How to Choose the Best Corrosion Resistance Metals

Metals that Rust vs. Metals that Resist Corrosion

All metals are prone to rusting, but the degree to which they rust depends on their type and the environmental conditions they’re exposed to. For example, metals exposed to moisture or saltwater environments tend to corrode faster.

Rust Formation

Rust occurs when metal reacts with oxygen in the air to form an oxide. When metal comes into contact with water, it ionizes, making it more susceptible to oxidization. The ease with which metal rusts is determined by its tendency to ionize (a concept known as ionization tendency). Simply put, metals with a higher ionization tendency, such as lithium or potassium, rust more easily, while metals like gold or platinum, which have a lower ionization tendency, are more resistant to corrosion.

3 Types of Corrosion-Resistant Metals

Although most metals rust, some metals are more resistant to corrosion due to their natural properties. Generally, there are three types of “corrosion-resistant” metals:

• Metals That Do Not Rust (e.g., Gold, Platinum)
  These metals have low ionization tendencies, making them inherently resistant to rust. However, they are often expensive, so using them requires careful consideration.
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• Metals that Form a Passive Oxide Layer (e.g., Aluminium, Titanium, Nickel, Stainless Steel)
  Some metals, like aluminium and titanium, form a passive oxide layer on their surface when exposed to oxygen. This layer prevents further reaction with oxygen, protecting the underlying metal from corrosion. Stainless steel, for instance, benefits from the chromium added to it, which forms a protective oxide film.
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• Metals Where Rust Acts as a Protective Layer (e.g., Copper, Zinc)
  Like metals that form a passive oxide layer, these metals protect their inner layers from further corrosion. However, the oxide film on these metals is not as strong, and it can be easily removed by acidic substances such as vinegar.
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Types of Anti-Corrosion Surface Treatments

To prevent corrosion in metals that are more susceptible to rust, surface treatments are applied. The most common method is to form a protective layer on the metal’s surface, preventing exposure to air and moisture. There are two main categories of surface treatments: organic and inorganic coatings.

Organic Coatings (e.g., Paint, Oil)
Painting is a classic example of organic coating. Applying oils or wrapping parts with rubber or plastic are other common organic methods used to protect metal surfaces.

Inorganic Coatings (e.g., Plating, Chemical Treatment)
Plating is a method of applying a thin metal layer, such as chrome or zinc, to protect the base metal. These coatings are either passivating metals (like chromium) or sacrificial metals (like zinc), which corrode first, protecting the underlying metal. Chemical treatments, like chromate or anodizing (for aluminum), are also common for enhancing corrosion resistance.

5 Surface Treatments for Corrosion Resistance and 4 Highly Corrosion-Resistant Metals

Let’s rank the corrosion resistance of nine different metals from highest to lowest and compare their strength, wear resistance, and magnetic properties. Clicking on “Surface Treatment” or “Materials” will provide more detailed information on each. Use this guide to make informed decisions for your next material selection.

• Surface Treatments for Corrosion Resistance
• Surface treatments effectively shield metals from oxidation, which occurs when they come into contact with oxygen. Keep in mind that surface treatments add cost and increase production time.