Guide to Metal Alloys & Their Importance

April 26, 2022 | Categorised in:

alloy samples

Dating back thousands of years, alloys have been a crucial discovery that has shaped our world ever since. Alloys allow us to create materials beyond the limits of naturally-occurring elements. But how are alloys defined, why are they so important, how do we create them, and what are common examples? In this piece, we’ll answer these questions and more, so let’s start at the beginning.

What is an alloy?

At its most basic definition, an alloy is a metal that’s made from two or more elements, at least one of which is a metal. It might be common to think of alloys as a “mixture of metals” but as long as one compound is a metal, the other can be a nonmetal element such as carbon or silicon. Alloys date back to 3500 BC, when bronze was invented to strengthen tools and weapons by combining copper and tin. Since then, we’ve discovered countless new alloys and refined them to provide desirable properties, beyond just strength. The alloys have also become more complicated, and can be categorized into:

  • Substitutional alloys: This type of alloy essentially replaces atoms that make up the lattice structure of the primary metal with atoms of the additional element. This can only happen if the atoms of both compounds are roughly similar in size, with an example being bronze. Copper and tin have similar atomic sizes and when mixed, the tin’s atoms can fit into the structure of the metal and the place of copper atoms.
  • Interstitial alloys: If the atoms of the alloying element (or elements) are much smaller than the atoms of the primary metal, they slip in between the atoms of the primary metal. This allows them to fill the gaps, or interstices, of the lattice structure of atoms that makes up the alloy.

Why are alloys used?

As we alluded to above, alloys can provide appealing characteristics that enhance the base metal’s strength, durability, conductivity, and more. In addition to thinking of alloys adding performance or properties to pure elements, mixing with other compounds can also reduce potential weaknesses as well. Because of this versatility, alloys represent the majority of metal products we use today.

How are alloys made?

The most common way of making alloys is also the oldest; simply by melting and mixing the compounds together, before allowing the alloy to cool and solidify. However, alloys can also be created by turning each of the components into a powdered form, mixing them together, and fusing everything together at high pressure and temperature. Another technique for producing alloys is called ion implantation, and involves firing ions into the surface layer of a piece of metal.

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Is steel an alloy?

Steel is an alloy and is considered among the strongest alloys available. It has a number of variations that provide various advantages for certain applications, and these versions can be either interstitial alloys or a combination of interstitial and substitutional alloys.

Steel’s composition

Basic steel is made by adding carbon (usually around 0.5% of the alloy) to iron, creating an interstitial alloy when the much smaller carbon atoms slip between the much larger iron atoms. While there is a huge range of steel grades and variations, one other common example is stainless steel, which exhibits a higher corrosion resistance without needing to be galvanized. This is accomplished by adding chromium and nickel to the alloy and makes it both an interstitial and substitutional alloy. The carbon atoms are much smaller than iron, but chromium and nickel are similarly-sized and act like a substitutional alloy by “replacing” iron atoms.

Examples of other common alloys

While steel is the most common alloy used today, there are plenty of other prevalent examples:

  • Brass: Alloy of copper and zinc and is often used in decorations, door locks, and brass musical instruments.
  • Bronze: Alloy of copper, tin, and either manganese, phosphorus, aluminum, or silicon. Often used in decorative applications, musical instruments, springs, and marine uses such as ship propellers.
  • Cast iron: Alloy of iron, carbon (more than 2%), and silicon and is often used in arch bridges, heavy-duty cookware, and automotive parts.
  • Pewter: Alloy of tin, copper, lead, and antimony and is often used in ornaments, tableware (before glass became more common), pendants, and other decorative objects.
  • Sterling silver: Alloy of silver and copper and is often used in cutlery, jewelry, musical instruments, and medical tools.
  • Aluminum: While aluminum is a pure element, aluminum alloy is made by adding manganese or copper and is often used in electronic technology, wind and solar energy management, automotive body panels, and shipbuilding.

Common alloying elements

As you may have noticed from the list above, there are a number of alloying compounds that are used in several common alloys. There are many other alloys that are more obscure but equally important, many of which share alloying elements. Some of these agents and their general properties added to an alloy are:

  • Nickel: Increases toughness and ductility
  • Copper: Increases corrosion resistance and facilitates precipitation hardening
  • Manganese: Increases strength and heat resistance
  • Silicon: Increases strength and lowers melting temperature
  • Chromium: Increases corrosion and abrasion resistance, hardness, and strength

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