Aluminium Alloy Series: 1xxx to 7xxx — Properties, Temper Designations and Uses

Wrought aluminium alloys are grouped into eight series by their four-digit Aluminum Association designation, each built around a principal alloying element that governs strengthening mechanism, corrosion behaviour and weldability. This guide works through the 1xxx to 8xxx series, explains the F/O/H/W/T temper system, and maps composition to mechanical properties and typical industrial use.

The Wrought Aluminium Designation System

Wrought aluminium alloys are identified under the Aluminum Association four-digit system (ANSI H35.1), adopted internationally with minor regional variants. The first digit designates the series based on the principal alloying element or, for the 1xxx series, purity level. The second digit indicates a modification to the original alloy composition or impurity limits; a zero means the original, unmodified alloy. For the 1xxx series, the final two digits express the minimum aluminium content above 99.00% — alloy 1050 is 99.50% minimum aluminium. For the 2xxx through 8xxx series, the last two digits carry no numerical meaning and simply distinguish individual alloys within the series (2014, 2024, 2219, and so on).

Non-Heat-Treatable Series: 1xxx, 3xxx, 4xxx, 5xxx

Alloys in the 1xxx, 3xxx and 5xxx series (and most of 4xxx) do not respond usefully to solution treatment and aging because their alloying elements either have negligible solid solubility variation with temperature or do not form a coherent, strengthening precipitate. These alloys are strengthened by grain boundary and solid solution effects combined with cold work, and their temper is tracked using the H-series system.

1xxx — Commercially Pure Aluminium

The 1xxx series covers aluminium of 99.00% purity or higher, with strength set almost entirely by trace iron and silicon content and by the degree of cold work. These alloys offer the highest electrical and thermal conductivity of any aluminium series, outstanding corrosion resistance from a stable, self-healing oxide film, and excellent formability, but low strength. Alloy 1350 (99.50% min., low copper) is the standard electrical conductor grade; 1100 and 1050 are used for chemical process equipment, foil and spun hardware.

3xxx — Aluminium-Manganese

Manganese additions of roughly 1.0–1.5% raise strength above the 1xxx series through solid solution strengthening and fine dispersoid formation, while retaining good formability and corrosion resistance. 3003 is the workhorse general-purpose alloy for cookware, heat exchanger tubing and chemical equipment; 3004 and 3104, with added magnesium, are the dominant alloys for beverage can bodies because they combine deep-drawability with adequate strength in the H19 temper.

4xxx — Aluminium-Silicon

Silicon lowers the melting point and improves fluidity, which makes 4xxx alloys the standard choice for welding and brazing filler wire — 4043 and 4047 are ubiquitous GMAW/GTAW filler metals for 6xxx and cast alloys. Most 4xxx wrought alloys are not age-hardenable, though 4032, with added copper, magnesium and nickel, is a precipitation-hardenable, low-expansion alloy used for forged automotive pistons.

5xxx — Aluminium-Magnesium

Magnesium in solid solution (typically 0.5–5.5%) gives the 5xxx series the best combination of strength, ductility, weldability and corrosion resistance among the non-heat-treatable alloys, including excellent resistance to seawater and industrial atmospheres. Strength increases with magnesium content and with degree of cold work (H-temper). 5052 is a general-purpose sheet alloy for fuel tanks and cabinetry; 5083 and 5086, at the high-magnesium end, are the standard alloys for shipbuilding, pressure vessels and cryogenic LNG containment because aluminium retains excellent toughness at low temperature. Alloys above roughly 3.5% Mg in the H32/H34 tempers can be susceptible to stress corrosion cracking through sensitisation if exposed to sustained temperatures above about 66°C, which is why the H116/H117 tempers with controlled microstructure are specified for marine plate.

Heat-Treatable Series: 2xxx, 6xxx, 7xxx

The 2xxx, 6xxx and 7xxx series contain alloying elements whose solid solubility in aluminium falls sharply with decreasing temperature. This allows a three-step precipitation hardening sequence: solution treatment at elevated temperature to dissolve the alloying elements, rapid quenching to retain a supersaturated solid solution, and aging (natural or artificial) to precipitate a fine, coherent second phase that impedes dislocation motion.

2xxx — Aluminium-Copper

Copper contents of roughly 2–6% enable precipitation of the metastable θ′ and equilibrium Al2Cu (θ) phases, giving the 2xxx series some of the highest strength-to-weight ratios in aluminium metallurgy — 2024-T3 and 2014-T6 remain standard aerospace skin and structural alloys. The trade-off is markedly lower corrosion resistance than magnesium- or manganese-bearing series, particularly susceptibility to intergranular corrosion and exfoliation, which is why 2024 sheet is frequently supplied clad with a thin layer of high-purity 1xxx aluminium (Alclad) for sacrificial protection. High-copper 2xxx alloys are also generally unsuited to fusion welding due to hot cracking.

6xxx — Aluminium-Magnesium-Silicon

Balanced additions of magnesium and silicon (targeting the Mg2Si stoichiometry) give the 6xxx series moderate strength with good corrosion resistance, weldability and, critically, excellent hot-extrudability, making this the dominant series for structural and architectural extrusions. 6061 is the most widely specified general engineering alloy in this series — readily welded, machined and anodised, and commonly supplied in T6 or T651 (stress-relieved by stretching) condition. 6063 has a leaner composition tuned for extrusion die filling and surface finish rather than peak strength, and dominates architectural window, door and curtain-wall sections. 6082, with higher manganese, is the equivalent high-strength structural grade common in European standards.

7xxx — Aluminium-Zinc-Magnesium(-Copper)

Zinc combined with magnesium (and, in the highest-strength grades, copper) forms MgZn2 (η′) precipitates that give the 7xxx series the highest strength of any wrought aluminium alloys — 7075-T6 reaches ultimate tensile strengths above 500 MPa, rivalling some low-alloy steels on a weight-adjusted basis. High-copper 7xxx alloys such as 7075 and 7050 are prone to stress corrosion cracking in the short-transverse grain direction and are usually specified in overaged T73 or T76 tempers for corrosion-critical aerospace applications, accepting a strength reduction of roughly 10–15% relative to T6 in exchange for substantially improved SCC resistance. Copper-free or low-copper 7xxx alloys, such as 7005, retain useful weldability and are used in welded bicycle frames and transport structures.

8xxx — Other Elements

The 8xxx series is a catch-all for alloying systems outside the other seven series. Aluminium-lithium alloys (8090 and related compositions) reduce density by roughly 3% per weight percent lithium while increasing elastic modulus, and were developed for aerospace weight savings, though their use has been tempered by anisotropy and fabrication cost. Iron- and tin-bearing 8xxx alloys serve niche roles such as foil (8011) and bearing alloys.

Temper Designations: F, O, H, W, T

The temper designation follows the four-digit alloy number after a hyphen (for example, 6061-T6) and describes the mechanical/thermal processing state, not the composition.

Basic Temper Codes

H-Series Subdivisions

The first digit following H identifies the basic sequence: H1 is strain hardened only; H2 is strain hardened and then partially annealed to reduce strength to a specified level; H3 is strain hardened and then stabilised by a low-temperature thermal treatment to prevent age softening in magnesium-bearing alloys. The second digit, 1 through 9, indicates the degree of strain hardening, with H18 corresponding to full-hard temper (roughly 75% reduction relative to O) and intermediate values such as H14, H16 spaced at approximately quarter- and three-quarter-hard levels.

T-Series Subdivisions

Orowan precipitation strengthening (simplified):

  Δσ ≈ (G · b) / L

  where
    Δσ = strength increment from precipitates (MPa)
    G     = shear modulus of the aluminium matrix (≈ 26 GPa)
    b     = Burgers vector magnitude of matrix dislocations (≈ 0.286 nm)
    L     = mean interparticle spacing of precipitates (nm)

  Peak aging (T6) minimises L for a given volume fraction by maximising the
  number density of fine, coherent precipitates; overaging (T7) coarsens
  precipitates, increasing L and reducing Δσ, in exchange for
  improved stress corrosion cracking resistance.

Corrosion Resistance and Weldability by Series

Corrosion performance and weldability track alloying content closely. Series relying on copper or high zinc content for strength — 2xxx and high-copper 7xxx — trade away corrosion resistance and fusion weldability. Series relying on magnesium or manganese in solid solution — 3xxx, 5xxx and 6xxx — retain both. This pattern is central to general corrosion mechanism considerations and to selecting a weldable structural grade.

Selecting a Series for Application

Practical alloy selection is a series-level decision before it becomes an individual-alloy or temper decision. Aerospace primary structure favours 2xxx (fatigue-critical tension skins) and 7xxx (compression-critical, high-strength members). Marine, cryogenic and welded pressure applications favour 5xxx. General structural, architectural and machined components favour 6xxx for its balance of weldability, corrosion resistance and extrudability. Packaging and heat exchanger applications favour 3xxx. Electrical conductors and chemical-resistant linings favour 1xxx.

Related Heat Treatment Concepts

The solution treatment and aging sequence used for 2xxx, 6xxx and 7xxx alloys parallels the quench-and-temper logic used in steel, though the underlying phase transformations and precipitate chemistry are entirely different. Readers new to phase transformation fundamentals may find it useful to review solid-state transformation basics before working through precipitation sequence diagrams for individual aluminium alloys.

Frequently Asked Questions

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