Material Spotlight: Aluminium Alloys & Their Properties — A Guide for Aluminium Casting Applications
Aluminium casting remains one of the most widely used manufacturing processes thanks to aluminium’s excellent strength-to-weight ratio, corrosion resistance, and versatility. But not all aluminium alloys behave the same — and choosing the right one can significantly impact performance, durability, machining time and final cost.
In this material spotlight, we explore the most commonly used aluminium alloys in aluminium casting, compare their strengths and weaknesses, and outline where each performs best.
1. Why Alloy Choice Matters in Aluminium Casting
When producing components via aluminium casting, alloy composition directly affects:
✔ Strength & hardness
Determines load-bearing capability, fatigue life and resistance to deformation.
✔ Corrosion behaviour
Critical for marine, food-grade and outdoor applications.
✔ Machinability
Influences cycle time, tool wear, achievable tolerances and finishing requirements.
✔ Fluidity & castability
Affects mould fill, thin-wall performance and consistency in complex shapes.
✔ Cost & heat treatment requirements
Some alloys perform well without heat treatment, while others require T6 heat treatment for optimal strength.
2. The Most Common Alloys Used in Aluminium Casting
Below is a practical comparison of the most widely used aluminium casting alloys for industrial applications.
🔹 LM6 (Al-Si12): High-Silicon Alloy for Superior Corrosion Resistance
Key Properties
- Excellent corrosion resistance
- Outstanding castability and flow
- Low shrinkage — ideal for complex castings
- Poor machinability
- Non-heat-treatable
Best Uses in Aluminium Casting
- Marine components
- Food and beverage equipment
- Pump housings
- Thin-wall and intricate shapes
- Parts exposed to moisture, chemicals or saltwater.
Strengths
- Among the best corrosion-resistant aluminium casting alloys
- Excellent fluidity for challenging mould designs
- Good wear resistance
Weaknesses
- Lower strength than heat-treated alloys
- Difficult to machine due to high silicon content
🔹 LM25 (Al-Si7Mg): Heat-Treatable Alloy for Strength and Versatility
Key Properties
- Can be heat-treated to T6 for high strength
- Good corrosion resistance
- Excellent impact performance
- Good weldability
- Better mechanical properties than LM6
Best Uses in Aluminium Casting
- Automotive structural parts
- Aerospace fittings and brackets
- Pressure-tight components
- Load-bearing housings and fixtures
Strengths
- Strong, reliable and highly versatile
- Performs well in structural and safety-critical components
- Good machining characteristics after heat treatment
Weaknesses
- Slightly lower fluidity than LM6
- Cost increases when T6 heat treatment is required.
🔹 LM4 (Al-Si5Cu3): General-Purpose Alloy with Strong Machinability
Key Properties
- Good machinability
- Medium corrosion resistance
- High wear resistance
- Strong mechanical properties without heat treatment
Best Uses
- Automotive castings
- Gears, levers and brackets
- General engineering applications
Strengths
- One of the easier alloys to machine
- Good strength without additional processing
Weaknesses
- Less corrosion resistant than LM6 or LM25
- Lower ductility
🔹 LM13 (Al-Si12CuNi): High-Temperature, High-Wear Alloy
Key Properties
- Exceptional wear and heat resistance
- Good dimensional stability
- Ideal for mechanically demanding environments
Best Uses in Aluminium Casting
- Pistons
- Cylinder heads
- Engine components operating under high thermal stress
Strengths
- Excellent performance under high load and temperature
- Long-term durability in harsh conditions
Weaknesses
- Reduced corrosion resistance
- Generally more expensive
3. Aluminium Casting Alloy Comparison
|
LM6
|
Low–Medium |
Very High
|
Poor |
Excellent
|
No |
|
LM25
|
High (T6)
|
High | Medium | Good |
Yes
|
|
LM4
|
Medium–High | Medium |
Good
|
Good | No |
|
LM13
|
High
|
Low–Medium | Medium | Good | Limited |
4. Recommended Alloys by Industry
Aerospace
- Ideal Alloy: LM25 (T6)
- Why: High strength-to-weight ratio and strong fatigue resistance.
Automotive
- Ideal Alloys: LM4 / LM25
- Why: Strong, durable, easily machined aluminium casting materials.
Marine
- Ideal Alloy: LM6
- Why: Outstanding corrosion resistance in saltwater environments.
Food & Beverage
- Ideal Alloys: LM6 & LM25
- Why: Clean surfaces, chemical resistance, good anodising behaviour.
High-Temperature Operation
- Ideal Alloy: LM13
- Why: Thermal stability and wear resistance under extreme conditions.
5. Machinability, Finishing and Cost Considerations
Machinability
- Best machinability: LM4
- Moderate: LM25
- Poor: LM6
Finishing
- Anodising works best on LM25 (bright finish).
- LM6 anodises well but typically has a greyer appearance.
- LM4/LM13 may produce darker tones due to copper or nickel content.
Cost Considerations in Aluminium Casting
Factors include:
- Alloy price
- Complexity of casting
- Machining time
- Heat treatment requirements
Most economical: LM6
Most expensive: LM13 and T6 heat-treated LM25
Most expensive: LM13 and T6 heat-treated LM25
Conclusion
Choosing the right aluminium alloy is essential for maximising performance in aluminium casting. Whether your priority is corrosion resistance, strength, machinability, or cost efficiency, understanding alloy characteristics helps make better design decisions and produce more reliable components.
Leave a Reply