for better corrosion resistance.
How to attach aluminum to steel
While it is relatively safe to use stainless steel fasteners on large aluminum surfaces, the opposite is not true. If you use aluminum rivets or other fasteners to join large steel pieces, corrosion will set in and destroy the fasteners, ultimately causing the parts to come loose.
When the pieces being joined are structural, use the strongest fasteners you can find. For example, when joining aluminum and steel, choose carbon steel bolts.
When bringing aluminum and steel into contact, you can also use a thin layer of non-absorbent insulate between them. Rubber or plastic can work, depending on the application. You can also use polypropylene tape or prime the parts with a protective coating. Even with such treatments having been done, you should use a corrosion-inhibiting material of some kind – such as pastes, washers, etc. – under the heads of bolts and screws as a further preventive measure.
As a leading stainless steel fastener specialist; and partnered with manufacturers and suppliers of the full range of stainless steel and aluminum use across all industries; Marsh Fasteners can help you ensure that you use the best products with the highest anti-corrosion qualities.
