What the T5 and T6 Tempers Mean in 6063
6063 is an Al-Mg-Si extrusion alloy (silicon 0.20-0.60% and magnesium 0.45-0.90% by weight) used throughout the architectural, transport, and appliance industries. The same alloy delivers very different performance depending on temper, and T5 and T6 are the two most common choices for extruded profiles, tubes, and pipes.
The T5 temper means the profile is cooled with air or a low-velocity quench as it leaves the extrusion press and is then artificially aged in an oven. Because cooling is gentle, internal stress stays low, the grain structure stays uniform, and the as-extruded surface remains clean and smooth - an ideal starting point for decorative anodizing, powder coating, and electrophoresis.
The T6 temper means the profile is solution heat-treated, rapidly water-quenched, and then artificially aged. The fast quench holds magnesium and silicon in supersaturated solution, producing a finer precipitation-hardening response. The result is significantly higher yield and tensile strength, at the cost of a slightly rougher surface and reduced bendability compared with T5.
Mechanical Property Comparison
The minimum values below follow EN 755-2 (aluminium and aluminium alloys - extruded rod, bar, tube, and profiles) for 6063 in the T5 and T6 tempers. Equivalent limits are mirrored in GB/T 5237.1 for building profiles and in JIS H4100 for 6063 extrusions.
| Property | 6063-T5 | 6063-T6 |
|---|---|---|
| Heat treatment | Air-cooled after extrusion, then artificially aged | Solution heat-treated, water-quenched, then artificially aged |
| Yield strength Rp0.2 (min) | 110 MPa | 160 MPa |
| Tensile strength Rm (min) | 150 MPa | 205 MPa |
| Elongation A (min) | 8% | 6% |
| Surface for anodizing | Excellent, low defect rate | Good |
| Extrudability | Excellent, suits complex dies | Moderate |
| Corrosion resistance | Excellent | Excellent |
Surface Finish and Anodizing Behavior
If the finished part is a consumer-facing profile that needs a uniform anodized color, a mirror polish, or a flawless painted surface, T5 is the safer specification. The gentle air cooling produces a consistent grain structure with fewer water-spot or streaking defects after etching and anodizing.
T6 profiles are perfectly serviceable and can also be anodized, but the quench step can introduce slight surface variation on large cross-sections. For parts that are hidden, painted, or purely structural, this makes no practical difference.
Choosing the Right Temper for Your Application
Use 6063-T5 when the priority is appearance and formability: window and door frames, curtain wall mullions, heat sinks for LED lighting, furniture frames, shower enclosures, and any highly complex or thin-walled section. The lower internal stress also makes T5 easier to bend and less prone to warping after machining.
Use 6063-T6 when the part carries mechanical or dynamic loads: heavy-duty machine guards, automation frames, marine and automotive brackets, high-pressure pipe fittings, walkways, and load-bearing railings. The extra 50 MPa of yield strength directly reduces permanent deformation under load.
For parts that must be bent, specify T5, or bend the profile in the softer T4 state and complete artificial aging to T6 afterwards. Avoid specifying T6 for cosmetic or complex-die parts; it raises cost without adding value.
Supply and Quality Considerations
When sourcing 6063 extrusions, request a material test certificate (MTC) with measured Rm, Rp0.2, and A values, and confirm the standard applied (EN 755-2, GB/T 5237.1, or JIS H4100). For export orders, require multi-layer packaging: EPE foam or kraft paper separation between profiles, waterproof shrink film to block salty sea air, and fumigated wooden crates or pallets with secure strapping.
Frequently Asked Questions
Can 6063-T6 pipe be bent without cracking? It is difficult. T6 is harder and less ductile than T5, and tight-radius rotary draw bending of T6 pipe often produces cracking or wrinkling on the outer arc. For bending applications, specify T5 or bend in the T4 condition before artificial aging to T6.
How much more expensive is T6 than T5? The premium is modest, usually a few percent, because T6 adds a solution heat-treatment and quenching step. The exact difference depends on ingot prices, profile cross-section, and order quantity, so request a split quotation for both tempers.
Which temper welds better? Both T5 and T6 weld well with TIG or MIG using 4043 or 5356 filler. Note that welding heat destroys the artificial aging in the heat-affected zone, so joint-adjacent strength drops to a baseline level regardless of the starting temper. Design the joint accordingly.
Can custom 6063 profiles be extruded to CAD drawings? Yes. Custom dies are standard practice for 6063. Send DWG, DXF, or PDF cross-sections; the die is engineered for the profile, and the recommended temper (T5 vs T6) is selected based on wall thickness, tolerances, and the required surface finish.
Do T5 and T6 have the same corrosion resistance? Yes. Corrosion resistance is governed by the 6063 chemistry, not the temper. Both tempers form a protective oxide layer and are suitable for outdoor and mildly marine environments when properly anodized or painted.
Which standards govern 6063-T5 and 6063-T6 extrusions? The most common are EN 755-2 and EN 573-3 in Europe, GB/T 5237.1 in China, and JIS H4100 in Japan. Mechanical minimums for T5 and T6 are consistent across these specifications.
