Aluminium products

Aluminium products manufacturing

The European aluminum industry includes over 600 plants across 30 European countries (figure 1) [1]:

alumina production
primary aluminium production
extrusion plants
rolling plants
recycling plants.

Figure 1 – European aluminium industry [1]

The main materials and products of the aluminum industry [2, 3] are presented below.

Materials production

Bauxite.
Bauxite, containing a high aluminium content, is extracted from ore deposits, mostly located in tropical areas [4].
Alumina.
Production begins with the refining of bauxite and its conversion through the Bayer chemical process to obtain alumina.
The resulting product, aluminium oxide (Al2O3), is calcined resulting in a product known as calcined alumina which takes the form of a white powder [4].
Aluminium.
Alumina is used as an input to the electrolytic process (Hall-Héroult process) which is carried out in tanks through which a high-intensity direct current passes.
The result is molten aluminium [4].
Unalloyed aluminium.
Aluminium without alloying elements where the minimum aluminium content is specified to be greater than 99,00%.
Refined aluminium.
Unalloyed aluminium of high purity (aluminium content of at least: 99,950% by mass) obtained by special metallurgical treatments.
Primary aluminium.
Unalloyed aluminium produced from alumina, typically by electrolysis, and with an aluminium content of 99,7% [2].

Figure 2 – It takes between four and five tonnes of bauxite to obtain about two tonnes of alumina which, in turn, will give one tonnes of aluminium [4]Figure 3 – The primary aluminium production process [5]

Figure 4 – Transportation of liquid aluminum [6]

The types of aluminium products

Unwrought products

Products obtained by casting without further hot or cold working:

Wrought products

Product that has been subjected to hot working and/or cold working:

Semi-finished products

Products that has undergone some processing and is supplied for further processing before it is ready for use.
Semi-finished products include wrought products and castings. It does not include ingots and billets.
The examples are:

aluminium extruded profiles
forgings and forging stock.

Aluminium powder products

Products obtained from fine aluminium powder by compacting and sintering, often followed by hot pressing and/or subsequent working.

Unwrought products, excepting castings

Ingots.
Cast products intended and suitable for remelting or forming by hot or cold working
Primary aluminium ingots.
Ingots of unalloyed or alloyed aluminium cast from primary aluminium and possibly a small amount of runaround
scrap.
Recycled aluminium ingots.
Aluminium ingots obtained by recycling of scrap
Ingots for remelting; remelt ingot.
Ingots intended and suitable for remelting.
Ingots for casting.
Ingots for remelting intended and suitable for the production of castings.
Ingots for rolling
Ingots for extrusion
Ingots for forging

Figure 5 – Remelt aluminum ingot (EN 576).
Poured into open molds.
Most often used in the form of small ingots - pigs.

Figure 6 – Rolling ingots [5]
The rolled ingots have a rectangular cross-section (up to 0,6 x 1,8 m).
They can be up to 9 meters and weighing up to 30 tonnes.
Rolled ingots are the starting material
for sheet aluminum products:
aluminum sheets, strips and foils.

Figure 7 – Direct-chill casting of aluminium extrusion ingots [4].
Raw material for extruded products
(extruded profiles, bars, pipe, wire).
Most extrusion ingots are cylindrical.

Figure 8 – Extrusion logs at entrance to the ingots heating furnace [8]

Figure 9 – A hot billet before loading into the extrusion press [8]

Castings

Casting.
Product at or near finished shape, formed by solidification of the metal in a mould or a die.
Sand casting.
Casting produced by pouring molten metal into a sand mould and allowing it to solidify.
Permanent mould casting.
Casting produced by introducing molten metal by gravity or low pressure into a mould constructed of durable material, typically iron or steel, and allowing it to solidify.
Low pressure die casting.
Permanent mould casting where the metal solidifies in a metal mould under low pressure (typically less than 1 bar above atmospheric pressure).
High pressure die casting.
Casting produced by introducing molten metal under substantial pressure, typically above 100 bars into a metal die and characterized by a high degree of fidelity to the die cavity.
Investment casting.
Precision casting formed by a three step process comprising:
a) fabrication of a ceramic mould around a wax or thermoplastic pattern with a refractory slurry that sets at room temperature;
b) removal of the pattern through the use of heat;
с) pouring of metal into this mould and allowing it to solidify.

Figure 10 – Examples of grenn sand casting.
From left: Heat Exchanger, Hat Profile, Brake Calipers, Knuckles – Source: Alcoa [8]

Figure 11 – Permanent mould machined from steel [9]

Figure 12 – Cylinder head. Low pressure die casting [8]

Figure 13 – High pressure die casting:
Automotive transmission cases [8]

Sheet and plate

Sheet.
Rolled product that is rectangular in cross section with nominal thickness less than 6 mm but not less than 0,20 mm and with slit, sheared or sawed edges.
In Europe, the term “sheet” is only used for rolled products supplied in straight length, for coiled sheet the term “strip” is used.
Coiled sheet.
Sheet in coils with slit edges.
Plate.
Rolled product that is rectangular in cross section and with thickness not less than 6 mm with sheared or sawn edges.
Hot rolled sheet/hot rolled plate.
Sheet or plate the final thickness of which is obtained by hot rolling.
A reroll plate is often called “slab”.
Cold rolled sheet/cold rolled plate.
Sheet or plate the final thickness of which is obtained by cold rolling.
Reroll stock.
Coiled sheet suitable and intended for further rolling.
Can stock.
Sheet or strip used for the fabrication of rigid cans including ends (lids) and tabs by drawing/ironing, pressing or forming operations.
Can stock covers can body stock, end (lid) stock and tab stock.
Foil stock.
Reroll stock suitable for further rolling to foil.

Figure 14 – Aluminium plate

Figure 15- Coiled aluminium sheets

Foil

Foil.
Flat rolled product of rectangular cross-section with uniform thickness equal to or less than 0,20 mm (200 microns).
Converter foil.
Foil, typically soft annealed, supplied for further processing such as colouring, printing, embossing or laminating.
Container foil.
Single rolled foil with a gauge above approximately 35 μm.
Produced at soft or intermediate temper.
Often involves alloys of the 3xxx and 8xxx series intended for press forming into smooth or wrinkled walled containers for foodstuffs and the like.
Consumer foil; household foil.
Foil intended for public use, principally for use in culinary applications such as cooking and storage.
Annealed foil.
Foil completely softened by thermal treatment.
Hard foil.
Foil fully work-hardened by rolling.
Intermediate temper foil.
Foil manufactured in an undetermined temper between “annealed” and “hard”.

Figure 16 – Aluminium foil

Profiles

Profile.
Wrought product that is long in relation to its cross-sectional dimensions which is of a form other than that of sheet, plate, rod, bar, tube, wire or foil.
For profiles sometimes the term “shape” or “section” is used.
Extruded profile.
Profile brought to final dimensions by extruding.
Cold-finished profile.
Profile brought to final dimensions by cold-working to obtain improved surface finish and dimensional tolerances.
Drawn profile.
Cold-finished profile brought to final dimensions by drawing through a die.
Seamless profile.
Hollow profile which does not contain any line junctures resulting from method of manufacture.

Figure 17 – Classification of aluminium extruded profiles (laugh, 1963) [11]

Tubes

Tube.
Hollow wrought product of uniform cross-section with only one enclosed void and with a uniform wall thickness, supplied in straight lengths or in coiled form; cross-sections are in the shape of circles, ovals, squares, rectangles, equilateral triangles or regular polygons and can have corners rounded, provided the inner and outer cross-sections are concentric and have the same form and orientation. Tubes can be formed by extrusion or by forming and joining of sheet.
Extruded tube.
Tube brought to final dimensions by extruding.
Drawn tube.
Tube brought to final dimensions by drawing through a die.
Sized tube.
Tube that, after extrusion, has been cold drawn a slight amount to minimize ovality.
Porthole tube/bridge tube.
Tube produced by extrusion of a solid billet through a porthole or bridge die.
The product is characterised by one ore more longitudinal extrusion seams.
Seamless tube.
Tube which does not contain any line junctures resulting from method of manufacture.
Tube stock.
Semi-finished tube suitable for the production of drawn tube.
Pipe.
Tube in standardized combinations of outside diameter and wall thickness.

Figure 18 – Extrusion aluminium tubes: round, rectangle, square and hexagonal

Figure 19 – Schematic of porthole die hollow extrusion [11].
(a) Cross section showing metal flow into port streams and around the mandrel.
(b) Billet entrance face of the die set