WHAT IS AN ALLOY?

WHAT IS AN ALLOY?

An alloy is a combination of a metal with at least one other metal or nonmetal. The combination must be part of a solid solution, a compound, or a mixture with another metal or nonmetal in order for it to be considered an alloy. The most common way to combine metals into an alloy is by melting them, mixing them together, and then allowing them to solidify and cool back to room temperature.

Why Are Alloys Used?

Metal alloys are used because they typically have enhanced mechanical or chemical properties. Alloying elements can be added to a metal to increase a number of properties including hardness, strength, corrosion resistance, machinability, and much more.

What Are Common Alloys?

Alloys are so abundant throughout the metalworking industry that there are too many to list. In fact, it is far less likely to work with a non-alloy, or “pure metal.” Even low carbon mild steel – perhaps the most frequently used material in metal fabrication – is an alloy of iron and carbon. An example of a steel alloy would be AISI 1018. Cast iron is another alloy of iron and carbon, with even higher amounts of carbon than mild steel.

Aluminum is often alloyed with other elements as well, giving it the attributes required for the desired application. For example, aluminum 6061 and 2024 have high additions of manganese or copper, respectively.

Alloys can also be extremely complex. Austenitic stainless steels, such as Grade 316, are a synthesis of iron, chromium, nickel, and some other metals and nonmetals. Bronze (which itself is an alloy of copper and tin) is often further alloyed with elements such as aluminum. Grade C954 is an example of an aluminum bronze alloy.

Tool steels like D2 are mostly made up of iron, but have many different additions of other metals and nonmetals such as chromium, vanadium, manganese, silicon, and carbon, depending on the desired mechanical properties.

What are Some Common Alloying Elements?

There are a wide variety of alloying elements that serve different purposes for different base materials.

Chromium is a metal frequently used to help alloys resist corrosion. Depending on the material, it can also increase hardness and strength.

Nickel is a metal often added to materials to increase toughness. Austenitic stainless steels have high additions of nickel which also acts as an austenite-promoter.

Copper is a metal used to make materials, such as aluminum, precipitation-hardenable. In steel, copper can increase corrosion-resistance, but can decrease the corrosion-resistance of aluminum.

Manganese is a metal usually alloyed to improve strength. Manganese alone as an alloying element is not affected very much by heat treatment, making it suitable for higher temperature applications.

Tungsten is a metal alloying element used to improve wear resistance (especially at high temperatures), toughness, and strength.

Lead is a metal alloying element that is used to improve machinability.

Silicon is a nonmetal alloying element. It is often used as a deoxidizer in metals. Silicon also increases strength and can reduce melting temperature.

Carbon is a nonmetal alloying element that is a necessary element to manufacture steel. Carbon additions are often used in steel and cast iron alloys to increase strength and hardness.

Want to learn more about common alloying elements? Check out our part 1 and part 2 of our “Common Alloying Elements” series.