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What Is Galvanneal?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 03 April 2014
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Galvanneal is a carbon steel product coated in a mixture of iron and zinc. This steel product is most famously used in the manufacture of cars, although it has a wide range of other uses as well, including in construction of structures and ships. Steel mills produce galvanneal by request for customers, and some manufacturing facilities may make their own galvanneal to control every step of the process.

The term “galvanneal” is a portmanteau of “galvanized” and “anneal.” Annealing is a process in which metal is subjected to a heat treatment to force it to develop specific desired properties. Galvanization is a process in which metal is coated in a material which will help it resist corrosion. Zinc is classically used for galvanization. The blend of these two processes is designed to give galvannealed steel some unique and very desirable properties which make it ideally suited to an array of applications.

In galvanneal, the steel is first dipped in a hot bath of zinc, as is done when materials are galvanized. Then, it is subjected to a secondary process in which iron is annealed with the zinc coating to create an iron-zinc blend on the surface of the metal. The galvanneal coating is a dull gray in color, unlike the distinctive spangled coating seen on metals galvanized with just zinc. The coating should also stay firmly adhered to the metal for its lifetime, thanks to the heat treatment process.

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Galvanneal comes in a variety of thicknesses, including custom sizes which can be created by request at a steel mill. The dull gray surface of galvanneal is very easy to paint, making it appealing for applications in which the metal will be painted, such as car manufacturing. The metal will also resist corrosion. Over time, however, corrosion can develop. Damage to the surface of the coating can expose the underlying steel, allowing rust to set in. Some causes of damage include highly corrosive chemicals, gouges, and collisions.

Galvannealing is a complicated process with a number of steps and a series of areas in which the process can go wrong, rendering the steel useless. Special equipment is required to complete the process, as well. As a result, galvannealed steel is more expensive than steel which has not been processed in this way. This product is used when high performance, safety, and reliability are desired. Cars, for example, must adhere to a number of safety standards and galvannealed steel assists with safety goals for car manufacturers.

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Discuss this Article

pleonasm
Post 3

@indigomoth - Just a tip. Bear in mind that if a car has got a rust problem, even if it has been repaired the rust is likely to start again. You can only really slow it down, not stop it, once it gets into the steel. So, make sure that if you are buying a car, they haven't hidden rust repairs, for example behind the tires and underneath the car.

Rust doesn't exactly develop overnight, so if you are diligent in catching damage to the zinc coating before it can get into the underlying metal you should be fine.

Once it's in, however, it's only a matter of time, so avoid buying a car where this is the case.

indigomoth
Post 2

@irontoenail - Unfortunately, rust can be difficult to prevent when you live by the ocean. The salty, humid air is exactly the right conditions for rust to develop.

Keeping the paint fresh is actually the best thing you can do, rather than putting some kind of conditioner on top of it, which is what I think your father might have been doing. Rust can only really develop in places where the paint has come off the galvanneal. So, after you get dinged by a stone, or anything like that, you have to be diligent and repaint.

The problem is to properly repaint and fill in the damaged galvanneal coating is quite expensive and anything else looks obvious and brings down the value of the car. I suppose you could always do touch ups in between the occasional repaint.

irontoenail
Post 1

Galvanneal steel is not at all rust proof, as I remember from when I lived by the ocean as a child. No matter what my father did, eventually our cars would start to develop little spots of rust.

Unfortunately, we didn't have a garage at the time, as there wasn't room at the house where we lived, so that probably added to the problem. But, he tried putting all kinds of different mixtures on the car, as I remember.

Of course, I don't remember exactly what the mixtures were, so maybe dad was just easily taken in by people who were selling the car equivalent of snake oil!

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