Among all the aluminum alloys available today, 6061 aluminum stands out as one of the most versatile, durable, and widely used materials across industries — especially in aerospace, automotive, marine, and structural engineering. Its unique combination of strength, corrosion resistance, and workability makes it a top choice for precision applications.
However, not all 6061 aluminum is the same. The alloy is available in multiple tempers or grades, each with slightly different mechanical properties, hardness, and processing characteristics.
So, what are the different grades of 6061 aluminum? How do 6061-T6, 6061-T4, and 6061-T651 differ? And which grade is best for your application?
In this detailed guide, SASAALUMINUM explains everything you need to know about the various grades of 6061 aluminum — from their production and heat treatment processes to their mechanical performance and industrial uses.
1. Overview of 6061 Aluminum Alloy
6061 aluminum is a heat-treatable, precipitation-hardened alloy primarily composed of magnesium (Mg) and silicon (Si) as its major alloying elements. It belongs to the 6xxx series, which are known for their excellent strength, corrosion resistance, weldability, and machinability.
Chemical Composition of 6061 Aluminum
| Element | Content (%) |
|---|---|
| Aluminum (Al) | 95.8–98.6 |
| Magnesium (Mg) | 0.8–1.2 |
| Silicon (Si) | 0.4–0.8 |
| Copper (Cu) | 0.15–0.4 |
| Chromium (Cr) | 0.04–0.35 |
| Iron (Fe) | ≤0.7 |
| Zinc (Zn) | ≤0.25 |
| Titanium (Ti) | ≤0.15 |
This balanced chemical composition gives 6061 aluminum its outstanding versatility — allowing it to be extruded, forged, welded, or machined with excellent dimensional accuracy and mechanical performance.
2. Understanding “Grades” or “Tempers” of 6061 Aluminum
The term “grade” of 6061 aluminum generally refers to its temper designation, which indicates how the alloy has been heat-treated or mechanically processed to achieve specific strength and hardness characteristics.
The Aluminum Association defines the temper system with letters and numbers, where:
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T indicates thermally treated (heat-treated).
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The following number (e.g., 4, 6, 651) specifies the exact process.
Each grade of 6061 offers a unique balance between formability, machinability, and strength.
3. Common Grades of 6061 Aluminum
Below are the most commonly used grades (tempers) of 6061 aluminum, along with their features, mechanical properties, and typical applications.
3.1 6061-O (Annealed Condition)
Overview
6061-O is the softest and most ductile form of the alloy. In this temper, the aluminum is annealed — heated and then slowly cooled — to remove internal stress and improve workability.
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 124 MPa (18 ksi) |
| Yield Strength | 55 MPa (8 ksi) |
| Elongation | 25–30% |
| Hardness | 30 HB |
Characteristics
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Extremely easy to form, bend, and deep draw.
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Ideal for cold forming, spinning, and bending operations.
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Low strength but high ductility.
Applications
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Aircraft fairings and panels
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Food and chemical handling equipment
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Ductwork and flexible components
3.2 6061-T4 (Solution Heat-Treated and Naturally Aged)
Overview
6061-T4 is solution heat-treated and then naturally aged at room temperature. This grade provides moderate strength with good formability.
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 210 MPa (30 ksi) |
| Yield Strength | 145 MPa (21 ksi) |
| Elongation | 16% |
| Hardness | 65 HB |
Characteristics
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Easy to form and bend before final aging.
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Moderate strength, ideal for components that will later be artificially aged (to T6).
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Can be welded and machined with minimal distortion.
Applications
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Structural parts requiring forming before hardening.
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Aircraft components, truck bodies, and frames.
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Automotive panels and marine fittings.
3.3 6061-T6 (Solution Heat-Treated and Artificially Aged)
Overview
6061-T6 is the most popular and widely used grade of the alloy. It undergoes solution heat treatment followed by artificial aging, significantly increasing its strength and hardness.
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 310 MPa (45 ksi) |
| Yield Strength | 276 MPa (40 ksi) |
| Elongation | 10–12% |
| Hardness | 95 HB |
Characteristics
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Excellent strength-to-weight ratio.
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High resistance to corrosion and oxidation.
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Good machinability and fair weldability.
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Maintains performance in both cryogenic and elevated temperatures.
Applications
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Aircraft and aerospace structures
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Bicycle frames, boats, and automotive components
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Pressure vessels, bridges, and scaffolding
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Defense and transportation equipment
3.4 6061-T651 (Stress-Relieved by Stretching)
Overview
6061-T651 is a stress-relieved version of 6061-T6, achieved by stretching the material after heat treatment. This process eliminates residual stresses that can cause warping during machining.
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 310 MPa (45 ksi) |
| Yield Strength | 276 MPa (40 ksi) |
| Elongation | 10% |
| Hardness | 95 HB |
Characteristics
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Identical strength to T6 but improved dimensional stability.
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Preferred for precision machining and thick plates.
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Excellent flatness and surface finish.
Applications
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Aerospace and automotive structural plates
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Precision-machined components
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Mold and tooling bases
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High-stress load-bearing applications
3.5 6061-T6511 (Extruded and Stress-Relieved)
Overview
6061-T6511 is the extruded version of T651, meaning it has been pushed through a die to form specific shapes (e.g., bars, tubes, and profiles) before being stress-relieved.
Mechanical Properties
Similar to 6061-T6 and T651.
Characteristics
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Enhanced strength and dimensional accuracy.
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Smooth surface finish ideal for architectural and aerospace parts.
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Excellent machinability and weldability.
Applications
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Aerospace extrusions and structural supports
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Automotive body frames and chassis
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Marine fittings and rail transport systems
3.6 6061-T42 (Solution Heat-Treated and Naturally Aged after Forming)
Overview
This grade is formed in the O condition, then solution heat-treated and naturally aged to reach the T4 temper. It’s commonly used when parts must be shaped before final strengthening.
Applications
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Aircraft frames and skin panels
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Formed structural parts and brackets
3.7 6061-T6510 / T652 (Specialized Heat Treatments)
Certain specialized grades, such as 6061-T6510 and 6061-T652, are produced under controlled heat treatment or stress relief processes for specific aerospace and defense applications. These grades are used when extreme precision, fatigue resistance, or microstructural control is required.
4. Comparison of 6061 Aluminum Grades
| Temper | Strength | Ductility | Machinability | Weldability | Typical Use |
|---|---|---|---|---|---|
| O | Low | Very High | Excellent | Excellent | Deep forming, ductwork |
| T4 | Moderate | High | Good | Excellent | Shaping before hardening |
| T6 | High | Moderate | Excellent | Good | Aerospace, automotive |
| T651 | High | Moderate | Excellent | Good | Precision machining |
| T6511 | High | Moderate | Excellent | Good | Extrusions, structural parts |
Each grade offers a specific balance between strength and formability, allowing engineers to choose the ideal temper for their manufacturing process.
5. Heat Treatment Process and Its Impact
The strength of 6061 aluminum comes from precipitation hardening, which involves precise heat treatment to control microstructural changes.
Step 1 – Solution Heat Treatment
Heated to about 530°C, dissolving alloying elements like Mg and Si into the aluminum matrix.
Step 2 – Quenching
Rapid cooling (usually in water) locks the solute atoms in place, creating a supersaturated structure.
Step 3 – Aging (Natural or Artificial)
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Natural aging (T4): Occurs at room temperature.
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Artificial aging (T6/T651): Accelerated at about 160–180°C for several hours to increase hardness and strength.
This process determines the final mechanical performance of each 6061 grade.
6. Applications of Different 6061 Grades
| Grade | Typical Industries | Example Applications |
|---|---|---|
| 6061-O | HVAC, food processing | Ducts, flexible tubing |
| 6061-T4 | Automotive, aerospace | Panels, formed parts |
| 6061-T6 | Aerospace, marine, defense | Frames, beams, pressure vessels |
| 6061-T651 | Precision engineering | Molds, dies, fixtures |
| 6061-T6511 | Architecture, transport | Extruded frames, profiles |
The wide range of grades ensures that 6061 aluminum can be adapted for virtually any industrial or engineering requirement.
7. Why Choose 6061 Aluminum
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Excellent Strength-to-Weight Ratio
Ideal for reducing structural weight without compromising safety. -
High Corrosion Resistance
Perfect for marine and outdoor environments. -
Great Machinability and Weldability
Simplifies fabrication, joining, and assembly. -
Versatile Heat-Treatable Options
Multiple grades to suit forming, machining, or high-strength needs. -
Cost-Effective
Offers premium performance at a competitive price point.
These qualities make 6061 one of the most trusted and cost-efficient aluminum alloys in the aerospace, marine, and transportation sectors.
8. SASAALUMINUM – Your Reliable Partner for 6061 Aluminum
SASAALUMINUM specializes in the production and export of 6061 aluminum alloy in all major grades — including O, T4, T6, T651, and T6511 — available in plates, sheets, bars, tubes, and extrusions.
Our Advantages:
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Certified to ASTM B209, B221, AMS 4027, and EN 485 standards
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Full EN 10204 3.1 / 3.2 certification for quality traceability
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Advanced heat treatment and extrusion facilities
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Custom sizes, precision cutting, and surface finishing services
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Global logistics and on-time delivery
With years of experience serving aerospace, marine, and engineering clients worldwide, SASAALUMINUM guarantees premium quality and technical reliability in every shipment.
Conclusion
The different grades of 6061 aluminum — from O to T6, T651, and beyond — offer engineers a complete range of performance options. Whether you need soft, formable material for fabrication or high-strength plate for aerospace structures, there’s a 6061 grade designed for your specific requirements.
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6061-O and T4 are perfect for forming and bending.
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6061-T6 is ideal for high-strength structural applications.
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6061-T651/T6511 provide superior stability for precision machining.
No matter the application, SASAALUMINUM delivers certified, high-quality 6061 aluminum products engineered to perform in the most demanding industries.
Post time: Oct-23-2025