Aluminium and Aluminium Alloys - Designations

Topics Covered

Introduction

Designations for Wrought and Cast Aluminium Alloys

Designations for Wrought Alloys

Work Hardened Aluminium Alloys

Solution Heat treated and Age Hardened Aluminium Alloys

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.

 

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.

 

Date Added: Apr 24, 2001 | Updated: Jun 11, 2013
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