Sacrificial coatings are an excellent way to protect an underlying base material from the effects of corrosion. A particularly popular combination is coating carbon steel with a layer of zinc, known as galvanised steel. There are, however, several different processes to apply this zinc layer. One notable process called galvannealing.
What is Galvanneal?
Galvanneal is similar to other galvanised steels. It is perhaps most similar to hot-dip galvanising. In order to create Galvanneal steel, the material is run through a liquid bath of zinc alloy. This zinc adheres to the surface without any large changes to the metallurgical properties of either the zinc layer or the steel. This is essentially the hot-dip galvanising process. For the galvannealing process, the galvanised steel is then passed through a low pressure, high volume air knife which blows excesses coating off of the steel before it solidifies. This leaves the steel with a thinner zinc coating compared to standard galvanised steel. The material is then placed into a furnace where it remains until the steel hits an annealing temperature for a determined amount of time. This allows the zinc and the surface of the steel to alloy with one another. The Galvannealed steel is then cut into specified dimensions.
Advantages and Disadvantages of Galvanneal
There are advantages to using Galvannealed steel over uncoated steel or other coated materials. Galvanneal is primarily designed to be painted. The matte finish of the zinc coating is much more absorbent than standard galvanised steel which allows paints to adhere to the surface far better. Galvannealed steel also has a zinc coating that is harder than many other types of galvanised steels. This increases its resistance to scratching and other types of coating damage that could expose the steel underneath to the environment. The formability and weldability of the Galvanneal coating is typically better than other types of galvanised steel. Using Galvanneal will also provide much better corrosion resistance than uncoated carbon steels.
A disadvantage of Galvanneal is that it does not offer the same level corrosion resistance as galvanised steel due to the thinner coating.
Common Applications of Galvannealed Steel
Applications of Galvanneal vary widely because many different types of steel can be Galvannealed. For instance, a thin low carbon steel may be Galvannealed and made into a bracket on an automobile frame, while a thick high-strength low-alloy steel may be Galvannealed and used in the structure of a building. Galvannealing can be performed on steels that are meant for forming, deep drawing, high-tensile stress applications, marine applications, welding operations, and many other activities.
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