Aluminium Alloy Properties

Engineering variability

• Yield and tensile strengths are tied to temper, product thickness and specification.
• Elastic modulus is far less temper-sensitive than strength.
• Thermal conductivity varies by alloy and temper; pure aluminium is substantially more conductive.
• The high thermal-expansion coefficient matters in mixed-material assemblies.

Selection note

Attractive where low mass, machinability, corrosion resistance and moderate strength are important. Fatigue, joining, galvanic compatibility and elevated-temperature strength should be checked separately.

Do not combine strength from one grade/condition with modulus, thermal data or temperature limits from another without checking compatibility. Where the overview shows a range, it is intended to expose variability—not establish allowable bounds.

Where it is specified

6061 and 6082 (Al-Mg-Si, heat treatable) are the general structural choice: extrusions, frames, marine fittings, machined brackets. Good strength, weldable, corrosion resistant.

5083 and 5754 (Al-Mg, work hardening) are the marine plate alloys — not heat treatable, but the best seawater resistance in the family and excellent weldability.

7075 and 7050 (Al-Zn-Mg-Cu) are aerospace structural alloys, approaching steel strength at a third the density, but effectively unweldable and prone to stress-corrosion cracking.

2024 (Al-Cu) is the classic damage-tolerant airframe skin alloy, usually clad because bare 2024 corrodes readily.

Cast alloys such as A356 and ADC12 dominate automotive housings, manifolds and wheels.

Chosen over what

Against steel: one third the density and one third the stiffness, so a part of equal stiffness needs greater section depth but still weighs roughly half. Aluminium wins where the section can be deepened and loses where space is fixed.

Against magnesium: heavier but far more corrosion resistant and far easier to handle safely.

Against composite: much cheaper, isotropic, recyclable and inspectable by conventional means, though without the specific stiffness of carbon fibre.

How it fails

No fatigue limit. Unlike steel, aluminium alloys have no endurance limit — the S-N curve keeps falling, so every cyclically loaded aluminium part has a finite life and must be designed to a specific number of cycles. This is the single most important difference from steel design.

Galvanic corrosion when coupled to steel, stainless or carbon fibre. Aluminium is anodic and is consumed; isolation or sealing at the joint is essential, and this is the usual cause of corrosion in mixed-material assemblies.

Stress-corrosion cracking in the 7xxx series, particularly in the peak-aged T6 temper. Overaged tempers (T73, T76) trade some strength for resistance, and that trade is routinely accepted in aerospace.

Softening in the heat-affected zone. Welding a 6061-T6 extrusion locally reverts the heat-affected zone toward annealed strength — a design must use the as-welded allowable, not the parent allowable, at every weld.

Fabrication notes

Machinability is excellent, 300–500% of B1112, limited mainly by built-up edge and chip control. High speeds, sharp polished flutes and good evacuation are the rule. Free-machining 2011 and 6262 add bismuth or lead where chip breaking matters.

Weldability is good for 5xxx and 6xxx by MIG or TIG with matching or 4043/5356 filler, poor to impossible for 2xxx and 7xxx, which crack. Friction stir welding changed this — it joins 2xxx and 7xxx in the solid state without melting, and is now standard for aerospace and rail panels.

Anodising both protects and decorates; hard anodising gives a wear surface. Note that anodising is electrically insulating and dimension-changing, which matters for fits and for bonding paths.

Forming is easiest in the O or T4 temper; forming a T6 extrusion invites cracking at tight radii.