What Are the Alloys of Aluminum?

Direct answer: aluminum alloys are classified by product route, alloy series and temper. A useful purchase description combines alloy, temper, product form, standard, dimensions and acceptance requirements.

Wrought and Cast Aluminum Are Different Families

Wrought alloys are mechanically processed into sheet, plate, foil, bar, tube, wire, extrusion or forging. Cast alloys are shaped from molten metal. Their designation systems, defect considerations, property directions and applicable specifications differ, so a cast alloy should not be substituted for a wrought designation by composition similarity alone.

Main Wrought-Alloy Series

• 1xxx: commercially pure aluminum for conductivity, formability and corrosion resistance
• 2xxx: aluminum-copper alloys used where higher strength and temperature performance are required
• 3xxx: aluminum-manganese alloys common in sheet products and formed applications
• 4xxx: aluminum-silicon alloys used in welding consumables and specialized products
• 5xxx: aluminum-magnesium alloys for sheet, plate, marine and welded applications
• 6xxx: aluminum-magnesium-silicon alloys widely used for extrusions and structural products
• 7xxx: aluminum-zinc-magnesium or aluminum-zinc-magnesium-copper alloys for high-strength applications
• 8xxx: specialized alloys outside the preceding series

Heat-Treatable and Non-Heat-Treatable Alloys

2xxx, 6xxx and 7xxx wrought alloys are generally strengthened through solution heat treatment and aging, although the exact response depends on alloy and product. 1xxx, 3xxx and 5xxx families are generally strengthened by cold work rather than precipitation heat treatment. Temper designations such as O, H, T4, T6 or T651 communicate processing condition and must be specified.

Product Form Changes the Available Properties

A property value from a thin sheet cannot automatically be applied to thick plate, bar, extrusion or forging. Grain direction, thickness, quench response, residual stress and manufacturing tolerances change with product form. Use the product-specific standard and size range for acceptance.

A Practical Alloy Selection Workflow

• Define load, temperature, corrosion exposure and design life
• Choose the required product form and fabrication route
• Identify welding, forming, machining and surface-treatment needs
• Select a specific alloy and full temper
• Check the governing standard for the actual thickness or section
• Define inspection, certificate and traceability requirements
• Validate critical properties with the responsible engineer