6063 Aluminum Tempers Explained: Differences Between T4, T5, T6, T64, and T66

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The main differences between 6063 aluminum alloy tempers (T4, T5, T6, T64, and T66) are defined by mechanical strength, hardness, and thermal cooling methods. This technical guide breaks down how each temper is achieved under the EN 755-2 standard and how to choose the right one for your production needs.

1. Production Workflow Diagram

The structural properties of the EN AW-6063 alloy are determined by how it is quenched (cooled) right after leaving the extrusion press and how it is aged inside the heat-treatment ovens.

[Extrusion Press Output]
       │
       ├──► Air Cool ──────────► Natural Aging ────────────────────────► T4 Temper
       ├──► Air Cool ──────────► Controlled Artificial Under-Aging ────► T64 Temper
       ├──► Forced Air Cool ───► Standard Oven Aging ──────────────────► T5 Temper
       └──► Water Quench ──────► Full Oven Aging ──────────────────────► T6 Temper
               │
               └──► (Optimized Chemistry & Rapid Quench) ──────────────► T66 Temper

2. Detailed Breakdown of EN 755-2 Tempers

Temper T4: Solution Heat Treated & Naturally Aged

Implementation: The profile is cooled naturally at ambient room temperature directly from the extrusion press, completely skipping the artificial aging oven.
Mechanical Properties: Lowest yield strength paired with maximum elongation and material flexibility.
Primary Uses: Ideal for complex cold-forming, deep bending, or secondary hydroforming.

Temper T5: Cooled & Artificially Aged

Implementation: Profiles are cooled quickly via a forced air draft straight out of the die, then placed into a hot aging oven (approx. 185°C–200°C) for several hours.
Mechanical Properties: Moderate strength with high dimensional stability and minimal internal stress.
Primary Uses: Standard architectural products, window frames, doors, and furniture trims.

Temper T6: Solution Heat Treated & Fully Artificially Aged

Implementation: Requires aggressive, immediate press quenching using high-velocity water sprays or intense air blasts to trap alloying elements. It then goes through a complete artificial aging cycle.
Mechanical Properties: High mechanical rigidity, high tensile strength, but reduced flexibility.
Primary Uses: Structural frames, ladders, automotive chassis, and load-bearing components.

Temper T64: Solution Heat Treated & Artificially Under-Aged

Implementation: Heated and quenched similarly to T6, but deliberately under-aged by cutting the oven baking time short or lowering the aging temperature.
Mechanical Properties: A middle-ground option offering higher strength than T4/T5, but retaining better bending capacity than T6.
Primary Uses: Specialized architectural profiles that must undergo localized bending during assembly.

Temper T66: High-Property Process Controlled

Implementation: A proprietary, highly optimized variant of T6. It requires strict chemical composition purity (keeping Magnesium and Silicon at the precise upper limits) combined with specialized flash quenching.
Mechanical Properties: Peak mechanical strength values for the 6063 alloy, exceeding standard T6 tensile limits by roughly 15–20 MPa.
Primary Uses: High-performance engineering components, solar panel mounting systems, and heavy-duty industrial framing.

3. Mechanical Property Comparison (EN 755-2 Limits)

The table below outlines the minimum mechanical values required by the EN 755-2 standard for profiles with a wall thickness up to 10 mm:

Temper	Tensile Strength (Rm Min)	Yield Strength (Rp0.2 Min)	Elongation (A Min)	Hardness (Typical)
T4	130 MPa	65 MPa	14%	~ 50 HB
T5	175 MPa	130 MPa	8%	~ 65 HB
T6	215 MPa	170 MPa	8%	~ 75 HB
T64	180 MPa	120 MPa	12%	~ 60 HB
T66	245 MPa	200 MPa	8%	~ 80 HB