Introduction

Pure aluminium is soft, ductile, corrosion resistant and has a high electrical conductivity, see Table 1. In consequence it is widely used for foil and conductor cables, but alloying with other elements is necessary to provide the higher strengths needed for other applications.

Table 1. Typical properties for aluminium

Property	Value
Atomic Number	13
Atomic Weight (g/mol)	26.98
Valency	3
Crystal Structure	Face centred cubic
Melting Point (°C)	660.2
Boiling Point (°C)	2480
Mean Specific Heat (0-100°C) (cal/g.°C)	0.219
Thermal Conductivity (0-100°C) (cal/cms. °C)	0.57
Co-Efficient of Linear Expansion (0-100°C) (x10-6/°C)	23.5
Electrical Resistivity at 20°C (µΩcm)	2.69
Density (g/cm3)	2.6898
Modulus of Elasticity (GPa)	68.3
Poissons Ratio	0.34

Designations for Wrought and Cast Aluminium Alloys

The main alloying elements are copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. Table 2 describes the system for wrought alloys. Cast alloys have similar designations and use a five digit system (table 2). Table 3 lists the designations, characteristics, common uses and forms of some widely used alloys.

Table 2. 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

Table 3. Some common aluminium alloys, their characteristics and common uses.

Alloy	Characteristics	Common Uses	Form
1050/1200	Good formability, weldability and corrosion resistance	Food and chemical industry.	S,P
2014A	Heat treatable. High strength. Non-weldable. Poor corrosion reistance.	Airframes.	E,P
3103/3003	Non-heat treatable. Medium strength work hardening alloy. Good weldability, formability and corrosion resistance.	Vehicle panelling, structures exposed to marine atmospsheres, mine cages.	S,P,E
5251/5052	Non-heat treatable. Medium strength work hardening alloy. Good weldability, formability and corrosion resistance.	Vehicle panelling, structures exposed to marine atmospsheres, mine cages.	S,P
5454*	Non-heat treatable. Used at temperatures from 65-200°C. Good weldability and corrosion resistance.	Pressure vessels and road tankers. Transport of ammonium nitrate, petroleum. Chemical plants.	S,P
5083*/5182	Non-heat treatable. Good weldability and corrosion resistance. Very resistant to sea water, industrial atmospheres. A superior alloy for cryogenic use (in annealed condition)	Pressure vessels and road transport applications below 65°C. Ship building structure in general.	S,P,E
6063*	Heat treatable. Medium strength alloy. Good weldability and corrosion resistance. Used for intricate profiles.	Architectural extrusions (internal and external), window frames, irrigation pipes.	E
6061*/6082*	Heat treatable. Medium strength alloy. Good weldability and corrosion resistance.	Stressed structural members, bridges, cranes, roof trusses, beer barrels.	S,P,E
6005A	Heat treatable. Properties very similar to 6082. Preferable as air quenchable, therefore has less distortion problems. Not notch sensitive.	Thin walled wide extrusions.	E
7020	Heat treatable. Age hardens naturally therefore will recover properties in heat affected zone after welding. Susceptible to stress corrosion. Good ballistic deterrent properties.	Armoured vehicles, military bridges, motor cycle and bicycle frames.	P,E
7075	Heat treatable. Very high strength. Non-weldable. Poor corrosion resistance.	Airframes.	E,P

Where: * = most commonly used alloys, S = sheet, P = plate and E = extrusions

Designations for Wrought Alloys

These alloys fall into two distinct categories

1. Those which derive their properties from work hardening.
2. Those which depend upon solution heat treatment and age hardening.

Work Hardened Aluminium Alloys

The 1000, 3000 and 5000 series alloys have their properties adjusted by cold work, usually by cold rolling.

The properties of these alloys depend upon the degree of cold work and whether any annealing or stabilising thermal treatment follows the cold work. A standardised nomenclature is used to describe these conditions.

It uses a letter, O, F or H followed by one or more numbers. It is presented in summary form in Table 4 and defined in Table 6.

Table 4. Standard nomenclature for work hardened aluminium alloys.

New Symbol	Description	Old BS Symbol
O	Annealed, soft	O
F	As fabricated	M
H12	Strain-hardened, quarter hard	H2
H14	Strain-hardened, half hard	H4
H16	Strain-hardened, three quarter hard	H6
H18	Strain-hardened, fully hard	H8
H22	Strain-hardened, partially annealed quarter hard	H2
H24	Strain-hardened, partially annealed half hard	H4
H26	Strain-hardened, partially annealed three quarter hard	H6
H28	Strain-hardened, partially annealed fully hard	H8
H32	Strain-hardened and stabilised, quarter hard	H2
H34	Strain-hardened and stabilised, half hard	H4
H36	Strain-hardened and stabilised, three quarter hard	H6
H38	Strain-hardened and stabilised, fully hard	H8

Table 5. Explanations of symbols used in table 4.

Term	Description
Cold Work	The nomenclature denotes the degree of cold work imposed on the metal by using the letter H followed by numbers. The first number indicates how the temper is achieved.
H1x	Strain-hardened only to obtain the desired strength without supplementary thermal treatment.
H2x	Strain-hardened and partially annealed. These designations apply to products which are strain-hardened more than the desired final amount and then reduced in strength to the desired level by partial annealing. For alloys that age-soften at room temperature, the H2x tempers have the same minimum ultimate tensile strength as the corresponding H3x tempers. For other alloys, the H2x tempers have the same minimum ultimate tensile strength as the corresponding H1x tempers and slightly higher elongation.
H3x	Strain-hardened and stabilised. These designations apply to products which are strain-hardened and whose mechanical properties are stabilised either by a low temperature thermal treatment or as a result of heat introduced during fabrication. Stabilisation usually improves ductility. This designation is applicable only to those alloys which, unless stabilised , gradually age soften at room temperature.
H4x	H4x Strain-hardened and lacquered or painted. These designations apply to products which are strain-hardened and which may be subjected to some partial annealing during the thermal curing which follows the painting or lacquering operation. The second number after H indicates the final degree of strain-hardening, number 8 being the hardest normally indicated. The third digit after H, when used, indicates a variation of a two digit temper. It is used when the degree of control of temper or the mechanical properties or both differ from, but are close to, that (or those) for the two digit H temper designation to which it is added, or when some other characteristic is significantly affected. The fully soft annealed condition is indicated by the letter O and the `as fabricated' ie material that has received no subsequent treatment is indicated as F. To illustrate; it can be seen that 3103-0 denotes a particular aluminium manganese alloy in the annealed, soft condition, whilst 3103-H16 denotes the same alloy strain-hardened to three quarters hard.

To illustrate this, by reference to Tables 2 and 4, we can see that 3103-0 is an aluminium manganese alloy in the soft annealed condition and 3103-H16 is the same alloy three quarters hard.

With the flexibility of compositions, degree of cold work and variation of annealing and temperature a wide range of mechanical properties can be achieved especially in sheet products.

Solution Heat Treated and Age Hardened Aluminium Alloys

The 2000, 4000, 6000, 7000 and 8000 series alloys respond in this way.

The wide choice of alloy compositions, solution heat treatment temperatures and times, quench rates from temperature, choice of artificial ageing treatment and degree to which the final product has been deformed permit a wide range of properties to be achieved. A system of standard designations is used, based upon the letter T followed a number after the alloy designation, to describe the various conditions. These are defined in Table 6.

Table 6. Definition of heat treatment designations for aluminium and aluminium alloys.

Term	Description
T1	Cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition. This designation applies to products which are not cold worked after cooling from an elevated temperature shaping process, or in which the effect of cold work in flattening or straightening has no effect on mechanical properties
T2	Cooled from an elevated temperature shaping process, cold worked and naturally aged to a substantially stable condition. This designation applies to products which are cold worked to improve strength after cooling from an elevated temperature shaping process, or in which the effect of cold work in flattening or straightening does have an effect on mechanical properties.
T3	Solution heat-treated, cold worked and naturally aged to a substantially stable condition. This designation applies to products which are cold worked to improve strength after solution heat-treatment, or in which the effect of cold work in flattening or straightening does have an effect on mechanical properties.
T4	Solution heat-treated and naturally aged to a substantially stable condition. This designation applies to products which are not cold worked after solution heat-treatment, or in which the effect of cold work in flattening or straightening does not effect mechanical properties.
T5	Cooled from an elevated temperature shaping process and then artificially aged. This designation applies to products which are not cold worked after cooling from an elevated temperature shaping process, or in which the effect of cold work in flattening or straightening does not effect mechanical properties.
T6	Solution heat-treated and then artificially aged. This designation applies to products which are not cold worked after solution heat-treatment, or in which the effect of cold work in flattening or straightening does not effect mechanical properties.
T7	T7 Solution heat-treated and overaged/stabilised This designation applies to products which are artificially aged after solution heat-treatment to carry them beyond a point of maximum strength to provide control of some significant characteristic other than mechanical properties.