Simple Ways to Prevent Galvanic Corrosion Between Aluminium and Stainless Steel

When working with both aluminium and stainless steel, there is a lot to think about to ensure that any structure you’re creating with these metals is safe and secure. Using both of these metals can bring many challenges to your project because they can come into electrical contact with each other, which causes galvanic corrosion. This can be a serious issue because it has the power to completely corrode one of the metals. The process can occur when creating marine structures, outdoor structures and even bridge guards, as well as in many industrial applications where aluminium and stainless steel need to be used together. This serious process can cause structures to deteriorate, become damaged or even break, posing a safety concern and negatively impacting your project. It can set you back massively in terms of both time and money, as it’s costly and time-consuming to repair or even start all over again. Due to this, it’s important to prevent this process from happening and understand exactly what galvanic corrosion is.

The process can be difficult to understand, which means it can feel impossible to work with the two metals together and prevent the corrosion from happening. Don’t worry, as at Rapid Metals, we understand the challenges many professionals face when creating structures with aluminium and stainless steel. This is why we’ve created this guide to help you understand galvanic corrosion, what happens when it starts and how you can prevent it to make your projects using these metals that little bit easier.

What Is Galvanic Corrosion?

Galvanic corrosion, also known as bimetallic corrosion or dissimilar metal corrosion, is an electrochemical process. This happens when two different metals come into electrical contact with each other and a suitable electrolyte is present, which allows the flow of electricity. When this occurs, it will cause one of the metals to corrode away while the other one stays intact. Both the chemical and electrical processes behind this unique occurrence can be quite complicated to understand. However, it’s essential to wrap your head around them because they have the potential to cause a whole lot of trouble to structures and systems that use different types of metal.

The key aspect to know about galvanic corrosion is that it doesn’t happen between every metal. It’s only something that occurs when there’s electrical contact between a positively charged metal and a negatively charged metal. The positive metal is known as the anode, and the negative metal is referred to as the cathode. This process also only happens when an electrolyte is present, as this is what lets electrons flow and strengthens the electrical contact between the two metals. Once they come into contact, the electrons in the anode will leave and go into the cathode, which is the reason why the anode corrodes away. Since the cathode takes those electrons from the anode, it stays intact with no damage to the metal at all.

Galvanic corrosion doesn’t always happen at the same speed, and the rate of the process can depend on several factors. These include how electrically dissimilar the metals are. The bigger the difference in electron count between them, the larger the rate of electron transfer will be. This means that when this is the case, the galvanic corrosion will be much faster than if the electron count is smaller. As well as this, the presence of an electrolyte, and what it is, will also affect the process. If it occurs in dry conditions with no electrolyte present, the galvanic corrosion process will stop on its own. However, if the metals come into contact with each other in fresh water, then this is an electrolyte that will make the corrosion process that bit faster. If it occurs in salt water, then this is a very effective electrolyte that creates rapid galvanic corrosion.

Galvanic Corrosion and Aluminium Corrosion

A very common type of galvanic corrosion is between aluminium and stainless steel. Every form of steel and aluminium will create a galvanic corrosion process in the right (or even wrong) conditions, but it’s an even bigger problem with aluminium and stainless steel. This isn’t due to their specific individual chemical properties. Instead, it’s due to the ways in which the metals are used together for.

On their own, aluminium and stainless steel offer excellent corrosion resistance, which is what makes them a popular choice to use for many situations. This is especially the case for situations where corrosion-resistant metals need to be used, such as outdoor or marine environments. Both of these situations give the dissimilar metals a chance to be in an electrolyte environment, especially when they’re in seawater, which quickly starts galvanic corrosion. When this happens, the stainless steel becomes the cathode and the aluminium becomes the anode, meaning that the concern with this is the aluminium corrosion that can occur.

Now, it may be easy to wonder how aluminium corrosion can be a problem when it is a metal that’s known for its exceptional corrosion resistance. Yes, aluminium does typically resist corrosion even when it’s exposed to seawater or other corrosives. It’s designed to prevent further corrosion by the surface of the metal reacting with oxygen in the atmosphere. This forms a layer of aluminium oxide that seals the rest of the metal underneath, protecting it from corroding fully. Even though aluminium has this protection, it can’t withstand aluminium corrosion from the galvanic process. This is because it works completely differently from any other environment. When electrolytes and stainless steel are present, the galvanic corrosion process degrades the structure of the aluminium on an atomic level that even a layer of oxide won’t stop it. This leads to all of the aluminium corroding down completely, while no stainless steel corrosion occurs and this metal stays intact with no damage.

As the process works differently and still causes aluminium corrosion, it also means that the usual ways to prevent the metal from corroding don’t actually stop it either. This means that any type of preventative care that works for oxidisation, such as stripping, cleaning and repainting or sealing the surface, won’t even protect the metal. These measures will only be a temporary fix that slows down the process, but the metal will still corrode away. The only way to combat galvanic corrosion between aluminium and stainless steel is to take specific measures to stop and prevent galvanic corrosion from occurring.

How To Prevent Galvanic Corrosion Between Aluminium and Stainless Steel

When it comes to how to prevent galvanic corrosion between aluminium and stainless steel, it can be challenging to ensure that it doesn’t occur. There are many steps you can take to help prevent the process from happening when both metals are being used in an environment where electrolytes are present. It is all about avoiding combinations of the three elements that cause galvanic corrosion, but when you need to process chemicals or operate in salty environments, it isn’t as simple as this.

The key to stopping galvanic corrosion between aluminium and stainless steel is to electrically separate the two metals. It’s important to break the electrical path between the two metals to help prevent the electrons from transferring from the aluminium to the stainless steel, causing aluminium corrosion. This can be done in numerous ways, such as:

• Insulating the metals: Putting an insulator between the two metals to prevent them from connecting can help to break the electrical path between them. This can be done by using plastic washers, rubber gaskets, painted surfaces, coatings, greases or nylon bushings. It’s best to insulate both metals, but just insulating the anode can help to slow the galvanic corrosion process down.
• Coatings: Coating the aluminium and stainless steel can also stop them from connecting electrically. Using dielectric coatings can prevent the process from happening. These create an insulating layer that blocks the electrical path and can come in paints and films. Simply painting the metals can be enough, but you can also use primer or zinc galvanised coatings.
• Eliminating electrolytes: It’s also effective to keep the metal surfaces covered, so that they can stay dry. This prevents standing water from reaching the metals, which carry the electrolytes and fuel the galvanic corrosion process. You can use clamp liners, wear pads or even pipe wraps between the dissimilar metals to eliminate the electrolytes.
• Sacrificial anodes: This is when you protect the anode (aluminium) from the cathode (stainless steel) by using another anode of a less noble material. You can use zinc, as this is less noble than aluminium, and put it in direct metallic contact with the aluminium metal. This will cause the zinc to protect the aluminium because when galvanic corrosion happens, the electrons of the zinc will pull out and transfer to the stainless steel, causing the zinc to corrode instead of the aluminium – hence the name sacrificial anode.
• Plating of galvanising: Plating or galvanising can be a great way to reduce galvanic corrosion. It can help to alter the electrons without completely changing their structure. You can plate the metals with fasteners made from gold, nickel, chrome or carbon steel.

Now that you know about aluminium corrosion due to the galvanic corrosion process, you can consider the environment you’re working with when needing to use aluminium and stainless steel together. If you need to use these two metals in an environment where electrolytes are present, you need to take measures to prevent the process from occurring. Without these necessary measures, you can quickly find that the aluminium becomes corroded, affecting the structure you’re working with and shortening its lifespan. If you don’t protect the aluminium from coming into contact with the stainless steel, then your project can corrode, become damaged or even break.

Whatever your project needs, if it requires the use of stainless steel and aluminium, you can rely on Rapid Metals to provide you with exactly what you’re looking for. We stock various types and lengths of both stainless steel and aluminium to suit your project requirements and create robust, high-quality structures that last. Our aluminium collection includes round, flat, square, sheet, angle and so much more to aid multiple projects. While our stainless steel collection has round, hexagon, square, flat and so much more to suit your needs. Each collection offers high-quality metal that is durable and long-lasting for a strong, flawless finish you can rely on.