Aluminium alloy designations by AA series — alloying element, typical application, hardness and whether the grade responds to heat treatment.
Data verified 2026-09-29 · based on n/a — the designation system is stable; compositions are registered as needed
Quick Answer
The first digit of an aluminium designation is the series, and it tells you the main alloying element: 1xxx pure, 2xxx copper, 3xxx manganese, 5xxx magnesium, 6xxx magnesium-silicon, 7xxx zinc. Only the 2xxx, 6xxx and 7xxx series are heat-treatable.
Hardness values are typical for the common temper of each grade. The temper designation — O, H, T4, T6 — follows the alloy number and matters as much as the alloy itself: 6061-O and 6061-T6 differ by a factor of three in strength.
The Four-Digit System
The AA designation encodes both the alloy family and the specific composition:
First digit — series, set by the principal alloying element. This is the part that matters most when choosing.
Second digit — a modification of the original alloy, or zero for the original.
Last two digits — a sequential identifier within the series. They do not encode composition the way steel designations do.
The temper follows a hyphen: 6061-T6 is alloy 6061 in the solution heat-treated and artificially aged condition. O is annealed, H is strain-hardened, T4 is solution treated and naturally aged, T6 is solution treated and artificially aged.
Choosing a Series
1xxx — pure. Excellent conductivity and corrosion resistance, very low strength. Electrical busbar, chemical equipment.
2xxx — copper. High strength and good fatigue performance, poor corrosion resistance without cladding, effectively unweldable. Aircraft skins.
3xxx — manganese. Moderate strength, good formability. Not heat-treatable. Cookware and signage.
5xxx — magnesium. Best corrosion resistance of the common series, good weldability, work-hardening. Marine work.
6xxx — magnesium and silicon. The general-purpose structural series: extrudable, weldable, heat-treatable, and the easiest aluminium to machine.
7xxx — zinc. The highest strength aluminium alloys, at the cost of corrosion resistance and weldability. Aircraft structure and moulds.
Frequently Asked Questions
What is the difference between 6061 and 7075?
7075 is substantially stronger — about 572 MPa tensile against 310 MPa for 6061 in the T6 temper — but it is less corrosion resistant, effectively unweldable and more expensive. 6061 is the general-purpose structural alloy; 7075 is used where strength is the limiting requirement.
Is aluminium 6061 heat treatable?
Yes. 6061 is a 6xxx series alloy and responds to solution treatment and artificial ageing, giving the T6 temper. The 1xxx, 3xxx and 5xxx series are not heat-treatable and gain strength only by strain hardening.
What does T6 mean in aluminium?
Solution heat treated and then artificially aged — the peak-strength condition for most heat-treatable alloys. Other common tempers are O (annealed), H (strain hardened) and T4 (solution treated and naturally aged).
Which aluminium is best for machining?
6061-T6 is the usual choice: it machines cleanly, holds tolerance well and is widely available. 2011 is a free-machining grade with better chip breaking but poorer corrosion resistance. All aluminium machines far faster than steel — ratings of 150–300% on the machinability scale are normal.
What is the strongest aluminium alloy?
The 7xxx series, and within it the high-zinc alloys such as 7075 and 7050, reaching about 570 MPa tensile in the T6 temper. This is comparable to some structural steels at roughly a third of the density.
Is 5052 or 6061 better for marine use?
5052, and the 5xxx series generally, has better corrosion resistance in salt water — it is the standard marine aluminium. 6061 is stronger and heat-treatable but less corrosion resistant, so it is usually specified with a protective coating in marine service.
Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.
#
Source
Type
Revision / method
[1]
Aluminium Association designation system, with properties from published alloy data
standard
n/a — designation system with periodic composition revisions — source
Data Sources
Standard
Revision
What it covers on this page
Aluminium Association International Alloy Designation System
n/a — the designation system is stable; compositions are registered as needed
alloy designations, series classification and temper nomenclature
Cross-checked against:
Designations and typical hardness values cross-checked against published aluminium reference charts
Heat-treatability classification verified against the AA series definitions
Typical values for the common temper of each grade. Temper matters as much as alloy — verify the specific temper's properties before design use.
Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.
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