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Before going to explain the different-different properties of metals. Let’s just have some knowledge about the Metals and Alloys.
Metals and Alloys:
The metals are defined as the element substances found in nature. They are available chemically combined with other elements.
Metals are extracted from there ores.
The most commonly used metals in engineering are aluminum, copper, tin, lead, zinc, magnesium. Generally, metals are a good conductor of heat and electric current. They are opaque and can be polished to high luster.
Pure metals are soft they are seldom used in practice.
To make the metal useful for engineering application, some desirable properties are imparted to the metals by the addition of some other metals or elements like carbon, Boron, Silicon, Phosphorus, etc such a combined metal is called alloy.
It is defined as the homogenous mixtures of two or more chemical elements at least one of which is a metal to obtain certain desirable qualities than those possessed by original metals themselves.
An alloy the metal which will be in large portion to which other elements are added is called base metal and the added elements are themselves called alloying elements.
Some of the most common alloys in engineering practice are iron, wrought iron and steel all of them are alloys of iron and carbon in varying proportions,
brass- alloy of Copper and Zinc
The bronze alloy of Copper and Tin
Gun metal-alloy of Copper, Tin, and Zinc
and There are some more also.
Advantages of alloy over pure metals:
Alloys are stronger than pure metals.
Alloys are harder and more durable than pure metals.
Alloys can we cast since their melting point are lower.
Alloys have higher resistance to the action of acids.
Alloys are highly resistant to corrosion.
we discussed metal and alloys because the next topic we going to study is totally based on the metals and alloys.
Properties of Metals:
The properties of the metal are defined as the special qualities or characteristics of metals that determine their suitability for a specific engineering application.
Although metals have a wide range of properties, the knowledge of the important properties will be helpful in the section of the metals for a specific application.
Few of the properties of the metals which are very important are:
- Mechanical properties
- Electrical properties
- Thermal properties
- Magnetic properties
- Chemical properties
Above all the 5 properties going to explain in details each by each. So,
1. Mechanical properties:
Mechanical properties of metal indicate the nature of its inherent behavior under the action of the external force.
Or, we can say mechanical properties are the properties of the metal which are associated with its ability to resist failure under the action of external forces.
Some of the most important Mechanical properties of the metal are:
This property of the metals by virtue of which they are able to regain the original shape and size after the removal of the load is called elasticity. It is a very important property, since all cutting tools and metallic objects to maintain their original shape while working and after the removal of the applied force.
For every metal, there will be a maximum limit up to which the force applied will not leave any deformation after it ceases to exist. This is the maximum limit is called the elastic limit.
If the Force Applied beyond the elastic limit the metal will retain the deformation even after removal of applied forces.
The plasticity may be defined as the property of metal by virtue of which a permanent deformation takes place without fracture whenever it is subjected to the action of external forces.
Most of the metals have been found to possess good plasticity. This property is very important in forming shaping and extruding operation.
Some metals are shaped in cold conditions, for example, deep drawing of sheets.
Many metals are shaped in hot condition, for example, rolling of structural Steels shapes and the forging of certain machine parts.
The ductility may be defined as the property of metals by virtue of which they can be drawn into wires or elongated before rupture takes place.
This property depends largely upon tenacity and to some extent on hardness. Ductility of a metal is higher when cold than hot, hence wires are drawn in cold condition.
The following common metals have ductility in decreasing order:
Gold, Platinum, silver, iron, copper, aluminum, nickel, Zinc, tin, and lead.
The bitterness may be defined as the property of metal by virtue of which it will fracture suddenly without any appreciable deformation.
Metals which are less ductile will be brittle. Cast iron is one of the best examples for brittle metals.
The hardness may be defined as the property of metal by virtue of which resist, abrasion, indentation, and scratch by relatively harder materials.
It is expressed related to the hardness of some standard minerals. Diamond, quartz, corundum, etc. are the harder minerals.
The standard test to determine the hardness of metals are brinell, rockwell and Vickers.
The hardness is an important property for cutting tool materials and the metallic component which have to resist wear while working
Toughness may be defined as the property of the metal by virtue of which we can observe maximum energy before fracture takes place.
It is measured by the amount of energy that is a unit volume of material has after being stressed up to the point of fracture. Toughness decreases with increase in temperature.
It is a very important property that is considered while selecting the material for power press, punch, pneumatic, hammer, etc.
Stiffness is also known as the rigidity of metal.
It may be defined as the property by virtue of which the metal will not deform or deflect when the load is applied.
Although still is stronger than cast iron, the later is preferred for machine beds and frames because it is more rigid and less likely to deflect with consequent loss of alignment and accuracy.
Resilience may be defined as the property of metal by virtue of which it stores energy and resists shock and impact loads.
It is measured by the amount of energy that can be stored per unit volume after stressed up to the elastic limit. The material of higher resistance is used for spring.
The creep may be defined as the property of metal by virtue of which it deforms continuously and slowly under a steady load.
Metal generally exhibit creep at Higher temperatures. The creep is considered as an important property while designing the part of IC engine and turbine blades as they are subjected to high pressure at high temperature.
2. Electrical properties:
The characteristic of a metal which enables the flow of electric current through it is called electrical properties. The most important electrical properties of metals are conductivity, Resistivity and dielectric strength.
The conductivity may be defined as the electrical property of the metal by virtue of which allows the flow of electric current.
It is also defined as the reciprocal of resistance.
The metals such as copper and Aluminium are good electrical conductors. Since they are also highly ductile, they are used for making electrical transmission wires.
Pure metals have good conductivity at room temperature. The material which is bad conductors is called insulators.
The resistivity may be defined as Electrical property of the metal by virtue of which it impedes or resists the flow of electric current.
It is also defined as the reciprocal of conductivity. It Increases linearly with increase in temperature.
The insulating material will have insulating ability up to a certain range of voltage. If the operating voltage is increased gradually, at some voltage it loses its insulating property. The minimum voltage that can be applied to the insulating material which results in the destruction the insulating properties of the material is defined as the dielectric strength. It is used in the selection of insulating materials.
3. Thermal properties:
Thermal properties of the metals are the characteristics of the metal which are in influenced by the application of heat. For example, when metals are heated, they observe the heat energy resulting in the change of dimension, the flow of heat from higher temperature region to load temperature region, liquefaction of metals from the solid state when temperatures are raised beyond the melting point, electrical conductivity, etc.
Thermal conductivity images the ability of the metal to transmit heat energy through it.
The higher the thermal conductivity the greater the rate at which heat is conducted.
Pure metals show only small changes in thermal conductivity with temperature. The thermal conductivity of Copper and Aluminium increases as the temperature decreases until a maximum reached.
All metals and alloys to a greater or lesser extent, expand when heated and contract when cooled. The amount of expansion and contraction will be proportional to the change in temperature.
The thermal expansion is the characteristic of metals and alloys. This property of the metals will be useful in the application such as shrink fit and bi-metal alloys.
The specific heat of a metal may be defined as the quantity of heat required to raise the temperature of unit mass of a substance through 1 Degree Celsius.
The melting point is defined as the temperature at which it begins to melt when the heat is added to it.
4. Magnetic properties:
Magnetic properties refer to the metal and alloys such as iron, steel and associated alloying elements such as cobalt and Nickel.
All other materials are non-magnetic. Metals and alloys are classified as either hard or soft. Hard magnetic materials retail magnetism after the initial magnetism for has been removed. Soft magnetic materials can be easily magnetized or demagnetized and the retain actually no magnetism when the magnetizing force is removed.
Magnetic materials are used in large variety of electrical and electronic component like computers, televisions, video cassettes, and transducer, etc.
Magnetic permeability is defined as a measure that indicates the ease which magnetism may be developed in the materials.
Hard magnetic materials have a low permeability Where are soft magnetic materials have a high permeability.
The coercive force is defined as the force which opposes the magnetizing force.
It is applied to remove previous magnetization or residual magnetism. The Coercive force must be very small in magnetic materials.
When a ferromagnetic material is subjected to gradually increasing magnetic field, simultaneously there will be a corresponding increase in the intensity of magnetization.
When the field strength is decreased to zero. In order to reduce it to zero, a certain amount of magnetic field is applied in the reverse direction.
A Similar phenomenon is observed even in the negative direction. The change in the intensity of magnetization always lags behind the change in the magnetic field strength. This phenomenon of magnetic materials called hysteresis.
5. Chemical properties:
Some of the important chemical properties considered in the selection of materials are corrosion, composition and acidity and alkalinity.
All metals are extracted from their ores. The considerable amount of energy is spent during the extraction process. As a result of pure metals possess more energy compared to their ores.
Metal will not be stable in their high energy state. As a result, pure metals have a tendency to revert back to their natural state. When pure metals are exposed to atmosphere our environment containing liquid and gases, the surface of the metal starts deteriorating due to the chemical reaction. The Surface deterioration caused by the chemical reaction is called corrosion.
The two simple examples of corrosion resulting of iron and formation of a green film on the surface of copper.
The properties of metal depending on the chemical composition of the elements present in the metals and alloys. By varying the proportion of the chemical composition the desired properties may be imparted.
Acidity and Alkalinity:
Acidity is the Acid characteristics of the metals. Alkaline is the characteristic which neutralizes the acidity. Corrosion of steel is minimized by mentioning the boiler water alkaline.
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