Malleability: Which Metals Can Be Hammered Thin?

Malleability is one of the key material properties engineers use to select an appropriate metal for use in a component or part of an assembly. It is as important as hardness and strength in many cases.

One of the reasons malleability is important is how it affects manufacturability. This article discusses what materials are highly malleable, and what real world applications they have.

What Is Malleability?

Malleability is defined as the ability of a material to be formed into different shapes by compressive forces, without cracking. It is one of the key material properties along with hardness, strength, ductility, etc.

One of the key reasons malleability is desired in certain materials is for ease of manufacturing. Many parts, particularly those produced in high quantities, are produced or re-shaped using compressive processes such as rolling, stamping or forming.

If a material is not sufficiently malleable, it will crack when subjected to such forces, rendering it useless.

Top Malleable Metals

Whilst alloying elements can be added to improve a metal’s malleability, there are a number of natural metals that have extremely high malleability. These include:

• Gold – used extensively in fine jewellery
• Silver – also used in jewellery and tableware
• Aluminum – used for aluminium foil, also formed into various shapes
• Lead – commonly used for roofing, where hammering to suit is vital

Alongside their other properties (rarity, electrical conductivity, ease of joining, etc), malleability is one of the key reasons why these materials are used for the purposes listed above. Each one requires the metal to be willing to take a new shape without fracturing.

Are there any Malleable Non-Metals?

Malleability is a key characteristic of metals, very few other materials display the same levels of plastic deformation without cracking. There are, however, a few exceptions, these include phosphorus and sulphur, both of which are lustrous solids at room temperature.

However, they do not exhibit the same levels of malleability as metals such as gold or silver.

Factors That Affect Malleability

Like any physical property, various things affect a metal’s malleability, and these are often exploited when used in manufacturing processes. These factors include:

• Purity
• Crystal structure
• Heat

There is a direct relationship between a metal’s composition and its malleability. Typically, materials that are of higher purity are more malleable. An example is copper and brass; the former is much more malleable than the latter, despite being an alloy mostly consisting of copper.

Impurities and alloying elements disrupt the uniform lattice structure of a pure metal, increasing the internal stresses as one layer slides over another to plastically deform.

Further disruption is caused by the differing atomic charges present, in a pure metal, all the atoms have equal attraction to one another. Adding in alloying elements or impurities disrupts this even distribution of force, causing cracking.

Heating most metals increases both their malleability and ductility. Blacksmiths use this principle to form steel with low malleability into complex shapes.

As metals are heated, the atoms gain kinetic energy, allowing them to move more freely in the material. Iron, for example, can easily be hammered flat when red-hot but would crack if this were done cold.

Real-World Applications of Malleable Materials in Industry and Manufacturing

Malleable materials are used all around us, whilst they are not always selected specifically for their malleability, it is often a helpful property during the manufacturing stage.

Gold

Gold is used extensively in jewellery and finely detailed objects such as clocks and ornaments. It is popular for this application mainly for its appearance and rarity, but also for its malleability.

As gold is so easy to form without the risk of cracking, it can be made into extremely intricate shapes. It is also commonly flattened into gold leaf, an extremely thin sheet of the material that can be used to add detail to items such as wooden furniture and books.

Copper

One of the most common uses for copper is in electrical conductors and wires. While copper’s ductility means it can be easily drawn into wires, its malleability allows it to be easily made into contacts and terminals.

This is especially useful as parts for things like consumer goods and vehicles are often made in large quantities, something that automated pressing and forming processes are heavily utilised for. Copper’s high malleability means these processes can produce complex parts in a small number of steps, without the risk of cracking.

Aluminum

Aluminum is both ductile and malleable. Like gold, it can be flattened into a very thin sheet, which we know as aluminum foil.

It is also used extensively for aerospace applications, thanks to its low density but high strength, its malleability lending itself well to forming flat panels for aeroplane bodies.

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