The amazing property of malleability in certain metals is put to good use in almost every sector of engineering. Manageable malleable metals can be hammered, rolled or pressed into thin sheets without breaking.
It’s similar to the concept of moulding dough, which can be spread out with a rolling pin, elongated using the hands, pushed through a hole using pressure to create strips, or even shaped back into its original mass. If the correct means are used to manipulate the material, the process can be carried out without breaking the continuity of the particles that compose the mass.
How was malleability discovered?
Born in 1814, French engineer Henri Édouard Tresca carried out extensive research in the field of non-recoverable deformations and plasticity. As a professor in Paris at the famous higher education establishment, the Conservatoire National des Arts et Métiers, he explored the theory through many experiments that he started in 1864.
He discovered the Tresca (the maximum shear stress) criteria of material failure – a discovery that was named after him. The Tresca is still used today to assess the criteria for ductile materials. His engineering skills and theories were instrumental in the building of the Eiffel Tower, whose creator, Gustave Eiffel, put Tresca third on the list of the 72 people who made its construction possible in 1887.
How is malleability measured?
Each metal’s malleability is measured by how much competitive stress or pressure it will withstand without breaking. The malleability is the property of a metal to de-form under compression, so it can be reshaped into a different form. Differences in various metals’ malleability is determined by the variance of their individual crystal structure.
What’s the science behind malleability?
The atoms are forced to roll over each other by the compression stress, placing them in new positions, without their metallic bond having been broken. Putting large amounts of stress on a malleable metal forces the atoms to permanently stay in their new positions.
The crystal structure of a harder metal makes it more difficult to mould the atoms into a new position without breaking the metallic bond. More grain boundaries exist in harder metals and hence the rows of atoms don’t line-up.
Metals are prone to fracturing at grain boundaries, as the atoms aren’t as strongly connected. When a metal has more grain boundaries, it tends to be more brittle, harder and less malleable.
Examples of malleable metals
Among the most manageable malleable metals are gold, iron, silver, copper, aluminium, lithium, tin and indium. Manufactured products that demonstrate malleability include lithium foil, gold leaf and indium shot. Harder metals that are less malleable include antimony and bismuth.
In the case of steel, the process is extremely slow, but with time, patience and the correct pressure, it will flow gently into any shape while in a solid condition. The flowing properties of the softer metals have been of great benefit in industry, particularly in the bending of pipes and other applications. Jewellery is crafted from gold, silver and platinum, while electronic circuits and cutlery are made from malleable metals.
What is ductility?
While malleability describes a metal de-forming through compression, ductility is the property which allows a metal to stretch without being damaged. Some metals have both good malleability and good ductility, such as copper: its ductility means it can be stretched into wires, while its malleability enables it to be rolled into copper sheets.
The two properties can also be exclusive, although the majority of malleable metals are also ductile. Most metals, become more malleable when heated, as the temperature affects the crystal grains within the metals.
What are the effects of temperature?
Temperature affects the behaviour of atoms, so heating most metals leads to the atoms having a more regular arrangement, thus reducing the number of grain boundaries, while producing a softer and more malleable metal. An example of this is heating zinc, which is brittle when its temperature is lower than 300°F. However, when it’s heated, it becomes malleable enough to roll into sheets.
Metals become liquids when heated to a temperature higher than their melting point, when their atoms move more freely and are randomly arranged. When they are cooled to a temperature lower than their melting point, the metals re-form to create crystalline structures.
Employing a number of techniques to produce the required results for our clients, Pipecraft specialises in tube bending, tube manipulation and metal fabrication. For further information about our bespoke solutions, please contact us.