Question

2) Explain the meaning of 4 different alloy codes by giving the composition and temper condition. State the applications in which these alloys can be used and explain the reasons why these alloys should be used in these specific applications.

Answer 1

The wrought and cast aluminums have different systems of identification; the wrought having a 4-digit system, and the castings having a 3-digit and 1-decimal place system.

For wrought alloys, the first digit (Xxxx) represents the principal alloying element that has been added to aluminium, and is used to describe the aluminium alloy series. - 1000 series, 2000 series and so on, up to 8000 series. The second single digit (xXxx), if different from 0, indicates a modification of the specific alloy, and the third and fourth digits (xxXX) are arbitrary numbers given to identify a specific alloy in the series.

Series 1000 is 99% Al. Series 2000 is copper, series 3000 is maganese, series 4000 is silicon, series 5000 is magnesium, series 6000 is magnesium and silicon, and series 7000 is zinc.

For cast alloys, the first digit (Xxx.x) indicates the principal alloying element, which has been added to the aluminum alloy. The second and third digits (xXX.x) are arbitrary numbers given to identify a specific alloy in the series. The number following the decimal point indicates whether the alloy is a casting (.0) or an ingot (.1 or .2).

There are also alloys that are heat-treatable, and those that are not. The 1xxx, 3xxx, and 5xxx series wrought aluminum alloys are non-heat treatable and are strain hardenable only. The 2xxx, 6xxx, and 7xxx series wrought aluminum alloys are heat treatable and the 4xxx series consist of both heat treatable and non-heat treatable alloys. The 2xx.x, 3xx.x, 4xx.x and 7xx.x series cast alloys are heat treatable. Strain hardening is not generally applied to castings.

The basic temper designations are:

F	As fabricated – applies to products of a forming process in which no special control over thermal or strain hardening conditions is employed
O	Annealed – applies to product which has been heated to produce the lowest strength condition to improve ductility and dimensional stability
H	Strain hardened – applies to products which are strengthened through cold-working. The strain hardening may be followed by supplementary thermal treatment, which produces some reduction in strength. The “H” is always followed by two or more digits
W	Solution heat-treated – an unstable temper applicable only to alloys which age spontaneously at room temperature after solution heat-treatment
T	Thermally treated - to produce stable tempers other than F, O, or H. Applies to product which has been heat-treated, sometimes with supplementary strain-hardening, to produce a stable temper. The “T” is always followed by one or more digits

Further to the basic temper designation, there are two subdivision categories, one addressing the “H” Temper – Strain Hardening, and the other addressing the “T” Temper – Thermally Treated designation.

The first digit after the H indicates a basic operation:

H1 – Strain Hardened Only.

H2 – Strain Hardened and Partially Annealed.

H3 – Strain Hardened and Stabilized.

H4 – Strain Hardened and Lacquered or Painted.

The second digit after the H indicates the degree of strain hardening:

HX2 – Quarter Hard      HX4 – Half Hard      HX6 – Three-Quarters Hard

HX8 – Full Hard           HX9 – Extra Hard

Subdivisions of T Temper – Thermally Treated

T1 - Naturally aged after cooling from an elevated temperature shaping process, such as extruding.

T2 - Cold worked after cooling from an elevated temperature shaping process and then naturally aged.

T3 - Solution heat treated, cold worked and naturally aged.

T4 - Solution heat treated and naturally aged.

T5 - Artificially aged after cooling from an elevated temperature shaping process.

T6 - Solution heat treated and artificially aged.

T7 - Solution heat treated and stabilized (overaged).

T8 - Solution heat treated, cold worked and artificially aged.

T9 - Solution heat treated, artificially aged and cold worked.

T10 - Cold worked after cooling from an elevated temperature shaping process and then artificially aged.

4 different alloy codes:

Aluminum 6061-T6

This is a 6000 series alloy, with roughly 96% aluminium, 1.2% magnesium and 0.8% silicon. T6 clearly means that this alloy has been heat treated and artificially aged. Material properties are excellent joining characteristics, good acceptance of applied coatings. Combines relatively high strength, good workability, and high resistance to corrosion. Because of these properties, this alloy finds use in aircraft fittings, camera lens mounts, couplings, marines fittings and hardware, electrical fittings and connectors.

Aluminium 5052-H32

This is a 5000 series alloy, with roughly 96% aluminium and 2.5% magnesium. H32 indicates strain hardening and stabilisation on the alloy with quarter hardening being the degree of hardening. This alloy has good workability, very good corrosion resistance, high fatigue strength, weldability, and moderate strength. This leads to its use in aircraft fuel/oil lines, fuel tanks, other transportation areas, sheet metal work, appliances and lighting, wire, and rivets.

Aluminium 6063-T4

This is a 6000 series aluminium alloy, with roughly 97% aluminium, 0.9% magnesium and 0.6% silicon. T4 indicates that it has been heat treated in a solution and naturally aged. This alloy has good workability, good corrosion resistance, high strength and moderate fatigue strength. It is used in pipes, railings, furniture, architectural extrusions, irrigation pipes, and transportation.

Aluminium 5083-H112

This is a 5000 series aluminium alloy, with roughly 95% aluminium and 4.5% magnesium. H112 indicates that it can only be strain hardened. This alloy has very good corrosion resistance (susceptible to deterioration after prolonged exposure to elevated temperatures) and moderate strength. It finds uses in transportation, pressure vessels, cryogenics, towers and drilling rigs, gas/oil piping, ordnance, and armor plating.