Alloys are composed of several chemical elements, of metallic or non-metallic origin. They often have improved properties compared to pure metals, such as greater mechanical strength or resistance to corrosion. Often made from iron, copper, nickel, titanium or aluminum, they are materials in their own right, with very specific characteristics.
Why make alloys?
An alloy is the combination of several chemical elements to form a final material. Manufactured from pure metals, they can also contain non-metallic components, the mixing of which results in the creation of new materials. Steel, for example, is an alloy of iron and carbon.
Most of the time, alloys have better mechanical or physical properties than pure metals. The alloying process inevitably modifies certain characteristics of the components. To make cast-iron, for example, we combine iron, which has a melting point of 1,538 degrees Celsius, with carbon, which has a lower melting point. Cast iron thus has a melting point lowered to around 1,250 degrees. However, contrary to popular belief, combining several chemical elements does not result in a combination, let alone an average of their properties, but in an entirely different material.
The result of alloying has physical and mechanical properties that are radically different from those of pure metals. Steel, for example, which combines iron and carbon, offers much better mechanical performance, on average 5 to 10 times better than pure iron. Similarly, aluminum alloys are 2 to 3 times stronger than aluminum alone.
The most common alloys
The most frequently encountered metal alloys are undoubtedly those made from iron, copper, nickel, titanium and aluminum.
The various steels, in particular stainless steels are certainly the best-known iron-based alloys . Highly versatile, they offer excellent resistance to corrosion and wear. Titanium alloys are mainly found in the medical, aerospace and sports and leisure industries, not least because of their light weight.
On the other hand, nickel-based alloys known as inconels are also widely used in industry for their excellent mechanical and corrosion performance. The combination of nickel with cobalt or chromium considerably increases the mechanical and heat resistance of these materials. As a result, inconels are widely used in the aerospace industry, notably for engine manufacture. There are also copper-nickel alloys, known as cupronickels. Other copper alloys can be combined with zinc or tin to produce brass or bronze. Copper is also one of the main components of an alloy used by the vast majority of human beings: nickel silver. Made from copper, zinc and nickel, nickel silver is used to manufacture coins and medals, as it is an unalterable, silver-colored alloy, highly resistant to corrosion and very malleable.
Rarer variants
Some rarer alloys have surprising properties. Made from titanium, nickel or copper, they can undergo several deformations and, following simple heating, regain their initial appearance. These are shape memory alloys. The design of these materials is based on the transformation of their crystalline structure. These alloys, still relatively unknown, are used in the manufacture of very long satellite antennas, which need to be bent for transport. Once on site, they simply need to be reheated to straighten themselves and take on their final shape.
Heat treatments for alloys
Unlike pure metals, alloys contain many different chemical elements. It therefore seems only logical that they should not all tolerate different heat treatments in the same way.
Thermal softening treatments
Softening heat treatments are used to make parts more malleable for further deformation or machining. There are several types of heat treatment, all of which appear to be suitable for the various alloys available. On the other hand, not all alloys can withstand hardening heat treatments.
Hardening heat treatments
While all alloys can be heat-treated to soften them, they are not as resistant to hardening operations. The purpose of hardening is to increase the mechanical strength of the material. Hardening processes include both thermochemical treatments and martensitic tempering. In the former, atoms are diffused onto the surface of the parts, creating new surface alloys and leading to surface hardening. Quenching, on the other hand, acts directly on the crystallographic structure of the part. In the case of alloys, martensitic quenching is used, which promotes the formation of martensite, a very hard component. For some alloys, the hardening mechanism is linked to the appearance of very hard precipitates: this is structural hardening.
However, only certain very specific alloy families can undergo thermochemical or martensitic hardening treatments. For example, of the various families of existing aluminum alloys, only the 2000, 6000 and 7000 series can undergo this type of operation , since heat treatment of these materials produces a hardening precipitate. Other aluminum alloys that do not form a hard precipitate cannot be hardened by heat treatment.
The Thermilyon Group can help you choose the alloy and heat treatment best suited to your needs. Tell us about your project here.
