Aluminum Alloys for Machining: 6061 vs 7075 vs MIC-6

Aluminum’s combination of light weight, machinability, and corrosion resistance makes it the default choice for countless machined components. But “aluminum” isn’t one material—it’s dozens of alloys with significantly different properties. The three most common grades for precision machining each solve different problems.

The Quick Answer

6061-T6: The default choice. Good strength, excellent machinability, corrosion resistant, weldable, widely available, reasonably priced.

7075-T6: When you need maximum strength. Aerospace and high-stress structural applications. More expensive, harder to machine, limited weldability.

MIC-6/Cast Tooling Plate: When flatness and stability matter most. Fixtures, tooling, precision bases. More expensive, not for structural loads.

Property Comparison

Property	6061-T6	7075-T6	MIC-6
Tensile Strength	45,000 psi	83,000 psi	24,000 psi
Yield Strength	40,000 psi	73,000 psi	17,000 psi
Hardness (Brinell)	95	150	65
Machinability	Excellent	Good	Excellent
Weldability	Excellent	Poor	Not recommended
Corrosion Resistance	Excellent	Good	Good
Anodizing	Excellent	Good	Good
Flatness Guarantee	No	No	Yes
Relative Cost	1.0x	1.3-1.5x	1.8-2.2x

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6061-T6: The Workhorse

If you’re unsure which aluminum to specify, 6061-T6 is almost always the right answer. It’s the most versatile, most available, and most cost-effective option for general-purpose machining.

Composition

6061 is a magnesium-silicon alloy (Al-Mg-Si). The T6 temper indicates solution heat treatment followed by artificial aging, producing optimal strength and hardness.

Why It Dominates

Availability 6061 is stocked everywhere in every form: sheet, plate, bar, rod, tube, extrusions. Need 3” round bar delivered tomorrow? 6061 is available. Need a custom extrusion profile? 6061 is the standard alloy.

Machinability 6061 machines beautifully. It produces clean chips, holds tight tolerances, achieves excellent surface finishes, and doesn’t destroy tools. Standard carbide tooling at aggressive feeds and speeds handles it easily.

Weldability Unlike 7075, 6061 welds reliably using standard TIG or MIG processes. Welded joints can achieve 70-80% of base metal strength with proper technique and filler selection.

Anodizing 6061 anodizes exceptionally well, producing consistent, attractive coatings in any color. Type II (decorative) and Type III (hardcoat) anodizing both work well.

Corrosion Resistance The passive oxide layer that forms naturally provides excellent atmospheric corrosion resistance. Anodizing improves it further.

Limitations

Strength ceiling At 45,000 psi tensile, 6061 handles most applications—but high-stress aerospace and structural components may need more. If calculations show you need stronger material, 7075 awaits.

Not free-machining While 6061 machines well, it’s not optimized purely for machining like 2011 or 6042. For ultra-high-volume production, specialized free-machining grades might offer efficiency gains.

Best Applications

• Structural components (brackets, frames, housings)
• Fluid handling (manifolds, valve bodies)
• Electronic enclosures and heat sinks
• Machine components (plates, brackets, spacers)
• Consumer products (sporting goods, furniture)

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7075-T6: Maximum Strength

When 6061 isn’t strong enough, 7075-T6 steps in. This zinc-based alloy delivers the highest strength of common aluminum grades—comparable to many steels at one-third the weight.

Composition

7075 is a zinc-copper-magnesium alloy (Al-Zn-Cu-Mg). The chemistry that provides exceptional strength also creates some trade-offs.

The Strength Advantage

7075’s 83,000 psi tensile strength nearly doubles 6061’s capability. This enables:

• Thinner sections for equivalent load capacity
• Weight reduction in strength-critical applications
• Higher safety margins without size increase
• Applications where 6061 calculations don’t close

Strength-to-weight comparison:

Material	Tensile (psi)	Density (lb/in³)	Strength/Weight
6061-T6	45,000	0.098	459,000
7075-T6	83,000	0.101	822,000
4140 Steel	95,000	0.284	335,000

7075 offers nearly 2.5x the strength-to-weight ratio of steel.

Trade-offs

Cost 7075 runs 30-50% more than 6061, depending on form and market conditions. For large components, the premium adds up.

Machinability 7075 is harder and more abrasive than 6061. Tools wear faster, cutting forces are higher, and surface finishes require more attention. It’s still aluminum—far easier than steel—but expect reduced productivity versus 6061.

Weldability 7075 is considered unweldable for structural applications. The zinc content causes hot cracking, and the heat-affected zone loses its strength advantage. Design 7075 parts to avoid welding; use mechanical fasteners instead.

Stress corrosion 7075 is susceptible to stress corrosion cracking in certain environments and stress states. Proper design and protective coatings mitigate risk, but it’s a consideration 6061 doesn’t require.

Best Applications

• Aircraft structures (ribs, spars, fittings)
• High-performance automotive (suspension, brackets)
• Recreational equipment (bicycle frames, climbing gear)
• Defense components
• Any application where strength-to-weight is critical

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MIC-6: Precision and Stability

MIC-6 (and similar ATP-5 and Alca Plus products) is a cast aluminum tooling plate designed for one thing: dimensional stability. It’s not for structures; it’s for fixtures, bases, and tooling where flatness and consistency matter.

What Makes It Different

MIC-6 is cast rather than rolled or extruded. The casting process, combined with stress-relief heat treatment and precision machining by the mill, produces plate with:

Guaranteed flatness Mill-certified flatness to ±0.015” per foot or better. Standard rolled plate has no flatness guarantee and often measures 0.030-0.060” out of flat.

Minimal internal stress The stress-relief process eliminates internal stresses that cause distortion after machining. Cut a pocket in rolled plate, and it may warp. MIC-6 stays flat.

Thickness consistency Precision-machined surfaces ensure consistent thickness across the plate. Critical when machining parallel features from both sides.

The Stability Trade-off

MIC-6’s mechanical properties are lower than 6061 or 7075:

• Tensile strength: 24,000 psi (vs. 45,000 for 6061)
• Yield strength: 17,000 psi (vs. 40,000 for 6061)
• Hardness: Brinell 65 (vs. 95 for 6061)

This isn’t a defect—it’s the inevitable result of the casting and stress-relief process. MIC-6 isn’t designed for structural loads; it’s designed for stability.

Best Applications

• Fixture plates and bases
• CMM fixtures (where stability is essential for accuracy)
• Vacuum chuck bases
• Tooling plates for production machinery
• Precision machine bases
• Optical bench components
• Any application where parts must stay flat after machining

When NOT to Use MIC-6

• Structural applications (use 6061 or 7075)
• Weight-critical designs (lower strength means thicker sections)
• High-volume production (cost premium rarely justified)
• Applications requiring welding

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Selection Guide

Default: 6061-T6 Unless specific requirements push you elsewhere, start here. Available, affordable, versatile.

High stress → 7075-T6 If 6061 doesn’t meet strength requirements, 7075 probably does. Check weldability requirements first.

Flatness critical → MIC-6 For fixtures, tooling, and precision bases where distortion is unacceptable. Accept the strength and cost trade-offs.

Cost-critical structural → 6061-T6 Even if 7075 works, 6061 might be adequate with modest design changes. Run the calculations before paying the premium.

Welded assembly → 6061-T6 7075 and MIC-6 don’t weld well. If the design requires welding, 6061 is the answer.

Machining Notes

6061-T6

• Feed: Aggressive (0.005-0.015” per tooth typical)
• Speed: High (800-1200 SFM)
• Produces long continuous chips; use chip breakers or appropriate geometry
• Coolant: Recommended but dry machining possible
• Excellent surface finish achievable

7075-T6

• Feed: Moderate (0.003-0.010” per tooth)
• Speed: Moderate (500-800 SFM)
• Higher cutting forces than 6061
• Coolant: Recommended
• Tool wear higher than 6061

MIC-6

• Feed: Aggressive (similar to 6061)
• Speed: High (similar to 6061)
• Soft material machines easily
• Minimal distortion after machining (the whole point)
• Watch for edge tearing due to softness

Working With NextGen Components

We stock all three grades in common sheet, plate, and bar sizes. For MIC-6 and 7075 in less common forms, short lead times are available from our distribution partners.

Need help selecting the right aluminum grade for your application? Contact our engineering team with your requirements.