6061 vs 7075 Aluminum for CNC Machining
Two workhorse alloys, two philosophies – weldable and corrosion-proof versus strong and aerospace-proven.
Published: 2026-09-07 4 min read
6061 and 7075 are the two aluminum alloys a CNC buyer meets most often. They share the same density (2.70 g/cm³) but follow different philosophies: 6061 is the weldable, corrosion-resistant, anodizing-friendly generalist; 7075 is the aerospace-grade strength specialist. Choosing wrong costs money in one direction or performance in the other.
Composition: Why They Behave Differently
| Element | 6061 | 7075 | Effect |
|---|
| Magnesium | 0.8–1.2% | 2.1–2.9% | Strength (both are Mg-bearing) |
| Silicon | 0.4–0.8% | ≤0.4% | Fluidity, weldability (6061) |
| Copper | 0.15–0.4% | 1.2–2.0% | Strength, and corrosion sensitivity (7075) |
| Zinc | ≤0.25% | 5.1–6.1% | Primary strengthener in 7075 |
| Chromium | 0.04–0.35% | 0.18–0.28% | Grain control, corrosion resistance (6061) |
| Balance | Al | Al | , |
6061 is an Al-Mg-Si alloy (the 6xxx series): moderate alloying, weldable, corrosion-tolerant, anodizes beautifully. 7075 is an Al-Zn-Mg-Cu alloy (7xxx series): heavily alloyed for strength, with the crack and corrosion sensitivity that heavy alloying brings.
Mechanical Properties (T6 Temper, Typical)
| Property | 6061-T6 | 7075-T6 | 7075 advantage |
|---|
| Tensile strength | ~310 MPa | ~570 MPa | ~1.8x |
| Yield strength | ~275 MPa | ~500 MPa | ~1.8x |
| Elongation | 8–12% | 5–11% | Comparable |
| Elastic modulus | ~69 GPa | ~72 GPa | Marginal |
| Hardness | ~95 HB | ~150 HB | ~1.6x |
| Density | 2.70 g/cm³ | 2.70 g/cm³ | None |
Typical published values; design against the specific mill certificate for your material lot.
On specific strength (strength per unit weight), 7075 is the clear winner, that is why aerospace structure, high-load bicycle parts and drone arms gravitate to it. On specific stiffness, the two are nearly identical, so if your part fails by deflection rather than fracture, a thicker 6061 section usually closes the gap at a fraction of the alloy cost.
Machinability on CNC
6061
Softer and gummier, prone to built-up edge. Use sharp, polished tools (uncoated or DLC), moderate speeds, and good coolant. Leaves a clean surface for finishing passes; ideal when secondary anodizing or cosmetic finish matters.
7075
Shears cleanly and chips break well, but higher hardness means tougher inserts and more cutting force. Generates more heat, thin sections need light passes. Its stiffness resists chatter on long thin walls.
Both
High thermal expansion: frictional heat distorts thin parts, use sharp tools, light finishing passes, coolant. Specify T651 plate for flatness after heavy material removal.
Corrosion, Anodizing and Welding
| Dimension | 6061 | 7075 |
|---|
| General atmospheric corrosion | Very good | Moderate to poor |
| Marine / salt exposure | Good (uncoated acceptable) | Poor, needs protection or T73 temper |
| Stress corrosion cracking | Not a concern | Susceptible in T6; T73 temper mitigates |
| Anodizing quality | Excellent (uniform, colors well) | (Poor) cloudy, uneven oxide |
| Weldability | Good (TIG/MIG routine) | Not recommended, crack-sensitive HAZ |
| Typical relative cost | Baseline | ~1.5–3x (form and market dependent) |
The anodizing row deserves emphasis for machined parts: any part that will be dyed or color-anodized should be 6061. 7075 parts in corrosive environments should be hard-anodized, plated, painted, or specified in the T73 temper.
Selection Guide
| Application | Recommended alloy | Rationale |
|---|
| General structure, brackets, frames | 6061-T6 | Sufficient strength, cheap, corrosion-tolerant |
| Precision plates, bases, fixtures | 6061-T651 | Stress-relieved, stays flat after machining |
| Anodized / colored cosmetic parts | 6061 | Uniform, dyeable oxide |
| Welded assemblies | 6061 | 7075 is effectively unweldable |
| Aerospace structure, high-load shafts | 7075-T6 / T73 | ~2x specific strength; T73 for SCC environments |
| Drone arms, RC structure | 7075-T6 | Stiffness + fatigue at low weight |
| Marine / outdoor load parts | 6061 (or 7075-T73 with coating) | Corrosion dominates outdoors |
| Prototype, one-off parts | Either, quote both | Alloy delta is small at low volume |
How FHY Quotes Aluminum CNC Work
FHY machines both alloys routinely (6061 for general structure, plates and anodized parts; 7075 for strength-critical aerospace and drone components. When you send a model, the review states which alloy the load case actually needs, recommends the temper (T6 vs T651 vs T73) for your flatness and environment, and flags distortion risk on thin sections before cutting starts. If 6061 with a thicker section meets the requirement, the quote says so) the goal is the cheapest part that survives its service life, not the most expensive alloy on the certificate.
Frequently Asked Questions
1. How much stronger is 7075 than 6061?
In the T6 temper, 7075-T6 reaches roughly 570 MPa tensile and 500 MPa yield, versus about 310 MPa and 275 MPa for 6061-T6 – nearly double the strength at similar density (2.70 g/cm³). That strength comes from its zinc and copper content (5–6% Zn, 1.2–2.0% Cu), which also makes it more sensitive to corrosion and stress cracking. If your part is strength-driven and weight-critical, 7075 delivers roughly twice the specific strength; if it is structure or assembly-driven, 6061 usually suffices at lower cost and better corrosion resistance.
2. Which alloy machines better on CNC?
Both are free-machining by general standards, but they behave differently. 6061 is gummier – it tends to build up on the tool edge, so sharp, highly-polished tools and adequate coolant matter. 7075 shears more cleanly and chips break well, but its hardness demands tougher tooling and generates higher cutting forces. In practice most shops rate both as easy; the real machining difference shows up on thin-wall parts, where 7075's higher stiffness helps resist chatter while 6061's softness risks smearing under heavy feeds.
3. Can 7075 aluminum be welded?
Generally no – 7075 is considered unweldable by conventional TIG/MIG processes because its high alloy content makes it extremely crack-sensitive in the heat-affected zone, and post-weld heat treatment cannot fully restore strength. 6061, by contrast, is one of the most weldable structural aluminums, and welded assemblies are routine. If your design needs welded aluminum structure, 6061 (or 5052 for sheet) is the standard choice; 7075 parts are joined mechanically or with adhesives.
4. What is the difference between 6061-T6 and 6061-T651?
Both are solution heat-treated and artificially aged (the T6). The T651 adds a controlled stress-relief stretching step after solution treatment, which reduces residual stress in plate. For CNC work, T651 plate stays flatter after material removal – the standard choice for precision-machined aluminum plates and bases. T6 applies to extrusions and forgings where stretching is not applicable. The chemistry is identical; the difference is dimensional stability after machining.
5. Which alloy anodizes better?
6061. Its composition produces a uniform, dense anodic oxide that takes dye and color well – the reason it dominates architectural and consumer parts. 7075 anodizes poorly by comparison: the zinc and copper content creates an uneven, often cloudy oxide, and achieving a consistent colored finish is difficult. Decorative anodized parts are 6061 almost by default; 7075 is typically finished by hard coat, plating, or paint where corrosion protection is needed.
6. Why is 7075 more expensive than 6061?
Three factors stack: costlier alloying elements (zinc and copper), tighter process control because 7075 is crack- and corrosion-sensitive, and demand concentrated in aerospace where price sensitivity is lower. In plate and bar, 7075 commonly costs 1.5–3x 6061 depending on form, temper and market. For machined parts the alloy delta is often small relative to total part cost – but at volume on simple parts, the difference is real and worth quoting both.
7. What is stress corrosion cracking in 7075?
A failure mode where sustained tensile stress plus a corrosive environment causes cracking – and 7075-T6 is particularly susceptible because of its copper-zinc chemistry. It matters for parts under constant load in humid or marine environments. The mitigation is temper selection: 7075-T73 (over-aged) trades some strength for dramatically improved SCC resistance, and it is the standard temper for marine and aerospace structural applications. Short-term dry-environment parts are unaffected in practice.
8. For a drone frame or bicycle part, which alloy should I use?
Drone frames and high-load bicycle components favor 7075 for its stiffness-to-weight and fatigue performance; recreational and mid-load frames often use 6061 for weldability and cost. The deciding question is whether the part is machined from solid (7075 common) or welded from tube (6061 required). For machined prototypes, either works – quote both and let the load case decide, since many drone and bicycle parts run 6061 with thicker sections at lower cost and equal performance.
9. How do I control distortion when machining thin aluminum parts?
Three rules: clamp to distribute force rather than concentrate it (vacuum or soft jaws over vises), machine symmetrically and step down progressively to release stress evenly, and specify T651 plate where flatness after machining matters. Aluminum's high thermal expansion means frictional heating also distorts thin sections – use sharp tools, light finishing passes, and coolant. For deep-pocket thin-wall parts, roughing in a stress-relieved condition and finishing after a stress-relief bake is standard practice.