Steel vs Aluminium: Which Material Is Best for Your Project?

When it comes to selecting materials for CNC machining, steel and aluminium stand out as two of the most common options, each with distinctive characteristics that influence design and production decisions. Understanding the differences between these two metals is essential for optimising performance, costs, and production efficiency.

In this guide we analyse steel vs aluminium in terms of:

• Steel or Aluminium: key characteristics compared

• Weight and performance: steel vs aluminium

• Mechanical strength and long-term durability

• Corrosion resistance

• Machinability and CNC precision

• Cost and sustainability

• When to choose Steel

• When to choose Aluminium

Steel or aluminium: key characteristics compared

Steel

Steel is an alloy of iron and carbon, often enriched with elements such as chromium, nickel, molybdenum or vanadium to improve its properties.

Common types:

• Carbon steel → a good compromise between strength and cost.

• Stainless steels (AISI 304, 303, 316, 316L, etc.) → excellent corrosion resistance, ideal for harsh environments or food/chemical applications.

In general, steel is:

• strong and versatile

• suitable for structural and mechanical applications

• available in a very wide range of alloys for specific requirements

Aluminium

Aluminium is a light and soft metal, almost always used in alloy form to increase its strength.

The most common alloys:

• Aluminium 6061 → highly versatile, good mechanical strength, excellent machinability; used in many sectors.

• Aluminium 7075 → one of the strongest alloys, used in aerospace, military, racing.

• Other alloys (5052, 6082, etc.) → for marine applications, lightweight structures, CNC-machined components.

Aluminium is:

• very lightweight

• naturally corrosion resistant thanks to its thin protective oxide layer

• ideal for components where weight is critical

Weight and performance: steel vs aluminium

The most obvious difference is weight:

• Steel → density ≈ 7.85 g/cm³
• Aluminium → density ≈ 2.7 g/cm³

Aluminium is therefore about three times lighter than steel.
This difference is crucial in sectors such as:

• aerospace
• automotive and motorbikes
• drones and robotics
• bicycles, sport, racing

With Weerg you can take advantage of:

• aluminium for light and precise components
• stainless steel (e.g. 316) for parts that must withstand high loads in harsh environments

Mechanical strength and long-term durability

Steel

In absolute terms, steel generally offers higher mechanical strength than aluminium.

• Both carbon steels and high-strength stainless steels (e.g. AISI 316) can withstand high loads, impacts and extreme conditions.
• It is the reference material for:
  • load-bearing structures
  • tools
  • critical industrial components

Aluminium

Aluminium has lower strength than steel, but an excellent strength-to-weight ratio.

• Alloys like 7075 can offer remarkable performance for the same weight, making them ideal for:
  • bicycle frames
  • drone parts
  • aerospace components
  • high-performance lightweight structures

In practice:

• if the constraint is maximum robustness → generally steel
• if the constraint is strength with minimum weight → aluminium alloys (e.g. 6061, 7075)

Corrosion resistance

Aluminium

Aluminium is naturally corrosion resistant thanks to a protective oxide film that forms on its surface.
It is therefore excellent for:

• humid or marine environments
• outdoor applications
• components for marine use (e.g. 6061 and 5052 alloys)

Steel

Non-stainless steel tends to corrode unless protected (painting, galvanisation, treatments).

For aggressive environments, the following are used:

• stainless steels AISI 304, 303, 316, 316L
  • 304/303 → good corrosion resistance in standard environments
  • 316/316L → excellent corrosion resistance, even in marine or chemically aggressive environments

Alternatively:

• treatments such as galvanising, bluing, painting help protect carbon steels.

Machinability and CNC precision

Aluminium

Aluminium is generally easier to machine:

• it can be milled and turned more quickly
• requires less power and causes less tool wear
• alloys like 6061 are known for their excellent CNC machining performance
• allows for complex geometries and high-quality finishes with reduced cycle times

Steel

Steel:

• is harder and stronger, and therefore more demanding to machine
• requires more robust tools and more conservative cutting parameters
• results in greater energy consumption and potential tool wear

With advanced machinery (such as Weerg’s 5-axis CNC machining), it is still possible to achieve:

• tight tolerances
• high-quality finishes even on demanding steels, such as AISI 316 stainless steel

Cost and sustainability

Cost

Generally:

• Steel is cheaper per kg than aluminium
• for large-scale projects (e.g. structures, industrial plants), steel is often the most cost-effective choice

Aluminium:

• costs more as a material, but
• can reduce weight, energy consumption and operating costs (e.g. lighter vehicles, easier-to-install structures)

Sustainability

Both steel and aluminium are highly recyclable and fit well within a circular economy framework.
Specifically:

• recycled aluminium requires far less energy than primary production
• steel is one of the most recycled materials in the world

When to choose Steel

Choose steel if:

• you need maximum strength and durability
• you work in contexts involving high loads and constant mechanical stresses
• you must create:
  • load-bearing structures
  • tools, brackets, plates, supports
  • components for industrial plants
• you are in a corrosive environment and can use stainless steel (e.g. 304, 316, 316L)

Steel is the natural choice for:

• bridges, buildings, heavy machinery, industrial equipment, mechanical tools

When to choose aluminium

Choose aluminium if:

• lightness is a priority
• you want to reduce weight, inertia and consumption (e.g. drones, vehicles, automation)
• you work in outdoor or marine environments (with suitable alloys)
• you need:
  • custom and complex components
  • excellent CNC machinability and reduced cycle times
  • a good balance between strength, weight and aesthetics

It is the ideal material for:

• aerospace, automotive, transport, marine, sport, industrial design

Conclusion

The choice between steel and aluminium always depends on the specific requirements of the project:

• Steel → robustness, durability, cost-effectiveness, high loads and stresses.

• Aluminium → lightness, corrosion resistance, excellent machinability and power-to-weight performance.

Thanks to Weerg’s advanced CNC machining, you can make the most of the properties of both materials, obtaining components that are precise, repeatable and optimised for real-world use.

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