Is Galvanized Steel Magnetic? Applications and Benefits
Galvanized steel is steel that has been coated with zinc to increase its corrosion resistance. This coating has little or no effect on the magnetic properties of the steel itself. The zinc coating acts as a sacrificial anode, making galvanized steel more durable than the uncoated version.
This article discusses the magnetic properties of galvanized steel. It also discusses both the advantages and real-world applications of galvanized steel.
Galvanized steel is ordinary steel that has been coated with a layer of zinc through a process called galvanization. This is done to make the steel more corrosion-resistant, since steel is an iron-based alloy, and iron is prone to rust when exposed to moisture.
There are several different galvanizing manufacturing processes available, but the most common one is called hot-dip galvanizing. Another way to coat steel with zinc is by spraying it on. However, the zinc layer produced by spray galvanizing is considerably weaker than that produced by hot-dip galvanization. During the hot-dip galvanization process, the steel to be coated is first cleaned, pickled in sulfuric acid, fluxed in a zinc-ammonium chloride solution, and then immersed in molten zinc.
The resultant zinc coating acts as both a physical and a chemical barrier to protect the underlying steel from corrosion. Corrosive agents can't get to the surface of the steel through the zinc coating. But even if a scratch or an edge exposes the steel to the atmosphere, the zinc can still protect it through an electrochemical process called "cathodic protection."
The zinc, the iron in the steel, and the corrosive fluid create a galvanic cell, driven by zinc's greater propensity than iron's to react with its environment. The zinc acts as the anode in this electrochemical cell, oxidizing in a reaction with the corrodant (electrolyte), and giving up electrons. These electrons move toward the cathode, which, in this case, is the steel to be protected. So the steel cathode is protected, while the zinc oxidizes, serving as what is called a "sacrificial anode." The zinc corrodes in preference to the steel.
Fortunately, zinc’s corrosion products (also called the “zinc patina”) adhere tightly to the zinc layer’s surface, slowing the rate of corrosion to somewhere between 1 and 10% of the expected rate for unprotected steel.
Galvanized steel is known for its strength, formability, and resistance to corrosive elements, which makes it widely used in such industries as: agriculture, solar power, automotive, and construction.
To learn more, see our guide on Galvanized Steel.
Yes, galvanized steel is generally magnetic, but only if the steel substrate is magnetic. This is because the steel base metal, which contains iron, is magnetic. Even though zinc is not magnetic, the layer of zinc added to the steel is thin enough that it doesn’t block or severely influence the magnetic properties of the base steel. This means that galvanization does not alter the magnetic properties of steel. It is important to note that not all steel alloys are magnetic. Austenitic stainless steel is not magnetic, for example. This means that any type of steel with an austenitic (face-centered cubic crystal lattice) microstructure will be non-magnetic. It is possible, however, to galvanize austenitic stainless steel or any other stainless steel. But there is no good reason to do so, since steel is galvanized to obtain corrosion resistance and stainless steel already has this property.
Yes, hot-dipped galvanized steel is magnetic. The zinc coating of the hot-dipped galvanizing process does not interfere with the magnetic strength of the steel substrate.
What makes galvanized steel magnetic is the magnetic properties of the steel substrate. This magnetic quality is a result of the ferrous nature of steel. The addition of the zinc coating primarily serves to provide corrosion resistance rather than affecting the steel's magnetic nature.
The process of galvanization generally has minimal impact on the magnetic properties of the steel. Steel is inherently magnetic due to its ferrous nature, and while zinc itself is not magnetic, the galvanized coating does not inhibit the magnetic properties of the steel. This is because the zinc layer is very thin compared to the thickness of the steel. Therefore, galvanized steel maintains its magnetic characteristics.
Galvanized steel is generally magnetic because the steel substrate itself is magnetic. Stainless steel, on the other hand, may or may not be magnetic. Stainless steel's magnetic properties depend on its type. Ferritic and martensitic stainless steels, which contain iron, carbon (0.03 to 1.2%), and chromium (12 to 17%), are magnetic. Austenitic stainless steels, which have a different microstructure (based on a face-centered cubic crystal lattice), are non-magnetic. Galvanized versions of stainless steel may or may not be magnetic, with austenitic stainless steel remaining non-magnetic. However, galvanizing is typically unnecessary and not recommended for austenitic steel and stainless steel.
Galvanized steel has a lot of different applications across multiple industries. Some of its real-world applications include:
- Strengthening Roads: Used to reinforce roads and bridges. Rebar is the most common application of galvanized steel. Its robust frame remains in pristine condition even as surrounding materials deteriorate. The self-healing properties of the zinc coating contribute to its durability. In other words, zinc's role as a sacrificial anode contributes to the durability of galvanized rebar.
- Building Framing: Provide robust support structures for buildings, including offices and apartments. The zinc coating allows them to endure minor damage or wear without compromising corrosion resistance.
- Outdoor Structures: Galvanized steel sheet is used for canopies, solar panels support, and more. It’s such a popular choice for outdoor applications because of its durability and resistance to corrosion. This makes it ideal for outdoor structures that might encounter rain and some wear exposure over the years.
- Drinking Water Pipes: Some water pipes that are used to supply drinking water are still made from galvanized steel.
- Workshop Equipment: Many bolts, nuts, wires, and tools are galvanized due to galvanization’s low cost and adequate corrosion resistance for the life of the hardware.
- Agricultural Applications: Some examples of the uses of galvanized steel in agriculture include its use as a material for storage silos and animal enclosures. It is ideal for these kinds of applications due to its resistance to both abrasive environments and corrosion. It’s also a cost-effective choice for long-lasting installations.
Galvanized steel has many benefits, including:
- Rust Resistance: The zinc layer acts as a protective barrier, shielding the iron in steel from moisture and oxygen, and significantly reducing the susceptibility to rust.
- Sacrificial Anode: The galvanized coating serves as a sacrificial anode, ensuring that any damaged steel remains shielded by the surrounding zinc layer. Even if a steel section is fully exposed, the zinc coating corrodes first, which protects the underlying steel.
- Long Lasting: Galvanization significantly extends the lifespan of industrial steel. In average environments, galvanized steel can endure for more than 50 years, and even in severe water exposure conditions, it can last over 20 years without the need for maintenance. This longevity also contributes to the cost-effectiveness and sustainability of galvanized steels.
- Low Cost: In terms of treated steel, galvanized steel is considered cheap compared to most other treated steel.
Galvanized steel, coated with a layer of zinc for corrosion resistance, although not as common, may exhibit altered magnetic properties due to the coating. It is crucial to assess the magnetic requirements of the specific environment and application. The thickness of the galvanized coating can influence magnetic performance, so selecting an appropriate coating thickness is important. Generally, the coating has no significant effect on the magnetic properties, but if the coating thickness is thicker than usual it might have some effect. Additionally, factors such as the type of galvanizing process used and the composition of the steel substrate can impact the magnetic behavior.
Although galvanized steel has numerous advantages, it also comes with some limitations. These include:
- Although galvanized steel is resistant to red rust, it can still develop “white rust”, a white, chalk-like product of the corrosion of the zinc coating..
- Galvanized steel is quite heavy compared to other lightweight corrosion-resistant materials like aluminum. However, aluminum comes at a greater price. This is also true for titanium. Stainless steel for the same strength, could also result in a smaller-volume, lighter-weight part.
- Not all objects can undergo the hot-dipping process—some items might be too large, while others might be too small or thin.
A common misconception about galvanized steel’s magnetism is that the zinc coating alters its magnetic properties. Many assume that the steel becomes non-magnetic after the zinc coating has been applied. In reality, galvanization has little to no impact on the steel's inherent magnetic characteristics, and it remains magnetic after the process.
Galvanized steel, properly applied, has a long lifespan. It is expected to last more than 50 years in average environments and over 20 years in harsh conditions (severe water or moisture exposure) without having to undergo any maintenance. However, when considering the impact of saltwater,, the longevity of galvanized steel may be affected.
Saltwater, due to its corrosive nature, can accelerate the corrosion process of metals, including galvanized steel. While galvanized steel provides excellent corrosion resistance, prolonged exposure to saltwater can still contribute to corrosion over an extended period.
Yes. Galvanized steel is considered an inexpensive material for the properties that it provides. It is considerably less expensive than other metals with similar properties, such as stainless steel, which is also considered to be corrosion-resistant. Also, galvanized steel can be very durable. The design life can be up to 100 years so the initial investment in galvanized steel is a very cost-efficient choice for long-lasting components, products, and construction materials.
Yes, tin is classified as slightly paramagnetic, which means it is weakly magnetic (attracted to a magnet). However, this attraction is sometimes so weak that some sources consider tin to be non-magnetic.
This article presented galvanized steel's magnetism, explained it, and discussed its applications and benefits. To learn more about galvanized steel, contact a Xometry representative.
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