Contact us How to reach us Partnership Weight Calculator
English
Version
Go to English version
Versione
Italiana
Passa alla versione Italiana

Aluminium

Index

General

Aluminium is a metal of the 3rd group, with atomic number 13 and atomic weight 26.98.

It is one of the more diffused elements on the earth's surface, although it is not present in metallic form, but as complex oxides (bauxite).

Historical traces of its usage are present since about 300 AC, but only in 1886 an industrial process for the production of the metal was developed (Charles Hall and Paul Heroult).

Before 1866 the applications of aluminium, whose production cost was extremely high, were limited to the field of jewels and art objects; after that date the first industrial applications started, in the field of shipbuilding, construction and electrical applications.

The first commercial alloys, aimed at improving the mechanical properties of industrially pure aluminium, appeared between 1890 and the end of the century; in 1905 the mechanisms of solution treating and ageing of aluminium alloys was investigated, and in 1910 an alloy containing 4% copper and 0.5% magnesium, named from the production site "duralumin", was patented; this alloy, with a substantially similar chemistry, is produced and widely used in our days under the name of 2017.

Back to index

Metals and alloys

Metals are chemical elements characterised by typical properties, like brightness (known as "metallic"), good electrical and thermal conductivity, formability. They seldom find applications in the modern technologies.

The addition to a metal (base metal) of quantities, in general small, of other metals (alloy metals), gives origin to metallic alloys (or plainly alloys), where with proper calibration of the additions of the alloy metals some properties of the base metal can be improved.

Metallic alloys are the basis for a wide number of components manufactured by the modern technologies.

The discovery, in pre-historical era, of the first alloys of copper with tin produced strong progresses for mankind, so that the corresponding period was called "the bronze age".

Changing type and quantity of metals additions to a base metal, alloys with properties also very different from each other can be obtained.

Back to index

Aluminium, the metal

Aluminium is extracted out of bauxite, an ore present in nature, through the Hall-Herault process.

Bauxite is finely ground and washed with water to remove silicates and clay.

The remaining bauxite is dried in an oven, finely ground sodium carbonate and calcium oxide are added, then the mixture is processed in a converter, reduced under pressure and sent to a decanter, where several impurities are removed.

The mixture passes through filters, is cooled and additionally processed in a separator, then agglomerated and filtered, and at last is baked in a calcinating oven.

The resulting material is alumina, aluminium sesquioxide, that looks like a dusty material.

Alumina is then melted in dedicated cells (smelters), containing melted cryolite (the cryolite mineral is melted using electric power).

Alumina, in form of powder, is put into the cryolite bath, where it is melted and reduced to aluminium metal, that sets below the cryolite.

Liquid aluminium is pumped from the bottom of the cell and transferred to a crucible, and then is poured to obtain ingots, or transferred to processing ovens.

Back to index

Aluminium alloys

For the production of primary aluminium alloys the liquid metal can be transferred to the processing oven directly from the smelter, or the metal can be added in form of ingots previously cast and solidified.

In both cases the alloying elements (silicon, copper, magnesium, manganese, zinc, etc) are added to the molten metal in order to obtain alloys with defined chemistry, and thus defined properties.

The mix of molten metals is then cast into ingots of the right shape and size in view of the subsequent processing.

Traditionally the aluminium alloys are divided into:

The following concepts apply to the latter

The aluminium alloys are nowadays identified by numerical codes, assigned by the Aluminum Association (AA), (e.g. 2024, 6082, 7075, etc.); such codes are now in general accepted by National and International Standards, in particular by the European Standards (EN).

The first digit of the code identifies the main alloying element added to aluminium (e.g.copper is the main addition in the 2xxx series alloys).

Every code refers to a well defined chemistry, that gives the alloy specific properties; for further details see section Alloys

manca

manca

Tabella Designazioni AA
Codifica AA Nomignolo
1xxx Alluminio puro
2xxx Avional
5xxx Peraluman
6xxx Anticorodal
7xxx Ergal

Back to index

Tempers

Many alloys can improve their strength and hardness through suitable heat treatments; these alloys are commonly called heat treatable alloys.

In general all the aluminium alloys change their properties if subjected to thermal, mechanical or thermomechanical treatments.

Heat treatments are cycles of heating and cooling under controlled conditions, that produce changes in the structure and consequently in the properties of the alloy.

The mechanical treatments consist in plastic deformations, generally at room temperature (strain hardening) of the alloy; these too provide for changes in the properties of the alloy.

The thermomechanical treatments consist in complex processing, including treatments of the two former types.

So, at the end of the day, the properties of an alloy come from:

Aluminum Association defines temper by means of conventional codes (e.g. T651 = solution treated, quenched, stress relieved by stretching and then artificially aged in order to achieve peak strength).

Every technological product is then defined by AA through a complex code, including:

E.g.: 7075 -T651 = alloy 7075 solution treated, quenched, , stress relieved by stretching and then artificially aged in order to achieve peak strength.

Back to index

Main properties

Aluminium and aluminium alloys show, in comparison to other technical materials, specific and in some cases unique physical properties, that make them particularly appealing to designers, manufacturers and end users; among these:

Low weight: specific gravity is much lower than other metals and alloys. With a value of 2.7 g/cubic cm aluminium has a weight per unit volume of about one third of iron, steel, copper, bronze, brass.

Therefore it is easier to handle, cheaper to transport and is particular attractive for aerospace and transportation in general, for moving parts and for those items and structures, where saving weight is of importance.

Back to index

Semi finished products

The products delivered by Aviometal include several families of semis, with different shapes and coming from different primary manufacturing technologies.

Manufacturing technologies determine some important properties of the products, such as dimensional tolerances, surface condition and, in many cases, mechanical properties.

Sheets are manufactured by cold rolling.

Plates are manufactured by casting (cast plates) or hot rolling (rolled plates).

Bars, tubes and shapes are manufactured by extrusion (extruded bars) or drawing (drawn bars); the two technologies produce different dimensional tolerances and surface conditions.

Back to index

Price

Products in aluminium alloys are considered much like as commodities; their prices is determined by a number of market factors.

Prices can fluctuate, due to balance of offer and demand and to other factors.

It should be reminded that the price of metal (London Metal Exchange) is only one component of the cost of products; additionally, manufacturing, handling and transportation costs shall be considered.

The price of the metal is fixed day by day at the London Metal Exchange (LME) in US$ per ton, and refers to ingots of commercially pure aluminium. This price is recorded on the main economical newspapers.

Besides the LME price one shall consider a "country" extra price typical of each country or geographical area, determined on the basis of the local market situation, an "alloy" extra price to switch from industrially pure aluminium of LME to the aluminium alloy slabs or billets which are the starting material for cast, rolled or extruded products, and whose price is influenced by size of slab or billet and alloy chemistry.

At last, the transformation cost (cost of rolling, extrusion, drawing) shall be added.

The price that the final customer pays includes all the above mentioned costs, plus the cost of service (handling, scraps if any, packing, transportation).

Back to index

Recycling

Recycling shall be considered within the total life cycle of a product, including manufacturing of the product, which is sold and used, and after disposal shall be collected, selected, reworked, made available for the manufacturing of a new product, and so on many many times.

From this standpoint the important thing is not that a product could be recycled, but that it is actually recycled.

Recycling is important for many reasons.

Storing of too big quantities of solid waste became a problem in developed countries; as much as possible they should be reworked for new usage.

The cost of recycled metal is lower than that of ore and electric power required to produce new metal.

Besides that, saving ore and electric power has an intrinsic value in view of environmental protection.

Recycling of aluminium allows saving 95% of the electric power required to produce new metal from ore; additionally, since 4 kg of bauxite are requested to produce 1 kg of metal, recycling 1 kg of metal allows saving 4 kg ore.

Experience showed that aluminium is one of the materials for which a recycling program is working since years, due to the high value of scrap, to the general attitude of people towards recycling of aluminium and to the strong attitude of industry towards recycling.

TAll aluminium products can be recycled, from packaging foil to car components, doors and windows, housekeeping tools; the maximum benefits is reached in case of heavy structures, like railway material, trucks and trailers. Well known is the case history of recycling, after more than 25 years service, of some hundreds railway coaches; in this case the value of the recycled metal reached 95% of the value of the metal used originally for the manufacturing of coaches.

We shall consider that there is no limit to the times aluminium can be recycled without losing its characteristic properties; no quality loss shall be expected using recycled aluminium, provided that the chemical analysis of the products conforms to the requirements of the applicable specifications.

Back to index

 

Powered by Antelma  -  Designed by Paolo Mandirola