What Do the Alloy Numbers on Aluminium Extrusions Mean?
The alloy designation on an aluminium extrusion tells you what the material is made of and how it will perform. For facade applications, the three alloys you will encounter most often are 6060, 6063, and 6005A. They are all part of the 6000 series - aluminium-magnesium-silicon alloys - which means they share a family of characteristics: good extrudability, reasonable strength, excellent corrosion resistance, and suitability for anodising and powder coating. The differences between them are in the detail, and those details matter for facade design and specification.
Understanding what each alloy offers - and why a particular alloy is selected for a particular component - helps specifiers, engineers, and installers make better decisions. It also helps explain why a cladding panel and the structural bracket holding it to the building are not made from the same material.
What Is 6060 Aluminium?
6060 is the softest of the three alloys discussed here. It has lower silicon and magnesium content than 6063 or 6005A, which gives it excellent extrudability - meaning it flows easily through extrusion dies and can form complex, thin-walled profiles with tight tolerances and smooth surface finish.
In the T5 temper (air-cooled after extrusion, then artificially aged), 6060 has a typical tensile strength of around 160-180 MPa and yield strength of around 120-140 MPa. These are modest numbers compared to structural alloys, but they are more than adequate for cladding panels and non-structural facade components where wind load resistance is achieved through profile geometry rather than raw material strength.
Where it is used: Cladding panels, decorative trims, battens, louvres, and non-structural facade elements. 6060-T5 is the standard alloy for interloQ interlocking rainscreen panels and conneQt aluminium battens.
Key advantages: Superior surface finish after extrusion, excellent response to anodising and powder coating, ability to form complex profiles with thin walls, lower extrusion pressure (which allows more intricate die designs).
What Is 6063 Aluminium?
6063 is closely related to 6060 and is sometimes used interchangeably in facade specifications. It has slightly higher silicon and magnesium content, which gives it marginally higher strength while retaining good extrudability and surface finish.
In the T5 temper, 6063 typically achieves tensile strength of around 175-190 MPa and yield strength of around 130-150 MPa. In the T6 temper (solution heat-treated and artificially aged), these values increase to approximately 205-245 MPa tensile and 170-215 MPa yield.
The practical difference between 6060-T5 and 6063-T5 in facade applications is small. Both are suitable for cladding panels and non-structural components. The choice between them often comes down to supply chain considerations, regional manufacturing preferences, and the specific extrusion die requirements rather than a meaningful performance difference on the building.
Where it is used: The same applications as 6060 - cladding panels, battens, trims, and non-structural members. 6063 is more common in North American and some Asian supply chains, while 6060 is more prevalent in European and Australian extrusion.
Key advantages: Slightly higher strength than 6060 in the same temper, excellent anodising response, widely available globally.
What Is 6005A Aluminium?
6005A is a step up in strength from 6060 and 6063. It has higher silicon content and additional manganese, which increases its mechanical properties while still allowing it to be extruded - though with more difficulty than the softer alloys.
In the T6 temper, 6005A achieves tensile strength of approximately 260-290 MPa and yield strength of around 215-255 MPa. This is a significant increase over 6060-T5 or 6063-T5 and places 6005A in the range suitable for structural applications.
Where it is used: Structural mullions, transoms, brackets, and load-bearing members in curtain wall and facade support systems. In the V&G product range, 6005A-T6 is specified for structural members in the 165CW unitised curtain wall system - the components that carry wind loads and dead loads back to the building structure.
Key advantages: Higher strength-to-weight ratio, suitable for structural calculations to AS/NZS 1664 (aluminium structures), good weldability compared to other structural alloys.
Trade-offs: Harder to extrude than 6060/6063, which limits profile complexity. Surface finish after extrusion is generally not as smooth, though this is rarely a concern for structural members that are concealed behind cladding panels or within the curtain wall cavity.
What Does the Temper Designation Mean?
The letter-number suffix after the alloy number indicates the temper - the thermal and mechanical processing the aluminium has undergone after extrusion.
T5 means the extrusion was cooled from the extrusion temperature (typically by air or fan), then artificially aged (heated to a specific temperature for a specific time to develop strength). T5 produces moderate strength and is the standard temper for non-structural facade components.
T6 means the extrusion was solution heat-treated (heated to a higher temperature to dissolve alloying elements into solution), quenched (rapidly cooled, usually with water), and then artificially aged. T6 produces higher strength than T5 and is specified where structural performance is required.
The choice between T5 and T6 is not arbitrary. T6 processing adds cost and is specified only where the application demands higher mechanical properties. For a cladding panel that resists wind load through its profile geometry and fixing pattern, T5 is appropriate. For a curtain wall mullion that carries wind load in bending over a multi-storey span, T6 is necessary.
Why Does the Alloy Choice Matter for Facades?
The alloy and temper combination determines three things that directly affect facade performance.
Structural adequacy. Facade engineers calculate wind load resistance, dead load support, and thermal movement based on the mechanical properties of the specific alloy and temper. Using the wrong alloy in a structural calculation - or assuming properties that do not match the supplied material - creates compliance risk.
Formability and profile design. Softer alloys allow more complex extrusion profiles, which is why cladding panels with interlocking joints, concealed fixings, and thin walls are typically 6060 or 6063. The profile does the engineering work, and the alloy enables the profile.
Surface finish and coating performance. Alloys with lower alloying element content produce cleaner surface finishes after extrusion, which directly affects the quality of anodised and powder-coated finishes. This is why visible facade elements favour 6060/6063 while concealed structural members use 6005A.
How Is This Reflected in V&G Products?
The V&G product range uses each alloy where its properties are best suited.
interloQ interlocking rainscreen panels are extruded from 6060/6063 in T5 temper. The complex interlocking profile requires excellent extrudability, and the visible face requires a surface finish that responds well to powder coating, anodising, and woodgrain finishes.
conneQt aluminium battens and adaptors use the same 6060/6063-T5 specification. These are non-structural components designed for visual performance and compatibility with interloQ and element13 installations.
165CW unitised curtain wall uses a combination: 6060-T5 for secondary framing and non-structural components, 6060-T6 for primary framing, and 6005A-T6 for structural members including mullions and load-bearing brackets. This reflects the different performance requirements within a single system - the structural members carry load, the framing members provide support and weather performance, and the finishing components provide the visual result.
Specifiers and engineers should reference the specific alloy and temper when writing facade specifications. “Aluminium” is not sufficient. The alloy, temper, and relevant standard (AS/NZS 1866 for extrusion tolerances, AS/NZS 1664 for structural design) should be called up explicitly.
Related Reading
- interloQ Specification Guide
- 165CW Curtain Wall System: Australian-Designed Specification Guide
- Wind Load Design for Aluminium Facade Systems
- Subframe Design for Aluminium Rainscreen Cladding
Last updated: 4 April 2026