Three aluminium alloys account for a large share of machined aluminium parts, and engineers frequently default to one of them out of habit rather than analysis. That default is usually 6061, which is often correct and sometimes leaves performance or money on the table.
The three differ substantially in strength, corrosion behaviour, weldability and cost, and each has applications where it is clearly right and others where it is clearly wrong.
This guide compares them on the criteria that matter for machined components.
The Three Alloys
6061 is a magnesium and silicon alloy, and the general-purpose workhorse of machined aluminium. Good all-round properties, excellent corrosion resistance, weldable, readily available and relatively inexpensive.
7075 is a zinc-based alloy and one of the strongest aluminium alloys available, with strength approaching some steels at a fraction of the weight. Poorer corrosion resistance, not readily weldable, and considerably more expensive.
2024 is a copper-based alloy with high strength and notably good fatigue resistance. Poor corrosion resistance in bare form, which is why it is commonly used clad. Long-established in aerospace.
Fuerza
7075 is the strongest of the three by a clear margin, particularly in the T6 temper. It is the standard choice where strength-to-weight is the dominant requirement.
2024 sits between the other two on ultimate strength but stands out for fatigue performance, which is why it persists in aerospace structural applications subject to cyclic loading.
6061 is the weakest of the three, though “weakest” here still means a capable structural material adequate for the large majority of applications.
The practical question is not which is strongest but whether your part’s loading actually requires more than 6061 provides. Specifying 7075 for a bracket that 6061 would carry comfortably adds cost and creates corrosion and welding constraints for no functional gain.
Resistencia a la corrosión
This is where the ranking reverses sharply.
6061 has excellent corrosion resistance and performs well in outdoor and marine-adjacent environments without protective treatment, though anodizing improves it further.
7075 has notably poorer corrosion resistance, and is also susceptible to stress corrosion cracking in certain tempers under sustained tensile stress. This is a genuine engineering consideration rather than a footnote. The T73 temper trades some strength for substantially improved stress corrosion resistance and is specified where that risk matters.
2024 has poor corrosion resistance in bare form. It is widely used in clad form, with thin layers of pure aluminium bonded to the surface for protection. Machining a clad sheet removes that protection wherever material is cut away, which is a practical constraint on machined 2024 parts.
For parts exposed to weather, moisture or corrosive environments, 6061 is the straightforward choice unless strength requirements rule it out. Where 7075 or 2024 is necessary in such an environment, protective treatment becomes mandatory rather than optional.
Machinability
All three machine well by aluminium standards, which is to say considerably better than steel.
6061 machines cleanly and predictably. In the T6 temper it produces good chip formation and surface finish. In softer tempers it can be gummy.
7075 is often considered the best machining of the three, producing excellent surface finish and clean chips.
2024 also machines well, with good chip characteristics.
Differences between them are modest enough that machinability alone rarely decides the choice. Where it matters is in cost, since all three cut at comparable rates, meaning the price difference between them is driven by material cost rather than machining time.
Soldabilidad
A clear differentiator.
6061 is readily weldable using standard aluminium welding processes. Welding reduces strength in the heat affected zone, and post-weld heat treatment restores it where required, but the alloy is designed to be welded.
7075 is not considered weldable by conventional fusion processes. It is prone to cracking, and welded joints do not develop reliable properties. Assemblies in 7075 are mechanically fastened or bonded.
2024 is similarly not readily weldable by conventional means, for the same reasons. Riveting is the traditional joining method in its aerospace applications.
If your design involves welding, 6061 is the practical option among these three.
Anodizing Response
All three anodize, but with different results.
6061 anodizes well and produces a consistent, attractive finish. It is a common choice where appearance matters.
7075 anodizes but the higher zinc content can produce a slightly different appearance, and colour consistency across batches can be less predictable.
2024 anodizes with the copper content affecting the result, typically producing a darker finish than 6061.
For cosmetic parts where colour consistency matters, 6061 is generally the safer choice. Our guide to anodizing types covers the process options in detail.
Cost and Availability
6061 is the least expensive of the three and the most widely stocked, in the widest range of forms and sizes. Availability is rarely an issue anywhere.
7075 costs noticeably more and is stocked in a narrower range of forms.
2024 costs more than 6061 and availability varies more by region and form, particularly in clad sheet.
The availability point matters practically. A supplier holding 6061 in stock quotes shorter lead times than one importing 7075 in an unusual size, and that difference can outweigh the material cost difference on a small order.
Comparison Summary
| Propiedad | 6061 | 7075 | 2024 |
| Relative strength | Moderado | Highest | Alta |
| Fatigue resistance | Moderado | Bien | Best of the three |
| Resistencia a la corrosión | Excelente | Pobre | Poor, usually clad |
| Soldabilidad | Bien | Not practical | Not practical |
| Machinability | Bien | Excelente | Bien |
| Anodizing consistency | Best | Variable | Darker finish |
| Relative cost | Lowest | Highest | Between |
| Availability | Widest | Moderado | Varies |
Choosing Between Them
Choose 6061 when: the part is general structural or mechanical, corrosion exposure is a factor, welding is involved, appearance and anodizing consistency matter, or cost and availability are priorities. This covers most machined aluminium parts.
Choose 7075 when: strength-to-weight is genuinely the binding constraint, the part is mechanically fastened rather than welded, and corrosion exposure is controlled or the part will be protected. Typical in aerospace structure, high-performance components and tooling.
Choose 2024 when: fatigue performance under cyclic loading is the driving requirement, typically in aerospace structural applications, and corrosion protection is designed in.
Tempers Matter as Much as Alloy
Alloy designation alone is incomplete. The temper, indicated by the suffix, determines properties substantially.
T6 is solution heat treated and artificially aged, the most common temper for machined structural parts in both 6061 and 7075.
T651 adds stress relief by stretching, which reduces internal stress and improves dimensional stability during machining. For parts with significant material removal, T651 is worth specifying because it distorts less.
T73 in 7075 trades some strength for substantially improved stress corrosion resistance.
T351 in 2024 is solution treated, stress relieved and naturally aged.
The stress relief point deserves emphasis for machined parts. When material is removed from a plate carrying internal stress, the remaining material moves. On a part machined from thick plate with heavy stock removal, this distortion can exceed the tolerance. Specifying a stress-relieved temper reduces it considerably.
Other Grades Worth Knowing
The three above dominate, but not every application suits them.
5052 offers excellent corrosion resistance and good formability, common in sheet metal work rather than machining.
6082 is common in Europe as a 6061 equivalent with slightly different properties.
2007 and 6262 are free-machining grades containing additives that improve chip breaking, suited to high-volume turned parts.
7050 offers similar strength to 7075 with better stress corrosion resistance in thick sections.
Where none of the main three quite fits, discussing alternatives with your supplier is worthwhile, since material availability and machining behaviour vary in ways that affect both cost and lead time.
Practical Points When Specifying
State the temper, not just the alloy. 6061 alone is incomplete.
Consider stress relief for parts with heavy material removal, since distortion during machining is a common and avoidable problem.
Confirm availability in your required form and size before finalising. A grade available as bar but not as plate in your thickness may add weeks.
Check whether a certificate is required, and whether it is included in the quote.
Do not over-specify strength. 6061 covers most applications, and specifying 7075 defensively adds cost while introducing corrosion and welding constraints.
Getting Material Advice for Your Part
Material selection interacts with geometry, tolerance, finish and volume, and the right choice sometimes differs from the obvious one.
Elite Mold Tech machines all three grades alongside a wide range of other materiales, with material recommendations provided as part of DFM review before quoting. Sending a drawing with your application requirements produces a material assessment covering availability and machining implications rather than a quote against whatever grade was specified.
Preguntas frecuentes
Q: Is 7075 aluminium stronger than 6061?
A: Considerably, particularly in the T6 temper, which is why it is used where strength-to-weight is critical. It costs more and has notably poorer corrosion resistance and is not practically weldable.
Q: Can you weld 7075 aluminium?
A: Not reliably by conventional fusion welding, since it is prone to cracking and welded joints do not develop dependable properties. Assemblies in 7075 are mechanically fastened or bonded instead.
Q: Which aluminium grade is best for CNC machining?
A: All three machine well, with 7075 often producing the best finish. Since machining rates are comparable, the choice should follow strength, corrosion and cost requirements rather than machinability.
Q: What does the T6 or T651 suffix mean?
A: T6 indicates solution heat treatment and artificial ageing. T651 adds stress relief by stretching, which reduces internal stress and improves dimensional stability during machining with heavy material removal.
Q: Why is 2024 aluminium usually clad?
A: Because bare 2024 has poor corrosion resistance. Cladding bonds thin pure aluminium layers to the surface for protection, though machining removes that protection wherever material is cut away.
