Aluminium alloys are a cornerstone of modern manufacturing, offering a unique combination of lightweight performance, corrosion resistance, and versatility across industries. Among the most commonly used alloys are A356‑T6 and 6063‑T6 aluminum, each with distinct properties, strengths, and ideal applications. In this article, we’ll break down the key difference between A356‑T6 and 6063‑T6 aluminium to help you choose the right alloy for your project.
What is A356-T6 Aluminium?
A356-T6 is a heat-treated version of the A356 aluminum alloy, where “T6” denotes a specific temper involving solution heat treatment followed by artificial aging. This process significantly increases the alloy’s strength, hardness, and mechanical performance while retaining good corrosion resistance and excellent castability. A356-T6 is widely used in automotive, aerospace, and marine applications, particularly for components like wheels, engine parts, and structural castings, where lightweight materials with high strength and durability are essential.
Aluminium A356 T6 Equivalent
The A356-T6 aluminum alloy has several international equivalents, mainly based on its chemical composition and mechanical properties. Some commonly referenced equivalents are:
| Standard / Region | Equivalent Alloy |
|---|---|
| ASTM (USA) | A356-T6 |
| EN (Europe) | AlSi7Mg0.3 |
| DIN (Germany) | G-AlSi7Mg0.3 |
| JIS (Japan) | ADC12 (similar, but slightly different Mg/Si content) |
| ISO | AlSi7Mg |
A356 T6 Material Properties
Mechanical Properties:
Tensile Strength (Ultimate): ~310–350 MPa
Yield Strength: ~240–270 MPa
Elongation at Break: 5–12% (depending on casting method)
Hardness (Brinell): ~95 HB
Physical Properties:
Density: ~2.68 g/cm³
Melting Range: 570–640°C
Modulus of Elasticity: ~70 GPa
Other Characteristics:
Excellent corrosion resistance, particularly in marine environments. Good fatigue strength and fracture toughness. Excellent dimensional stability during heat treatment and machining. This combination makes A356-T6 ideal for automotive, aerospace, and marine applications where lightweight yet strong components are required.
Aluminum A356 T6 Composition
A356-T6 is an aluminum-silicon-copper (Al-Si-Cu) casting alloy that is heat-treated to the T6 condition. Its typical chemical composition is approximately:
Silicon (Si): 6.5–7.5%
Iron (Fe): 0.2% max
Copper (Cu): 0.2–0.4%
Manganese (Mn): 0.05–0.35%
Magnesium (Mg): 0.25–0.45%
Nickel (Ni): 0.1% max
Zinc (Zn): 0.1% max
Titanium (Ti): 0.1–0.2%
Aluminum (Al): Balance (~92–93%)
The T6 designation indicates that the alloy has undergone solution heat treatment followed by artificial aging, giving it enhanced mechanical properties like high strength and good wear resistance.
A356 T6 Heat Treatment Process
The A356-T6 aluminum alloy achieves its high strength and mechanical properties through a controlled T6 heat treatment process, which involves solution treatment, quenching, and artificial aging. Here’s the process in detail:
Solution Treatment:
Heat the cast A356 alloy to 540–550°C (1000–1020°F) for 6–12 hours. This dissolves the soluble magnesium and silicon phases into a solid solution. The goal is to homogenize the microstructure and maximize solute content for strengthening.
Quenching:
Rapidly cool the alloy in water or a water-based quench to room temperature. This traps the magnesium and silicon in a supersaturated solid solution. Quenching must be done promptly to avoid the formation of coarse precipitates, which would reduce strength.
Artificial Aging (Precipitation Hardening):
Reheat the alloy to 155–160°C (310–320°F) for 6–8 hours (sometimes up to 10 hours depending on the desired properties). This step allows fine precipitates of Mg₂Si to form, which hinder dislocation motion and increase strength. Cooling to room temperature completes the T6 temper, providing the final hardness and mechanical properties.
What is 6063-T6 Aluminium?
6063-T6 is a heat-treated version of the 6063 aluminum alloy, where “T6” indicates a specific temper achieved through solution heat treatment followed by artificial aging. This process enhances the alloy’s strength and hardness while retaining excellent corrosion resistance, good machinability, and smooth surface finish. 6063-T6 is widely used in architectural applications, structural components, piping, and automotive parts where a combination of moderate strength, excellent finishing characteristics, and corrosion resistance is required.
Aluminium 6063-T6 Equivalent
The 6063-T6 aluminum alloy has several international equivalents based on its chemical composition and mechanical properties. Common references include:
| Standard / Region | Equivalent Alloy |
|---|---|
| ASTM (USA) | 6063-T6 |
| EN (Europe) | AlMg0.7Si |
| DIN (Germany) | AlMgSi0.7 |
| JIS (Japan) | A6063 |
| ISO | AlMgSi0.7 |
6063-T6 Material Properties
Mechanical Properties:
- Tensile Strength (Ultimate): ~190–240 MPa
- Yield Strength: ~145–200 MPa
- Elongation at Break: 8–12%
- Hardness (Brinell): ~70–80 HB
Physical Properties:
- Density: ~2.70 g/cm³
- Melting Range: 608–650°C
- Modulus of Elasticity: ~69 GPa
Other Characteristics:
- Excellent corrosion resistance, especially in marine and architectural environments.
- Good surface finish and anodizing capability.
- Moderate strength with excellent formability.
- Ideal for extrusion applications such as window frames, tubes, and architectural trim.
Aluminum 6063-T6 Composition
6063-T6 is an aluminum-magnesium-silicon (Al-Mg-Si) alloy, typically containing:
| Element | Composition (%) |
|---|---|
| Silicon (Si) | 0.2–0.6 |
| Iron (Fe) | 0.35 max |
| Copper (Cu) | 0.1 max |
| Manganese (Mn) | 0.1 max |
| Magnesium (Mg) | 0.45–0.9 |
| Chromium (Cr) | 0.1 max |
| Zinc (Zn) | 0.1 max |
| Titanium (Ti) | 0.1 max |
| Aluminum (Al) | Balance |
The T6 designation indicates that the alloy has undergone solution heat treatment and artificial aging to improve strength and hardness while maintaining corrosion resistance and surface quality.
6063-T6 Heat Treatment Process
The 6063-T6 aluminum alloy achieves its mechanical properties through a controlled T6 heat treatment process, consisting of solution treatment, quenching, and artificial aging:
Solution Treatment:
- Heat the alloy to 510–540°C (950–1000°F) for 6–12 hours.
- This dissolves magnesium and silicon phases into a uniform solid solution.
Quenching:
- Rapidly cool the alloy in water to room temperature.
- Quenching traps magnesium and silicon in a supersaturated solid solution.
- Immediate quenching is essential to avoid coarse precipitate formation.
Artificial Aging (Precipitation Hardening):
- Reheat to 160–175°C (320–347°F) for 6–12 hours.
- Fine Mg₂Si precipitates form, increasing strength and hardness.
- Cooling to room temperature completes the T6 temper, providing final mechanical properties and improved surface characteristics.
A356-T6 vs 6063-T6 Aluminum, What’s the Difference?
| Feature | A356-T6 | 6063-T6 |
|---|---|---|
| Alloy Type | Al-Si-Cu casting | Al-Mg-Si wrought |
| Form | Castings | Extrusions |
| Tensile Strength | 310–350 MPa | 190–240 MPa |
| Yield Strength | 240–270 MPa | 145–200 MPa |
| Elongation | 5–12% | 8–12% |
| Hardness | ~95 HB | ~70–80 HB |
| Density | 2.68 g/cm³ | 2.70 g/cm³ |
| Applications | Wheels, engine parts, aerospace, marine | Window frames, pipes, structural profiles |
| Price | ~ US$2,700/tonne (~US$ 2.70/kg) for A356 alloy. | ~ US$3.40/kg (~US$3,400/tonne) listed for 6063 alloy. |
A356‑T6 vs 6063‑T6 Aluminium, Which Should You Choose
Strength vs formability: A356‑T6 gives you higher strength but is less ideal for thin‑walled extrusions or parts needing complex bending/forming. 6063‑T6 offers better formability but lower strength.
Process compatibility: If you plan to cast the part, A356‑T6 is practically the go‑to. If you plan to extrude or draw profiles, 6063‑T6 is more suitable.
Cost and manufacturing complexity: Castings may require more complex tooling and heat‑treatment control; extruded profiles might be more cost efficient for certain shapes.
Surface finish and visible parts: For visible, anodised or finished architectural parts, 6063‑T6 often wins. For hidden structural parts, the strength of A356‑T6 might matter more.
Duration and treatment: Remember that both are T6 tempers (solution treated & artificially aged) but their application contexts differ (casting vs wrought).