While we generally consider metals some of the hardest materials on the planet, several metals are soft and easily pliable. Malleability measures how easily a metal can be hammered or rolled into thin sheets and is a key property for many industrial and artistic applications. It allows metals to be formed into various shapes and sizes, from delicate jewelry to expansive metal sheets used in architectural designs. What are the most malleable metals?
Is Metal Malleable?
Malleability is a property that allows a material to be deformed under compressive stress; in other words, it refers to the ability of a metal to be shaped, bent, or stretched into thin sheets without breaking. This property is a key characteristic that makes metals versatile and valuable in various applications, from manufacturing and construction to art and electronics. Some metals, such as gold and silver, are exceptionally malleable. Other metals, such as steel, can be made malleable through various processes, including heating and alloying with other elements.
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Why are Metals Malleable?
Metals are malleable due to the unique nature of their atomic structure and the type of chemical bonds that hold these atoms together. In metallic bonds, atoms are arranged in a tightly packed, crystalline structure, and the electrons in the outer shells of these atoms are delocalized, meaning they are not bound to any specific atom but are free to move throughout the metal. This sea of delocalized or free electrons contributes to the cohesion and stability of the metal while allowing the atoms to slide past each other under force without breaking the bond.
When a malleable metal is subjected to compressive forces, such as hammering or rolling, the layers of atoms can slide over each other relatively easily. This sliding mechanism allows the metal to change shape without fracturing. The ability to deform in this way is due to several factors:
Metallic Bonding – The non-directional nature of metallic bonds means that no matter how the atoms are arranged, the bonding remains strong and uniform throughout the structure. This uniformity allows the metal to withstand deformation without the bonds breaking.
Crystal Structure – The crystalline structure of metals also plays a significant role in their malleability. Some crystal structures, such as face-centred cubic (FCC) and hexagonal close-packed (HCP), allow for more slip planes. Slip planes are directions within the crystal lattice where atoms can easily slide past one another. Metals with these crystal structures tend to be more malleable.
Ductility – Malleability is closely related to another property called ductility, which is the ability of a metal to be drawn into wires. Both properties stem from the ability of metal atoms to undergo significant plastic deformation.
Temperature – The malleability of metals can also be influenced by temperature. Heating a metal typically increases its malleability by allowing the atoms more freedom to move, making it easier for the layers to slide over each other.
Different metals exhibit varying degrees of malleability based on their atomic structure, the presence of alloying elements, and the processing methods they have undergone. Gold, for example, is extremely malleable due to its atomic structure, allowing it to be beaten into sheets so thin that they become transparent. Other metals, like steel, can be made more malleable through processes such as annealing, which involves heating and then slowly cooling the metal to reduce its hardness and increase its workability.
What is the Difference Between Ductility, Malleability, and Hardness?
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Before we can answer that question, we need to distinguish between the three properties that best describe soft metals:
Ductility – A material’s ability to change its shape and be drawn into wire without losing strength or breaking. We use special test equipment to measure elongation. To increase metal hardness, we can add certain alloys without decreasing the ductility.
Malleability – The ability of a material to deform permanently under compression without rupture. Ancient cultures defined it as the ability of a metal to be beaten into thin sheets. This property measures the ability of a metal to be rolled or hammered into a sheet. It is another form of plasticity. Although there is no specific test, we usually test the malleability of metal as hardness using either Rockwell or Brinell testing methods.
Hardness – The ability to withstand localized permanent deformation. This refers primarily to dents in the material. We can also use this term to describe a material’s resistance to deformation via:
- Abrasion
- Cutting
- Penetration
- Scratching
Put simply, there are three key differences between ductility, malleability, and hardness:
- Malleability and ductility refer to a material’s ability to deform under different types of stress (compressive for malleability, tensile for ductility) without breaking. Hardness, however, refers to the material’s resistance to being deformed or damaged under load.
- Malleability focuses on deformation through compressive forces (e.g., hammering or rolling into sheets), while ductility concerns the ability to withstand tensile stress (e.g., being stretched into a wire).
- Hardness is about resistance to deformation and abrasion, while malleability and ductility are about the flexibility and deformability of a material.
Types of Metal Hardness
Knowing the hardness of a metal is especially key in engineering design applications to ensure the material is suitable and will perform as needed.
There are three types of hardness:
Indentation – This is a material’s resistance to permanent deformation due to a localized continuous load. The process involves applying a constant load to the material until an impression is formed. The Rockwell hardness scale is commonly used to measure indentation hardness.
Rebound – This measure accounts for the material’s elastic hardness. The Leeb hardness test measures rebound hardness. A diamond-tipped hammer impacts the material and returns the energy, causing the hammer to bounce. The opposite of elastic hardness is plastic (indentation) hardness, where the object or material does return to its original shape after deforming.
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Scratch – This measure is the material’s ability to resist scratches and abrasion on its surface. The Mohs Scale measures scratch hardness on a scale of 1 to 10, with talc being a value of 1 and diamonds sitting at 10.
The Importance of Temperature
While several factors may impact the malleability of metal, the most significant are:
- Temperature
- The strength of the metallic bond
As the temperature increases, the metal’s valence electrons gain the necessary energy to move. This increases the vibration of the atoms, resulting in more collisions with drifting electrons. As the temperature rises, the distance between atoms increases, decreasing the strength of the material.
Yield stress also decreases with increased temperature, making the forming processes easier to perform. We advise caution as repeated stress can cause some materials, such as brass, copper, iron, silver, and steel, to become brittle.
What is the Most Malleable Metal?
Malleability in metals is a tricky topic. As we mentioned earlier, there is no subjective test to measure this property. Usually, we test it as hardness.
Gold and silver are the most malleable and ductile metals. In their pure states, gold and silver are too soft to make objects that will retain their shape. The malleability of gold and silver allows the creation of thin wires and sheets essential for detailed artistic work, electronic components, and decorative items. Both metals exhibit a combination of beauty and practicality, offering unmatched workability for various traditional and high-tech applications.
Gold’s atomic structure allows it to be beaten into sheets so thin that they become nearly transparent, known as gold leaf. This extreme malleability has made gold invaluable in various applications, from crafting intricate jewelry to its use in electrical connectors and even in aerospace technology for its excellent conductivity and resistance to corrosion. Interesting fact – we can draw an ounce of gold into a wire over 40 miles long!
Silver ranks just after gold in terms of malleability. It can also be hammered into very thin sheets, a quality that has been exploited for centuries in the arts and manufacturing. Silver’s excellent thermal and electrical conductivity and malleability make it highly sought after for electrical applications, jewelry, and tableware. Silver’s antimicrobial properties are used in medical devices and water purification systems.
The most malleable metals are as follows from least to most malleable:
- Tin (Sn)
- Zinc (Zn)
- Iron (Fe)
- Nickel (Ni)
- Copper (Cu)
- Aluminum (Al)
- Silver (Ag)
- Lead (Pb)
- Gold (Au) – The most malleable metal. We can roll gold into sheets thin enough to transmit light.
For those working on projects requiring metals that can be easily shaped or stretched or require a high resistance to wear, Metal Supermarkets is your go-to source. With an extensive selection of metals, including some of the most malleable metals available, we can help you find the perfect metal for your needs. Shop online for malleable metals at Metal Supermarkets, or visit your closest store and bring your projects to life with the highest quality materials available.
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