Aluminium is one of the most versatile metals used in modern engineering, construction, transportation, and manufacturing. Among the many grades available, the 5 series (5xxx) and 6 series (6xxx) aluminium alloys stand out as two of the most commonly used categories. They each have unique compositions, mechanical properties, and application advantages that make them suitable for different industries.
So, what is the difference between 5 series and 6 series aluminium? While both share excellent corrosion resistance, good formability, and a high strength-to-weight ratio, they differ in their main alloying elements, heat treatment behavior, and mechanical characteristics.
In this in-depth guide, SASAALUMINUM explains the key distinctions between the 5xxx and 6xxx aluminium series—covering their composition, processing, physical and mechanical properties, and where they are best applied.
1. Understanding Aluminium Alloy Series
Aluminium alloys are grouped into series based on their principal alloying elements, which determine their core characteristics.
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1xxx series: Essentially pure aluminium (99% or higher), offering excellent corrosion resistance and conductivity but low strength.
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2xxx series: Aluminium-copper alloys known for high strength and used mainly in aerospace.
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3xxx series: Aluminium-manganese alloys offering good corrosion resistance and moderate strength.
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4xxx series: Aluminium-silicon alloys typically used in welding wire and automotive parts.
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5xxx series: Aluminium-magnesium alloys known for superior corrosion resistance and weldability.
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6xxx series: Aluminium-magnesium-silicon alloys that combine medium strength with excellent machinability and heat-treatability.
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7xxx series: Aluminium-zinc alloys with the highest strength, used in aerospace and defense applications.
Among these, the 5xxx and 6xxx series are the most common in general engineering, architectural, and transportation industries.
2. Composition Difference Between 5 Series and 6 Series Aluminium
The key distinction lies in their main alloying elements and how these elements influence performance.
5 Series Aluminium (Al-Mg Alloys)
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Primary Alloying Element: Magnesium (Mg)
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Typical Alloying Range: 3–6% Mg, sometimes with small additions of manganese (Mn) or chromium (Cr).
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Examples: 5052, 5083, 5A06, 5754.
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Characteristics: Non-heat-treatable, strengthened through cold working, offering high corrosion resistance and excellent weldability.
6 Series Aluminium (Al-Mg-Si Alloys)
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Primary Alloying Elements: Magnesium (Mg) and Silicon (Si).
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Typical Alloying Range: Mg (0.8–1.2%), Si (0.4–1.0%), sometimes with copper (Cu) or chromium (Cr).
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Examples: 6061, 6063, 6082, 6005.
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Characteristics: Heat-treatable alloy, medium strength, excellent formability, and superior surface finish.
In simple terms, 5 series aluminium focuses on corrosion resistance and weldability, while 6 series aluminium emphasizes heat-treatable strength and machining capability.
3. Strengthening Mechanisms
The way each series gains its strength is fundamentally different.
5 Series – Work Hardened (Non-Heat-Treatable)
5xxx series aluminium alloys cannot be strengthened through heat treatment. Instead, they rely on cold working (rolling, stretching, or drawing) to increase strength by introducing dislocations in the crystal structure.
For example:
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5052-H32 is strain-hardened to achieve higher strength.
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The “H” temper designations (like H32, H34, H116) indicate the degree of work hardening.
6 Series – Precipitation Hardened (Heat-Treatable)
6xxx series alloys can be heat treated to improve mechanical strength through precipitation hardening. During this process, finely dispersed magnesium silicide (Mg₂Si) particles form within the alloy, significantly increasing hardness and tensile strength.
Common heat-treated tempers include:
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T5: Cooled from extrusion temperature and artificially aged.
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T6: Solution heat-treated and artificially aged for maximum strength.
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T651: Stress-relieved version of T6 for improved stability in machining.
4. Mechanical Properties Comparison
| Property | 5 Series (Typical: 5083-H116) | 6 Series (Typical: 6061-T6) |
|---|---|---|
| Tensile Strength (MPa) | 275–350 | 310–350 |
| Yield Strength (MPa) | 150–275 | 270–310 |
| Elongation (%) | 12–25 | 10–17 |
| Hardness (HB) | 85–95 | 95–100 |
| Density (g/cm³) | 2.66 | 2.70 |
Both series offer comparable strength levels, but 6xxx alloys like 6061 achieve strength through heat treatment, while 5xxx alloys rely on cold working.
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5 series: Excellent ductility and toughness for formed or welded structures.
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6 series: Balanced strength and machinability for complex shapes.
5. Corrosion Resistance and Surface Behavior
5 Series Aluminium
Thanks to its high magnesium content, 5xxx aluminium exhibits outstanding corrosion resistance, especially in marine, coastal, and chemical environments. The protective oxide film resists attack from saltwater and industrial pollutants.
It also performs well in cryogenic conditions, making it ideal for shipbuilding, storage tanks, and offshore applications.
6 Series Aluminium
While still corrosion resistant, 6xxx alloys have slightly lower resistance than 5xxx series due to the presence of silicon and copper. However, with proper anodizing or surface treatments, 6xxx alloys achieve excellent durability for architectural and automotive uses.
They are also preferred for visible applications because they offer superior surface finish and anodizing response.
6. Weldability and Fabrication
5 Series Aluminium
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Excellent weldability with minimal loss of strength.
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Commonly welded using TIG or MIG processes.
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No need for post-weld heat treatment.
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Suitable for large welded structures like ship hulls and pressure vessels.
6 Series Aluminium
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Good weldability, though heat from welding may slightly reduce strength in the heat-affected zone.
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Post-weld heat treatment can restore mechanical strength.
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Preferred for structural frames, pipelines, and extrusions that require precise assembly.
Both series perform well in fabrication, but 5xxx is better for large welded assemblies, while 6xxx is preferred for machined or precision-engineered parts.
7. Formability and Machinability
Formability
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5 Series: Excellent formability and deep drawing capability, ideal for complex shapes and sheet metal fabrication.
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6 Series: Good formability, but less ductile; best suited for extrusions and profiles.
Machinability
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5 Series: Moderate machinability; tends to be softer and can produce built-up edges during cutting.
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6 Series: Excellent machinability; widely used in CNC machining for precision parts and molds.
Thus, for sheet forming, the 5 series is more adaptable, while for machining and extrusion, the 6 series excels.
8. Heat Treatment and Processing
5 Series (Non-Heat-Treatable)
Cannot be strengthened by heat treatment; properties are improved through mechanical processing. Annealing at 345°C can restore ductility after cold work.
6 Series (Heat-Treatable)
Responds strongly to heat treatment. Typical T6 treatment involves:
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Solution Heat Treatment at 530°C.
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Quenching to retain supersaturated solid solution.
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Artificial Aging at 160°C to precipitate Mg₂Si particles.
This process gives 6xxx alloys like 6061-T6 and 6082-T6 their high strength.
9. Weight and Density Comparison
Both 5xxx and 6xxx aluminium alloys have very similar densities—around 2.66–2.70 g/cm³, which is one-third the weight of steel. The weight difference is negligible, but 5xxx alloys are slightly lighter due to lower silicon and copper content.
This makes both series ideal for lightweight structural applications, where minimizing weight without sacrificing strength is critical.
10. Surface Finish and Aesthetic Properties
One of the main advantages of 6xxx aluminium over 5xxx is its superior surface finish after extrusion or anodizing.
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6xxx alloys (especially 6063) can produce mirror-like finishes for architectural use.
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5xxx alloys are typically used in industrial or structural applications where appearance is less critical.
Therefore, the 6 series dominates in decorative and visible structures such as window frames, automotive trims, and aerospace panels.
11. Cost Comparison
In general, 6 series aluminium is slightly more expensive due to the complex heat treatment and alloying process. However, it provides greater versatility and machinability for advanced components.
5 series aluminium remains more cost-effective for large structures requiring corrosion resistance rather than intricate machining.
12. Typical Applications
Applications of 5 Series Aluminium
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Marine and Shipbuilding: Hulls, decks, and superstructures (5083, 5A06).
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Transportation: Truck bodies, fuel tanks, and pressure vessels.
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Storage Tanks: LNG and cryogenic vessels due to low-temperature toughness.
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Architectural Structures: Bridges and exterior panels requiring corrosion protection.
Applications of 6 Series Aluminium
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Automotive: Body panels, chassis components, and wheels (6061, 6082).
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Construction: Doors, windows, curtain walls, and railings (6063).
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Aerospace: Structural frames, fittings, and landing gear components.
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Machinery and Electronics: Precision parts, heat sinks, and extruded profiles.
In summary:
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5xxx = corrosion-resistant and weldable.
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6xxx = heat-treatable and highly machinable.
13. Example Alloy Comparison
| Alloy | Series | Main Element | Temper | Key Features | Typical Use |
|---|---|---|---|---|---|
| 5052 | 5xxx | Mg | H32 | Excellent corrosion resistance, weldability | Marine components, fuel tanks |
| 5083 | 5xxx | Mg | H116 | High strength, seawater resistance | Ship hulls, LNG tanks |
| 6061 | 6xxx | Mg + Si | T6 | Balanced strength, machinability | Automotive parts, frames |
| 6063 | 6xxx | Mg + Si | T5 | Smooth surface finish, extrusion-friendly | Architectural profiles |
| 6082 | 6xxx | Mg + Si | T6 | High strength, good fatigue resistance | Structural components |
14. Choosing Between 5 Series and 6 Series Aluminium
When selecting the right alloy for your project, consider these factors:
| Requirement | Recommended Series |
|---|---|
| High corrosion resistance | 5 Series |
| Structural strength and rigidity | 6 Series |
| Marine or chemical environment | 5 Series |
| High machinability and finish | 6 Series |
| Large welded components | 5 Series |
| Extruded profiles and architectural use | 6 Series |
In short:
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Choose 5xxx when corrosion resistance and weldability are priorities.
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Choose 6xxx when strength, machinability, and heat-treatable properties are more important.
15. Environmental Sustainability
Both 5xxx and 6xxx series aluminium alloys are 100% recyclable without performance loss. Recycling requires only about 5% of the energy used in primary production, reducing emissions and costs. This makes both alloys environmentally friendly choices for modern industries committed to sustainability.
SASAALUMINUM continues to promote eco-friendly aluminium solutions through recycling and precision processing technologies for the automotive, marine, and architectural markets.
16. Future Trends
The demand for both 5 and 6 series aluminium alloys is increasing rapidly with the growth of electric vehicles, renewable energy systems, and lightweight construction.
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5xxx alloys will continue to dominate shipbuilding, LNG storage, and corrosion-critical industries.
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6xxx alloys will expand further in automotive, aerospace, and energy-efficient building systems where extrusion versatility is key.
Ongoing research focuses on improving alloy purity, fatigue resistance, and surface treatment technologies for both series.
17. Conclusion
So, what is the difference between 5 series and 6 series aluminium?
The primary difference lies in their composition and strengthening methods.
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5 series aluminium (Al-Mg) is non-heat-treatable, strengthened by cold working, and offers excellent corrosion resistance and weldability—perfect for marine and chemical applications.
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6 series aluminium (Al-Mg-Si) is heat-treatable, providing higher strength, better machinability, and smoother finishes—ideal for architectural, automotive, and aerospace components.
Both alloy families deliver lightweight, durable, and cost-effective solutions across industries, ensuring aluminium remains one of the most valuable materials in modern engineering.
For companies seeking reliable, certified aluminium solutions, SASAALUMINUM supplies a full range of 5xxx and 6xxx series products with professional support, ensuring consistent quality and global delivery performance.
Post time: Oct-27-2025