What is Metal Alloy?
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.
A metal alloy is a substance that combines more than one metal or mixes a metal with other non-metallic elements.
For example, brass is an alloy of two metals: copper and zinc. Steel is an alloy of a metallic element (iron) and a small amount — up to 2% — of a non-metallic element (carbon).
When compared to metals, alloys differ in their properties and characteristics, such as composition, applications, how they’re made, and cost. Keep reading to learn more about alloys.
Alloys are an example of “teamwork makes the dream work,” since each substance within the alloy lends its own properties to the solution or mixture.
Some alloys will take the best attributes of each contributing element and create a final product that is harder, more durable, and/or more resistant to corrosion.
The careful chemistry that goes into creating these precise ratios ultimately produces substances with unique, useful properties.
How are alloys made?
In most cases, alloys are mixed from commercially pure elements. Mixing is relatively easy in the liquid state but slow and difficult in the solid state, so that most alloys are made by melting the base metal—for instance, iron, aluminum, or copper—and then adding the alloying agents.
Care must be taken to avoid contamination, and in fact purification is often carried out at the same time, since this is also done more easily in the liquid state.
Examples can be found in steelmaking, including the desulfurizing of liquid blast-furnace iron in a ladle, the decarburization of the iron during its conversion to steel, the removal of oxygen from the liquid steel in a vacuum degasser, and finally the addition of tiny amounts of alloying agents to bring the steel to the desired composition.
The largest tonnages of alloys are melted in air, with the slag being used to protect the metal from oxidation.
However, a large and increasing amount is melted and poured entirely in a vacuum chamber. This allows close control of the composition and minimizes oxidation.
Most of the alloying elements needed are placed in the initial charge, and melting is done with electricity, either by induction heating or by arc melting.
Induction melting is conducted in a crucible, while in arc melting the melted droplets drip from the arc onto a water-cooled pedestal and are immediately solidified.
Sometimes an inhomogeneous, composite structure is desired, as in cemented tungsten carbide cutting tools. In such cases, the alloy is not melted but is made by powder metallurgical techniques
Digging a bit deeper into alloy chemistry demonstrates why alloys are so useful in such a wide variety of industries.
Because alloys combine different elements, they contain atoms of different sizes. How these atoms combine and interact with one another gives alloys their classification. In alloy chemistry, an alloy can be classified as substitutional or interstitial, according to its atomic arrangement.
Substitutional alloys
A substituational alloy is formed from atom exchange mechanisms. The metallic components have similar atomic radii and chemical-bonding capabilities, so the atoms from one metal can occupy the same sites as their counterpart in the atomic metal lattice. Well-known substitutional alloys include brass and bronze.
Interstitial alloys
An interstitial alloy is formed when smaller atoms from one element fill the holes of the metal lattice. The atoms from each element do not occupy the same sites.
Steel is an example of an interstitial alloy. In the case of steel, the smaller carbon atoms fill in spaces between iron atoms.
Chemistry is fascinating, but we’ll get to the point: in both instances, the atoms in the alloy are unable to slide over each other as easily as those in a pure metal, meaning that the alloy is stronger and harder than either of the pure metals used to create it.
Think of it like velcro: if you only have one side of the velcro, it won’t stick to itself as firmly as the contrasting loops and hooks will grip together.
Properties Of Alloys
There are more than 100 properties a material could have, but we’re going to focus on the ones we think are most important for metals and alloys, they are:
Mechanical Properties
Brittleness
Metal is brittle if it breaks when it’s exposed to small amounts of stress. Often, brittle material will create a ‘snap’ sound when it breaks, such as plastic or ceramics. The alloy steel is brittle at low temperatures, but this depends on composition and processing.
Cast iron is known for being a brittle metal. It has a low tensile strength which means it will break before it bends. Because it cannot be bent without breaking, casts are used to shape the metal in its liquid form.
One of the most popular uses of cast iron is skillets, pans and pipes; the automotive industry also uses cast iron for cylinder heads, cylinder boxes and gearbox heads.
Ductility
Ductility is metal’s ability to be pulled away or elongated into a wire without breaking. Think about taking a lump of plasticine in your hand and slowly pulling it in opposite directions with either hand.
You can see the wires in the plasticine start to break as you pull it apart. It’s the same process with metal, but it isn’t as obvious.
There are plenty of ductile metals, such as copper and platinum. Copper is commonly used for wiring and platinum is stretched out to make jewellery. Platinum is the most ductile metal.
Malleability
People often get malleability confused with ductility, but metal can be malleable without being ductile.
While ductility refers to the capacity of metal to stretch (tensile stress), malleability refers to its capability to shape (compressive stress).
Shaping could mean being pressed or rolled into thin sheets. For example, you could take a lump of gold or aluminium and press it into a thin sheet to make gold leaves.
However, this is a rare use of malleable metal, and you can find them in most areas of life, such as aluminium tin cans, ornaments and kitchen utensils.
Elasticity
Elasticity refers to the capacity of metal to be deformed and then move back into its original shape. Contrast this to ductility and malleability where the metal stays in the position it is stretched or shaped into.
For example, let’s consider steel wire and rubber wire. Which one do you think is more elastic? It seems like a rubber wire would be the logical answer, but it’s wrong.
Rubber is more stretchable than steel, but it doesn’t go back to its original formation after the stress is reduced, whereas steel does.
The wire would snap after a certain amount of pressure, whereas steel would move a little and move back a little.
Most metals are elastic to some degree, as the range of movement will be small.
Hardness
Hardness refers to the ability of metal to resist denting or abrasions following force or impact. Because there are so many different methods of testing hardness, the correct definition is often confused.
For example, hardness has nothing to do with ductility or brittleness; metal can be hard, as well as ductile or brittle.
Tungsten is one of the hardest alloys on the planet. It is often used in mining to create drilling and excavation tools, as well as marine vehicles, aircraft turbines and blades in stationary power supplies.
Fatigue
Fatigue is the weakening of metal after a period of pressure is applied, causing localised structure damage and cracks in the metal.
Once a crack has appeared, the sequence of pressure will continue to worsen it until it gets to a critical size and the metal fails.
Most metals will experience some fatigue, but it isn’t easy to tell on some of them. For example, aluminium is rumoured to have no fatigue limit, which isn’t true.
The fatigue limit on aluminium isn’t as apparent as the fatigue limit on steel, so it’s a challenge to know when it will fail.
Physical Properties
Density
When we talk about density, we’re talking about how heavy metal is. The weight of metal is determined by how many atoms are packed into the surface area. Density refers to how the metal interacts with other materials.
For example, the densest metals osmium and iridium would sink in water because it is denser, whereas lithium would float due to its low density.
Dense metals have plenty of applications such as bullets and radiation shielding (lead), and weights from anchors to paperweights – which will often be covered in a ‘prettier’ chrome.
Melting Point
The melting point of the metal is quite simple; it’s at what point the metal changes from a solid to a liquid. At this point, the metal is in equilibrium between both states.
The melting point is important because most metals and alloys are combined at the liquid point. For example, to make an alloy wheel, you would liquify aluminium and magnesium, and add other elements.
The melting point of metal will determine what is it used for, for example, tungsten has one of the highest melting points, so it is used in lightbulbs to combat the heat generated.
Chemical Properties
Corrosion Resistance
Corrosion is the gradual destruction of metal by chemical or electrochemical interaction with the environment, which is usually oxygen or sulfates.
Rusting is a typical example of corrosion, which is the formation of iron oxides on the metal. There are numerous ways to protect from corrosion, such as surface treatments or cathodic protection.
Stainless steel is a prime example of a corrosion-resistant metal. It’s strong, easy to maintain, has a long-life cycle and is recyclable.
Stainless steel is used in countless day-to-day products such as zips, fridges and huge structures like The Chrysler Building and the One World Trade Center.
Reactivity
Reactivity refers to how metal interacts with part of its surrounding environment, like air or water. Some metals are more reactive than others and will react vigorously to an encounter with air or water.
Potassium is the most reactive metal when it comes into contact with water and air. The oxygen in the air causes the potassium to burst into a purple flame, and it tarnishes at room temperature.
When placed into water, potassium bounces around on the top of the water with the same purple flame and dissolves into a colourless liquid.
Just because metal is reactive, it doesn’t mean it can’t be used in the alloying process; for example, magnesium is often combined with other metals to prevent rust.
What Are The Different Types Of Alloys?
Alloys combine a base metal with other elements to change its composition and strengthen its intrinsic properties. There are many different types of metal alloys, and the combinations within are nearly endless. Here are some of the most popular alloys and their applications.
Stainless Steel Alloys
Stainless steel is an alloy comprised of iron and carbon. You can differentiate between various steel alloys by the addition of other elements, such as nickel, copper, or manganese.
Stainless steel is famous for its use in kitchen appliances, cookware, and cutlery. Its stunning finishes range from matte to shiny, and it’s incredibly durable and easy to clean. Its anti-corrosive properties also make it useful in machinery applications.
Aluminum Alloys
On its own, aluminum isn’t the strongest metal—but when you add elements such as iron, copper, or zinc, you increase its strength and durability.
These alloys are lightweight and corrosion-resistant, and they’re often more affordable than other alloys. They also tolerate extreme temperatures very well. Aluminum alloys are common in mechanical engineering and aerospace manufacturing.
Bronze Alloys
Bronze contains copper and other additives. The additional ingredient may be tin, silicon, aluminum, manganese, phosphorus, or various other elements. Though they’re similar in color and appearance, bronze is not the same thing as brass—the latter is a combination of copper and zinc.
Bronze’s dull color is recognizable in medals, sculptures, and musical instruments. Its hardness and resistance to corrosion have also made it popular in ships and other nautical applications.
Nickel Alloys
Nickel is one of the most versatile metals. These alloys are often combinations of nickel and iron, copper, molybdenum, or chromium.
These alloys resist corrosion and oxidation well, and the wide range of compositions makes them applicable to several industries. This includes marine piping systems, pressure valves, or pump shafts. They’re also common in gas or steam turbines and medical equipment.
Example Of An Alloy
Brass
Brass is an alloy of copper and zinc. Brass has a low melting point and is extremely workable and durable. It is used in applications where low friction and resistance to corrosion is required such as:
- Locks
- Bearings
- Ammunition components
- Appliance parts
- Decoration
Phosphor Bronze
Phosphor bronze is composed of copper alloyed with 0.5-11% tin and 0.01% phosphorus. It is resistant to corrosion and fatigue and should be used in:
- Welding rods
- Bushings
- Bearings
- Springs
- Switch parts
- Ship propellers and other applications in the marine environment
Steel
Steel is an alloy of iron and carbon. It has a high tensile strength and low cost. Mead Metals stocks many classifications of steel such as stainless steel, annealed and tempered spring steel and cold rolled steel. It is often used in:
- Automotive parts
- Infrastructure
- Construction
- Household products
- Kitchen appliances
Beryllium Copper
Also known as Alloy 25 or BeCu, beryllium copper is a copper alloy with 0.5%-3% beryllium. It is weldable, ductile, and has non-magnetic and non-sparking qualities.
It is resistant to oxidation, corrosion, and non-oxidizing acids. Additionally, beryllium copper has excellent thermal and electrical conducting capabilities. It is often used in:
- Electronic connector contacts
- Small springs
- Musical instruments
- Computer components
- Tools for hazardous environments such as aerospace engineering and metalworking
List of Examples of Alloys
| Alloy | Components | Comments |
| Amalgam (Dental) | Mercury, Silver, Tin, Copper | Hg content is about 50%, Ag is 22-32%. About 1% Zn may also be added. |
| Brass | Copper, Zinc | Cu content is about 65% in the softest brasses and 35% in the hardest brasses. May also contain Pb, Si, Sn, Fe, Al, and Mn. |
| Bronze | Copper, Tin | Sn content is about 12%. Other elements such as Al, As, Mn, Ni, P, Si, and Zn may be added to improve strength or ductility. |
| Duralumin | Aluminum, Copper, Manganese, Magnesium | Al content is 95%, Cu 4%, Mg 0.5%, and Mn 0.5%. May also contain Si. The alloy is stronger than pure Al for structural use in cars, aircraft, etc. |
| Pewter | Tin, Copper, Antimony, Bismuth | Sn content is 85-99%. Lead and silver may also be added. |
| Solder | Tin, Lead | Sn content is 5 – 70%. More Sn leads to higher shear and tensile strength. For specialist applications, other elements including Bi, Ag, and Zn can be added. |
| Solder (Lead Free) | Tin, Zinc, Copper | Sn content is 50 – 95%. Cu may be replaced by Ag. |
| Steel | Iron, Carbon | C content is usually lower than 2%. |
| Steel (Stainless) | Iron, Chromium, Carbon | Cr content is at least 12%; Ni may also be added to inhibit corrosion. |
| Steel (Tool) | Iron, Carbon, Manganese, Chromium, Tungsten, Silicon, Vanadium | C content is 0.6 – 1.3%. Other elements vary from 0 – 2%. |
Advantage of Alloys
Compared to pure metals, alloys have better corrosion resistance, lower costs, higher strength and better workability. The alloys’ production and composition determine specifics such as machinability, ductility and brittleness.
Alloys offer multiple benefits that pure metals don’t have. By using alloys, you get the advantage of a custom blend of metals that combines the materials’ positive attributes.
Depending on the components in the alloy, the products that use them could have the following benefits over objects made from pure metals:
- Corrosion resistance
- Better solderability
- Durable parts
- Lighter weight for the strength
- Thermal conductivity
- Electrical conductivity
Experts in choosing alloys and combining the metals to make them in the perfect proportions can optimize their properties for the product used.
Disadvantages of Alloys
The limitations of alloys compared to pure metals are listed below:
- Less Ductile: Alloys are typically less ductile than their pure metal constituents. While this can be a functional benefit in a finished part, it increases processing costs. Keep this in mind during the design process.
- Difficult to Weld: Alloys have lower melting points than their pure metal counterparts. This makes alloys harder to weld.
- Difficulty in Recycling: Alloys are more difficult to recycle than pure metals because alloys have many constituent materials.
- Can Be More Prone to Corrosion: While many alloys experience improved corrosion resistance over pure metals, this is not true for all alloys. Some are more susceptible to different forms of corrosion, such as galvanic or intergranular corrosion, which is less likely to occur with pure metals.
- Environmental Concerns: The production of some alloys can release hazardous and harmful fumes into the atmosphere. Creating alloys often requires more intense levels of energy, increasing their carbon footprint.
Application of Alloys
Alloys appear everywhere – any metal parts you encounter in your day, from a bicycle frame to a spoon, from a crane to a car, are made from alloys, as we rarely use pure metals. Some typical applications of the common alloy groups are:
#1. Construction.
We see Steel and Aluminum alloys used often in construction, exploiting their elevated strength and durability. The range of construction applications is extensive, from rebar (mild steel) to faucets (brass), from sidings (Aluminum) to beams (hot or cold rolled steel), from window frames (Aluminum) to handrails (stainless steel).
#2. Transportation.
We also see Aluminum alloys being heavily utilized in the entire transport sector. Airframes and skins/control surfaces (Aluminum), truck chassis (steel and Aluminum), monocoque car bodies (steel), fuel tanks (Aluminum or steel), engines (Cast Iron, Aluminum).
They are typically high strength-to-weight ratio, are corrosion-resistant, and recyclable. Aluminums weight influences fuel efficiency by reducing overall vehicle weight while still fulfilling strength requirements, while steel is heavier but more fatigue-resistant.
#3. Electronics.
Alloys play a wide range of key roles in electrical components, offering tunable beneficial properties like high conductivity, high resistance, strength, and corrosion/electrochemical resistance.
Cupro-Nickel and brass alloys are used in electrical wiring, switchgear, and connectors because of their superior electrical conductivity combined with mechanical durability.
Nickel-chromium and Manganese alloys are used in resistors and heating elements, where precise electrical resistance and heat tolerance are required.
The choice of alloys for electrical/electronic applications seeks performance, longevity, and operational efficiency.
By tailoring the composition of these alloys, the desired balance of electrical and physical properties can be tuned, making various alloys key to modern electrical and electronic devices.
#4. Medical Devices.
Alloys are vital in medical devices, a major industry that Xometry services, delivering the required biocompatibility, strength, and corrosion resistance for implants, joint replacements, and stents, which must integrate well with and be tolerated by body tissues and fluids.
Surgical instruments and dental devices are from various alloys, ensuring durability and precision. Typical metals/alloys tolerance of sterilization methods without degrading is central to their suitability for medical applications, patient safety, and device longevity.
#5. Jewelry
Gold, Silver, Platinum, and other precious metals are used in jewelry. Despite their attractive properties, they are rarely used in pure form, as they are typically too soft to serve durably.
Bronze, Cupro-Nickel, Nickel-Silver, and many more alloys are used to create lower cost jewelry. Alloying allows selection/control of the colors that can be obtained, which are not possible with pure metals.
#6. Manufacturing.
Alloys serve in all aspects of manufacturing, making both the machines/tools that perform the tasks, the buildings that house the machines, and the products that the machines make.
Few areas of manufacture use pure metals – examples being chemical/catalytic processes and electrical conductors (typically high purity Copper or Aluminum).
How Is an Alloy Different From a Pure Metal?
Chemistry
You can trace the distinction between metals and alloys back to the elements that compose them. All the atoms in a pure metal are the same.
For instance, chromium is a pure metal since it’s on the periodic table. In contrast, atoms of various elements mesh to form an alloy. Stainless steel, for instance, combines chromium, iron, and carbon.
Strength
Alloys are composites of many metals, each contributing desirable features while canceling out the negative features of others. By doing so, an alloy has superior strength compared with the original metals.
Since pure metals can weaken, alloying is beneficial to generate a harder metal complex. Unlike pure metal, which consists of identical atoms, metal alloys include various elements.
Alloys of metals are often significantly stronger and harder than pure metals because of their tightly packed atoms.
Gold is a prime example of this. In its purest form, gold is a surprisingly malleable and pliable metal. But you can blend gold with zinc, copper, or silver to create beautiful, durable alloy jewelry.
Heat-Resistance
Alloys have a variety of melting points due to the combination of metals they contain and their respective melting points.
When you combine metals, the melting point can increase, even if one metal melts at a relatively low temperature.
This has enormous practical value for industrial applications like aircraft engines, where temperatures may reach very high levels.
Stimuli Response
Adding alloying elements to pure metals like iron is a major benefit because of how fast and powerfully they respond to external stimuli.
Pure metals may rust, oxidize, or corrode over time due to environmental factors like oxygen and water.
Alloys, on the other hand, are mixtures of less reactive metals that extend the life of the material they form. For example, the chromium in stainless steel makes it resistant to corrosion.
Understanding the differences between alloys and pure metals indicates why alloy is a great resource. Since 1976, Thin Metal Sales has provided customers with high-quality, thin-gauge sheet metals.