Aluminium coatings are surface coatings of metals which display excellent corrosion resistance. The process of producing this coating is called aluminizing, a thermo-chemical process that diffuses aluminium into the surface of metals. The most common material subjected to aluminizing is steel.
Benefits of Aluminium Coatings
- Price: Compared to processes that deliver similar results, aluminizing is more cost-effective in practice.
- High yield strength: Aluminium is one of the most ductile metals on earth. It affects yield strength positively.
- Variety of application: Aluminium coatings can be applied to mild steels, low alloy steels and high carbon steels.
- Oxidation resistance: The aluminium coating forms two layers that protect the steel core. On the very surface, a thin aluminium oxide layer is formed. Underneath, the aluminium is mixed with steel and silicon, which is added in the aluminizing process in small quantities. Below that, there is the steel core which retains its original yield strength and other material properties. The aluminium coating prevents the steel from reacting with the oxygen and other harmful elements and acts as a barrier and protector.
- Sulfidation resistance: The coating does not only protects the steel core from oxidation but also from H2S, SO2 and SO3 attacks.
Disadvantages of Aluminium Coatings
While aluminium coatings offer many benefits in the way of chemical attacks, they are not the right choice in terms of surface hardening. Aluminium is one of the softest metals that exist and is therefore not fit for applications that are put under a lot of stress. If you are looking for a treatment that improves surface hardness, boronizing is a better choice for you. At Bortec, we make use of our own patenized boronizing treatment that can not only increase hardness up to 2800 HV but also displays great wear resistance and resistance against acid chemicals. While aluminizing is a good choice for applications that require good resistance against acids, boronizing is more of an allround answer because we can improve other mechanical properties as well. Read more about boronizing here.
Process of Aluminizing
The thermochemical diffusion process starts by heating aluminium in a furnace along with the workpiece, forming an oxide layer at the surface once it cools. This acts as a barrier against acids and other chemicals.
Aluminium coatings can be applied through various methods. The most common is hot dipping, a galvanic coating that uses high temperature baths to create protective coatings. The steel workpiece must be cleaned before hot dipping to ensure that the aluminium atoms will adhere to the surface of the material. The material is then submerged into a bath made of aluminium and silicone (11%) at temperatures between 700 and 750 °C. The silicone is added to stretch the aluminium layer even thinner. Once the workpiece is air dried, the aluminium will already be diffused into the surface of the steel work piece.
Areas of Applications
Aluminium coatings can be applied to a wide range of areas. The most common are found in applications that have to withstand high heat, humidity and chemical attacks. Therefore, aluminium coatings can be found in boiler parts, chimneys, ducts, plants, and tubes and pipes. Generally, aluminizing is applied when decent corrosion resistance is needed.
If you’re not sure whether aluminium coating meets your demands, you can contact us here. We offer a specialized and patented boriding treatment that significantly improves hardness, corrosion resistance and thermal stability for a large number of steel types. We would love to advise you on the best hardening treatment of your metal workpieces.