C355 (AlSi5Cu1Mg)
Premium heat-treatable alloy that bridges the gap between A356 and A380, with high strength for aerospace and defense applications.
The 355.0/C355 family is a high-strength Al-Si-Cu-Mg alloy that combines silicon castability with copper- and magnesium-driven precipitation hardening. The C355.0 version is higher purity (ultra-low iron ≤0.20%), achieving better mechanical properties and greater toughness — making it preferred in aerospace, defense, and demanding structural components. It bridges the strength gap between A356 (more ductile) and A380 (die casting). We manufacture it from a primary aluminum base to guarantee low iron content and optimal T6 heat-treatment response.
International Nomenclature
| Standard | Designation |
|---|---|
| AA (USA) | 355.0 / C355.0 |
| EN (Europa) | EN AC-45300 · AlSi5Cu1Mg |
| UNS | A03550 / A33550 |
| ISO | Al-Si5Cu1Mg |
| ASTM | B26 (arena) / B108 (molde permanente) |
Chemical Composition
| Element | Symbol | Percentage |
|---|---|---|
| Aluminum | Al | Balance |
| Silicon | Si | 4.5–5.5% |
| Copper | Cu | 1.0–1.5% |
| Magnesium | Mg | 0.40–0.60% |
| Iron | Fe | ≤0.20% (C355) · ≤0.6% (355.0) |
| Manganese | Mn | ≤0.10% (C355) · ≤0.50% (355.0) |
| Zinc | Zn | ≤0.10% (C355) · ≤0.35% (355.0) |
| Titanium | Ti | ≤0.20% |
| Others (each) | — | ≤0.05% |
| Others (total) | — | ≤0.15% |
Physical Properties
| Property | Value |
|---|---|
| Density | 2.71 g/cm³ |
| Melting Range | 546–621 °C |
| Electrical Conductivity | ~37% IACS |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength (UTS) | ~241 MPa (T6, arena) |
| Tensile Strength (UTS) | ~290 MPa (T6, molde permanente) |
| Yield Strength | ~172–190 MPa (T6) |
| Elongation | 3–4% (T6) |
| Hardness | 80–90 HB |
Key Characteristics
- Premium heat-treatable alloy with copper and magnesium for precipitation hardening
- Bridges the strength gap between A356 (ductile) and A380 (die casting)
- Higher-purity C355 version with ultra-low iron (≤0.20%) for maximum toughness
- Excellent T6 temper response for aerospace and defense applications
- Good castability and pressure tightness for leak-proof components
- Manufactured from a primary aluminum base to guarantee low iron content
Industries & Applications
Aerospace
Gearbox housings, structural casings, high-strength components
Defense
Critical structural components, military equipment housings
Automotive
Suspension components, engine mounts, high-performance parts
Machinery
Pump bodies, pressure valves, gearcases
Special Notes
The "C" prefix in C355.0 designates a higher-purity version (controlled iron and trace elements) versus standard 355.0. Copper (1.0–1.5%) raises strength and hardness above A356, while magnesium enables precipitation hardening in the T6 temper. We manufacture it from a primary aluminum base to guarantee Fe ≤0.20% and optimal heat-treatment response, ideal for aerospace and defense parts demanding strength and reliability.
Frequently Asked Questions
What is C355 (AlSi5Cu1Mg) alloy and what is it used for?
C355 is a premium, heat-treatable Al-Si-Cu-Mg casting alloy (3xx.x series) that bridges the strength gap between A356 (more ductile) and A380 (die casting). Its high strength and toughness make it the preferred choice in aerospace and defense applications such as gearbox housings, structural casings, and critical military components, plus demanding automotive parts (suspension, engine mounts) and machinery (pump bodies, pressure valves).
What is the chemical composition of C355 and what does each alloying element contribute?
C355 contains silicon 4.5–5.5%, copper 1.0–1.5%, and magnesium 0.40–0.60%, with the remainder aluminum (balance). Silicon provides castability; copper raises strength and hardness above A356; and magnesium enables precipitation hardening during T6 heat treatment. The C355 version also holds iron ultra-low (≤0.20%) with controlled trace elements for maximum toughness.
Is C355 heat-treatable, and what strength does the T6 temper deliver?
Yes, C355 is heat-treatable and responds excellently to the T6 temper thanks to copper- and magnesium-driven precipitation hardening. In the T6 condition it reaches a tensile strength (UTS) of ~241 MPa in sand and ~290 MPa in permanent mold, with a yield strength of ~172–190 MPa, 3–4% elongation, and 80–90 HB hardness.
How does C355 differ from standard 355.0?
The "C" prefix in C355.0 designates a higher-purity version versus standard 355.0, with controlled iron and trace elements. In C355 iron is limited to ≤0.20% (vs ≤0.6% in 355.0), manganese to ≤0.10% (vs ≤0.50%), and zinc to ≤0.10% (vs ≤0.35%). This higher purity yields better mechanical properties and greater toughness, which is why C355 is preferred in aerospace and defense.
Why is low iron content preferred, and how does TP guarantee it in C355?
Iron forms brittle intermetallic phases that reduce toughness and ductility, so keeping it low is critical in demanding structural parts. At Transformación Puebla we manufacture C355 from a primary aluminum base to guarantee ultra-low iron (≤0.20%) and an optimal T6 heat-treatment response; primary aluminum avoids the iron contamination typical of recycled scrap.
What casting processes does C355 support, and under which standards is it supplied?
C355 offers good castability and pressure tightness, making it suitable for both sand and permanent-mold casting to produce leak-proof components. T6 properties are specified for both routes (ASTM B26 for sand and ASTM B108 for permanent mold). Its equivalent designations include AA 355.0 / C355.0, EN AC-45300 (AlSi5Cu1Mg), UNS A03550 / A33550, and ISO Al-Si5Cu1Mg.
Need C355 (AlSi5Cu1Mg)?
We manufacture this alloy in ingots, donuts, and bars to your exact specifications.