Choosing aluminum for your next machined part isn’t just about cost — it’s about understanding how different grades perform under cutting tools and whether they’ll meet your design requirements. With over 15 years machining aluminum components for aerospace, medical, and audio applications, we’ve helped engineers navigate the trade-offs between machinability, strength, and surface finish quality.
Aluminum is generally easy to machine, but success depends on selecting the right grade for your application. 6061-T6 machines beautifully with standard tooling, while 7075-T6 offers higher strength but requires more aggressive cutting parameters and careful chip management.
Find the best aluminum grades for tight tolerances, avoid machining issues, and compare surface finishes and costs with steel and other materials.
Table of Contents
Can Aluminum Meet My Part's Mechanical Requirements?
Most steel parts operating under normal loads can switch to 6061-T6 aluminum, but parts experiencing high deflection, heavy cyclic loading, or sliding wear require design modifications or 7075-T6 upgrade. Use this quick assessment: if your current steel part visibly flexes under working loads, aluminum will flex 3x more and likely needs geometry changes.
Decision Framework:
- Low-stress housings/brackets → 6061-T6 with same geometry
- Parts that currently flex in steel → Add 25-50% wall thickness or switch to 7075-T6
- High-cycle applications (>10,000 cycles) → 7075-T6 with stress relief machining
- Sliding/wearing surfaces → Consider steel inserts or surface treatments
We’ve converted hundreds of steel medical enclosures to 6061 with zero geometry changes, achieving 15% cost reduction plus easier anodizing for corrosion resistance. However, a precision linear actuator required upgrading to 7075 and adding 0.040″ wall thickness to maintain positioning accuracy under load.
Steel vs Aluminum Comparison:
Application Type Steel Performance 6061-T6 Suitability 7075-T6 Alternative
Static housings Standard baseline Direct replacement Unnecessary upgrade
Loaded brackets Minimal deflection May need thickness boost Maintains steel performance
Cyclic components High fatigue life Requires stress analysis Comparable to steel
Precision assemblies Rigid reference Deflection may affect fit Better dimensional stability
Design Takeaway: Run a simple deflection check first – if your steel part moves >0.003″ under load, aluminum needs design changes. For precision assemblies, 7075’s improved stiffness often justifies the 30% material cost increase.
Which Aluminum Grade Balances Machinability with My Strength Needs?
6061-T6 offers the best machinability-to-strength ratio for most applications, machining cleanly with standard tooling while delivering adequate strength for brackets, housings, and enclosures. 7075-T6 provides 80% higher strength but requires slower feeds, sharper tools, and more careful chip management. 2024-T4 falls between them but has limited availability.
For general purpose parts under moderate stress, 6061-T6 provides the optimal balance of easy machining and adequate performance. We machine 6061 brackets at 1,200 SFM with minimal tool wear, achieving ±0.005″ tolerances routinely. The same part machined in 7075 requires 800 SFM, flood coolant, and carbide tooling – adding 40% to machining time but delivering twice the load capacity.
Aerospace applications often justify 2024-T4 or 7075-T6 despite machining complexity when weight savings matter more than cost. However, lead times extend 1-2 weeks for 7075 and 2-3 weeks for 2024 compared to readily available 6061 stock, which can impact project schedules.
Aluminum Grade Comparison:
Grade Relative Strength Machinability Cost Factor Lead Time Tool Life
6061-T6 Baseline (100%) Excellent 1.0× Standard Normal
7075-T6 High (180%) Good* 1.3× +1–2 weeks 60% of normal
2024-T4 High (160%) Fair* 1.4× +2–3 weeks 50% of normal
*Requires modified speeds/feeds and carbide tooling
For borderline strength requirements, consider 6061 with design optimization like added ribs or thicker walls before upgrading to 7075 – often cheaper overall when factoring machining complexity and availability.
Design Takeaway: Start with 6061-T6 unless your load analysis proves you need higher strength. The machining cost savings with 6061 often offset the need for slightly thicker walls or additional ribs compared to 7075.
How Does Aluminum Perform in My Operating Environment?
Aluminum excels in most environments due to natural oxide formation, but requires anodizing protection if your application involves salt exposure, frequent chemical contact, or outdoor weathering. Type II anodizing adds 15-20% to part cost but eliminates ongoing maintenance. The key decision: does your current material need protective coating? If so, aluminum often provides better protection at lower total cost.
Environmental Assessment Guide: If your part experiences salt spray, acidic cleaning chemicals, or year-round outdoor exposure, anodizing is essential. For indoor applications or occasional outdoor use, raw aluminum performs indefinitely. We’ve tracked automotive brackets through 5 years of temperature cycling from -20°F to 200°F without cracking or warping, while medical enclosures survived 1,000+ autoclave cycles with zero degradation.
To validate aluminum for your environment, run a simple exposure test: machine a sample part in your target aluminum grade, expose it to your actual operating conditions for 30-90 days, then inspect for pitting, discoloration, or dimensional changes. This eliminates guesswork before committing to production tooling.
Protection Cost Analysis:
Environment Aluminum Solution Added Cost vs Raw Aluminum Steel Alternative Total Steel Cost vs Raw Steel
Indoor clean Raw aluminum +0% Raw steel + paint +25%
Outdoor weather 6061 + anodizing +18% Steel + powder coat +35%
Chemical exposure 6061 + hard anodizing +28% Stainless steel +60%
Marine environment 6061 + anodizing +18% Steel replacement every 2-3 years +150%
Design Takeaway: Calculate total lifecycle cost, not just material cost. If your steel part needs any protective coating or shows corrosion or wear after 2-3 years, aluminum with appropriate surface treatment typically delivers lower total cost of ownership.
What Design Restrictions Should I Consider for Aluminum Parts?
Aluminum requires thicker walls (minimum 0.060″ for structural parts), shorter unsupported spans, and radiused corners compared to steel designs due to different machining and stress characteristics. Avoid deep narrow pockets, sharp internal corners, and features that create machining access problems. Design for aluminum’s properties rather than directly substituting steel geometry.
Design Restriction Framework: Keep wall thickness above 0.040″ for non-structural features and 0.060″ for load-bearing sections to prevent machining distortion and maintain dimensional accuracy. Limit unsupported pocket depths to 4:1 depth-to-width ratios to avoid tool deflection and chatter. Add 0.030″ minimum radius at internal corners since sharp edges concentrate stress and are difficult to machine cleanly.
We regularly optimize steel designs for aluminum manufacturing by adding strategic ribs instead of increasing overall thickness – often improving functionality while reducing material cost. A medical housing originally designed with complex internal geometry in steel required redesign to eliminate undercuts and improve tool access, resulting in 30% faster machining and better surface finish.
Machining access drives many aluminum design restrictions. Avoid features requiring long, thin tools or complex tool paths. Deep pockets with narrow openings create tool deflection issues, while sharp internal corners require EDM or specialized tooling that increases cost significantly.
Aluminum Design Optimization:
Steel Design Challenge Aluminum Restriction Optimized Solution Manufacturing Benefit
0.040″ thin walls Machining deflection Increase to 0.060″ or add ribs Holds tolerances, reduces scrap
Sharp internal corners Tool access/breakage 0.030″ radius minimum Standard tooling, faster cycles
Deep narrow pockets Tool deflection Widen openings or split features Better surface finish, tool life
Complex undercuts Requires multiple setups Eliminate or relocate features Single-setup machining
Design Takeaway: Plan aluminum parts for standard 3-axis machining with good tool access. Thicker sections, generous radii, and simplified geometry often deliver better performance than complex steel equivalents while reducing manufacturing cost and lead time.
How Does Aluminum's Thermal Expansion Affect My Design?
For most indoor applications under 100°F, aluminum’s thermal expansion is negligible and requires no design changes. Above 100°F operating temperature or temperature swings greater than 50°F, aluminum expands roughly twice as much as steel and needs accommodation. Use this simple check: if your current steel part operates hot enough to be uncomfortable to touch, thermal expansion matters.
Quick Thermal Assessment: Calculate potential expansion using: part length (inches) × 0.000013 × temperature change (°F) = expansion (inches). A 10″ aluminum bracket heated from 70°F to 170°F expands 0.013″ – enough to affect precision fits or create assembly stress in mixed-material designs.
For assemblies mixing aluminum with steel components, the differential expansion creates the real problem. We’ve seen outdoor enclosures where aluminum panels expand 0.010″ more than steel frames during summer heating, causing binding and seal failure. The solution: slotted mounting holes and flexible connections at material interfaces.
Temperature Impact Decision Guide:
- Room temperature equipment (±20°F) → Ignore thermal expansion, use standard clearances
- Outdoor equipment (-20°F to 140°F) → Add 0.002″ clearance per inch of aluminum dimension
- Heated assemblies (>150°F operation) → Use expansion joints, spring-loaded connections
- Mixed aluminum/steel assemblies → Slot holes in aluminum, rigid mount steel components
Most electronics enclosures, indoor brackets, and room-temperature assemblies never see enough temperature variation to matter. Focus thermal design efforts on outdoor equipment, automotive applications, or anything operating above 120°F.
Design Takeaway: Don’t over-engineer for thermal expansion unless your application genuinely sees wide temperature swings. For high-temperature or outdoor applications, add strategic clearances and avoid rigid aluminum-to-steel connections that create assembly stress.
What's the Cost Difference vs My Current Material Choice?
Aluminum typically costs 15-30% less than steel for machined parts when factoring total manufacturing cost, despite higher raw material prices. The savings come from faster machining speeds, longer tool life, and eliminated finishing requirements. However, simple steel processes like laser cutting or stamping may remain cheaper than machined aluminum.
For machined brackets and housings, aluminum often delivers 20-25% cost reduction compared to steel due to superior machinability and reduced secondary operations. We’ve converted steel medical enclosures to aluminum, achieving 22% cost reduction through faster cycle times and eliminated painting requirements. A precision audio faceplate dropped from $85 in steel to $65 in aluminum due to improved surface finish and faster material removal.
The total cost equation: aluminum’s higher material cost ($3-4/lb vs steel’s $1-2/lb) gets offset by machining advantages. Aluminum removes 2-3x faster than steel and often eliminates coating steps that steel parts need.
Material Cost Analysis:
Part Type Steel Total Cost 6061-T6 Cost 7075-T6 Cost Primary Cost Driver
Machined brackets 1.0× baseline 0.75–0.85× 0.90–1.10× Cycle time savings
Complex housings 1.0× baseline 0.70–0.80× 0.85–1.00× Setup consolidation
High-tolerance parts 1.0× baseline 0.80–0.90× 0.95–1.15× Better dimensional stability
Simple stampings 1.0× baseline 1.20–1.50× 1.40–1.80× Process change penalty
Design Takeaway: Aluminum delivers the greatest cost advantage over steel for complex machined parts requiring tight tolerances or multiple operations. Simple, high-volume steel parts may remain more economical unless aluminum provides functional benefits.
What Surface Finish and Tolerances Can I Expect from Aluminum Machining?
For most applications, specify ±0.005″ tolerances and Ra 3.2 μm surface finish – aluminum achieves these easily with standard machining, keeping costs low. Tighter specifications are possible but expensive: ±0.002″ tolerances add 25-30% to machining cost, while Ra 0.8 μm finishes require additional operations.
Specification Selection Guide: Use ±0.005″ for general brackets and housings, ±0.003″ for mating surfaces that need good fit, and ±0.002″ only for critical assembly features like bearing bores or precision alignment pins. For surface finish, Ra 3.2 μm works for hidden surfaces, Ra 1.6 μm for visible areas, and Ra 0.8 μm for appearance-critical parts or sealing surfaces.
We deliver medical device housings with ±0.003″ tolerances straight from the machine – the same parts in steel would require secondary grinding operations. Audio equipment benefits from aluminum’s natural surface quality, achieving mirror-like finishes that eliminate polishing steps needed for stainless steel equivalents.
Cost Impact of Tighter Specifications:
- ±0.005″ to ±0.003″ → adds 10-15% machining time
- ±0.003″ to ±0.002″ → adds 25-30% machining time, requires climate control
- Ra 3.2 to Ra 1.6 μm → adds 15% for finishing passes
- Ra 1.6 to Ra 0.8 μm → adds 30-40% for specialized tooling/techniques
Design Takeaway: Reserve tight tolerances and fine finishes for features that truly need them. Aluminum’s standard machining capabilities often exceed what your application actually requires, so avoid over-specifying to keep costs reasonable.
What Post-Processing Options Work Best with Aluminum?
Anodizing provides the most versatile finishing option for aluminum, offering corrosion protection, color choices, and improved wear resistance at 15-25% additional cost. Clear anodizing preserves the natural aluminum appearance while adding durability, while colored anodizing enables brand matching and aesthetic enhancement. For indoor applications, bead blasting or machined finishes often suffice without additional coating.
Post-Processing Selection Guide: Choose clear anodizing for outdoor exposure or high-wear applications, colored anodizing for appearance-critical parts, and bead blasting for uniform matte finishes on visible surfaces. Powder coating works well for aluminum but adds thickness that may affect tight-fitting assemblies – typically 0.002-0.004″ per surface.
We regularly anodize medical device housings to achieve biocompatible surfaces that withstand repeated sterilization cycles. Audio equipment benefits from black anodizing for professional appearance and EMI shielding enhancement. Aerospace brackets often receive clear anodizing for corrosion protection without weight penalty or dimensional changes.
Aluminum’s natural oxide layer provides basic protection, making additional finishing optional for many indoor applications. However, fingerprint resistance, color matching, or enhanced durability often justify anodizing costs. Avoid chrome plating on aluminum – the process is complex and expensive compared to anodizing alternatives.
Aluminum Finishing Comparison:
Finish Type Cost Impact Thickness Added Best Applications Durability
As-machined +0% None Indoor, hidden parts Good
Bead blast +5–8% None Uniform appearance Good
Clear anodizing +15–20% 0.0002–0.0005″ Outdoor, wear surfaces Excellent
Colored anodizing +20–25% 0.0002–0.0005″ Appearance parts Excellent
Powder coating +25–35% 0.002–0.004″ High durability needs Very good
Design Takeaway: Plan for anodizing thickness if parts have tight-fitting assemblies – the 0.0005″ coating thickness can affect critical dimensions. For most applications, clear anodizing provides the best balance of protection and cost without affecting fit or function.
How Will Aluminum Affect My Assembly Process?
Converting from steel to aluminum assemblies requires three key changes: increase fastener thread engagement by 50%, reduce torque specifications by 20-30%, and add thread-locking compound for vibration resistance. Most assembly processes remain the same, but aluminum’s softer threads and different thermal expansion need accommodation to prevent joint failure.
Assembly Conversion Checklist: Replace steel fasteners with stainless steel hardware to prevent galvanic corrosion, specify longer bolt engagement (1.5x diameter minimum vs 1x for steel), and reduce assembly torque values to prevent thread stripping. Train assembly teams to recognize aluminum’s different “feel” during tightening – it strips suddenly without the gradual resistance that steel provides.
We’ve helped manufacturers transition medical device assemblies from steel to aluminum, preventing assembly failures by updating torque specifications and fastener selection. A common mistake: using steel assembly torques on aluminum threads, which strips 30% of joints during initial production runs.
Critical Assembly Changes:
- Torque specifications: Reduce steel values by 25% for aluminum threads
- Fastener engagement: Minimum 1.5x diameter depth vs 1x for steel
- Thread locking: Always use medium-strength compound for vibration resistance
- Galvanic protection: Stainless fasteners or isolating washers for mixed materials
Watch for stripped threads from steel torque values and galvanic corrosion at aluminum-steel interfaces in humid environments. Test your assembly process with 10-20 prototype units to verify proper torque values and joint integrity before production.
Design Takeaway: Update assembly procedures before production – don’t assume steel assembly methods work for aluminum. Create aluminum-specific work instructions highlighting thread engagement, torque values, and fastener requirements to prevent costly field failures.
Conclusion
Aluminum delivers excellent machinability, cost savings, and performance for most precision components, but success depends on proper grade selection and design optimization. Focus on 6061-T6 for general applications, plan for aluminum’s thermal and structural characteristics, and specify realistic tolerances to control costs. Contact us to explore manufacturing solutions tailored to your aluminum machining requirements.
Frequently Asked Questions
Yes, anodizing aluminum parts with threads is standard practice. However, anodizing adds 0.0002-0.0005″ thickness, which may require tapping holes slightly larger to maintain proper thread engagement after coating. We typically recommend masking critical threads or opening them up pre-anodizing.
To minimize warping, avoid long unsupported spans, use thicker material when possible, and balance cutouts symmetrically. We also recommend specifying relief slots or adding shallow bends to increase structural rigidity. Post-process flattening or stress-relief operations may be needed for tight flatness specifications.
For structural aluminum brackets, maintain minimum 0.060″ wall thickness to prevent deflection and machining distortion. Non-load-bearing features can go down to 0.040″, but thinner sections may require specialized fixturing and slower machining speeds to maintain dimensional accuracy.
For most CNC machined parts, ±0.005″ is achievable with standard tooling and processes. Going tighter than ±0.002″ often requires specialized fixturing or climate-controlled environments, which increases cost significantly. We recommend tolerancing only critical features tightly and keeping others at ISO 2768-m levels for cost efficiency.
Aluminum can gall against stainless steel under high contact pressure or repeated assembly cycles. Use anti-seize compound on threads, reduce assembly torque by 25%, and consider anodized aluminum or coated fasteners for high-wear applications to prevent material transfer.
6061-T6 is the most commonly used grade due to its excellent machinability and moderate strength. If your part requires higher tensile performance, 7075 offers superior strength but costs more and is harder on tools. 2024 is another high-strength option but has poor corrosion resistance.
