Overview of Alloys
Pure metals are usually never used in industries for manufacturing purposes. Usually, we observe that a combination of metals is used to enhance the properties of a single metal.
We know that your metals have certain important physical properties such as density, malleability, ductility, conductivity, boiling point, melting point etc. However, these properties can be slightly changed and also enhanced by mixing two or more metals together as per the need.
This combination of metals is known as an alloy. An alloy is a homogeneous mixture of two or more metals. It may also contain metal and non-metal. Alloys give more strength and last for a longer time as compared to metals.
What is an Alloy?
Alloy is a homogeneous mixture that consists of two or even more metals, homogeneous means denoting a process involving substances in the same phase, it could be liquid, solid or gas form. It can even consist of a metal and a nonmetal. These metals are mixed in a fixed proportion by mass in molten states. Alloying is a method used to improve the properties of metals. The various properties that can be achieved by using this method are bronze, brass, nichrome, pewter, steel, duralumin, solder and amalgam. Pure metals can not be used for manufacturing processes in industries and hence alloys are made to enhance the properties of pure metals.
Importance of Alloys
Alloy plays great importance in the manufacturing process but it does have a few more important and advantages. Let us look at the top 5 advantages of Alloys.
Alloys help to increase the metal hardness as it is a mixture of more than one metal or nonmetal. The constituent elements do not have tensile strength as much as alloys and hence it's a great option for increasing hardness in metals.
The melting point of pure metals is very high and alloying helps to reduce the melting point range. For example, If you add 62% of tin and 38% of lead alloy we would have an alloy with the lowest melting point than either of the pure metals. This confirms that alloying reduces the melting point range of metals.
Metals are used in various industries and have been used almost in everything around us. The weather can influence the metal resulting in corrosion. Hence, by alloying the resistance increases and cannot be influenced by chemicals or weather conditions.
The process of alloying changes the metal colour when mixed together, two different metals or one metal and another non-metal. The colour that is obtained is different.
Alloying helps in the good casting of metals, as pure metals tend to solidify when melted and contract as well. After they are alloyed they tend to expand and result in a good casting.
Alloys - Constituents and Uses
Stainless Steel is made of Iron and chromium-nickel and is mostly used in manufacturing surgical instruments, watches and making of utensils.
Coin metal is made of copper and nickel and is used to make coins.
Solder is made of tin and lead and is used for soldering.
Bell Metal is made of copper and tin and is used for bell casting and for statue construction as well.
Duralumin is made of aluminium, copper and manganese; it is used for the construction of wires, bars, aeroplanes, ships, etc.
Bronze is made of copper and zinc and is used in making window frames, bearings, bushings, sculptures, etc.
Sterling Silver is made of silver and copper and is used in making medals, coins, art, utensils, jewellery, medical instruments, etc.
Brass is made of copper and zinc and is used in musical instruments, decorative items, etc.
What are the Advantages of Using Alloys Over Metals?
Alloys have certain advantages over metals. Some of them are as follows.
An alloy has more tensile strength than its constituent elements. We can increase the hardness of a metal by mixing it with another metal or nonmetal.
Metals melt at very high temperatures. When a pure metal is alloyed with another metal or nonmetal, its melting point reduces.
Metals are extremely susceptible to chemical and weather attacks. Alloys, on the other hand, are more resistant to corrosion. When a metal is alloyed, it becomes inert, thereby enhancing its corrosion resistance.
Alloying can be used to change the colour of the base metal. By mixing another metal or nonmetal, the alloy so formed will have a different colour.
When pure metals are solidified after melting, they tend to contract a little. However, when they are alloyed, they tend to expand on solidification. This helps to obtain good castings.
Various Alloys and Their Composition
Bronze was the first to be discovered; it is a mixture of copper (88%) and tin (12%). Very small quantities of zinc, nickel or manganese may be added to improve the overall properties.
Steel is made by mixing iron and carbon (1%). It is harder and resistant to corrosion.
Brass is made by mixing copper (60-85%) and zinc (15-40%). Other elements may be added in smaller proportions. Brass is made to enhance the electrical properties of copper.
Alnico is an alloy formed by mixing iron with nickel, cobalt and aluminium (Al-Ni-Co). It is a ferromagnetic substance and is used in permanent magnets.
Solder is an alloy of tin and lead. It has a low melting point and is used to repair or join two pieces of metals.
Cast iron is formed by mixing iron (96-98%) with carbon (2-4%). Some traces of silicon may also be found. This alloy has a good castability, doesn't get deformed and has a low melting point.
Sterling silver is formed by mixing 92.5% silver with 7.5% of another metal, usually copper. Silver gets corroded and turns black if the air contains sulphur compounds. In order to reduce the tarnishing of silver, copper or other metals can be mixed to form this alloy.
Nichrome is an alloy formed using nickel, chromium and iron. It has a very high resistance, a high melting point, ductility etc. It offers resistance to the flow of electrons and does not get oxidised easily.
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Everyday Uses of Alloys
Alloys have wide-ranging applications in our everyday life. Some of the most common uses of alloys are as follows:
Mini sculptures, medals and some musical instruments are made from bronze.
Steel is used for the construction of railways, bridges, roads, airports etc. It is also used for making household utensils and other products.
Locks, door handles, doorknobs, electrical appliances, zippers, musical instruments, decoration and gifting items are made from brass.
Permanent magnets are made from alnico.
Solder is used to permanently join electrical components.
Sterling silver is used to make surgical instruments, musical instruments, cutlery and pieces of jewellery.
Alloys of aluminium are lightweight, therefore used for making bodies of aircraft and their parts.
Alloys of titanium are extensively used in the aerospace industry because of their high-temperature strength and superplastic behaviour.
Amalgam, which is an alloy of mercury, is used for medical activities. It is also used to fill tooth cavities.
Certain alloys of gold such as rose gold, are used for jewellery making purposes.
Fun Facts:
Many alloys that contain silver in their name usually do not contain silver as one of their constituent elements. They are called 'silver' only because of their colour. Examples of this are Tibetan silver and German silver.
Stainless steel, which is formed by mixing iron, small quantities of carbon and chromium is called 'stainless' because chromium gives it resistance from any kind of stain or iron rust. The chromium reacts with oxygen to form a thin layer of chromium oxide, which acts as the protective layer against any further corrosion.
Iron is the most used metal globally but it cannot be used in its pure form as it is soft and stretchable when heat is applied. At the same time if you add a very small amount of carbon to iron it becomes hard.
Copper is a good conductor of electricity and hence is used in wires to transmit electricity but the same copper when mixed with zinc or tin, we get alloys brass and bronze are not good conductors of electricity.
FAQs on Uses of Alloys
1. Explain the difference between steel and stainless physics.
Steel is formed when carbon is added to iron to increase its hardness. Steel has a higher carbon content and a low melting point. Stainless steel contains a higher amount of chromium. This chromium forms a layer of chromium oxide that acts as a barrier against corrosion. It does not allow any stains or marks to appear on the surface. This is why stainless steel does not get rusted or corroded.
So, containing higher carbon content has more strength as compared to stainless steel. Steel is used for manufacturing bridges, railways and buildings. Stainless steel on the other hand, is mostly used for making utensils and household items.
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2. What are the applications of alloy in the aerospace industry?
Aluminium is a lightweight metal and its alloys are widely used in the aerospace industry. Specially designed alloys allow the aircraft industry to manufacture high strength parts for jet engines. These parts have to deal with the extremities of pressure, temperature and vibration. Stainless steel, nickel, copper, titanium and their alloys are used for making engine blocks. They also provide high strength and the ability to function at very high temperatures. These alloys are designed to have extreme strength, corrosion resistance and efficiency at unusually high temperatures.
3. Why can alloys not be separated even though it's a mixture?
Alloys consist of a mixture of more than one metal, it can also be a mixture of a metal and non-metal. Even though it's a mixture it cannot be separated into individual components. Alloy is considered as a mixture as it has all properties and constituents of a mixture and also has variable composition. Hence, the metals mixed to make alloys cannot be separated by physical means and if done using chemicals you would have to dissolve both the metals and separate them.
4. What are the conditions for alloys?
The explanation for alloy formation - Transition metals have atomic sizes that are highly similar to one another, which contributes to their ability to create alloys. Because the atomic sizes of the two metals are so close, one metal can easily replace the other in its lattice and produce a solid solution. This solid solution is known as an alloy. Examples of alloys are brass, bronze, copper, stainless steel, duralumin, solder, bell metal, coin metal, etc.
5. What does a physical change of alloy mean?
A physical change is a type of change in which the shape of the matter is altered but not transformed into another material. It is possible to change the size or shape of matter, but no chemical reaction happens. The majority of physical changes are reversible. It's worth noting that whether or not a process is reversible isn't a true criterion for whether or not it's a physical change. Smashing a rock or shredding paper, for example, are physical alterations that cannot be reversed.
