The short answer
6061-T6 is the everyday aluminum for machined parts: it machines cleanly, welds, anodizes evenly and is easy to buy in plate, bar and tube. 7075-T6 is the high-strength choice: roughly 1.5 to 2 times the yield strength of 6061-T6, at the cost of weldability, corrosion resistance and price. Most designs should start with 6061 and move to 7075 only when a calculation or test shows that the extra strength is needed.
The rest of this article explains where that rule of thumb comes from and where it breaks down.
Head-to-head
The table lists typical handbook values for the T6 temper. Your material certificate gives the minimum values guaranteed for your specific stock, and those are the ones to design with.
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Main alloying elements | Magnesium, silicon | Zinc, magnesium, copper |
| Typical yield strength | ~275 MPa | ~500 MPa |
| Typical tensile strength | ~310 MPa | ~570 MPa |
| Typical elongation | ~12% | ~11% |
| Density | 2.70 g/cm³ | 2.81 g/cm³ |
| Typical thermal conductivity | ~167 W/m·K | ~130 W/m·K |
| Weldability (arc welding) | Good, with strength loss near the weld | Generally not recommended |
| General corrosion resistance | Good | Fair; benefits from a protective finish |
| Typical anodized appearance | Even, clear or dyed | Can look slightly darker or less uniform |
Two numbers stand out. Yield strength nearly doubles, which is why 7075 is used for highly loaded brackets, fixtures and structural parts. Density barely changes, so the strength gain comes with almost no weight penalty. That combination is what makes 7075 attractive in aerospace, sporting goods and robotics.
What the difference means in practice
Stiffness does not change
Both alloys have nearly the same elastic modulus, around 69–72 GPa. A 7075 bracket will deflect almost exactly as much as the same 6061 bracket under the same load. If your problem is deflection or vibration, changing alloy will not help; changing geometry will.
Strength does change
If a part yields or fails in a load test, 7075 can be a direct fix without redesign. It is also useful where space is tight and the section cannot simply be made thicker.
Fatigue
Both alloys have a fatigue behaviour typical of aluminum: there is no true endurance limit, so cyclic loads need careful analysis. Where fatigue is the main concern, 2024-T3/T351 is sometimes chosen for its crack-growth resistance, and surface finish and edge breaks matter as much as alloy choice.
Machining both alloys
Both machine well, and both are among the most common materials in CNC shops. A few differences are worth knowing:
- 7075 is harder and tends to give a slightly better surface finish and crisper edges straight off the cutter
- 6061 can produce longer chips and slightly more burrs on thin edges
- 7075 thin walls are stiffer in yield but still flex the same under cutting forces, so wall-thickness rules do not relax
- Large, heavily pocketed parts in either alloy can move after machining as internal stresses release; stress-relieved tempers such as T651 and T7351 reduce this
Ask for the stress-relieved plate tempers (T651 for both alloys, or T7351 for 7075) when removing a large share of the stock. They are the normal form for plate and help flatness on big parts.
Welding and joining
6061 is widely welded with filler alloys such as 4043 or 5356. The heat-affected zone loses a large part of its T6 strength, so welded structures are designed with that reduced strength, or are re-heat-treated after welding.
7075 is generally regarded as unsuitable for conventional arc welding because it is prone to cracking. Join 7075 parts with fasteners, adhesive or interference fits. If a design needs both welding and high strength, consider a welded 6061 frame with bolted 7075 inserts at the highly loaded points.
Corrosion and finishing
6061 has good general corrosion resistance and is often used bare indoors. 7075, with its copper content, is more susceptible to corrosion and to stress-corrosion cracking in the T6 temper. The T73 and T7351 tempers trade some strength for much better resistance to stress-corrosion cracking and are common in demanding environments.
Both anodize well. Type II anodizing gives clear or dyed colors; 6061 tends to produce the more even, predictable color. 7075 may look slightly darker or warmer, which matters if parts in both alloys must match side by side. Hard anodizing (Type III) works on both and adds wear resistance. Chemical conversion coating is a lighter alternative where electrical conductivity must be kept.
Choosing by scenario
Enclosures, housings and general brackets
6061-T6. Strength is rarely the limit, cosmetic anodizing is easier to match, and stock is readily available.
Highly loaded structural parts, fixtures and tooling plates
7075-T6 or T651, provided the part is not welded and the environment is not aggressive. Use T7351 where stress-corrosion cracking is a concern.
Formed sheet parts
Neither is ideal. 5052-H32 bends much more easily and is the usual choice for sheet metal enclosures.
Heat sinks and thermal parts
6061 conducts heat noticeably better than 7075. Alloys in the 6000 series, including extrusion grades, are the normal choice.
Welded frames
6061, designed for the reduced strength near welds.
Other aluminum alloys worth knowing
| Alloy | Why you might choose it |
|---|---|
| 2024 | Good fatigue and crack-growth behaviour; often clad for corrosion protection |
| 5052 | Excellent formability and corrosion resistance for sheet metal |
| 6063 | Extrusion alloy with fine surface finish for profiles |
| 6082 | Common structural alloy in Europe, similar role to 6061 |
| MIC-6 / cast plate | Very flat and stable for fixture plates; lower strength |
Availability and cost drivers
Both alloys are stocked widely as plate and round bar, but 6061 is available in more forms and sizes, including tube, angle and many extruded profiles. 7075 is mostly bought as plate and bar. When a part needs an unusual size or form, 6061 is usually easier to source quickly.
7075 raw material typically costs more than 6061 for the same size, and that difference shows up most on large, mostly solid parts where material is a big share of the total. On small, heavily machined parts, machine time dominates and the alloy choice has less effect on the final price.
Lead time can matter as much as cost. If a project is on a tight schedule, ask whether the required plate thickness is in stock in the chosen alloy and temper before committing the design.
Common mistakes when choosing between them
- Switching to 7075 to cure a stiffness problem, when only geometry will help
- Specifying 7075 for a welded frame
- Mixing alloys on parts that must match after anodizing without testing color first
- Leaving out the temper, so a softer condition arrives
- Using 6061 for tight bends in sheet, where it tends to crack on the outside of the bend
- Forgetting that 7075-T6 in a damp, stressed environment may need the T73 temper or a protective finish
A short design review often catches these before the first order. It is much cheaper to change a material note than a finished batch.
A note on testing
When in doubt, test. Material certificates confirm the stock meets its specification, but the real check is a prototype under representative loads. A quick machined prototype in each alloy often settles the question faster than further analysis, especially when deflection, fit and finish all matter.
Writing the material callout
Be specific. "Aluminum" alone invites substitution. A clear callout names alloy, temper and, where relevant, a specification, for example "6061-T6 or T651" or "7075-T7351 plate". If a substitute is acceptable, say so on the drawing; if it is not, say that too.
- Name alloy and temper together
- Allow the stress-relieved plate temper for large parts
- State the finish and whether dimensions apply after finishing
- Ask for material certificates when traceability matters
Next steps
If you are unsure which alloy fits, upload the model through the quote form and describe the loads and environment in the notes. The reviewing engineer can suggest an alloy and temper and flag features that would be easier to make in one or the other.