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Aluminium Round Bars


Aluminium Sheets


Aluminium Foils

13

magnesiumaluminium silicon

B

Al

Ga

periodic table - Extended Periodic Table

 

 

General

Name, Symbol, Number

aluminium, Al, 13

Chemical series

poor metals

Group, Period, Block

13, 3, p

Appearance

silvery

Atomic mass

26.9815386(8) g/mol

Electron configuration

[Ne] 3s2 3p1

Electrons per shell

2, 8, 3

Physical properties

Phase

solid

Density (near r.t.)

2.70 gcm−3

Liquid density at m.p.

2.375 gcm−3

Melting point

933.47 K
(660.32 C, 1220.58 F)

Boiling point

2792 K
(2519 C, 4566 F)

Heat of fusion

10.71 kJmol−1

Heat of vaporization

294.0 kJmol−1

Heat capacity

(25 C) 24.200 Jmol−1K−1

Vapor pressure

P/Pa

1

10

100

1 k

10 k

100 k

at T/K

1482

1632

1817

2054

2364

2790

 

Atomic properties

Crystal structure

face centered cubic, 0.4032 nm

Oxidation states

3
(amphoteric oxide)

Electronegativity

1.61 (Pauling scale)

Ionization energies
(more)

1st: 577.5 kJmol−1

2nd: 1816.7 kJmol−1

3rd: 2744.8 kJmol−1

Atomic radius

125 pm

Atomic radius (calc.)

118 pm

Covalent radius

118 pm

Miscellaneous

Magnetic ordering

paramagnetic

Electrical resistivity

(20 C) 26.50 nΩm

Thermal conductivity

(300 K) 237 Wm−1K−1

Thermal expansion

(25 C) 23.1 mm−1K−1

Speed of sound (thin rod)

(r.t.) (rolled) 5000  ms−1

Young's modulus

70 GPa

Shear modulus

26 GPa

Bulk modulus

76 GPa

Poisson ratio

0.35

Mohs hardness

2.75

Vickers hardness

167 MPa

Brinell hardness

245 MPa

CAS registry number

7429-90-5

Selected isotopes

Main article: Isotopes of aluminium

iso

NA

half-life

DM

DE (MeV)

DP

26Al

syn

7.17105y

β+

1.17

26Mg

ε

-

26Mg

γ

1.8086

-

27Al

100%

Al is stable with 14 neutrons

 

References

 

Aluminium or aluminum is a silvery and ductile member of the poor metal group of chemical elements. In the periodic table it has the symbol Al and atomic number 13.

Aluminium is found primarily in the bauxite ore and is remarkable for its resistance to corrosion (due to the phenomenon of passivation) and its light weight. Aluminium is used in many industries to manufacture a large variety of products and is very important to the world economy. Structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building in which light weight, durability, and strength are needed.

Properties

A piece of aluminium metal about 15 centimetres long, with a U.S. cent included for scale.

Enlarge

A piece of aluminium metal about 15 centimetres long, with a U.S. cent included for scale.

Aluminium is a soft, lightweight metal with normally a dull silvery appearance caused by a thin layer of oxidation that forms quickly when the metal is exposed to air. Aluminium is nontoxic (as the metal), nonmagnetic, and nonsparking. It has a tensile strength of about 49 megapascals (MPa) in a pure state and 400 MPa as an alloy. Aluminium is about one-third as dense as steel or copper; it is malleable, ductile, and easily machined and cast. It has excellent corrosion resistance and durability because of the protective oxide layer. Aluminium mirror finish has the highest reflectance of any metal in the 200-400 nm (UV) and the 3000-10000 nm (far IR) regions, while in the 400-700 nm visible range it is slightly outdone by silver and in the 700-3000 (near IR) by silver, gold, and copper. It is the second-most malleable metal (after gold) and the sixth-most ductile. Aluminium is a good heat conductor.

Bohr Diagram.

Enlarge

Bohr Diagram.

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Applications

Whether measured in terms of quantity or value, the use of aluminium exceeds that of any other metal except iron, and it is important in virtually all segments of the world economy.

Pure aluminium has a low tensile strength, but readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today almost all materials that claim to be aluminium are actually an alloy thereof. Pure aluminium is encountered only when corrosion resistance is more important than strength or hardness.

When combined with thermo-mechanical processing aluminium alloys display a marked improvement in mechanical properties. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength to weight ratio.

Aluminium is an excellent reflector (approximately 99%) of visible light and a good reflector (approximately 95%) of infrared. A thin layer of aluminium can be deposited onto a flat surface by chemical vapor deposition or chemical means to form optical coatings and mirrors. These coatings form an even thinner layer of protective aluminium oxide that does not deteriorate as silver coatings do. Nearly all modern mirrors are made using a thin coating of aluminium on the back surface of a sheet of float glass. Telescope mirrors are also made with aluminium, but are front coated to avoid internal reflections, refraction, and transparency losses. These first surface mirrors are more susceptible to damage than household back surface mirrors.

Some of the many uses for aluminium are in:

Aluminium is also a superconductor at low temperatures, with a superconducting critical temperature of 1.2 kelvins.

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Engineering use

Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO). Selecting the right alloy for a given application entails considerations of strength, ductility, formability, weldability and corrosion resistance to name a few. A brief historical overview of alloys and manufacturing technologies is given in Ref.[2] Aluminum is used extensively in modern aircraft due to its light weight.

Improper use of aluminium can result in problems, particularly in contrast to iron or steel, which appear "better behaved" to the intuitive designer, mechanic, or technician. The reduction by two thirds of the weight of an aluminium part compared to a similarly sized iron or steel part seems enormously attractive, but it should be noted that it is accompanied by a reduction by two thirds in the stiffness of the part. Therefore, although direct replacement of an iron or steel part with a duplicate made from aluminium may still give acceptable strength to withstand peak loads, the increased flexibility will cause three times more deflection in the part.

Where failure is not an issue but excessive flex is undesirable due to requirements for precision of location or efficiency of transmission of power, simple replacement of steel tubing with similarly sized aluminium tubing will result in a degree of flex which is undesirable; for instance, the increased flex under operating loads caused by replacing steel bicycle frame tubing with aluminium tubing of identical dimensions will cause misalignment of the power-train as well as absorbing the operating force. To increase the rigidity by increasing the thickness of the walls of the tubing increases the weight proportionately, so that the advantages of lighter weight are lost as the rigidity is restored.

Aluminium can best be used by redesigning the part to suit its characteristics; for instance making a bicycle of aluminium tubing which has an oversize diameter rather than thicker walls. In this way, rigidity can be restored or even enhanced without increasing weight. The limit to this process is the increase in susceptibility to what is termed "buckling" failure, where the deviation of the force from any direction other than directly along the axis of the tubing causes folding of the walls of the tubing.

The latest models of the Corvette automobile, among others, are a good example of redesigning parts to make best use of aluminium's advantages. The aluminium chassis members and suspension parts of these cars have large overall dimensions for stiffness but are lightened by reducing cross-sectional area and removing unneeded metal; as a result, they are not only equally or more durable and stiff as the usual steel parts, but they possess an airy gracefulness which most people find attractive. Similarly, aluminium bicycle frames can be optimally designed so as to provide rigidity where required, yet have flexibility in terms of absorbing the shock of bumps from the road and not transmitting them to the rider.

The strength and durability of aluminium varies widely, not only as a result of the components of the specific alloy, but also as a result of the particular manufacturing process; for this reason, it has from time to time gained a bad reputation. For instance, a high frequency of failure in many early aluminium bicycle frames in the 1970s resulted in just such a poor reputation; with a moment's reflection, however, the widespread use of aluminium components in the aerospace and automotive high performance industries, where huge stresses are undergone with vanishingly small failure rates, proves that properly built aluminium bicycle components should not be unusually unreliable, and this has subsequently proved to be the case.

Similarly, use of aluminium in automotive applications, particularly in engine parts which must survive in difficult conditions, has benefited from development over time. An Audi engineer commented about the V12 engine, producing over 500 horsepower (370 kW), of an Auto Union race car of the 1930s which was recently restored by the Audi factory, that the aluminium alloy of which the engine was constructed would today be used only for lawn furniture and the like. Even the aluminium cylinder heads and crankcase of the Corvair, built as recently as the 1960s, earned a reputation for failure and stripping of threads in holes, even as large as spark plug holes, which is not seen in current aluminium cylinder heads.

Often, aluminium's sensitivity to heat must also be considered. Even a relatively routine workshop procedure involving heating is complicated by the fact that aluminium, as opposed to steels, will melt without first turning red. Forming operations where a blow torch is used therefore requires some expertise since no visual signs reveal how close the material is to melting. Aluminium also will accumulate internal stresses and strains under conditions of overheating; while not immediately obvious, the tendency of the metal to "creep" under sustained stresses results in delayed distortions, for instance the commonly observed warping or cracking of aluminium automobile cylinder heads after an engine is overheated, sometimes as long as years later, or the tendency of welded aluminium bicycle frames to gradually twist out of alignment from the stresses accumulated during the welding process. For this reason, many uses of aluminium in the aerospace industry avoid heat altogether by joining parts using adhesives; this was also used for some of the early aluminium bicycle frames in the 1970s, with unfortunate results when the aluminium tubing corroded slightly, loosening the bond of the adhesive and leading to failure of the frame. Stresses from overheating aluminium can be relieved by heat-treating the parts in an oven and gradually cooling, in effect annealing the stresses; this can also result, however, in the part becoming distorted as a result of these stresses, so that such heat-treating of welded bicycle frames, for instance, results in a significant fraction becoming misaligned. If the misalignment is not too severe, once cooled they can be bent back into alignment with no negative consequences; of course, if the frame is properly designed for rigidity (see above), this will require enormous force.

Aluminium's intolerance to high temperatures has not precluded its use in rocketry; even for use for constructing combustion chambers where gases can reach 3500K. The Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat region; in fact the extremely high thermal conductivity of aluminium prevented the throat from reaching the melting point even under massive heat flux, and good reliability and light weight resulted.