Aluminum bar 6063-T5 and 6061-T6 are the two dominant alloys for architectural profiles, frames and structural extrusions. This guide compares the two alloys on strength, surface finish, extrudability and cost, with selection guidance for window frames, curtain walls, railings and structural components.
Aluminum bar and profile is one of the largest categories in architectural metalwork, with two alloys dominating extrusion orders: 6063 for visible architectural profiles where surface finish and complex shapes matter, and 6061 for structural applications where higher strength is required. The call between them is one of the most common specification questions on aluminum profile orders, and getting it wrong leads to either overpaying for strength that is not needed, or under-specifying and seeing profiles deflect or fail under load.
6063-T5 vs 6061-T6: Strength Numbers
6063-T5 aluminum has minimum yield strength of about 18,000 psi (125 MPa) and ultimate tensile of about 22,000 psi (150 MPa). 6061-T6 aluminum has minimum yield of 35,000 psi (240 MPa) and ultimate tensile of 42,000 psi (290 MPa), roughly twice the strength of 6063-T5. The strength difference is significant enough that 6061 is the required alloy for structural members carrying meaningful load, while 6063 is the standard for visible architectural profiles where the load is small and the surface finish matters most.
When 6063-T5 Is the Right Specification
6063-T5 aluminum is the standard specification for most architectural profiles: window frames, door frames, curtain wall mullions and transoms, railing posts and rails, sun-shading louvres, light fixtures, and display systems. The alloy extrudes easily into complex thin-walled shapes, accepts anodizing and powder coating to a beautiful finish, and has the smoothest as-extruded surface of any common aluminum alloy. For visible architectural work where the profile is decorative and load is modest, 6063-T5 is the right call.
When 6061-T6 Is the Necessary Upgrade
6061-T6 aluminum is the right specification for structural profiles carrying significant load: structural mullions in high-rise curtain walls, machine frames, truck and trailer structural members, ladders, platforms, walkways, and any profile that will see mechanical loading in service. 6061 also machines better than 6063, so it is the standard for machined bar and billet stock used in brackets, fittings, and structural connectors. The trade-off is harder extrusion (the higher alloy content makes the billet stiffer and harder to push through complex dies) and a slightly rougher as-extruded surface that may need more finishing.
Surface Finish, Anodizing and Welding
For anodized architectural profiles, 6063 gives a brighter, more uniform anodized finish because of its lower alloy content and cleaner microstructure. 6061 anodizes to a slightly darker, less uniform tone, which is acceptable for structural or hidden applications but is rarely chosen for visible premium architecture. Both alloys weld by TIG and MIG with 4043 or 5356 filler, but the heat of welding softens the T5 or T6 temper in the heat-affected zone, so welded assemblies are often re-heat-treated or designed with the softened zone in mind.
What to Specify on the Aluminum Bar RFQ
State the alloy and temper (6063-T5 or 6061-T6), the bar profile (round, square, rectangular, hex, or custom extrusion), the dimensions, the tolerance (per ASTM B221 or EN 755), and the surface finish (mill, anodized, powder coated). For architectural profiles, default to 6063-T5 with anodizing or powder coating per the project specification. For structural members, default to 6061-T6. Always confirm the mill supplies the test report per EN 10204 3.1 with actual yield and tensile strength, since the T5 vs T6 distinction depends on proper heat treatment.
Related Resources from Baobin Steel
- Aluminum bar catalog – 6063, 6061 and other alloys
- Aluminum products overview – grades and tempers
- Request a quote – send your profile drawing for aluminum bar pricing