6061-T6 vs 6061-T651 Aluminum - Which Is Better for Precision Machining?
6061-T651 Aluminum Properties and Advantages
6061-T651 aluminum undergoes the same solution heat treatment and artificial aging as T6, but with an additional stress-relief stretching process. This step significantly reduces internal stresses, minimizing warping during machining.
As a result, 6061-T651 aluminum is ideal for precision components that require tight tolerances and dimensional stability.
| Chemical Composition | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Al 97% | Cu 0.3% | Si 0.6% | Mn 0.2% | Fe 0.7 % Max | |||||
| Mg 1% | Zn 0.3% Max | Ti 0.2% Max | Cr 0.2% Max | Other 0.2% | |||||
| PHYSICAL PROPERTIES | ||||||
|---|---|---|---|---|---|---|
| Density | Electrical conductivity (% IACS) | Thermal conductivity (BTU-in/hr-ft²-°F) | Specific heat capacity | Thermal expansion (1/°F) | Melting Point (°F) | |
| 0.0975 | 47.11 | 1250 | 0.214 | 0.00001310 | 1140 | |
| Mechanical Properties | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Property | Minimum | Maximum | |||||||
| Yield Strength Range (Rp0.2 Offset) (ksi) | 8 | 39 | |||||||
| Tensile Strength Range (Rm) (ksi) | 16 | 45 | |||||||
| Elongation (AL=5 x Ø) | 12.0% | 25.0% | |||||||
| Brinell Hardness (H) | 30 | 123 | |||||||
| Modulus of Elasticity (ksi) (E): 10000 | |||||||||
| Machineability General Index: 30% | |||||||||
How Machinable Is 6061-T651 Aluminum?
Although 6061-T651 aluminum may feel slightly tougher during cutting than T6, its stress-relieved structure allows for more predictable machining. This reduces part movement, lowers rework rates, and improves accuracy-especially for large plates or thin-walled designs.
Recommended Tools for Machining 6061-T651
Tungsten carbide tools are strongly recommended
HSS tools can be used but wear rapidly
Sharp edges and positive rake angles help prevent built-up edges
For high-volume or deep machining operations, carbide tooling ensures better surface quality and tool longevity.
Cutting Parameters and Cooling for 6061-T651
High cutting speeds prevent rough surfaces
Balanced feed rates improve chip control
Light lubrication prevents chip welding
Excess coolant may interfere with smooth cutting
6061-T651 produces long chips similar to T6, but chip breaking is generally easier due to its improved stability.
Typical Applications of 6061-T651 Aluminum
6061-T651 aluminum is widely used in:
Aerospace structural components
Automotive frames and precision housings
CNC-machined tooling plates
Machinery and equipment requiring flatness and stability
Parts machined from 6061-T651 maintain dimensional accuracy even after extensive material removal.
Physical Properties: Differences Between 6061 T6 and T651
| Property | T6 | T651 |
| Yield Strength | 276 Mpa | 276 Mpa |
| Tensile Strength | 310 Mpa | 310 Mpa |
| Density | 2.7 g/cc | 2.7 g/cc |
| Elastic Modulus | 69 GPa | 69 GPa |
| Hardness (Brinell) | 93 | 93 |
| Thermal Expansion Coefficient | 24 µm/m-°C | 24 µm/m-°C |
| Thermal Conductivity | 170 W/m-K | 170 W/m-K |
| Fatigue Strength | 96 MPa | 96 MPa |
| Weldability | Good | Excellent |
| Machinability | Fair | Excellent |
| Corrosion Resistance | Good | Good |
6061-T6 vs 6061-T651 Aluminum: Key Comparison
| Factor | 6061-T6 | 6061-T651 |
|---|---|---|
| Strength | High | Comparable |
| Stress Relief | No | Yes |
| Machinability | Good, may distort | Excellent, stable |
| Dimensional Stability | Moderate | High |
| Best Use | General machining | Precision machining |
Which Should You Choose: 6061-T6 or 6061-T651?
Choose 6061-T6 aluminum for general machining, cost efficiency, and high-strength parts
Choose 6061-T651 aluminum when tight tolerances, flatness, and post-machining stability are critical
For aerospace, EV battery enclosures, thin-wall components, and complex CNC machining, T651 is the superior option.
Heat Treatment Differences Between 6061-T6 and 6061-T651
Both tempers reach similar strength levels:
Tensile strength: ~310 MPa
Yield strength: ~276 MPa
However, the post-treatment stretching of T651 significantly improves machining reliability and dimensional consistency without sacrificing strength.
GNEE - Your Reliable Supplier of 6061-T6 and 6061-T651 Aluminum
GNEE provides high-quality 6061-T6 and 6061-T651 aluminum plates, sheets, bars, and profiles for aerospace, automotive, and industrial machining applications. With stable quality and flexible customization, GNEE helps manufacturers achieve precision, efficiency, and performance.
