What is an alloy

alloy

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alloy, metallic substance composed of two or more elements, as either a compound or a solution. The components of alloys are ordinarily themselves metals, though carbon, a nonmetal, is an essential constituent of steel.

Alloys are usually produced by melting the mixture of ingredients. The value of alloys was discovered in very ancient times; brass (copper and zinc) and bronze (copper and tin) were especially important. Today, the most important are the alloy steels, broadly defined as steels containing significant amounts of elements other than iron and carbon. The principal alloying elements for steel are chromium, nickel, manganese, molybdenum, silicon, tungsten, vanadium, and boron. Alloy steels have a wide range of special properties, such as hardness, toughness, corrosion resistance, magnetizability, and ductility. Nonferrous alloys, mainly copper–nickel, bronze, and aluminum alloys, are much used in coinage. The distinction between an alloying metal and an impurity is sometimes subtle; in aluminum, for example, silicon may be considered an impurity or a valuable component, depending on the application, because silicon adds strength though it reduces corrosion resistance.

The term fusible metals, or fusible alloys, denotes a group of alloys that have melting points below that of tin (232° C, 449° F). Most of these substances are mixtures of metals that by themselves have low melting points, such as tin, bismuth, and lead. Fusible alloys are used as solder, in safety sprinklers that automatically spray out water when the heat of a fire melts the alloy, and in fuses for interrupting an electrical circuit when the current becomes excessive.

Many fusible alloys are formulated to melt at 90–100° C (194–212° F); for example, Darcet’s alloy (50 parts bismuth, 25 lead, 25 tin) melts at 98° C. By replacing half the tin in Darcet’s alloy with cadmium, the alloy Wood’s metal, which melts at 70° C, is obtained. See also amalgam; ferroalloy; intermetallic compound.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Adam Augustyn.

Alloys

A lmost every material we could ever want is lurking somewhere in the planet beneath our feet. From the gold we wear as jewelry to the oil that powers our cars, Earth’s storehouse of amazing materials can supply virtually every need. Chemical elements are the basic building blocks from which all the materials inside Earth are made. There are 90 or so naturally occurring elements and the majority of them are metals. But, useful though metals are, they’re sometimes less than perfect for the jobs we need them to do. Take iron, for example. It’s amazingly strong, but it can be quite brittle and it also rusts easily in damp air. Or what about aluminum. It’s very light but, in its pure form, it’s too soft and weak to be of much use. That’s why most of the «metals» we use are not actually metals at all but alloys : metals combined with other substances to make them stronger, harder, lighter, or better in some other way. Alloys are everywhere around us—from the fillings in our teeth and the alloy wheels on our cars to the space satellites whizzing over our heads. Let’s take a closer look at what they are and why they’re so useful!

Photo: High-strength superalloys like this one, made from «intermetallic» titanium aluminide (TiAl), are used in extreme applications (like aerospace engines) where «ordinary» aluminum and steel alloys are unsuitable. Photo by courtesy of NASA Glenn Research Center.

Contents

What is an alloy?

Photo: This sample of a titanium-zirconium-nickel alloy is being made to levitate (float in mid air) using electricity. It’s one of many remarkable new materials being developed for possible use in space. Photo by courtesy of NASA Marshall Space Flight Center (NASA-MSFC).

You might see the word alloy described as a «mixture of metals», but that’s a little bit misleading because some alloys contain only one metal and it’s mixed in with other substances that are nonmetals (cast iron, for example, is an alloy made of just one metal, iron, mixed with one nonmetal, carbon).

The structure of alloys

Artwork: Substitution alloys and interstitial alloys: In these diagrams, the black circles represent the main metal and the red circles are the alloying agents.

Substitution alloys

Interstitial alloys

Photo: It’s not just the basic ingredients (the metals and other constituents) that affect the properties of an alloy; how those ingredients combine is very important too. Pouring or stirring speeds, pouring temperatures, and cooling rates are some of the factors that can affect the physical properties of alloys. Photo of brass alloy casting by Jet Lowe, courtesy of US Library of Congress, Prints & Photographs Division, Historic American Engineering Record.

How do alloys behave?

People make and use alloys because metals don’t have exactly the right properties for a particular job. Iron is a great building material but steel (an alloy made by adding small amounts of nonmetallic carbon to iron) is stronger, harder, and rustproof. Aluminum is a very light metal but it’s also very soft in its pure form. Add small amounts of the metals magnesium, manganese, and copper and you make a superb aluminum alloy called duralumin, which is strong enough to make airplanes. Alloys always show improvements over the main metal in one or more of their important physical properties (things like strength, durability, ability to conduct electricity, ability to withstand heat, and so on). Generally, alloys are stronger and harder than their main metals, less malleable (harder to work) and less ductile (harder to pull into wires).

Chart: The same main metal can produce very different alloys when it’s mixed with other elements. Here are four examples of copper alloys. Although copper is the main metal in all of them, each one has quite different properties.

How are alloys made?

Photo: Scientists at NASA Ames have developed a technique called high-pressure gas atomization for simplifying the production of magnesium alloys. Photo by courtesy of US Department of Energy.

Some common alloys and what we use them for

There are zillions of different alloys used for zillions of different purposes. We’ve listed about 25 of the more common (or otherwise interesting) ones in the table below. There are lots of different variations on most alloys and the precise mixture can vary widely, so the percentage figures you see quoted in different books will often not agree exactly.

Iron (50%+), aluminum (8–12%), nickel (15–25%), cobalt (5–40%), plus other metals such as copper and titanium.

Mercury (45–55%), plus silver, tin, copper, and zinc.

Babbitt metal («white metal»)

Tin (90%), antimony (7–15%), copper (4–10%).

Friction-reducing coating in machine bearings.

Copper (65–90%), zinc (10–35%).

Door locks and bolts, brass musical instruments, central heating pipes.

Copper (78–95%), tin (5–22%), plus manganese, phosphorus, aluminum, or silicon.

Decorative statues, musical instruments.

Iron (96–98%), carbon (2–4%), plus silicon.

Metal structures such as bridges and heavy-duty cookware.

Copper (55%), nickel (45%).

Cupro-nickel (copper nickel)

Varying proportions of copper and nickel. The most common variety uses 90% copper and 10% nickel, but other varieties include 70% copper and 30% nickel. Other varieties use small amounts of aluminum, chromium, tin, or manganese.

Aluminum (94%), copper (4.5–5%), magnesium (0.5–1.5%), manganese (0.5–1.5%).

Automobile and aircraft body parts, military equipment.

Copper (80–90%), tin (3–10%), zinc (2–3%), and phosphorus.

Guns, decorative items.

Iron (64%), nickel (36%), which explains its alternative names: FeNi36 and 64FeNi.

Pendulum clocks and scientific instruments that need to resist heat expansion. The unusual name is shortened from the word «invariability» (because the size of an invar block changes very little when it’s heated).

Fuel-rod containers in nuclear reactors.

Nickel (66%), copper (31.5), plus smaller amounts of carbon, silicon, manganese, and iron.

Highly corrosion-resistant alloy used in airplane bodies and shipping components.

Nickel (80%), chromium (20%).

Firework ignition devices, heating elements in electrical appliances.

Nickel (50–55%), titanium (45–50%).

Shape-memory alloy used in medical items, spectacle frames that spring back to shape, and temperature switches.

Tin (80–99%) with copper, lead, and antimony.

Ornaments, used to make tableware before glass became more common.

Varies. Old-fashioned solders contain a mixture of tin (50-70%), lead (30-50%), copper, antimony, and other metals. Newer solders dispense with lead for safety reasons. A typical modern solder has 99.25 percent tin and 0.75 percent copper.

Connecting electrical components into circuits.

Iron (80–98%), carbon (0.2–2%), plus other metals such as chromium, manganese, and vanadium.

Metal structures, car and airplane parts, and many other uses.

Iron (50%+), chromium (10–30%), plus smaller amounts of carbon, nickel, manganese, molybdenum, and other metals.

Jewelry, medical tools, tableware.

Cobalt (67%), chromium (28%), tungsten (4%), nickel (1%).

Coating for cutting tools such as saw teeth, lathes, and chainsaws.

Silver (92.5%), copper (7.5%).

Cutlery, jewelry, medical tools, musical instruments.

Typically (but not always) nickel-based: nickel (45–70%), chromium (14–30%), plus smaller amounts of various other metals (common ones such as iron, molybdenum, and copper, or more unusual ones like rhenium, hafnium, and ruthenium) and nonmetals (for example, silicon, carbon, or phosphorus).

Protective, high-temperature materials widely used in aerospace engine applications where aluminum and steel are unsuitable. Examples include the Inconel® family, Waspaloy®, Hastelloy® alloys, and the CMSX alloys (such as CMSX-4®).

White gold (18 carat)

Gold (75%), palladium (17%), silver (4%), copper (4%)

Bismuth (50%), lead (26.7%), tin (13.3%), cadmium (10%).

Solder, melting element in fire sprinkler systems.

Find out more

Photo: This fuel tank from the Space Shuttle was made from a super-light aluminum-lithium alloy, so it’s a whopping 3400 kg (7500 lb) lighter than the tank it replaced. Cutting weight from the basic structure of the Shuttle meant it could carry heavier payloads (cargo). Photo by courtesy of NASA Kennedy Space Center (NASA-KSC).

On this web site

Articles

Books

General introductions to materials science and engineering

These books explain the basic concept of matching materials to the jobs they need to do. That’s the essential idea behind most alloys—essentially metals «enhanced» to do specific jobs better than they would in their pure, natural state.

More detailed books

It’s quite hard to find simple, general books about alloys; search instead for books on «engineering materials» and you should find something appropriate.

Organizations

Please do NOT copy our articles onto blogs and other websites

Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.

Text copyright © Chris Woodford 2008, 2020. All rights reserved. Full copyright notice and terms of use.

Inconel is a registered trademark of Huntington Alloys Corporation
Monel is a registered trademark of International Nickel Co.
Waspaloy is a registered trademark of United Technologies Corporation
Hastelloy is a registered trademark of Haynes International, Inc.
Names of specific CMSX alloys (such as CMSX-4) are registered trademarks of Cannon-Muskegon Corporation.

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What Is an Alloy? Definition and Examples

An alloy is a substance made by combining together two or more elements where the primary element is a metal. Most alloys form by melting the elements together. Upon cooling, an alloy crystallizes into a solid, intermetallic compound, or mixture that cannot be separated using a physical method. Although an alloy may contain metalloids or nonmetals, it displays the properties of a metal.

The primary metal in an alloy is called its base, solvent, or matrix. Secondary elements are called solutes. Undesirable elements are called impurities. If the alloy consists of only two elements, the result is a binary alloy. If three elements, the result is a ternary alloy. Varying the percentage of elements creates binary systems, ternary systems, quaternary systems, and so on.

Examples of Alloys

Familiar examples of alloys include brass, bronze, stainless steel, 14k gold, sterling silver, and cast iron.

How Alloys Are Made

Two methods lead to alloy formation. These methods may be combined to form a third type of alloy.

Some alloys form from a combination of atom exchange and interstitial mechanisms. For example, stainless steel has carbon atoms in its interstices, plus nickel and chromium atoms replace some carbon atoms.

Alloys form by atom exchange, interstitial placement, or a combination of methods. (image credit: Hbf878)

Alloy Uses

By design, alloys have chemical and physical properties that are superior for an application than a pure element. So, over 90% of metals in commercial use are alloys. Alloys improve over pure elements in terms of corrosion resistance, heat resistance, hardness, machinability, improved wear, or special electrical or magnetic properties. Sometimes the improvement simply reflects cost-effectiveness, where an alloy retains the key properties of a pure metal but is less expensive.

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.

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

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What is an Alloy?

Introduction

An alloy is a substance which is formed when two or more metals are combined. They can also be formed when metals are combined with other elements. However, the properties which alloys exhibit are different from the individual properties of these elements. When you compare it to the pure metals, alloys are stronger and harder. Alloy examples include red gold which is made by combining gold and copper together. Another example of alloy includes white gold which is an amalgamation of silver and gold. Today, we will learn about what is an alloy in chemistry, alloy definition and constituents of alloy.

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Alloy Definition

Let us now learn what alloy means in chemistry.

An alloy refers to a combination of two or more metals, or a metal combined with one or more elements. The resulting alloy has different properties than the original elements altogether, like increased strength and hardness. For example, when elemental iron is combined with non-metallic silicon or carbon, it yields steel or silicone steel.

Constituents of Alloy

Now that you have learned about what the meaning of alloy is, let us look at what the constituents of alloy are. An alloy consists of two or more elements, either as a compound or a solution. The components of alloys are generally metals. However, carbon is an exception to being a non-metal and an important constituent of steel. Alloys are usually produced when the mixture of its constituents is melted.

Properties of Alloy

When you have learnt about what is meant by alloy, learning the properties of alloy becomes easier.

An alloy is a substance that has metallic properties and is composed of two or more elements, out of which at least one is a metal. A metal, having metallic properties, is a material, which, when freshly made, fractured, or polished, demonstrates a lustrous appearance. It also conducts heat and electricity as well.

Metals are generally malleable, which means that they can be easily hammered into thin sheets. They are also ductile, meaning that they can be drawn into wires as well. A metal can either be a chemical element like iron, or an alloy like stainless steel. Most of the pure metals are either very brittle, soft, chemically reactive to be practically used. When different ratios of metals are combined as alloys, it modifies the original properties of metals to give desirable characteristics. Alloys are generally made to keep them less brittle, corrosion-resistant, harder, or even have a more desirable luster and color.

Therefore, alloying of metal helps us to use the metal in daily life application. This process also helps in making different types of metals perfect for use (by modifying its properties ).

Alloy Examples

Let us now look at some of the alloy examples.

Steel

Steel is an alloy of carbon and iron. It is a popular alloy because of its low cost and higher tensile strength. However, many different types of steels consist of different amounts of carbon along with several other elements like manganese, phosphorus, sulfur, chromium, copper, nickel, and molybdenum. Primarily, the composition of iron is accounted for by iron, which is at least 75% of the total alloy’s weight. It also consists of different amounts of carbon and many other elements depending on the type of steel. Since steel has higher tensile strength and affordability, it is used in the infrastructure and construction of buildings, bodies of vehicles and electrical appliances.

Bronze

Bronze is known to be an alloy of tin and copper. It is commonly used in heavy tools and gears, coins, medals, trophies and even in different forms of electrical hardware. The strength of bronze varies depending on the alloys that are used in the alloying. You must know that bronze is much superior compared to pure copper when it comes to hardness. It is also more ductile and machineable compared to pure copper.

Nichrome

Nichrome is an alloy of chromium and nickel. However, it is also common for the nichrome alloys to consist of iron and other similar elements. Nichrome is primarily used in resistance wires. It also has its application in several electrical appliances like bread toasters and space heaters. Nichrome alloys are also used in dental fillings.

Brass

Types of Alloy

Alloys are classified as :

On the Basis of Principle Metal in the Alloy : Examples are copper alloy, iron alloy, lead alloy. A copper alloy has copper as a major constituent, i.e, Bronze.

On the Basis of Phases : There can be single phase alloys (consist of a uniform face) and double phase alloys ( consist of two different phases). Example of single phase alloy is brass which has 30% Zn + 70 % Cu. Example of Double phase alloys is muntz metal which has 60% Cu + 40% Zn.

On the Basis of Iron Content : On the basis of iron content, Alloys are classified as ferrous alloys and non ferrous alloys. The alloys which contain Fe as a constituent are known as ferrous alloys whereas the non-ferrous alloys do not contain Fe as a constituent. Example of ferrous alloys is Stainless steel made of Fe + Cr. Example of non-ferrous alloys is Solder which has Pb + Sn.