Metals and Alloys - Secondary 4

When being used, the materials of a technical object can undergo constraints causing deformations. The materials are also likely to deteriorate. Therefore, special attention must be given to the choice of materials depending on the purpose of the technical object involved.

In nature, metals are rarely found in their pure state. More often, they are mixed with other substances in ores in the Earth's crust. Once the ores are mined, they can undergo various processes to separate the different substances in the ore.

Apart from ores, metals are also found in meteorites.

Over 90 different metals can be found in the periodic table of elements. Metals generally have a lustrous (or shiny) appearance and conduct heat, as well as electricity. Since the metals have a wide variety of properties, only some of them are used frequently to manufacture technical objects.

The following tables show some of the most commonly used metals along with their mechanical, physical and chemical properties (called physicochemical). Metals are more likely to be used in the form of an alloy than in the form of an element (in their pure state).

When developing a technical object, materials are chosen for their specific properties. It is the reason why alloys are often more useful than metals in their pure state. In fact, mixing substances makes it possible to combine their properties. In some ways, metals are customised to obtain an alloy with specific properties to meet our needs. It is possible, for instance, to increase the hardness of a metal, thus improving its resistance to wear while maintaining good malleability.

Alloys are generally classified into two categories: ferrous alloys and non-ferrous alloys.

Iron is one of the most common elements in the Earth's crust. It is ductile (can be stretched), malleable (can be flattened into sheets), and magnetic. However, iron in its purest form is not resistant to corrosion or wear. By combining it with carbon, its rigidity and hardness can be increased. Depending on the proportions of iron and carbon found in the alloy, its properties will be modified differently.

The most common ferrous alloys include iron and carbon. Nevertheless, iron can be alloyed with other elements like chromium, nickel, and many other elements.

The following tables display several examples of ferrous alloys as well as their properties.

Non-ferrous alloys have various properties. Most magnetic alloys are, in fact, ferrous alloys, but some non-ferrous alloys can also be magnetic. To find out, a magnet can be used. If the magnet is attracted to the alloy, then the alloy is magnetic.

The following tables show several examples of common non-ferrous alloys and their properties.

Tempering involves heating an alloy that has already been quenched. Tempering must be done at a precise temperature that is lower than the quenching temperature.

Tempering allows the alloy to regain some ductility and resilience while preserving the hardness gained through quenching. The higher the tempering temperature, the more ductile and less hard the alloy will be.

Annealing involves heating an alloy and then letting it cool slowly.

Annealing somewhat reduces the hardness of an alloy. It also helps restore its original properties after it has undergone another heat treatment or been deformed. For example, annealing is used to eliminate traces of welding.

All metals are different, so their properties may vary greatly from one metal to another. However, certain properties are found in several metals. In fact, in terms of mechanical properties, the metals and alloys used to manufacture technical objects are often ductile and malleable (e.g., iron, aluminum, brass, etc.). With regard to physical and chemical properties, they are often lustrous substances, and effective electrical and thermal conductors. As for magnetism, it is particularly noticeable in iron, nickel, cobalt, and some other less common metals.

The tables above show the properties of metals and alloys commonly used to manufacture technical objects.