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

If you need a versatile, cost-effective material for general machining, 6061-T6 is your answer. It offers good strength, excellent machinability, corrosion resistance, reliable weldability, wide availability, and reasonable pricing. When your application demands maximum strength and weight savings justify higher costs, 7075-T6 delivers nearly double the tensile strength of 6061, though you’ll sacrifice weldability and pay more for material and machining. For fixtures, tooling plates, and precision bases where dimensional stability matters more than load-bearing capacity, MIC-6 cast tooling plate provides guaranteed flatness and stress-free machining behavior that rolled plate simply cannot match.

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 makes 6061 the path of least resistance for most projects. It’s stocked everywhere in every form: sheet, plate, bar, rod, tube, and extrusions. Need 3-inch round bar delivered tomorrow? 6061 is available. Planning a custom extrusion profile? 6061 is the standard alloy extruders work with.

Machinability is where 6061 really shines. It produces clean chips that clear efficiently, holds tight tolerances without drama, achieves excellent surface finishes with standard techniques, and doesn’t destroy cutting tools. Standard carbide tooling running at aggressive feeds and speeds handles 6061 with ease, making it economical for both prototypes and production runs.

Unlike its stronger cousin 7075, 6061 welds reliably using standard TIG or MIG processes. Welded joints can achieve 70-80% of base metal strength with proper technique and appropriate filler selection, making fabricated assemblies practical without mechanical fasteners.

Anodizing results are consistently excellent with 6061. The alloy takes both Type II decorative anodizing and Type III hardcoat anodizing well, producing uniform, attractive coatings in virtually any color.

Corrosion resistance comes naturally from the passive oxide layer that forms on aluminum surfaces. This provides excellent protection in atmospheric conditions, and anodizing improves durability further for demanding environments.

Limitations

The strength ceiling at 45,000 psi tensile handles most applications comfortably, but high-stress structural components may need more. When your engineering calculations show inadequate safety margins with 6061, it’s time to consider 7075.

While 6061 machines well, it’s not optimized purely for chip-breaking the way free-machining alloys like 2011 or 6042 are. For ultra-high-volume production where cycle time savings compound into significant cost differences, those specialized grades might offer efficiency gains worth investigating.

Best Applications

6061 excels in structural components like brackets, frames, and housings. It’s the standard choice for fluid handling applications including manifolds and valve bodies. Electronic enclosures and heat sinks benefit from its machinability and thermal conductivity. General machine components—plates, brackets, spacers, and mounting hardware—are natural 6061 territory. Consumer products from sporting goods to furniture commonly specify 6061 for its combination of properties and finish quality.

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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 worth understanding before specifying it.

The Strength Advantage

With 83,000 psi tensile strength, 7075 nearly doubles 6061’s capability. This opens design possibilities that simply don’t exist with lower-strength alloys. You can specify thinner sections for equivalent load capacity, directly reducing weight. Strength-critical applications benefit from meaningful weight reduction. Higher safety margins become achievable without increasing component size. And applications where 6061 calculations don’t close—where stress levels exceed what the material can handle—become feasible with 7075.

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

That strength-to-weight ratio tells the story: 7075 offers nearly 2.5 times the strength-to-weight performance of steel, making it the material of choice when every ounce matters.

Trade-offs

Cost runs 30-50% higher than 6061, depending on form and market conditions. For large components or high-volume production, that premium accumulates into real money.

Machinability suffers compared to 6061. The harder, more abrasive material wears tools faster, generates higher cutting forces, and demands more attention to achieve quality surface finishes. It’s still aluminum—far easier than steel—but expect reduced productivity compared to machining 6061.

Weldability is essentially nonexistent for structural applications. The zinc content causes hot cracking during welding, and the heat-affected zone loses the strength that justified choosing 7075 in the first place. Design 7075 parts to avoid welded joints entirely; mechanical fasteners are the solution.

Stress corrosion cracking susceptibility exists in certain environments and stress states that wouldn’t affect 6061. Proper design practices and protective coatings mitigate the risk, but it’s an additional consideration that 6061 doesn’t require.

Best Applications

7075 finds its home in high-performance automotive components like suspension arms and structural brackets. Recreational equipment including bicycle frames and climbing gear leverage its strength-to-weight advantage. Heavy-duty industrial equipment benefits when weight reduction matters for handling or installation. Agricultural equipment components see increasing 7075 usage. Any application where strength-to-weight is the critical selection criterion points toward 7075.

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MIC-6: Precision and Stability

MIC-6 (along with similar products like ATP-5 and Alca Plus) 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 more than strength.

What Makes It Different

MIC-6 is cast rather than rolled or extruded, and that fundamental difference in manufacturing changes its behavior completely. The casting process, combined with stress-relief heat treatment and precision machining at the mill, produces plate with characteristics that rolled plate cannot match.

Guaranteed flatness is the headline feature. MIC-6 carries mill certification to plus or minus 0.015 inches per foot or better. Standard rolled plate offers no flatness guarantee and routinely measures 0.030 to 0.060 inches out of flat—a deviation that causes real problems for precision fixturing.

Minimal internal stress distinguishes MIC-6 from rolled material. The stress-relief process eliminates the internal tensions that cause rolled plate to distort after machining. Cut a deep pocket in rolled plate and watch it warp as you release trapped stresses. MIC-6 stays flat because there’s no stored stress to release.

Thickness consistency across the plate results from the precision-machined surfaces at the mill. This matters when machining parallel features from both sides of the plate—you need to know the material is uniform.

The Stability Trade-off

MIC-6’s mechanical properties run significantly lower than 6061 or 7075. Tensile strength is 24,000 psi compared to 45,000 for 6061. Yield strength is 17,000 psi versus 40,000 for 6061. Brinell hardness is 65 compared to 95 for 6061.

This isn’t a defect—it’s the inevitable result of the casting and stress-relief process that enables MIC-6’s dimensional stability. The material isn’t designed for structural loads; it’s designed to stay flat and true after machining.

Best Applications

MIC-6 excels as fixture plates and bases where flatness determines accuracy. CMM fixtures demand stability, and MIC-6 delivers it. Vacuum chuck bases benefit from the guaranteed flatness. Tooling plates for production machinery stay true over time. Precision machine bases maintain their geometry. Optical bench components require the stability MIC-6 provides. Any application where parts must stay flat after machining points toward MIC-6.

When NOT to Use MIC-6

Structural applications should use 6061 or 7075—MIC-6 lacks the strength. Weight-critical designs suffer because lower strength means thicker, heavier sections to achieve equivalent capacity. High-volume production rarely justifies the cost premium. Applications requiring welding should look elsewhere, as MIC-6 doesn’t weld reliably.

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Selection Guide

Default: 6061-T6. Unless specific requirements push you elsewhere, start here. It’s available, affordable, and versatile enough for most applications.

High stress demands 7075-T6. If 6061 doesn’t meet strength requirements, 7075 probably does. Check weldability requirements first—if you need to weld, you’ll need a different approach.

Flatness critical means MIC-6. For fixtures, tooling, and precision bases where distortion is unacceptable, MIC-6 is the answer. Accept the strength and cost trade-offs as the price of stability.

Cost-critical structural applications point back to 6061-T6. Even if 7075 works from a strength standpoint, 6061 might be adequate with modest design changes like increased section thickness. Run the calculations before paying the premium.

Welded assemblies require 6061-T6. Since 7075 and MIC-6 don’t weld well, designs requiring welded joints should specify 6061.

Machining Notes

6061-T6 machines aggressively. Feed rates of 0.005 to 0.015 inches per tooth are typical, with surface speeds of 800 to 1200 SFM. The material produces long continuous chips, so use chip breakers or appropriate tool geometry. Coolant is recommended but dry machining works. Excellent surface finishes are readily achievable.

7075-T6 requires more moderate parameters. Feed rates of 0.003 to 0.010 inches per tooth work well, with surface speeds of 500 to 800 SFM. Cutting forces run higher than 6061, coolant is recommended, and tool wear exceeds what you’d see with 6061.

MIC-6 machines easily at parameters similar to 6061—aggressive feeds and high speeds. The soft material removes readily, and distortion after machining is minimal (which is the entire point of choosing MIC-6). Watch for edge tearing due to the material’s softness; sharp tools and appropriate cutting parameters prevent it.

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.