Background: Same Alloy, Different Tempers
Alloy 6063 is an aluminum-magnesium-silicon extrusion alloy that can be delivered in several tempers. The temper code describes the mechanical treatment and heat treatment that the alloy has received. T5 means the product was cooled from an elevated temperature and then artificially aged. T6 means the product was solution heat treated, rapidly quenched, and then artificially aged. The difference in processing is small in time but significant in outcome: T6 material develops a finer dispersion of magnesium-silicide precipitates, which translates into higher yield strength and hardness. Understanding this distinction helps buyers avoid paying for T6 where T5 is sufficient, or under-specifying T5 where load resistance is critical.
Mechanical Property Data
Typical values for extruded sections show 6063-T5 with ultimate tensile strength near 205 MPa and yield strength near 175 MPa, while 6063-T6 reaches about 240 to 260 MPa ultimate and 215 MPa yield. Hardness rises from roughly 60 to 70 HB in T5 to 73 to 85 HB in T6. The exact guaranteed minima are defined in standards such as GB/T 5237.1 for Chinese architectural profiles and EN 755-2 for European sections. For identical geometry, the higher yield strength of T6 allows a lighter section to carry the same load, which is why T6 is common in structural glazing and roof systems.
Cost and Production Differences
The T6 route adds a full solution heat treatment furnace and quenching facility, so it consumes more energy and extends the production cycle. Distortion risk is also higher because the profile must be quenched from around 525 degrees Celsius. T5 uses the residual heat of extrusion with controlled cooling followed by aging, which is faster and cheaper. For profiles with a high surface-area-to-thickness ratio, T5 also shows better dimensional stability after heat treatment. Buyers should therefore compare the total cost including straightening and finishing when deciding between the two tempers.
Corrosion Resistance and Surface Finish
Both tempers inherit the good general corrosion resistance of alloy 6063 in atmospheric and mildly acidic environments. Neither is considered a marine-grade alloy, and in coastal or industrial atmospheres a protective anodic film or powder coating is recommended. T6 generally yields a more uniform anodized finish because the solution treatment homogenizes the microstructure and dissolves coarse particles. For exposed architectural surfaces with Class AA anodizing, T6 often produces a more consistent color tone.
Application Scenarios
6063-T5: window frames, door sections, curtain wall mullions, handrails, sunshades, and decorative trims.
6063-T6: roof trusses, mezzanine structures, bus frames, truck platform sections, heat sinks, and ladder components.
Both tempers: electrical enclosures, machine guards, and interior fit-out systems where appearance and corrosion resistance are required.
Decision Checklist
Determine the governing load by structural calculation, not by feel.
Check the local standard, such as GB/T 5237 or EN 755, for minimum guaranteed properties.
Ask the supplier for mill test certificates listing temper, tensile, yield, and elongation.
Confirm whether welding will be performed, since weld zones lose temper strength.
Frequently Asked Questions
Common tempers are O (annealed), H12/H14/H16/H18 with their H2x equivalents for sheet work, and H112 or F for thick plate; the temper is chosen by the forming operation and the final strength required.
EN 573-3 and ISO 209 define the chemical composition, EN 485-2 the mechanical properties of sheet, GB/T 3880.2 the Chinese equivalent, and ASTM B209 the US product standard.
Store dry and off the floor with the protective interleaving in place, keep the bundles separated from steel and other metals, and handle with care so the surface is not scratched or stained.
Yes, but weldability depends on the alloy family: 3xxx and 5xxx alloys weld readily, 6xxx alloys weld with good strength, and 1xxx pure alloys weld easily for non-structural service.
Mill finish is standard; bright, embossed, anodized and color-coated finishes are available for architectural and decorative service, and the finish is specified on the order.
Sheet is typically supplied from 0.2 mm to 6.0 mm and plate from 6 mm upward, with coil widths from 500 mm to about 2000 mm depending on mill capability and the ordered temper.
