How to Choose Between Aluminum Alloy, Stainless Steel, and PEEK?

A Practical Material Selection Guide for Precision CNC Parts

Choosing the wrong material can lead to repeated prototyping failures — or even worse, costly redesigns after mass production. This guide helps engineers make the right decision between aluminum alloy, stainless steel, and PEEK based on real engineering factors.

I. Mechanical Properties: Strength vs Weight

Key Insights:

• Aluminum offers the best strength-to-weight ratio
• Stainless steel has high strength but is heavy
• PEEK has low stiffness and is not for structural load

II. Corrosion Resistance: Real Engineering Conditions

Corrosion resistance depends heavily on environment — especially chloride exposure.

Key Points:

• Aluminum: good in air, weak in seawater
• 304: fails in chloride environments
• 316L: required for marine / chemical use
• PEEK: excellent chemical resistance

III. Machining Cost Comparison

Typical cost comparison (same part):

• Aluminum 6061: $40–70 → Best cost-performance
• 316L Stainless: $100–160 → High machining time
• PEEK: $80–130 → Expensive raw material

Stainless steel is expensive mainly due to machining time, not material price.

IV. Surface Treatment Compatibility

Aluminum:

• Anodizing (color / hard)
• Best for appearance parts

Stainless Steel:

• Electropolishing (Ra0.1 possible)
• Passivation

PEEK:

• Usually no surface treatment needed

V. Final Material Selection Guide

• Lightweight structural parts → Aluminum 7075 / 6061
• Corrosion + strength → Stainless Steel 316L
• Chemical resistance / insulation → PEEK