Corrosion resistance is often treated as a simple material property, but it’s an essential selection decision for engineers. Choosing the right corrosion-resistant metal is a matter of considering its environment, how long it will last, and the necessary tradeoffs in terms of cost, weight, and machinability.
This guide compares stainless steel, aluminium, brass, bronze, and nickel supper alloys in terms of their corrosion resistance. Read on to learn the real-world applications of each material, when it doesn’t make sense, and the best grades to buy.
What is Corrosion Resistance?
Corrosion resistance is a measure of a metal’s ability to resist deterioration when exposed to environmental stressors. Corrosion is most often caused by saltwater, chemical exposure, or extreme heat and causes oxidation, rust, or other types of breakdown that causes metal to deteriorate and become unstable.
Some metals are inherently corrosion resistant. These materials have a thin oxide layer that resists deterioration. Others are made more corrosion resistant with surface treatments and coatings.
Stainless Steel
When it comes to corrosion resistant metals, stainless steel is among the most common. Its high chromium content, typically at least 10.5%, creates a protective layer on the surface of the material that protects the metal.
Stainless steel performs well in environments with mild chemical exposure. It tends to do well in food processing environments, non-saltwater applications, and medical equipment. For high-stress environments like marine applications or those with chemical exposure, it’s essential to select stainless steel grade carefully, as not all will be sufficient.
The most common stainless steel corrosion-resistant grades include:
- Grade 316: Also known as marine grade stainless steel, 316 stainless contains molybdenum, which improves its corrosion resistance. It’s sufficient in saltwater environments.
- Grade 317: This grade contains more molybdenum and more nickel than 316 stainless, making it a good choice for acidic environments or those with high levels of chloride.
Aluminium Alloys
Aluminum forms a thin oxide layer on its surface that naturally protects it from corrosion. While it isn’t the most corrosion-resistant material, it’s a good option for a lightweight metal with some corrosion resistance.
Stainless steel performs well in aerospace, transportation components, and other applications where weight matters. It does well in freshwater environments, but shouldn’t be used in saltwater environments without a protective coating. It also isn’t a great option for high-temperature or acidic environments.
The most common corrosion-resistant aluminiums include:
- Grade 2024: This aluminum alloy contains copper, giving it high strength and good resistance. It’s commonly found in aircraft structures, fasteners, and other applications.
- Grade 7075: This grade offers strong corrosion resistance alongside exceptional strength, making it one of the highest-performing structural aluminums available.
- Grade 6061: A moderately corrosion resistant material, 6061 aluminium is also quite strong.
Brass and Bronze
Copper alloys like brass and bronze provide excellent corrosion resistance in specific environments. Bronze, for instance, is highly resistant to seawater corrosion, particularly when it contains tin or aluminium.
Brass and bronze corrosion resistance make it a great choice for fluid systems and marine components, particularly when high wear resistance is also important. These materials perform well in marine hardware, valve components, pump components, and fluid handling systems. They aren’t great in high-load applications or when in contact with oxidizing acids.
Choose these brass and bronze for corrosion resistance:
- Brass 360: This alloy contains copper, zinc, and lead, making it extremely resistant to corrosion. Its protective patina makes it an excellent choice for plumbing fixtures and other wet environments.
- Nickel-aluminum bronze: Nickel-aluminium bronze (NAB) has exceptional corrosion resistance, even when exposed to seawater and harsh chemical environments. It’s often used in chemical processing, for ship parts, and in other highly corrosive environments.
Nickel Superalloys
Nickel-based super alloys are among the most corrosion-resistant metals available. They’re the best choice when high corrosion resistance and temperature strength are required. Nickel alloys typically contain elements like chromium, molybdenum, and niobium.
Nickel superalloys can be pricey, so they should be reserved for extreme environments that warrant a high cost material. They perform well in chemical processing equipment, high-temperature environments, and other severely corrosive environments. They’re not ideal when only general corrosion resistance is required, or when another, lower-cost material would be sufficient.
The most corrosion resistant nickel superalloys include:
- Nickel 600 ANN: This nickel superalloy resistant to stress corrosion, cracking corrosion, and caustic corrosion. When looking for a material that is both corrosion and oxidation resistance, Nickel 600 ANN is a good choice.
- Nickel 625 ANN: Another nickel-based superalloy, Nickel 625 is corrosion and oxidation resistant up to 2,000 F. It’s often used in nuclear reactor components, marine equipment, and other high-stress environments.
Fry Steel: An Experienced Metal Supplier
Selecting the right corrosion-resistant metal is only one part of the metal procurement process. It’s also important to work with an experienced specialty metal supplier to ensure material consistency, traceability, certification, and reliability.
At Fry Steel, we carry a wide range of corrosion-resistant metals including stainless steels, aluminium alloys, and nickel-based materials. With ISO 9001, AS9100D, and AS9120 certifications, we provide full material traceability and documentation.
For a metal supplier who will help you select materials that meet your performance requirements, choose Fry Steel. Find a rep in your area today.
