Aluminium and Aluminium Alloys - Fabrication

Topics Covered

Fabrication

Wrought Alloys

Rolled Products

Plate

Sheet

Shate

Foil

Extrusion

Castings

Fabrication

Aluminium alloys may be fabricated by casting, rolling, extrusion, forging and drawing but different compositions lend themselves to some process more readily than others. Considerable effort has gone into designing alloys with properties that meet the customer's needs using the most cost effective fabrication methods. Table 1 provides the designations of some of these alloys.

Table 1. Designations for alloyed wrought and cast aluminium alloys.

Major Alloying Element

Wrought

Cast

None (99%+ Aluminium)

1XXX

1XXX0

Copper

2XXX

2XXX0

Manganese

3XXX

 

Silicon

4XXX

4XXX0

Magnesium

5XXX

5XXX0

Magnesium + Silicon

6XXX

6XXX0

Zinc

7XXX

7XXX0

Lithium

8XXX

 

Unused

 

9XXX0

Wrought Products

Rolled Products

Rolled Products comprise some 70% of wrought aluminium in the form of plate, shate, sheet and foil. The usual starting stock is rectangular cast ingot or slab which may weigh as much as 20 tonnes.

Plate

Plate is produced by hot rolling, with perhaps some final cold work to improve tolerances and surface finish, in the thickness range 6 to 250 mm.

Sheet

Sheet is produced in the thickness range 0.2 to 6 mm by cold rolling on mills which generate a very flat, closely toleranced material with the required surface finish.

Shate

Shate (sheet and plate) is a name sometimes given to material in the range 4 to 6 mm, which is the crossover between sheet and plate.

Foil

Foil always has a gauge less than 0.2 mm and it can be as low as 9µm.

Most rolled products are made from the 1000, 3000 and 5000 series alloys but the 2000, 6000, 7000 and 8000 series alloys are also used.

Extrusion

Whilst the rolling of aluminium accounts for the bulk of wrought products, the hot extrusion of the metal is of great importance as it offers the opportunity to produce almost any shape in cross section. A preheated billet is placed into the press container and squeezed through a shaped steel die by a ram. It is claimed that the customer can ask for 'any shape'. This is true within the constraints of billet and press size plus die complexity and design. In practice some extruders have produced more than 100,000 different die shapes so the scope for developing custom sections is clear.

Most aluminium alloys can be, and indeed probably are, extruded. However in practice the bulk of commercial extrusion is in the 6000 series alloys which offer the optimum combination of ease and speed of extrusion and the ability to form complex shapes, thin sections, with good surface finish and the convenience of any final heat treatment and surface finishing. Extruded bar and section is frequently used as a starting stock for forgings and cold drawn products such as wire and tube

Castings

However versatile the extrusion process it provides only two dimensional shapes. Casting on the other hand allows complex three dimensional products to be made and development work on the process over the past decade has greatly extended the ability of castings to be used in critically stressed applications. Sand, permanent mould and die casting techniques are all employed. The choice of process depends upon quantity of castings required, end use and quality and property considerations. Formerly die castings were not suitable for heat treatment but special techniques have now been developed to overcome this constraint.

Casting alloys are now designated by a five figure number code as described in Table 1.

 

Primary author : Roy Woodward

Source : Materials Information Service, edited by Stephen Harmer

 

For more information on Materials Information Service please visit The Institute of Materials.

 

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