Aluminium Alloys for CNC Machining: 6061 vs 7075 vs 2024

Picking the Right Alloy for CNC

When you're getting parts CNC machined from aluminium, the alloy grade matters just as much as the design. Different alloys machine differently, have vastly different strength characteristics, and respond differently to heat treatment and surface finishing. Choose wrong and you're either paying too much for material you don't need, or your part won't perform in service.

This guide covers the four aluminium alloys most commonly used for CNC machined components: 6061, 7075, 2024, and 6082. We'll explain the differences, break down heat treatment so it actually makes sense, and help you pick the right grade for your application. For sheet metal grades (5005, 5052, 5083), see our guide to aluminium for sheet metal.

6061-T6 — The All-Rounder

6061-T6 is the default CNC machining aluminium worldwide, and for good reason. It chips cleanly, holds tight tolerances, produces an excellent surface finish, and is readily available as plate, billet, round bar, flat bar, tube, and extrusions.

In the T6 temper it delivers 310 MPa tensile strength and 276 MPa yield — strong enough for the vast majority of engineering applications. It anodises beautifully with consistent colour, making it the go-to for parts that need to look as good as they perform.

Key strengths:

• Excellent machinability — clean chip formation, good surface finish
• Widely available in all common forms and sizes
• Anodises consistently (clear, black, or colour)
• Good corrosion resistance
• Reasonable cost

Limitations:

• Not as strong as 7075 or 2024 for high-stress applications
• Welding reduces strength in the heat-affected zone by 40-60% (reverts to ~T4 temper)
• Not ideal for sheet metal bending — tends to crack on tight radii

Typical applications: Jigs and fixtures, brackets, adapters (like our ZF 8HP 2WD adapter kit), housings, automotive components, general engineering parts, prototype machining.

If you're unsure which alloy to specify, 6061-T6 is almost always the right answer.

7075-T6 — The High-Strength Option

7075 is the go-to when you need maximum strength from aluminium. At 570 MPa tensile and 505 MPa yield in the T6 temper, it's approaching mild steel territory while being a third of the weight.

It's an aluminium-zinc-magnesium-copper alloy originally developed for aircraft structural components, and it's still the primary alloy for aerospace applications. It machines well — not quite as cleanly as 6061, but very good — and the higher hardness means less burring on sharp edges.

Key strengths:

• Very high strength-to-weight ratio
• Good machinability
• Excellent fatigue resistance
• Good for thin-walled or highly stressed parts

Limitations:

• Significantly more expensive than 6061 (typically 2-3x the material cost)
• Poor weldability — generally considered non-weldable for structural joints
• Lower corrosion resistance than 6061 (the copper content is the culprit)
• Anodises well but with a slightly different colour tone than 6061
• Less readily available in large plate sizes

Typical applications: Aerospace structural components, high-performance automotive (suspension, uprights, hubs), firearms components, rock climbing equipment, high-stress brackets and linkages, competition motorsport parts.

Only specify 7075 when you genuinely need the extra strength. For most engineering parts, 6061-T6 is strong enough and significantly cheaper.

2024-T351 — The Fatigue Specialist

2024 is another aerospace alloy, but its standout property is fatigue resistance rather than raw strength. It performs exceptionally well under cyclic loading — repeated stress and strain — which is why it's used extensively in aircraft fuselage skins and wing structures.

At 470 MPa tensile and 325 MPa yield in T351 temper, it sits between 6061 and 7075 on strength. It machines well, though it can be slightly gummier than 6061.

Key strengths:

• Outstanding fatigue resistance
• Good machinability
• High damage tolerance (resists crack propagation)
• Good strength

Limitations:

• Poor corrosion resistance — the copper content makes it susceptible to intergranular corrosion. Usually requires anodising, Alodine coating, or paint for protection
• Not weldable (structural welding causes severe cracking)
• Anodises with a yellowish tint rather than the clean silver of 6061
• More expensive than 6061

Typical applications: Aircraft skins and structural members, components subject to high cyclic loading, fatigue-critical parts, aerospace fittings.

Unless your part sees significant cyclic loading, 2024 is rarely the best choice for general CNC work. Its poor corrosion resistance and weldability make it a specialist alloy.

6082-T6 — The European Alternative

6082 is widely used in Europe and is gaining popularity in Australia. It's very similar to 6061 but with slightly higher strength (330 MPa tensile, 290 MPa yield) and slightly better corrosion resistance.

It's a direct substitute for 6061 in most applications and machines nearly as well. The main difference is availability — 6061 is more widely stocked in Australia, while 6082 dominates the European supply chain.

Key strengths:

• Slightly stronger than 6061
• Excellent corrosion resistance
• Good machinability
• Anodises well

Limitations:

• Less readily available than 6061 in Australia
• Marginally more expensive
• Same welding limitations as 6061 (heat-affected zone loses temper)

Typical applications: Structural components, bridges, cranes, transport applications, any application where 6061 would work but slightly higher strength is beneficial.

Comparison Table

Heat Treatment Explained

Understanding heat treatment helps you make sense of temper designations and know what to expect when your parts are machined or welded.

How Precipitation Hardening Works

The alloys in this guide (6061, 7075, 2024, 6082) are all heat-treatable. They get their strength from a process called precipitation hardening:

1. Solution heat treatment — The alloy is heated to a high temperature (e.g. ~530°C for 6061) to dissolve the alloying elements into a uniform solid solution.
2. Quench — Rapidly cooled (usually in water) to lock the dissolved elements in place in a supersaturated state.
3. Ageing — Held at a moderate temperature (e.g. ~175°C for 6061) for several hours. This causes tiny precipitate particles to form within the aluminium matrix, and these particles block dislocation movement — which is what gives the material its strength.

Temper Designations

• T4 — Solution treated + naturally aged (left at room temperature). Lower strength, more ductile than T6. Useful when you need to form the part before final hardening.
• T6 — Solution treated + artificially aged. Peak strength and hardness. The standard temper for CNC machined parts.
• T651 — T6 plus stress relief by controlled stretching (1-3%). This is important for CNC work because it removes internal stresses that cause the part to warp when you machine away material. If you're machining from thick plate, always specify T651.
• T351 — Solution treated, stress relieved by stretching, then naturally aged. The standard temper for 2024 plate.
• O (annealed) — Fully softened. Maximum ductility. Heat to ~415°C and slow cool. Useful when you need to form aluminium that's too hard, then re-heat-treat afterwards.

Why Welding 6061-T6 Is Problematic

When you weld 6061-T6 (or any heat-treated aluminium), the heat from welding creates a heat-affected zone where the material reverts to roughly T4 temper — losing 40-60% of its strength locally. The precipitates that give T6 its strength dissolve back into solution.

Post-weld heat treatment (re-solution treat + age) can recover the full T6 properties, but you need an oven large enough for the entire part and the dimensional distortion from quenching must be acceptable. For welded aluminium structures where this isn't practical, the 5xxx series alloys (5052, 5083) are often a better choice since they don't suffer this issue — see our guide to aluminium grades for sheet metal for details.

Which Grade Should You Choose?

• General CNC machined parts — 6061-T6 (or T651 for thick plate). Nothing beats it for all-round performance and value.
• High-stress or lightweight critical parts — 7075-T6. When you need the strength and can justify the cost.
• Fatigue-critical or aerospace — 2024-T351. When cyclic loading is the primary concern.
• European supply chain or slightly higher strength — 6082-T6. Drop-in alternative to 6061.
• If in doubt — 6061-T6. It's the default for a reason.

Get Your Parts Machined

Need CNC machined aluminium parts? Get in touch with your STEP file and we'll provide a detailed quote. For simpler parts, try our instant CNC quoting tool for immediate pricing. Compare aluminium with other metals using our Material Comparison Tool, or estimate part weight with our Material Weight Calculator.