6061 Aluminum Temper Comparison: Key Differences, Cost, and Applications of T6, T651, and T6511

 

Selecting the right 6061 aluminum temper—whether T6, T651, or T6511—can be confusing. Each temper has different mechanical properties, manufacturing processes, and dimensional stability, and choosing the wrong one can lead to higher machining costs, reduced part performance, or even project delays.

 

Imagine investing in 6061 CNC machined parts only to discover that your chosen temper can’t handle the required load, warps during machining, or suffers premature corrosion. Not only does this waste material and labor, but it can also jeopardize the quality and reliability of your final product. Many businesses overlook these differences and end up with expensive mistakes that could have been avoided with better upfront knowledge.

 

By understanding the 6061 aluminum temper properties of T6, T651, and T6511, you can select the right option for your project’s strength, dimensional stability, and corrosion resistance needs. This guide will compare their properties, costs, and applications—so you can work with CNC machining factories confidently and avoid costly surprises.

• Tip: Always confirm with your CNC machining service provider which temper will best balance your project’s strength and machinability needs before committing to bulk production.

 

The key difference between 6061 aluminum T6, T651, and T6511 is stress relief and dimensional stability. T6 is heat-treated and naturally aged, T651 is stress-relieved by stretching, and T6511 is stress-relieved by stretching and minor straightening. These differences affect machinability, performance, and cost for aluminum CNC machined parts.

 

Understanding the differences between these 6061 aluminum tempers is more than just a technical detail—it’s the foundation for ensuring your parts meet exact specifications without costly surprises. In the sections ahead, we’ll break down each temper’s mechanical properties, manufacturing process, cost considerations, and application suitability, so you can choose with confidence for your 6061 CNC machined parts project.

• Tip: If you’re unsure which section to focus on, start by identifying your project’s most critical requirement—strength, stability, machinability, or corrosion resistance.

 

 

 

6061 Aluminum Tempering Overview

 

Tempering is a controlled heat treatment process that tailors the mechanical and physical properties of 6061 aluminum to match specific application needs. In CNC machining, tempering directly influences strength, hardness, ductility, corrosion resistance, and dimensional stability—factors that determine whether your parts will perform reliably in service.

 

For 6061 aluminum CNC machined parts, the most common tempers are T6, T651, and T6511. All three start from the same 6061 alloy composition, but their differences come from post-heat-treatment processing. T6 is solution heat-treated and artificially aged to reach maximum strength. T651 is T6 with added stress relief through stretching, reducing internal residual stress. T6511 undergoes the same stress relief as T651 but also has minor straightening to meet strict dimensional tolerances.

 

Why is this important? Because choosing the wrong temper can lead to problems like part distortion during machining, insufficient strength for load-bearing applications, or overpaying for properties your project doesn’t need. Understanding 6061 aluminum temper properties ensures you get the best balance of cost, performance, and machinability.

 

Tip: When requesting quotes from CNC machining factories, specify both the alloy (6061) and temper (T6, T651, or T6511) to avoid miscommunication and ensure accurate pricing.

 

 

 

 

 

 

 

Key Differences in 6061 Aluminum Tempering

 

Although 6061 aluminum T6, T651, and T6511 come from the same base alloy, their tempering processes create distinct performance profiles. The main differences lie in stress relief, dimensional stability, and final machinability—critical factors for achieving precision in aluminum CNC machined parts.

 

T6 temper is achieved through solution heat treatment and artificial aging, giving it maximum tensile and yield strength. However, T6 aluminum retains some internal stresses from the heat treatment process. This means that during CNC machining, especially in high-precision or thin-walled parts, T6 may experience slight warping or distortion.

 

T651 shares the same heat treatment as T6 but adds a stretching process—usually between 1.5% and 3%—to relieve internal stresses. This stress relief greatly improves dimensional stability, making T651 better suited for precision machining where tolerance consistency is critical.

 

T6511 follows the same treatment as T651 but undergoes minor straightening to meet specific shape tolerances, such as in extrusions. This combination of stress relief and precision straightening makes T6511 ideal for applications requiring both structural performance and accurate geometry.

 

In short:

• T6 = Maximum strength, less stress relief.
• T651 = Strength + stress relief for improved stability.
• T6511 = Strength + stress relief + dimensional correction for precision profiles.

Tip: If your project requires long, thin components, T6511 can save time and cost by reducing secondary straightening operations after machining.

 

 

 

 

6061-O, 6061-T4, 6061-T6, and 6061-T651: Key Differences in 6061 Aluminum Tempers

 

 

The 6061 aluminum alloy is versatile, and its properties change significantly depending on the temper. Each temper—O, T4, T6, and T651—has unique mechanical characteristics, processing steps, and ideal applications. Understanding these differences is critical for ensuring your 6061 CNC machined parts meet both performance and cost requirements.

 

6061-O is the fully annealed condition, offering maximum ductility but the lowest strength. It’s easy to form and bend, making it ideal for complex shapes or parts requiring extensive forming before machining. However, its lower strength means it is less suited for high-load applications.

 

6061-T4 is solution heat-treated and naturally aged. It offers a good balance of strength and ductility, making it a common choice for parts that require forming followed by further aging to increase hardness. It’s easier to machine than O temper but not as strong as T6 or T651.

 

6061-T6 is solution heat-treated and artificially aged to achieve maximum strength. This makes it excellent for structural applications but introduces residual stresses that can cause distortion during machining, especially in thin or intricate parts.

 

6061-T651 is essentially T6 that has been stress-relieved by stretching. This process significantly improves dimensional stability, making it ideal for precision machining where tight tolerances are critical.

 

In short:

• O = Maximum ductility, lowest strength.
• T4 = Balanced ductility and strength, suitable for post-forming aging.
• T6 = Maximum strength, potential machining distortion.
• T651 = T6 strength + superior stability for CNC machining.

Tip: For projects requiring both high strength and precise tolerances, T651 is usually the best investment, reducing the risk of rework and wasted material in CNC machining services.

 

 

6061 Aluminum Temper Properties Comparison

 

 

• Tip: When ordering 6061 CNC machined parts from CNC machining factories, specify both the alloy and temper in your RFQ. This avoids misunderstandings, ensures accurate pricing, and helps your machining partner prepare the right tooling and cutting parameters.

 

 

 

 

Aluminum T6, T651, and T6511: Manufacturing Process Comparison

 

 

 

 

The primary differences between aluminum T6, T651, and T6511 tempers come from their heat treatment and post-treatment stress-relief processes. While they share the same 6061 alloy chemistry, the manufacturing steps they undergo directly affect their mechanical properties, dimensional stability, and suitability for aluminum CNC machined parts.

 

T6 Process: The 6061 aluminum is first solution heat-treated—heated to a specific temperature to dissolve alloying elements into a solid solution—then quenched rapidly, usually in water. This is followed by artificial aging at a controlled temperature to maximize hardness and strength. The result is high mechanical strength but with internal stresses that can cause slight distortion during CNC machining.

 

T651 Process: This begins with the same T6 heat treatment, but an additional stretching operation (1.5–3% elongation) is performed to relieve residual stresses. This significantly improves dimensional stability, making T651 preferred for applications requiring tight tolerances and consistent machining accuracy.

 

T6511 Process: Similar to T651, this temper also undergoes stretching for stress relief. However, after stretching, the material is straightened to meet precise shape tolerances—commonly for extruded products. This combination makes T6511 ideal for long profiles, rails, or structural components that must maintain both strength and geometry after machining.

 

• Tip: If your CNC machining services involve long extrusions or precision profiles, ordering in T6511 temper can reduce or eliminate post-machining straightening work, saving both time and cost.

 

Manufacturing Process Comparison: Aluminum T6 vs. T651 vs. T6511

 

 

 

• Tip: If your project requires long profiles or complex shapes, T6511 can minimize post-machining corrections, while T651 is ideal for block or plate stock in high-precision CNC machining services.

 

 

 

 

Aluminum T6, T651, and T6511: Mechanical Property Comparison

 

 

 

 

Mechanical properties are a decisive factor when selecting between aluminum T6, T651, and T6511 tempers. While all three share the same base alloy composition, subtle differences in post-heat-treatment processing can lead to variations in tensile strength, yield strength, hardness, ductility, and machinability. For manufacturers ordering aluminum CNC machined parts, these property differences can mean the distinction between consistent quality and costly rework.

• Tip: Always match the temper’s mechanical properties with your application’s actual load, wear, and machining requirements to avoid over-engineering or underperforming parts.

 

T6 Mechanical Properties

 

6061 aluminum T6 offers maximum strength among the three tempers, with a typical ultimate tensile strength of around 290 MPa (42 ksi) and yield strength of 240 MPa (35 ksi). Its Brinell hardness averages 95, making it well-suited for load-bearing structures. However, T6 retains residual stresses from heat treatment, which can cause dimensional changes during CNC machining—especially in thin sections or complex geometries.

• Tensile Strength: ~290 MPa (42 ksi)
• Yield Strength: ~240 MPa (35 ksi)
• Elongation: ~8–10%
• Hardness (Brinell): ~95
• Machinability: Good, but with distortion risk in high-precision parts

Tip: For high-strength parts where slight dimensional changes are acceptable, T6 is cost-effective and widely available in CNC machining factories.

 

 

T651 Mechanical Properties

 

6061 aluminum T651 has nearly identical tensile and yield strength to T6 but with enhanced dimensional stability thanks to its stretching process. This stress relief minimizes warping during machining, making it a preferred choice for precision components. Its machinability is excellent compared to T6 when tight tolerances are critical.

• Tensile Strength: ~290 MPa (42 ksi)
• Yield Strength: ~240 MPa (35 ksi)
• Elongation: ~8%
• Hardness (Brinell): ~95
• Machinability: Excellent for tight tolerances; minimal distortion risk

Tip: If you need both T6-level strength and consistent machining accuracy, T651 will reduce the need for secondary straightening or remachining.

 

 

T6511 Mechanical Properties

 

6061 aluminum T6511 mirrors T651 in mechanical performance but gains an advantage in geometric precision due to a straightening process after stretching. This makes it ideal for long extrusions and complex profiles where shape accuracy is critical after machining.

• Tensile Strength: ~290 MPa (42 ksi)
• Yield Strength: ~240 MPa (35 ksi)
• Elongation: ~8%
• Hardness (Brinell): ~95
• Machinability: Excellent for extrusions and long parts with precise shape requirements

Tip: For long aerospace rails, marine frames, or structural extrusions, T6511 minimizes both stress-related distortion and geometry deviation, reducing finishing costs in CNC machining services.

 

 

Mechanical Property Comparison: Aluminum T6 vs. T651 vs. T6511

 

             

• Tip: When working with CNC machining factories, request T651 for precision blocks/plates and T6511 for long extrusion profiles to reduce rework and improve cost efficiency in CNC machining services.

 

 

 

 

Aluminum T6, T651, and T6511: Microstructural Differences

 

 

While aluminum T6, T651, and T6511 share the same 6061 alloy chemistry, the differences in their microstructure come from their heat treatment, stress relief, and straightening processes. Microstructure—the arrangement of grains and precipitates within the metal—directly influences machinability, strength, and dimensional stability in aluminum CNC machined parts. A well-understood microstructure ensures that your chosen temper will deliver the mechanical performance you expect in service.

• Tip: Always consult with your CNC machining services provider about the temper’s microstructure when tolerances are tight or the part is load-bearing. Microstructural stability can prevent costly machining issues.

 

 

T6 Microstructure

 

In 6061 aluminum T6, the solution heat treatment dissolves magnesium and silicon into a solid solution, followed by artificial aging that precipitates Mg₂Si particles uniformly throughout the matrix. This fine, evenly distributed precipitate structure gives T6 its maximum strength and hardness. However, the absence of stress relief means residual tensile stresses are locked into the grain boundaries, which can cause distortion when material is removed during CNC machining.

 

 

T651 Microstructure

 

6061 aluminum T651 begins with the same precipitation-hardened structure as T6 but undergoes stretching to relieve residual stresses. This stretching slightly elongates grains and redistributes precipitates, leading to a more stable microstructure. The result is less distortion during machining and more consistent dimensional control—especially in thick plates or blocks.

 

 

T6511 Microstructure

 

6061 aluminum T6511 shares T651’s stress-relieved precipitation-hardened structure but includes an additional straightening step for extrusions. This mechanical adjustment doesn’t significantly alter precipitate distribution but ensures that the extruded grain alignment remains consistent along the length of the profile. For long or complex shapes, this yields both microstructural stability and superior geometry retention after machining.

• Tip: If your design involves long extruded parts, T6511’s controlled grain alignment can reduce internal stress hotspots, extending the service life of 6061 CNC machined parts.

 

 

Microstructural Differences: Aluminum T6 vs. T651 vs. T6511

 

 

 

• Tip: For precision extrusion-based designs, T6511 offers the combined benefits of stress relief and shape control, reducing finishing time in CNC machining services.

 

 

 

 

Aluminum T6, T651, and T6511: Stress Relief Properties

 

 

In CNC machining, internal stresses in aluminum can cause dimensional shifts, warping, and surface defects during or after cutting. This is why understanding the stress relief properties of 6061 aluminum in T6, T651, and T6511 tempers is crucial for engineers, machinists, and buyers seeking precision results. Each temper undergoes different post-heat-treatment processes, directly impacting stability and performance in CNC machining services.

 

 

T6 – No Stress Relief Treatment

 

T6 aluminum is solution heat-treated and artificially aged, but it is not stress relieved. This means that while it offers the highest strength among the three tempers, residual stresses remain locked in the metal from quenching. During CNC machining, especially with deep cuts or thin walls, these stresses can release and lead to part distortion. T6 is best suited for applications where strength is critical and minor dimensional shifts are acceptable.

 

 

T651 – Fully Stress Relieved by Stretching

 

T651 undergoes the same heat treatment and aging as T6 but adds a mechanical stretching step (typically 1–3% elongation) to relieve internal stresses. This process minimizes warping and distortion during machining. As a result, T651 is preferred for precision aluminum CNC machined parts where tight tolerances are required. It offers an optimal balance of strength and stability.

 

 

T6511 – Stress Relieved and Straightened for Extrusions

 

T6511 is specific to extruded aluminum profiles. After heat treatment and stretching for stress relief, it undergoes minor straightening to correct shape deviations caused during extrusion. This temper is ideal for long, complex profiles such as aerospace rails or marine frames, where maintaining straightness during machining and assembly is essential.

 

 

Here’s the Aluminum T6, T651, and T6511: Stress Relief Properties comparison table:

 

 

 

 

 

 

 

Aluminum T6, T651, and T6511: Dimensional Stability Comparison

 

 

 

 

When it comes to CNC machining, dimensional stability determines how well a material maintains its shape and size during and after cutting. The difference between T6, T651, and T6511 tempers lies mainly in residual stress levels and stress relief treatments.

 

• T6 Aluminum is solution heat-treated and artificially aged, but it is not stress-relieved. This means it retains high residual stresses from the manufacturing process. During CNC machining—especially when removing large amounts of material—these stresses can be released unevenly, causing warping, bending, or twisting. Thin-walled parts and long profiles are particularly vulnerable.
• T651 Aluminum undergoes mechanical stretching after heat treatment, which relieves internal stresses. As a result, it offers excellent dimensional stability, making it a top choice for tight-tolerance machining, precision components, and large parts that must maintain shape even after heavy milling.
• T6511 Aluminum is similar to T651 but is produced for extrusions. It is both stretched and straightened, ensuring superior stability in long, linear profiles such as aerospace rails, marine frames, and structural supports. This makes it ideal for applications where both length and accuracy are critical.

In short:

• T6 = strongest but least stable
• T651 = strong and very stable for general CNC work
• T6511 = strong, very stable, and best for long extrusion parts

 

Here’s the Dimensional Stability Comparison Table for Aluminum T6, T651, and T6511:

 

 

 

 

 

 

 

 

 

Aluminum T6, T651, and T6511: Machinability and Manufacturing

 

 

When selecting the right aluminum temper for CNC machining projects, it’s important to balance strength, stability, and machinability. While 6061-T6, 6061-T651, and 6061-T6511 share the same base alloy, differences in stress-relief methods and manufacturing processes lead to noticeable variations in cutting performance, part stability, and surface finish quality. Understanding these differences helps manufacturers reduce scrap, improve tolerances, and optimize production efficiency.

 

 

 

 

T6 Aluminum

 

Manufacturing Process: T6 temper is solution heat-treated and artificially aged to achieve maximum strength. However, it is not stress-relieved, meaning internal stresses from processing remain.

Machinability: While T6 offers excellent cutting speeds and good surface finishes, its higher residual stress can cause part distortion during heavy milling or when machining thin-walled components. It’s suitable for smaller parts or where high tensile strength is more important than dimensional stability.

 

 

T651 Aluminum

 

Manufacturing Process: T651 is produced by taking T6 material and mechanically stretching it to relieve internal stresses before aging. This step significantly reduces the risk of warping.

Machinability: Offers superior dimensional stability during CNC machining, making it ideal for tight-tolerance, large, or high-precision parts. Cutting speeds and surface finish quality are similar to T6, but part rejection rates are lower due to reduced distortion.

 

 

T6511 Aluminum

 

Manufacturing Process: T6511 is similar to T651 but is specifically made for extrusions. It is stretched and straightened after extrusion to improve straightness and relieve stress.

Machinability: Provides excellent stability for long profiles and linear components. Particularly well-suited for aerospace rails, marine frames, and structural supports where length accuracy is critical. Cutting behavior is comparable to T651, but workholding and fixturing are easier because of improved straightness.

 

 

Here’s the comparison table for Aluminum T6, T651, and T6511: Machinability and Manufacturing Differences:

 

 

 

 

 

 

Aluminum T6, T651, and T6511: Corrosion Resistance Comparison

 

 

Corrosion resistance is a crucial factor when selecting aluminum alloys for CNC machining, especially in industries such as aerospace, marine, and automotive where exposure to harsh environments is common. While 6061 aluminum inherently has good corrosion resistance due to its magnesium and silicon content, the tempering process (T6, T651, T6511) can slightly influence performance. However, the differences are not as pronounced as in mechanical properties or dimensional stability.

 

 

T6 Aluminum

 

6061-T6 aluminum provides good corrosion resistance in most environments, including atmospheric exposure and freshwater. However, due to the lack of stress-relief processing, residual stresses may increase the risk of stress-corrosion cracking (SCC) in highly demanding conditions. It is still widely used for general-purpose CNC machined parts but may require additional surface treatments (like anodizing) for marine or chemically aggressive environments.

 

 

T651 Aluminum

 

Since T651 is mechanically stretched to relieve stress, it offers slightly better resistance to stress-corrosion cracking compared to T6. The stretching process minimizes internal stress concentrations, reducing the likelihood of premature failure in corrosive settings. Thus, T651 is considered more reliable than T6 for structural components and precision CNC parts that must perform in variable environmental conditions.

 

 

T6511 Aluminum

 

T6511 shares similar corrosion resistance with T651, as both undergo stress-relief stretching. However, because T6511 is specifically used for extrusions, it is often chosen for long profiles exposed to marine or industrial environments. When paired with protective coatings, anodizing, or conversion coatings, T6511 extrusions offer outstanding long-term durability.

 

 

Summary:

• T6: Good corrosion resistance, but slightly more prone to stress-corrosion cracking.
• T651: Improved resistance due to stress relief, suitable for high-precision and load-bearing CNC parts.
• T6511: Similar to T651, ideal for extruded profiles used in corrosive environments.

 

 

Here’s the Aluminum T6, T651, and T6511: Corrosion Resistance Comparison table:

 

 

 

 

 

 

 

Aluminum T6, T651, and T6511: Cost and Availability Comparison

 

 

When choosing between aluminum T6, T651, and T6511 for CNC machining, cost and availability play a decisive role alongside mechanical and corrosion-resistant properties. Each temper is produced through different processing steps, which affect not only performance but also price and market accessibility. Understanding these differences helps manufacturers and buyers optimize material selection for both budget and lead time.

 

 

T6 Aluminum

 

6061-T6 aluminum is the most widely available and generally the least expensive of the three options. It is produced in large volumes, making it easy to source in sheets, plates, bars, and tubes. Its lower cost and broad distribution make it the default choice for CNC machining services where extreme stress relief or extrusion form isn’t critical.

 

 

T651 Aluminum

 

6061-T651 aluminum undergoes additional stretching for stress relief, which adds extra processing cost compared to T6. As a result, T651 is slightly more expensive but still readily available, especially in plate form. For CNC machining factories that require high dimensional stability and reduced residual stresses, the modest price difference is often justified.

 

 

T6511 Aluminum

 

6061-T6511 aluminum is specifically used for extruded profiles, such as rods, bars, and complex shapes. Its cost is usually comparable to or slightly higher than T651, depending on profile complexity and supplier. However, availability can vary, as not all suppliers stock the full range of extrusion sizes. It is often selected when long, stable profiles are required for aerospace or structural applications.

 

 

Summary:

• T6: Cheapest, most widely available, best for general machining.
• T651: Slightly more expensive, but widely available in plates; better choice for precision machining.
• T6511: Cost similar to T651, but availability depends on extrusion profile demand.

 

 

Here’s the Aluminum T6, T651, and T6511: Cost and Availability Comparison table:

 

 

 

 

                

                

 

Aluminum T6, T651, and T6511: Application-Specific Properties

 

 

6061 aluminum alloys in T6, T651, and T6511 tempers are widely used across industries because of their unique balance of strength, machinability, corrosion resistance, and dimensional stability. However, each temper offers different advantages depending on the specific application. By comparing their suitability in aerospace, automotive, construction, marine, and electronics, manufacturers can determine the most effective choice for performance, cost, and reliability.

 

 

 

Aerospace

 

In aerospace engineering, precision and dimensional stability are critical. 6061-T651 and 6061-T6511 are often preferred because they undergo stress relief, reducing the risk of warping after machining. These tempers are commonly used in structural components, fuselage frames, and aerospace rails. While T6 is strong and widely available, its lack of stress relief makes it less suitable for high-precision aerospace assemblies.

 

 

Automotive

 

For automotive parts where cost efficiency and machinability are priorities, 6061-T6 is often the go-to choice. It provides a good balance of strength and weight, making it ideal for engine components, brackets, and performance parts. T651 may be chosen for parts requiring tighter tolerances and stability, while T6511 is useful in extruded automotive profiles such as chassis rails and suspension arms.

 

 

Construction

 

In construction, strength-to-weight ratio and cost are major considerations. 6061-T6 is widely used for structural beams, scaffolding, and architectural applications due to its affordability and high availability. For precision load-bearing structures, 6061-T651 may be preferred. T6511 extrusions are also employed in frameworks and support structures that require both strength and corrosion resistance.

 

 

Marine Corps (Marine Applications)

 

Marine environments require strong corrosion resistance. 6061-T6 is commonly used in boat fittings, docks, and marine hardware due to its balance of corrosion resistance and affordability. However, 6061-T651 and T6511 are often chosen for critical structural marine parts, such as masts, rails, and hull components, where stress relief ensures long-term dimensional stability under harsh conditions.

 

 

Electronics

 

In electronics, aluminum is valued for its thermal conductivity and machinability. 6061-T6 is often used for heat sinks, housings, and enclosures due to its wide availability and low cost. 6061-T651 can be preferred in precision-machined electronic components that demand tighter tolerances. 6061-T6511 extrusions are less common but may be used for custom profiles in electronic housings or structural supports.

 

 

Here’s the comparison table for Aluminum T6, T651, and T6511: Application-Specific Properties:

 

 

 

 

 

 

 

Choosing the Right Temper for Your Aluminum CNC Machined Part Project

 

 

Selecting the right temper of 6061 aluminum is a critical decision in CNC machining. Different tempers—such as T6, T651, and T6511—affect not only the material’s strength but also its dimensional stability, machinability, corrosion resistance, and cost. Choosing the wrong option can lead to performance issues, reduced service life, or higher production expenses. By understanding each property, manufacturers and engineers can make the most cost-effective and performance-driven decisions for their projects.

 

 

Strength Requirements

• T6 provides the highest strength among common 6061 aluminum tempers, making it ideal for load-bearing parts, structural components, and high-performance applications.
• T651 offers nearly identical strength but with added stress relief, making it more reliable for critical aerospace and industrial uses.
• T6511, being extrusion-based, provides strength while allowing more complex geometries but may slightly vary depending on profile thickness.

 

 

Dimensional Stability

• T6 may retain residual stress from heat treatment, leading to minor warping during machining.
• T651 undergoes controlled stretching for stress relief, ensuring excellent dimensional stability—perfect for aerospace or precision machining.
• T6511 also offers stress relief but is tailored for extruded shapes, making it reliable for long or complex profiles where stability is crucial.

 

 

Machinability

• T6 machines well but may introduce stress-related distortion in tight-tolerance parts.
• T651 is the preferred choice for high-precision CNC machining, as stress relief minimizes movement during cutting.
• T6511 allows complex extrusion machining, although surface finishing may require more processing depending on the profile.

 

 

Corrosion Resistance

• All three (T6, T651, and T6511) offer excellent corrosion resistance, comparable across marine and outdoor environments.
• Surface finishing methods such as anodizing or powder coating further enhance corrosion resistance for all tempers.
• T651 and T6511 are often favored in marine or aerospace industries where long-term exposure is critical.

 

 

Cost and Availability

• T6 is the most cost-effective and widely available, making it the go-to option for general CNC machining.
• T651 comes at a slightly higher price due to stress relief processing but offers superior stability for precision parts.
• T6511 is priced similarly to T651 but its availability depends on extrusion demand—ideal for specialized profiles.

 

Here’s a clear comparison table for Choosing the Right Temper for Your Aluminum CNC Machined Part Project:

 

 

6061 Aluminum Tempers: Selection Guide

 

 

 

 

 

 

 

Conclusion

 

When it comes to CNC machining projects, choosing the right 6061 aluminum temper—whether T6, T651, or T6511—depends on balancing strength, stability, machinability, corrosion resistance, and cost.

• 6061-T6 is the most cost-effective and widely available option, making it ideal for general applications where high strength and good corrosion resistance are needed.
• 6061-T651 offers superior dimensional stability thanks to stress-relief processes, making it the best choice for precision CNC machining in industries like aerospace and defense.
• 6061-T6511 provides a balance of strength and stability tailored for extruded shapes, serving marine, aerospace, and construction projects that demand custom profiles.

Ultimately, the right temper ensures not only better performance and durability but also cost efficiency for your CNC machined parts. Partnering with professional CNC machining services or experienced CNC machining factories can help you make the optimal material selection and achieve superior-quality results.

 

 

 

 

 

 

 

FAQs: 6061 Aluminum Tempers

 

 

1. What are the different tempers of 6061 aluminum?

 

6061 aluminum is available in several tempers, including O (annealed), T4, T6, T651, and T6511. Each temper offers a different balance of strength, machinability, corrosion resistance, and dimensional stability, making them suitable for different CNC machining applications.

 

 

2. What is the difference between T6 and T651 tempers?

 

Both T6 and T651 are solution heat-treated and artificially aged, but T651 undergoes stress-relief stretching, which reduces residual stresses. This makes 6061-T651 more dimensionally stable and better for precision CNC machined parts.

 

 

3. What are the different temper grades of aluminum?

 

Aluminum tempers are categorized as F (as fabricated), O (annealed), H (strain-hardened), W (solution heat-treated), and T (thermally treated), with subcategories like T4, T5, T6, and T651, depending on processing methods.

 

 

4. How is 6061 aluminum tempered?

 

Tempering involves solution heat treatment, quenching, and artificial aging. For example, 6061-T6 is solution heat-treated, quenched in water, and aged to maximize strength.

 

 

5. What is the difference between T4 and T6 tempers? Which is better, T4 or T6?

• T4: Solution heat-treated and naturally aged, offering good formability but lower strength.
• T6: Artificially aged, providing much higher strength but less formability.
  

For CNC machining, T6 is generally better, but for bending or forming, T4 may be preferred.

 

 

6. What is the difference between T5 and T6 aluminum tempers?

• T5: Cooled from an elevated temperature shaping process and artificially aged.
• T6: Solution heat-treated before aging.
  

T6 generally offers higher strength than T5.

 

 

7. What is the difference between T6 and T73 tempers?

• T6: Maximum strength, standard temper.
• T73: Lower strength but improved stress-corrosion resistance.
  

T73 is often used in aerospace where corrosion resistance is critical.

 

 

8. How can you determine the temper of aluminum?

 

Temper is usually marked on material certifications and supplier datasheets. Physical testing (hardness or tensile strength) can also help verify the temper.

 

 

9. What is the difference between 6061-T6 and 7075-T6 aluminum?

• 6061-T6: Excellent corrosion resistance, good machinability, and more affordable.
• 7075-T6: Much higher strength but lower corrosion resistance and higher cost.
  

6061-T6 is common for general CNC machining; 7075-T6 is often used in aerospace and defense.

 

 

10. What are the disadvantages of 6061 aluminum?

 

While versatile, 6061 aluminum has lower strength than 7075, limited fatigue resistance, and can deform under very high loads.

 

 

11. What is the most common 6061 temper?

 

6061-T6 is the most widely used temper due to its excellent balance of strength, corrosion resistance, and availability.

 

 

12. How is the tempering temperature calculated?

 

Tempering involves precise heat treatment cycles based on aluminum grade and desired properties, usually controlled between 160–190°C (320–375°F) for aging.

 

 

13. What is the optimal tempering temperature for aluminum bending?

 

For bending, softer tempers like 6061-O or 6061-T4 are optimal, as they allow more ductility before cracking.

 

 

14. What is the difference between T651 and T6511 tempers?

 

Both are stress-relieved versions of T6.

• T651: Applied to rolled or forged products.
• T6511: Applied to extrusions.
  

Both improve dimensional stability in CNC machining.

 

 

15. What is the T4 temper?

 

T4 means solution heat-treated and naturally aged. It is softer and easier to form than T6.

 

 

16. What is the difference between 6061-T6 and 6061-T651 aluminum?

 

Both share the same strength, but T651 undergoes stress relief, making it more stable for precision machining, especially for larger parts.

 

 

17. What is the difference between 6061-O and 6061-T6?

• 6061-O: Fully annealed, very soft, excellent formability.
• 6061-T6: Heat-treated and aged, high strength, widely used in CNC machining.

 

18. What is the difference between 6061-T6 and T7?

• T6: Maximum strength, standard for most applications.
• T7: Over-aged for better corrosion resistance but with slightly lower strength.