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What Is a Corrosion Resistant Metal?
Corrosion-resistant metals are materials that are highly resistant to chemical breakdown caused by moisture, oxygen, or other substances. These metals, such as stainless steel, aluminum, titanium, and certain alloys, contain elements that form a protective oxide layer or passivation layer to prevent deterioration. This characteristic makes them ideal for use in harsh environments, such as marine, chemical processing, and outdoor construction, where durability and longevity are crucial.
Common Corrosion Resistant Metal
Corrosion-resistant metals are of different types, each with special attributes and uses. We’ll explore typical corrosion-resistant materials below:
Aluminum
Aluminum is a standard workhorse metal for various applications. Aluminum metal exhibits good corrosion resistance due to the passive oxide layer that it forms on its surface. 1xxx, 3xxx, and 5xxx aluminum grades exhibit the most resistance to corrosion even though most grades of aluminum exhibit high chemical resilience in the family
| Series | Primary Alloying Element | Characteristics |
|---|---|---|
| 1xxx | 99% minimum aluminum | Great corrosion resistance, excellent workability |
| 3xxx | Manganese | Good corrosion resistance, moderate strength |
| 5xxx | Magnesium | Very good corrosion resistance, medium strength |
| 6xxx | Magnesium and Silicon | Good corrosion resistance, strong, easily machined |
- 1xxx Series: This grade of aluminum has a high purity of 99% aluminum and provides outstanding corrosion-resistant properties in typical applications.
- 3xxx Series: This series has manganese as its primary alloying element. Hence, its resilience against corrosion is lower than that of 1xxx aluminum. However, its high ductility is ideal for cold-forming applications with corrosion resistance requirements.
- 5xxx Series: The 5xxx grade of aluminum contains high manganese content and exhibits similar corrosion resistance as 3xxx aluminum.
- 6xxx Series: 6xxx series offers a balance of corrosion resistance, strength, and machinability, popular in structural applications.
Superalloys
These are high-performance metals specially engineered to provide exceptional corrosion resistance and mechanical properties at high temperatures. As a result, these grades of corrosion-resistant metals are used in energy and aerospace applications. However, the matrix element of a superalloy sets it apart from others.
- Cobalt Superalloy: Cobalt superalloys are metals with superior hot corrosion resistance and have a higher melting point than other superalloys.
- Nickel Superalloy: Nickel alloys are the most commonly used superalloys because they are generally cheaper than all versions of cobalt superalloy. These metals offer high strength and outstanding corrosion-resistant properties.
- Iron Superalloy: These superalloys exhibit high corrosion resistance and strength at room temperature. They are more economical than the nickel and cobalt superalloys.
Copper Alloy
Pure copper and its alloys, including bronze (copper and tin) and brass (copper and zinc), exhibit corrosion-resistant performance. Due to their excellent resistance to corrosive elements, these red metals are widely used for electrical, plumbing, architectural, and marine applications.
Stainless Steel
Stainless steel is a term that comprises a variety of corrosion-resistant metals. The constituting elements of a steel alloy determine its degree of corrosion resistance. Steel alloys provide excellent corrosion resistance, making them applicable to environments with high temperatures and aggressive chemicals. The chromium content forms a chromium oxide passive layer on their surface, protecting them from degradation.
Manufacturers use many stainless steel alloys for several applications across industries, such as food processing, chemical processing, automotive, pharmaceuticals, and architecture. These alloys can be grouped into three major classes according to their microstructure, including:
- Austenitic Stainless Steel: These alloys are commonly regarded as 300 series stainless steel. Stainless steel 304 and 316 are typical grades of stainless steel in this category. Depending on the grade, austenitic stainless steel often comprises alloying elements, including 18% chromium and 8% nickel, with slight traces of manganese and nitrogen. This range of alloys is the most corrosion-resistant metal available on the market.
- Ferritic Stainless Steel: Ferritic stainless steel belongs to the 400 series stainless steel. This range of alloys often contains a much higher chromium content of about 27%, increasing its resistance. However, it is more ductile due to its lower carbon content. 430A is a typical stainless steel alloy in this category.
- Martensitic Stainless Steel: These are stainless steel alloys in the 400-series. 420A is a widely used steel alloy in this category. It contains 18% chromium, a higher carbon content, and no nickel. Although the martensitic stainless steel class is more rigid than other corrosion-resistant metals, it exhibits low corrosion resistance compared to the 300 steel series.
Titanium
Titanium has vast applications in the aerospace industry due to its excellent strength-to-weight ratio. Manufacturers often use titanium for industrial applications because of its excellent corrosion-resistant properties. Like most corrosion-resistant metals, the passive oxide layer on titanium’s surface is responsible for its resistance to corrosive elements.
However, if the passive oxide layer breaks off, it can quickly reform in the presence of moisture and oxygen. Titanium’s remarkable corrosion resistance makes it a commonly used material in applications that work with chlorine solutions, such as in the chloralkali industry, because it exhibits extraordinary resistance to these chemicals.
Galvanized Steel
Galvanized Steel is a metal with rust-resistant properties. These metals have a zinc coating, which acts as rust resistance and prevents further oxidation. This zinc coating prevents oxygen and water from getting to the underlying steel. Galvanized carbon steel exhibits excellent corrosion resistance, aesthetic appeal, and high recyclability. Manufacturers often use galvanized steel for automotive parts, construction components, and many other applications requiring high corrosion resistance.
Typical Ways of Improving the Corrosion Resistance of Metals
A metal is resistant to corrosion when it can withstand the adverse effects of particularly harsh environments. Manufacturers and product designers often employ specific procedures to improve a metal’s corrosion resistance because some metals are more corrosion-resistant than others. Here are some of the standard methods:
- Anodizing: This electrochemical method develops a controlled oxide film on the surface of metals like titanium and aluminum. Aluminum oxide improves the metal’s resistance to corrosion and other desirable attributes, such as a surface for dyeing or coloring.
- Surface Polishing: Applying polish to a metal’s surface helps to eliminate flaws, create a smoother surface finish, and reduce further corrosion. Hence, surface polishing improves corrosion resistance and surface appeal.
- Spray Paint Processing: Spray painting the surface of metals forms a protective film on it. This coating is a barrier that prevents corrosive elements and moisture from the metal’s surface. However, you must carefully prepare the metal’s surface and select a suitable paint or coating to achieve the best results.
- Electroplating: Electroplating is an electrolysis process that improves a metal surface by depositing a layer of one metal onto another. The plated or deposited layer forms a protective barrier, improving the metal’s corrosion resistance. Nickel, chromium, and zinc are typical metals used for electroplating.
Conclusion
Corrosion-resistant metals are machining materials with inherent properties that prevent degradation due to exposure to corrosive elements or environments. These metals listed are integral to different industries because they ensure the longevity and continuous performance of different metallic structures and components. Understanding these corrosion-proof metals and their characteristics will help guide their usage.
AT-Machining is an expert CNC machining service provider with good years of experience in producing corrosion-resistant metal components. Our trained engineers and machinists have in-depth knowledge of various production processes and advanced corrosion protection methods. Contact us today to learn how to efficiently choose a corrosion-resistant metal for your metal products. Submit your CAD files; we offer instant quotes and DfM feedback!
