ALUMINUM

Introduction

Aluminum is the most abundant metal in the Earth's crust, and the third most abundant element therein, after oxygen and silicon.

It is a silvery-white metal. It is light-weight, non-toxic, and can

be easily machined or cast. Pure aluminum is soft and ductile, but

can be strengthened by alloying with small amounts of copper, magnesium, and silicon.

Introduction

Iron ore output for 2009 was almost 210 million tonnes globally, while that of Aluminum is 2.8 million tonnes.

Aluminum weathers far better than iron.

Aluminum is a strongly reactive metal that forms a high-energy chemical bond with oxygen.

Aluminum is very active galvanically, and will sacrifice itself to any other metal it contacts either directly or indirectly.

Aluminum

Aluminum is strong, corrosion resistant, non sparking,

It also conducts electricity and heat well, and is readily weldable by MIG or TIG processes.

In terms of ease of construction, aluminum is excellent. 

Aluminum provides the option to make use of much greater plate thickness within a given weight budget, so that strength can be greater than with steel.

Physical properties

Material

Density g/cm3

Melting Point 0 C

Specific Heat J/kg0 K

Thermal Cond. W/m0K

Electric resistivity Ohm*m

Coefficient of thermal expansion10-6/C at 20 °C

Aluminum

2.70 669.7 945 237 0.282*10-7

23.86

Carbon steel

7.872 1425-1540

481 64.9 1.40*10-

7

10.8

Wrought iron

7.5–7.8 1540 500 59 11.1

Mechanical Properties

Material

Tensile Strength(MPa)

Elongation%

Hardness(HB)

Yield strength (MPa)

Poisson’s Ratio

Young’s Modulus(GPa)

Strength:weight

Aluminum

89.6 60% 34.47 0.33 69

Carbon steel

295 30 49 (RB) 165 0.303 200

Wrought iron

234–372

159–221

0.278 193

Aluminum

Aluminum reaches its "endurance limit" sooner than steel in terms of flexure.

endurance limit: The stress level below which a specimen will withstand cyclic stress indefinitely without exhibiting fatigue failure. Rigid, elastic, low damping materials such as thermosetting plastics and some crystalline thermoplastics do not exhibit an endurance limit. Also known as FATIGUE LIMIT.

Flexure: A curve, turn, or fold, such as a bend.

Aluminum properties

Flexural strength, also known as modulus of rupture, bend strength, or fracture strength, a mechanical parameter for brittle material, is defined as a material's ability to resist deformation under load.

The principal interest in using non-sparking materials is to avoid ignition of combustible or explosive materials.

Aluminum is non ferromagnetic, a property of importance in the electrical and electronics industries.

Aluminum Weathering

Resistance to weathering is equal in importance to light weight in number of applications and volume of metal consumed.

Those aluminum alloys that are especially formulated for outdoor exposure are regularly used without paint or other protective finish. Numerous installations have been exposed for 30 years with no loss of structural integrity.

The performance of aluminum in combination with organic coatings. Properly applied paint coatings on aluminum exhibit maximum adhesion, and local penetrations of the coating seldom expand.

Aluminum Rigidity

The property of an object that it strongly resists changing its shape OR

the property of a solid body to resist deformation, which is sometimes referred to as rigidity

When exposed to air, aluminum does not oxidize progressively

The tight chemical oxide bond is the reason that aluminum is not found in nature; it exists only as a compound.

Aluminum

Cold working the metal approximately doubles its strength.

In other attempts to increase strength, aluminum is alloyed with elements such as manganese, silicon, copper, magnesium, or zinc. The alloys can also be strengthened by cold working.

Some alloys are further strengthened and hardened by heat treatments. At subzero temperatures, aluminum is stronger than at room temperature and is no less ductile.

Alloying Aluminum

Most of the physical properties--density, melting-temperature range, heat content, coefficient of thermal expansion, and electrical and thermal conductivities--are changed by addition of one or more alloying elements.

Electrochemical properties and corrosion resistance are strongly affected by alloying elements that form either solid solutions, or additional phases, or both.

Wrought aluminum

Those aluminum products that have been subjected to plastic deformation by hot- and cold working mill processes (such as rolling, extruding, and drawing, either singly or in combination), so as to transform cast aluminum ingot into the desired product form.

One significant change being implemented by designers of automobiles and military vehicles today is converting driveshafts, radiators, cylinder heads, suspension members, and other structural components to aluminum.

Wrought aluminum

A four-digit number usually designates wrought aluminum alloys. (1xxx, 3xxx, 4xxx, and 5xxx)

this corresponds to a specific alloying element combination.

To develop strength, heat-treatable wrought alloys are solution heat treated, then quenched and precipitation hardened.

Wrought aluminum alloys are also strengthened by cold working

Wrought Aluminum

wrought aluminum products also may be classified into heat treatable and non-heat-treatable alloys.

Initial strength of non-heat-treatable alloys depends on the hardening effects of elements such as manganese, silicon, iron, and magnesium, singly or in various combinations.

Because these alloys are work hardenable, further strengthening is made possible by various degrees of cold working, denoted by the H series of tempers.

Wrought aluminum

Easy for cold working & hot working, machining & welding.

Commercial wrought aluminum products are divided basically into five major categories based on production methods as well as geometric configurations. These are:

· Flat-rolled products (sheet, plate, and foil) · Rod, bar, and wire · Tubular products · Shapes · Forgings

Casting Aluminum

Aluminum can be cast by all common casting processes. Aluminum casting alloys are identified with a unified, four-digit (xxx.x) system.

Commercial casting alloys include heat-treatable and non-heat-treatable compositions. Alloys that are heat treated carry the temper designations 0, T4, T5, T6, and T7. Die castings are not usually solution heat treated because the temperature can cause blistering.

Aluminum Castings

Good fluidity for filling thin sections Low melting point relative to those required for

many other metals Rapid heat transfer from the molten aluminum to

the mold, providing shorter casting cycles Hydrogen is the only gas with appreciable

solubility in aluminum and its alloys, and hydrogen solubility in aluminum can be readily controlled by processing methods

Many aluminum alloys are relatively free from hot-short cracking and tearing tendencies

Chemical stability Good as-cast surface finish with lustrous surfaces

and little or no blemishes

Selection of Casting Alloys

Casting process considerations: fluidity, resistance to hot tearing, solidification range

Casting design considerations: solidification range, resistance to hot tearing, fluidity, die soldering (die casting)

Mechanical-property requirements: strength and ductility, heat treatability, hardness

Service requirements: pressure tightness characteristic, corrosion resistance, surface treatments, dimensional stability, thermal stability

Economics: machinability, weldability, ingot and melting costs, heat treatment

Aluminum Castings

Castings are usually moderately good enough to be used for welding & machining purposes. They can offer better corrosion resistance than wrought products.

Aluminum automotive pistons generally are permanent mold castings. This design usually is superior in economy and design flexibility.

The alloy most commonly used for passenger car pistons has a good combination of foundry, mechanical, and physical characteristics, including low thermal expansion.

Heat treatment improves hardness for improved machinability.

Cost

Stainless steel is frequently in competition with aluminum for parts and structures requiring resistance to weathering or other corrosive environments. The ingot price advantage of aluminum is maintained in fabricated products such as sheet and plate.

0.22 kg of aluminum has the same conductive capability as 0.45 kg of copper. To complete the cost comparison it is, of course, necessary to make allowances for fabricating both materials into final form.

Physical Properties

Coefficient of thermal expansion μm/m ·°C

Thermalconductivityat 25 °CW/m ·°C

Electricalconductivityat 20 °C(%IACS)

Densityg/cm3

Wrought Aluminum

23.75 234 62% 2.705

Casting Aluminum

23.86 0.57 65% 2.713

Mechanical Properties

Tensile strength (MPa)

Yield strength (MPa)

Elongation (%)

Modulus ofElasticity(GPa)

Hardness(HB)

Wrought Aluminum

130 120 5 69 35

Cast Aluminum