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Metals That Don’t Rust — And Ones That Do

You likely know rust to be the flaky, reddish corrosion on metal surfaces. The term “rust” actually refers to iron oxidation — in simple terms, it’s the combination of iron and oxygen. Any metal that contains iron can rust, while other metals react to oxygen in other ways.

Rust can destroy metal objects and render them useless, requiring expensive and time-consuming replacement. The easiest way to avoid rust is to choose the right metals.

Only iron can rust. That means other metals that do not contain iron are not susceptible to rusting. This makes them ideal for outdoor placement, as they’ll last much longer in natural conditions. Learn about which metals don’t rust, as well as which metals do rust.

What Metals Don’t Rust?

Rust is a chemical reaction, so the right elements must be involved for rust to form. Rust can only occur when there are iron, oxygen and water molecules. Any other reaction, by definition, is not rust. Metals with little to no iron content, also known as non-ferrous metals, will not rust, though they may react to oxygen in other ways. Common metals that don’t rust include:

  • Aluminum
  • Stainless Steel
  • Bronze
  • Copper

WHY DOESN’T ALUMINUM RUST?

Aluminum is rustproof. The reason for this is simple — aluminum contains no iron. Aluminum is a standalone element on the periodic table, which means it contains nothing but itself. During production, a manufacturer might add small amounts of magnesium, silicon, copper or other elements to make the end product stronger. Aluminum’s properties make it a practical choice for outdoor electrical enclosures or other outdoor metal objects.

WHY DOESN’T STAINLESS STEEL RUST?

Regular steel is a combination of iron and carbon, as well as small amounts of other elements. Stainless steel is a bit different. Though steel does contain iron, stainless steel also contains the element chromium, which is highly corrosion-resistant.

Chromium protects the steel from rusting because chromium combines with oxygen before iron does. Since the iron never has a chance to combine with oxygen, rust never forms. Additionally, stainless steel is popular because it resists the growth of bacteria and stays stable in extreme temperatures.

WHY DOESN’T BRONZE RUST?

Bronze does not rust due to its minimal iron content. Keep in mind, however, bronze can react to oxygen in other ways. Bronze is not naturally occurring like pure aluminum or iron. Instead, bronze is a mixture of copper and tin. This composite structure makes it more resistant to corrosion, but it’s not completely immune. It’s stronger than copper alone, but it may deteriorate as time passes.

WHY DOESN’T COPPER RUST?

Copper will never rust for the same reason as bronze — it contains too little iron. Though it will not rust, copper can form a green film, or patina, on its surface over time. However, this patina will not flake the way rust does. Instead, it creates an even, thick coating on top of the copper itself. Many people actually prefer the look of oxidized copper to its original state.

Just think of the Statue of Liberty. Her copper skin originally looked brown, but it has turned green over time due to the copper’s oxidation. This green film is as thick as the original layer of copper and actually helps Lady Liberty withstand weathering. You can also see this same effect on older pennies, which may start to look green.

Metals That Do Rust

Any metal that contains a significant portion of iron, also known as “ferrous” metals, can rust. Metals that will rust include:

  • Steel
  • Cast iron
  • Wrought iron

WHY DOES STEEL RUST?

Because steel is a mixture of iron and carbon, it will definitely rust. What differentiates steel and stainless steel is the element chromium — chromium forms a shield against rusting, which makes stainless steel more corrosion-resistant. The more chromium content, the better. Regular steel has no such protection against rusting.

WHY DOES CAST IRON OR WROUGHT IRON RUST?

Any form of iron can rust when exposed to oxygen and water molecules. Cast iron is a combination of iron, carbon and silicon. Though it’s known for its resistance to wear, it can rust. Wrought iron, on the other hand, contains only trace amounts of carbon. It’s nearly pure iron, so rust is likely to form.

You can protect iron objects from rust by regularly applying paint and removing rust spots with a wire brush. You should also keep iron objects as dry as possible — wipe down cast iron pots and pans with a towel after washing, rather than letting them air-dry. Additionally, wash them right away instead of leaving them to soak. Iron requires much more attention and maintenance than other metals when it comes to avoiding corrosion.

Practical Applications

You may recall an adult reminding you to bring your bike into the garage before a rainstorm — otherwise, it would get wet and potentially rust. However, some metal objects, such as outdoor electrical enclosures, need to remain permanently outside. Metal objects placed outdoors have to be able to withstand natural conditions including rain and humidity.

If these objects were susceptible to rust, they would need replacing far too often. This would be expensive and time-consuming, but it would also pose a safety hazard. An electrical enclosure degrading due to rust could be highly dangerous.

For these types of applications, aluminum and stainless steel are popular choices. Aluminum will not rust, so it’s safe to use outdoors. It has other valuable features as well, such as:

  • It’s strong enough to withstand hard impacts.
  • It can dissipate heat for safe temperature control.
  • It’s lightweight compared to other metals.

Like aluminum, stainless steel is a common choice for outdoor metal objects. Stainless steel has impressive temperature stability. It’s both fireproof and resistant to cold temperatures. If a metal object needs to endure an extreme climate — a desert, for instance, where temperatures can rise and fall dramatically in short timespans — stainless steel is one of the safest choices.

Learn More About Outdoor Metal Enclosures

APX Enclosures offers National Electrical Manufacturers Association (NEMA) certified enclosures. They’re built to withstand any conditions — rain, snow ice, fire, dirt, dust, bacteria and extreme temperatures. You can customize your enclosure to fit your exact needs. APX Enclosures provides electrical enclosures for a wide variety of industries, from civil engineering to telecommunications.

Learn which metals are the strongest options for outdoor applications. If you are looking for a tough, non-corrosive and stable electrical enclosure, contact APX Enclosures today.

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