Steel is one of the world’s most common building components, and for good reason. It’s durable, versatile, and exceptionally strong, making it ideal for applications across virtually every industry.
However, steel does have one weakness: corrosion. Iron in the steel can react with oxygen and moisture in the air, forming iron oxide, a reddish-brown substance more commonly known as rust. This rust can weaken the structural integrity of metal by corroding its surface, which is particularly problematic for applications where strength and durability are crucial.
Luckily, there are effective ways to prevent steel from rusting. One of the best protective measures is hot-dip aluminising – coating the steel with a thin layer of aluminium or aluminium alloy through immersion in a molten aluminium bath. This creates a highly corrosion-resistant barrier that seals the steel surface from moisture and oxygen.
At MG Metals, we supply premium-quality, custom-cut steel and specialty metals for sectors across the UK. Read our guide below to discover what hot-dip aluminising is, how it works, and its many advantages.
What Is Hot-Dip Aluminising?
Hot-dip aluminising is used to apply a layer of aluminium or aluminium alloy to the surface of a metal substrate, typically steel. The process involves immersing the metal substrate in a bath of molten aluminium, allowing the aluminium to bond with the substrate’s surface. Here’s a general overview of how it works:
- The metal substrate is cleaned to remove any contaminants or oxides from its surface. It’s often dipped into a flux bath afterwards to further clean the surface and promote the wetting of the aluminium.
- The prepared metal is then immersed in a bath of molten aluminium. The temperature of the bath is high enough to keep the aluminium in a liquid state.
- The aluminium from the bath diffuses into the surface of the metal substrate, forming a metallurgical bond. This process provides a protective layer of aluminium on the substrate.
- After the desired coating thickness is achieved, the metal is removed from the aluminium bath and allowed to cool and solidify. This results in a uniform aluminium coating on the substrate.
Hot-dip aluminising is commonly used in industries where corrosion resistance and high-temperature performance are critical, such as in the production of automotive exhaust systems, industrial equipment, and components for applications in aggressive environments.
What Types of Hot-Dip Aluminising Are There?
There are two main types of hot-dip aluminising processes: aluminium-silicon alloy coating and pure aluminium coating.
In the aluminium-silicon process, the steel is coated by immersing it in a bath of molten aluminium containing 5% to 11% silicon. The added silicon improves adhesion of the coating to the steel. This type of coating is well-suited for high temperature applications where corrosion resistance and heat tolerance are needed, such as in furnaces, ovens, heaters, and baking pans.
In the pure aluminium process, the steel is coated by dipping it in a bath of molten, commercially pure aluminium. This coating provides excellent atmospheric corrosion resistance. Products made using this type of coating include corrugated roofing, siding drying ovens, and air conditioner condenser housings.
What Are the Benefits of Hot-Dip Aluminising Steel?
There are plenty of benefits to coating steel in aluminium. Here are some of the most notable:
Hot-dip aluminising dramatically improves the corrosion resistance of steel through the formation of a durable aluminium coating.
By immersing steel in a bath of molten aluminium, a metallurgical bond is formed that integrates the aluminium with the steel surface. This alloy layer acts as a barrier that protects the underlying steel from corrosion.
This enhanced resistance can significantly extend the service life of the steel substrate, reducing maintenance costs and improving reliability for aluminised steel structures and components.
Steel already has a high heat resistance, with most types having melting points around 1400°C (2552°F). However, coating it with a layer of aluminium can take this a step further. The aluminium acts as an additional protective barrier against heat transfer, providing insulation to the underlying steel and improving its resistance to oxidation and scaling at high temperatures.
Hot-dip aluminising can improve the aesthetic appearance of steel surfaces. The aluminium coating often provides a smooth and uniform finish, enhancing the overall look of the steel and making it more visually appealing.
While the initial cost of hot-dip aluminising may be higher than some other coating methods, the long-term benefits, including extended service life and reduced maintenance costs, make it a cost-effective choice in many applications.
Aluminised steel remains formable and weldable, allowing it to be used in various manufacturing processes without sacrificing these important properties. This makes it versatile for a range of applications.
Are Aluminised and Galvanised Steel the Same Thing?
Though both provide improved corrosion resistance, aluminised and galvanised steels utilise different coating processes to achieve this goal.
- Galvanised steel is coated by hot-dipping the steel into a bath of molten zinc. The zinc reacts with the steel surface to form zinc iron alloys that protect the underlying base metal. If the coating gets damaged, the zinc will sacrificially corrode before the base metal, providing cathodic protection. Galvanised coatings are suitable for applications requiring general corrosion resistance.
- Aluminised steel, on the other hand, is produced by hot-dipping steel into a bath of molten aluminium. This produces an alloy coating of iron and aluminium that protects the steel through both barrier and galvanic means. The aluminium coating also provides heat resistance, making aluminised steel well-suited for high temperature applications like automotive exhaust components.
In summary, galvanised steel relies on zinc as a sacrificial coating for corrosion protection, while aluminised steel utilises an aluminium coating for both corrosion and heat resistance. The best coating to use depends on the specific requirements of the application at hand.
Get the Right Steel for Your Project with MG Metals
Bring your next fabrication project to life with MG Metal’s wide selection of steel components! We carry mild and stainless steel in a variety of grades, sizes, and finishes to meet your specifications. Simply tell us your requirements, and we’ll precision-cut the exact pieces you need with our state-of-the-art equipment.
If you’re unsure what type of steel you’re in need of, our experienced team can recommend the right type of steel and which treatments are suitable for it.