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. What is an alloy and why are they created?
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. They are created to enhance the properties of the primary metal, such as increasing its strength, hardness, or resistance to corrosion. For example, pure iron is relatively soft and rusts easily, but when alloyed with carbon, it forms steel, which is much stronger.
2. What are the constituent metals of Brass and Bronze, and where are they commonly used?
Brass and Bronze are two common alloys with distinct compositions and uses:
- Brass is an alloy primarily made of copper and zinc. Due to its gold-like appearance and corrosion resistance, it is often used for decorative items, plumbing fittings, and musical instruments.
- Bronze is an alloy consisting mainly of copper and tin. It is very hard and resistant to corrosion, making it ideal for statues, medals, coins, and marine hardware.
3. What are some important uses of alloys in our daily lives?
Alloys are integral to modern life. Common examples include:
- Stainless Steel (iron, chromium, nickel, carbon) used for kitchen utensils, cutlery, and surgical instruments due to its resistance to rust and stains.
- Duralumin (aluminium, copper, magnesium) used in aircraft frames and high-performance vehicles because it is lightweight yet strong.
- Solder (tin, lead/copper) used in electronics for joining components on a circuit board.
- Gold Alloys used in jewellery, where pure gold is mixed with metals like copper or silver to increase its durability.
4. What is the main difference in composition and properties between steel and stainless steel?
The primary difference lies in the addition of chromium. While steel is an alloy of iron and carbon, stainless steel is an alloy of iron, carbon, and a significant amount of chromium (at least 10.5%). This chromium forms a passive, self-repairing layer of chromium oxide on the surface, which gives stainless steel its characteristic high resistance to rust and corrosion, a property regular steel lacks.
5. How does the structure of an alloy make it harder than its pure constituent metals?
In a pure metal, the atoms are arranged in a regular, uniform lattice, allowing layers to slide over one another easily when force is applied. When another element is introduced to form an alloy, its atoms (which are often of a different size) disrupt this regular lattice structure. This distortion makes it much more difficult for the layers of atoms to slip, thereby increasing the overall hardness and strength of the material.
6. Why are alloys like duralumin and titanium alloys so crucial in the aerospace industry?
The aerospace industry requires materials with a high strength-to-weight ratio. Pure metals are often either too heavy (like steel) or too soft (like aluminium). Alloys provide the solution:
- Duralumin (aluminium alloy) is nearly as strong as steel but significantly lighter, making aircraft more fuel-efficient.
- Titanium alloys are used for engine parts and structural components because they are extremely strong, lightweight, and can withstand very high temperatures without losing their structural integrity.
7. Can non-metals be used in alloys? Provide an important example.
Yes, non-metals play a crucial role in some of the most important alloys. The most prominent example is carbon in steel. A small amount of carbon atoms fits into the spaces between the larger iron atoms in the metallic lattice. This introduction of a non-metal element significantly increases the hardness and strength of the iron, transforming it from a relatively soft metal into the strong, versatile material known as steel.
8. What is amalgam and what is its specific use?
An amalgam is a special type of alloy where one of the constituent metals is mercury. The most common application of amalgam is in dentistry. A dental amalgam is an alloy of mercury with other metals like silver, tin, and copper. It has been widely used as a durable and affordable material for filling dental cavities.
9. Why are alloys considered homogeneous mixtures and not compounds?
Alloys are considered mixtures because they exhibit the properties of their constituent elements and do not have a fixed chemical formula or melting point. The components of an alloy are not chemically bonded and can be mixed in variable compositions to achieve different properties. For example, the percentage of zinc in brass can be varied. In contrast, a compound has a fixed ratio of elements bonded chemically and has properties entirely different from its constituents.
10. Besides strength and corrosion resistance, what other properties can be modified by creating an alloy?
Creating an alloy allows for the fine-tuning of several properties beyond just strength. Other key modifications include:
- Lowering the melting point: For example, Solder has a lower melting point than its components (tin and lead), making it useful for joining electronic parts without damaging them.
- Modifying electrical conductivity: The electrical resistance of an alloy is generally higher than that of its pure metal components.
- Changing the colour and lustre: Alloying gold with copper creates 'rose gold', changing its appearance for use in jewellery.
