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Metallurgy

2007 Schools Wikipedia Selection. Related subjects: Materials science

   Metallurgy is a domain of materials science and of materials
   engineering that studies the physical and chemical behaviour of
   metallic elements, their intermetallic compounds, and their mixtures,
   which are called alloys.

Extractive metallurgy

   Extractive metallurgy is the practice of separating metals from their
   ore, and refining them into a pure metal. In order to convert a metal
   oxide or sulfide to a metal, the ore must be reduced either chemically
   or electrolytically.

Metallurgy in production engineering

   In production engineering, metallurgy is concerned with the production
   of metallic components for use in consumer or engineering products.
   This involves the production of alloys, the shaping, the heat treatment
   and the surface treatment of the product. The task of the metallurgist
   is to achieve design criteria specified by the mechanical engineer,
   such as cost, weight, strength, toughness, hardness, corrosion and
   fatigue resistance, and performance in temperature extremes.

   Common engineering metals are aluminium, chromium, copper, iron,
   magnesium, nickel, titanium and zinc. These are most often used as
   alloys. Much effort has been placed on understanding one very important
   alloy system, that of purified iron, which has carbon dissolved in it,
   better known as steel. Normal steel is used in low cost, high strength
   applications where weight and corrosion are not a problem. Cast irons,
   including ductile iron are also part of this system.

   Stainless steel or galvanized steel are used where resistance to
   corrosion is important. Aluminium alloys and magnesium alloys are used
   for applications where strength and lightness are required.

   Most engineering metals are stronger than most plastics and are tougher
   than most ceramics. Composites of plastics and materials such as glass
   fibre and carbon fibre rival metals in applications requiring high
   tensile strength with little weight. Concrete rivals metals in
   applications requiring high compressive strength and resistance to the
   effects of water. Wood rivals metal in applications requiring low cost
   and availability of materials and low cost of construction, as well as
   in applications requiring certain aesthetics.

   The operating environment of the product is very important; a
   well-designed material will resist expected failure modes such as
   corrosion, stress concentration, metal fatigue, creep and environmental
   stress fracture. Ferrous metals and some aluminium alloys in water and
   especially in an electrolytic solution such as seawater, corrode
   quickly. Metals in cold or cryogenic conditions tend to lose their
   toughness becoming more brittle and prone to cracking. Metals under
   continual cyclic loading can suffer from metal fatigue. Metals under
   constant stress in hot conditions can creep.

Production engineering of metals

   Metals are shaped by processes such as casting, forging, rolling,
   extrusion, sintering, metalworking, machining and fabrication. With
   casting, molten metal is poured into a shaped mould. With forging, a
   red-hot billet is hammered into shape. With rolling, a billet is passed
   through successively narrower rollers to create a sheet. With
   extrusion, a hot and malleable metal is forced under pressure through a
   die, which shapes it before it cools. With sintering, a powdered metal
   is compressed into a die at high temperature. With machining, lathes,
   milling machines, planing machines and drills are used to cut the cold
   metal to shape. With fabrication, sheets of metal are cut with
   guillotines or gas cutters and bent into shape.

   " Cold working" processes, such as rolling and fabrication, where the
   product’s shape is altered while the product is cold, can increase the
   strength of the product by a process called work hardening. Work
   hardening creates microscopic defects in the metal, which resist
   further changes of shape.

   Various forms of casting exist in industry and academia. These include
   sand casting, investment casting (also called the “ lost wax process”),
   die casting and continuous casting.

   Welding is a technique for joining certain ferrous metals and certain
   aluminium alloys. The metals in the weld and on both sides of the join
   are generally similar alloys. Brazing is a technique for joining
   copper-based metals.

   Metals can be heat-treated by annealing, quenching, tempering and case
   hardening to alter properties of toughness, hardness or resistance to
   corrosion. Annealing is used to make a shaped product tougher by
   reducing the effects of work hardening, it also softens the metal.
   Quenching and case hardening are used to make a shaped product harder.
   Quenching by it self makes the metal very hard and very brittle,
   tempering after quenching is used to reduce the brittleness and improve
   overall properties.

   Electroplating is the main surface treatment technique and involves
   bonding a thin layer of another protective metal such as gold, silver,
   chromium or zinc to the surface of the product to reduce corrosion.

Electrical and electronic engineering

   Metallurgy is also applied to electrical and electronic materials where
   as metals such as aluminium, copper, tin and gold are used in power
   lines, wires, printed circuit boards and integrated circuits.

   Soldering is a method of joining metallic electrical conductors where
   high strength is not required.

Metallurgical techniques

   Metallurgists study the microscopic and macroscopic mechanisms that
   cause a metal or alloy to behave in the way that it does, i.e. the
   changes that occur on the atomic level that affect the metal's (or
   alloy's) macroscopic properties. Examples of tools used for microscopic
   examination of metals are optical and electron microscopes and mass
   spectrometers.

   Metallurgists study crystallography, the effects of temperature and
   heat treatment on the component phases of alloys, such as the eutectic
   and the properties of those alloy phases.

   The macroscopic properties of metals are tested using machines and
   devices that measure tensile strength, compressive strength and
   hardness.

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