Choosing the right material is one of the most critical decisions in CNC machining.
Among all options, aluminum and steel are two of the most commonly used metals. Each offers distinct mechanical properties, cost implications, and machining behavior—making them suited for different use cases.
This guide breaks down the key differences between aluminum and steel for CNC machining, so you can determine which metal aligns best with your application, tolerance requirements, budget, and performance goals.
Why Material Choice Matters in CNC Machining
CNC machining is a subtractive manufacturing method where material is removed from a solid workpiece using precise cutting tools.
Material selection impacts:
Machining speed
Tool wear and cost
Dimensional tolerance
Surface finish
Mechanical strength and corrosion resistance
Application suitability
Choosing aluminum or steel has a direct influence on your part’s performance, manufacturing time, and total cost.
Aluminum: Lightweight and Easy to Machine
Aluminum is widely favored for its excellent machinability, corrosion resistance, and weight-to-strength ratio.
Key Properties:
| Attribute | Value Range |
|---|---|
| Density | ~2.7 g/cm³ (lightweight) |
| Tensile Strength | 90–570 MPa (grade-dependent) |
| Thermal Conductivity | High (~205 W/m·K for 6061) |
| Corrosion Resistance | Excellent (especially 6061, 5052) |
| Machinability | Very high (easier on tools) |
Pros of CNC Machining Aluminum:
High machining speed: Cuts faster than steel, reducing cycle time
Lower tool wear: Less abrasive to tooling
Good surface finish: Requires minimal post-processing
Lightweight: Ideal for aerospace, automotive, and portable devices
Corrosion-resistant: Often eliminates the need for coatings
Popular Grades for CNC Machining:
6061-T6: General-purpose alloy, strong and corrosion-resistant
7075-T6: High-strength aerospace-grade alloy
2024: Great fatigue resistance, used in aerospace
5052: Excellent weldability and corrosion resistance
Steel: Stronger, Tougher, and More Wear-Resistant
Steel offers significantly higher strength and hardness, making it ideal for parts exposed to heavy loads, abrasion, or impact.
Key Properties:
| Attribute | Value Range |
|---|---|
| Density | ~7.8 g/cm³ (heavier than aluminum) |
| Tensile Strength | 350–2,000 MPa (grade-dependent) |
| Thermal Conductivity | Lower (~50 W/m·K) |
| Corrosion Resistance | Low unless coated (stainless excluded) |
| Machinability | Moderate to low (depends on alloy) |
Pros of CNC Machining Steel:
Higher strength: Suitable for structural, load-bearing applications
Better wear resistance: Withstands friction, impact, and pressure
Wider hardness range: Useful in high-temperature or industrial uses
Tighter tolerances: Dimensional stability for fine mechanical components
Popular Grades for CNC Machining:
1018: Mild carbon steel, cost-effective and easy to machine
4140 (Chromoly): High strength and toughness, used in tooling and motorsports
316 Stainless Steel: Corrosion-resistant, ideal for food, medical, and marine use
304 Stainless Steel: General-purpose corrosion-resistant alloy
Comparison Table: Aluminum vs. Steel for CNC Machining
| Feature/Property | Aluminum | Steel |
|---|---|---|
| Weight | Lightweight (~2.7 g/cm³) | Heavy (~7.8 g/cm³) |
| Machinability | Excellent (faster, cleaner cuts) | Moderate to difficult |
| Tool Wear | Low | Higher (especially with hard alloys) |
| Surface Finish | Smooth, requires less post-work | May need finishing depending on grade |
| Strength | Moderate | High (load-bearing capability) |
| Corrosion Resistance | High (natural oxide layer) | Low (unless stainless or coated) |
| Cost (Material) | Generally lower | Higher for alloy/stainless grades |
| Thermal Conductivity | High (dissipates heat well) | Lower, may retain heat |
| Application Suitability | Aerospace, auto, consumer goods | Tooling, industrial, structural |
Applications of CNC Machined Aluminum vs. Steel
Aluminum Applications:
Aerospace Components: Fuselage structures, brackets, mounting systems
Automotive Parts: Housings, heat sinks, engine parts, control arms
Consumer Electronics: Laptop bodies, drone frames, heat-dissipating parts
Medical Devices: Lightweight external frames and casings
Robotics: Lightweight components requiring high precision
Steel Applications:
Tooling and Fixtures: Dies, punches, and press tools
Machine Components: Shafts, gears, couplings, drive systems
Industrial Equipment: Load-bearing frames, press arms, drive housings
Automotive: Suspension parts, fasteners, engine components
Construction: Bolts, brackets, and reinforcements
CNC machining supports a wide range of applications for both metals—explore detailed use cases in this CNC metal machining applications guide.
CNC Machining Considerations for Each Metal
Machining Aluminum:
Use high-RPM spindles and sharp carbide tools
Air or minimal coolant needed
Chips evacuate easily, reducing cycle interruptions
Suitable for tight-tolerance parts without stress relief
Machining Steel:
Requires slower feed rates and lower spindle speeds
Uses more aggressive coolants to manage heat buildup
Tends to work-harden during cutting—may need specialized tools
Surface finishing (grinding, polishing, coating) may be necessary
Cost and Production Considerations
| Cost Factor | Aluminum | Steel |
|---|---|---|
| Raw Material Cost | Generally lower | Higher (especially alloys) |
| Machining Time | Faster | Slower due to hardness |
| Tooling Costs | Lower (less wear) | Higher (frequent replacement) |
| Energy Consumption | Lower | Higher |
For large production runs, these cost differences become substantial. Aluminum is often more cost-effective when time, tool life, and ease of machining are prioritized. Steel is better when performance and durability outweigh machining efficiency.
Which Metal Should You Choose?
Choose aluminum if your application requires:
Lightweight design
Faster turnaround
Lower machining cost
Good corrosion resistance
Thermal conductivity
Choose steel if your application requires:
High strength under load
Wear resistance or impact strength
Temperature stability
Structural rigidity
Long part lifecycle in harsh conditions
In some cases, hybrid designs use aluminum for non-load-bearing parts and steel for critical structures.
Final Thoughts
Both aluminum and steel are essential in CNC machining, and the best choice depends entirely on your project’s performance, budget, and timeline requirements.
Aluminum offers speed, cost-efficiency, and lightness—ideal for most prototyping, aerospace, and consumer applications.
Steel provides strength, wear resistance, and longevity—making it the go-to for industrial and structural parts.
The right material unlocks the full potential of your CNC part.
Need help determining the best option for your part? Explore custom solutions and real-world examples on the applications of CNC machine for metal page.
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