Classification of the wrought alloy series – aluminium designations
There are eight series of wrought alloys. These are designated by a 4 digit number which may be preceded or followed by letters.
A prefix is used to designate the standard AA (Aluminium Association) or EN AW (European Standard); e.g. EN AW 1050.
A suffix “A” indicates a national variation of an alloy; e.g. EN AW 5005A.
The first number expresses the main alloying element, as to be found in next list.
- 1xxx : pure alloys
- 2xxx : copper based alloys
- 3xxx : manganese based alloys
- 4xxx : silicium based alloys
- 5xxx : magnesium based alloys
- 6xxx : Mg Si based alloys
- 7xxx : Zn Mg based alloys
- 8xxx : special alloys
For the 1xxx series, the 3rd and 4th digits indicate the 0.XX% of aluminium higher than 99.00%; e.g. Al99.50 is in accordance with EN AW 1050.
For the other series, the 3rd and 4th digits only serve to differentiate between various alloys.
The second digit indicates alloy modifications of an already existing alloy.
Temper designations of the wrought alloys – aluminium tempers
The mechanical properties can vary greatly depending on the thermo-mechanical processing. For this reason, when selecting a product, besides the alloy, the temper should be specified.
The temper of an alloy can be tuned to meet specific application requirements. There are 2 categories of alloys in this respect :
- Heat treatable alloys: the mechanical properties can be tuned through thermal treatment on top of the work hardening processes. This is possible for alloys belonging to the 2xxx, 6xxx and 7xxx series which can be precipitation or age hardened.
- Non-heat treatable alloys: for these alloys the mechanical properties are obtained through hot and/or cold working mechanisms with intermediate and/or final annealing. This is done for the alloys belonging to the 1xxx, 3xxx, 4xxx and 5xxx series.
Non-heat treatable alloys are strengthened by cold-work. The temper is expressed as H followed by at least 2 digits : Hxx.
The second digit expresses the degree of cold work, such as :
- 2 = 2/8 hard
- 4 = 4/8 hard
- 6 = 6/8 hard
- 8 = fully hard
- 9 = extra hard
The first digit expresses the treatment, such as :
- 1 = cold worked + intermediate annealed
- 2 = cold worked + partially annealed
- 3 = cold worked + stabilized
- 4 = cold worked + baked
A typical anodised aluminium sheet is in accordance with EN AW 5005-H14.
Heat treatable alloys gain their strength by solution heat treating and ageing. Of the 9 different tempers, T3, T6 and T7 are the most important.
- T3 = solution heat treated + cold worked + naturally aged
- T6 = solution heat treated + artificially aged
- T7 = solution heat treated + overaged
What is DC – Direct Chill Semi-Continuous Cast?
The starting stock for most rolled products is the DC (Direct Chill Semi-Continuous Cast) ingot.
The DC ingot is usually cooled after casting to room temperature and then reheated to around 500°C (preheating) prior to successive passes through a hot rolling mill. The strip from the hot rolling mill is coiled for transport to the cold mill.
Anodising qualities are typically produced through a direct chill semi-continuous cast due to the benefits of a good surface quality and a fine grain structure.
What is CC – Continuous Cast ?
The alloys are cast in form of continuous strips. The aluminium casting is then cold rolled. Continuous cast is not well suited for an anodising process as this casting method gives a thicker defective surface layer and a non-homogeneous microstructure.
What is Anodising Quality ?
Every alloy (with exception of the 6xxx series) can be anodised, but one should make difference between ‘Anodisable Quality’ and ‘Anodising Quality’.
For architectural and design applications, the use of an Anodising Quality is a necessary because this will ensure :
- A consistent quality across different casting batches.
- A consistent quality in different gauges and widths.
- Tight tolerances in chemical composition will ensure colour uniformity.
An ‘Anodisable Quality’ may some surface defects and is, therefore, not recommended for surface critical applications such as architectural and design applications.
Most rolling mills offer an EN AW 5005-H14 AQ. Some rolling mills have an anodising quality in accordance with EN AW 5754 or EN AW 1050.
What alloys can be anodised?
Almost every alloy can be anodised, with exception from the 6xxx series since smud will remain after etching.
The most common anodised alloys are :
- EN AW 5005
- EN AW 5754
- EN AW 3003, 3103, 3004, 3005, 3105
- EN AW 1050
What is the minimum order quantity to be anodised?
For safety and quality reasons, a coil must have a minimum length of 500 meters.
Does continuously anodised aluminium offer UV resistance?
The UV resistance is depending on the colour, as specified in table underneath.
Colour UV resistance Natural UV resistance Bronze UV resistance with anodic layer thickness >= 5 µm Gold Good UV resistance with an anodic layer thickness >= 10 µm but for outdoor applications 15 µm is recommended. Black Good UV resistance with anodic layer thickness >= 15 µm Grey Not intended for outdoor applications (no UV resistance)
Is the anodic layer compatible with food?
Restrictions on sealing concentration should be taken into consideration.
With our standard process, we will execute the sealing with a hot water solution with no more than 10 g/l of nickel acetate and 1 g/l of cobalt acetate.
A food compatibility certificate is possible upon request and will demand specific measurements. A certificate per order will be issued and the sealing will be executed with a hot water solution with no more than 8g/l of nickel acetate and 1 g/l of cobalt acetate.
Can anodising be done on textured surfaces?
Continuous anodising is also possible on textured surfaces, such as treadplates, perforated aluminium, stucco surfaces, hammered surfaces and brushed surfaces.
Is double-sided anodising possible?
With the standard process, the anodic layer thickness will be guaranteed on the recto side; whilst the verso side will have an anodic layer thickness of 30-50% of the anodic layer thickness of the recto. The verso anodic layer thickness will not be guaranteed.
Double-sided anodising, with a guaranteed anodic layer thickness on both recto and verso, is possible upon request for natural colours, but only in specific combinations :
- 3 µm / 3 µm
- 5 µm / 5 µm
- 6 µm / 4 µm
- 7 µm / 5 µm
- 12 µm / 6 µm
What minimum layer thickness is necessary to offer corrosion resistance for outdoor applications?
Various countries have their local requirements. Generally, it is considered that an anodic layer of at least 15 microns is necessary to offer corrosion resistance. Close to the sea or in harsher environments, an anodic layer thickness of 20 microns is recommended.
How do I need to specify in order to guarantee a uniform aspect for large building façade projects?
Colour and gloss variations can have various root causes, and, therefore, the specification should be designed to reduce as far as possible any possible variations.
First and foremost, a high quality aluminium substrate homologated by Coil for architectural applications should be specified. Ideally, the metal should be out of a single casting and rolling batch.
The use of different metal substrates (e.g. from different suppliers) in the same façade has to be avoided where possible as there are colour and gloss differences from one mill source to another.
It is recommended that all the metal is anodised in a single batch in one anodising campaign.
When coloured products are used, the customer and supplier should agree in advance a range of acceptable colour variation, based on reference samples.
Coil’s C-Iconic product is designed specifically to include all the production parameters designed to guarantee a very uniform surface across large facades.
What standard guarantees do I get?
A 10 year guarantee on :
- minimum anodic layer thickness measured following the Eddy Current method in accordance to ISO 2360.
- full sealing of the anodic layer
- for UV-resistant colours, no fading during 10 years (starting from the treatment date) due to UV-light influences. Maximum delta E of 5 (reference = measurement during production).
This guarantee does not cover any damage to or changes of the anodic layer resulting from :
- inappropriate handling, storing and/or cleaning
- any post-anodising transformation or operation
- exposure to environments or substances that are known to be or may be harmful for anodised aluminium surfaces.
- plastic foil application and/or removal to/from the anodised surface.
- Acts of God such as flooding, storm, heavy hail or other natural disasters.
Upon request, a Certificate of Compliance can be obtained containing supplementary measurements that are documented and certified by Coil.
For architectural applications, a Certificate of Compliance is recommended.
Upon request for specific projects, Coil is able to offer a simple, quibble-free Lifetime Guarantee covering the design life of the building.