Alloy Design and Temper Selection
6063 is the classic Al-Mg-Si extrusion alloy. Low copper and iron content give it a bright, uniform surface after anodizing, while a balanced magnesium to silicon ratio supports fast extrusion of solid and hollow sections, including square rod. National standard square rod is supplied in O, T4, T5, T6 and T66 tempers, and T5 and T6 dominate machined and anodized parts because no further heat treatment is needed after extrusion.
The relevant standard chain is GB/T 3190 for chemical composition, GB/T 3191 for extruded bars and rods, GB/T 6892 for general engineering extruded profiles and GB/T 5237.1 for architectural profiles. EN 573-3, EN 755-2, the ISO 6362 series and ASTM B221 describe equivalent European and international requirements, so a square rod ordered to a national standard can be matched to an overseas drawing without changing the material.
National Standard Composition Limits
6063 is deliberately lean in alloying additions. Magnesium and silicon form the strengthening phase Mg2Si, while copper and manganese are kept at trace level to protect conductivity and surface appearance.
| Element | Content, wt% |
|---|---|
| Silicon | 0.20 - 0.60 |
| Iron | 0.35 max |
| Copper | 0.10 max |
| Manganese | 0.10 max |
| Magnesium | 0.45 - 0.90 |
| Chromium | 0.10 max |
| Zinc | 0.10 max |
| Titanium | 0.10 max |
| Other elements, each / total | 0.05 max / 0.15 max |
| Aluminium | Balance |
Because zinc and titanium are held low, the anodic oxide layer formed in sulphuric acid electrolyte stays clear and takes dye evenly, which is why window, door and display profiles are produced from this alloy in very large volumes.
Mechanical and Physical Properties by Temper
Temper designations follow ANSI H35.1. T5 is cooled from the extrusion press and artificially aged, while T6 is solution heat treated and then artificially aged to a higher strength level.
| Property | 6063-T5 | 6063-T6 |
|---|---|---|
| Tensile strength | 186 MPa | 241 MPa |
| Yield strength, 0.2% offset | 145 MPa | 214 MPa |
| Elongation | About 12% | About 12% |
| Brinell hardness | About 60 HB | About 73 HB |
| Electrical conductivity | About 55% IACS | About 53% IACS |
| Physical property | Typical value |
|---|---|
| Density | 2.70 g/cm3 |
| Elastic modulus | 68.9 GPa |
| Poisson ratio | 0.33 |
| Thermal conductivity | About 200 W/m-K |
| Thermal expansion, 20-100 C | 23.4 um/m-K |
| Melting range | 585 - 650 C |
Strength is well below 6061-T6 in the same temper, but ductility, extrusion quality and surface finish are better. For parts that are anodized, bent and assembled rather than heavily loaded, that trade is usually the right one.
Dimensions, Tolerances and Fabrication
Square rod is extruded from roughly 6 mm to 100 mm side and supplied in straight lengths, most commonly 3 m to 6 m
Cut length tolerance is normally positive only, allowing for trimming at the fabricator
Dimensional tolerance on the side follows the product standard, with straightness held to about 2 mm per metre
Soft tempers such as O and T4 bend and form easily, while T5 and T6 are best machined, drilled and tapped
Machining in T6 produces a cleaner cut edge than T5, which matters for visible anodized faces
Welding is straightforward with common arc processes, and strength is recovered locally in the heat affected zone by natural ageing
Anodizing to ISO 7599 or a national architectural specification at 10 - 25 um gives the normal protective and decorative finish
Powder coating at 60 - 80 um is specified where colour matching across a large project matters more than metallic appearance
Applications and Finishing Practice
Architectural profiles, window and door frames, curtain wall mullions and shopfront sections
Heat sink bases, LED light housings and electronic enclosure frames
Irrigation pipes, greenhouse framing and agricultural structures
Vehicle body sections, bus and rail interior trim, ladders and step rails
Furniture frames, fencing, railing and general fabrication stock
Electrical and control cabinets where moderate conductivity and light weight are both useful
Because the alloy extrudes to tight profile detail, square rod and matching sections can be designed so that components locate on each other without extra machining. Anodizing adds negligible weight, keeps thermal performance intact and protects the surface in humid and industrial atmospheres, while the clear oxide keeps the metallic appearance expected in visible architectural work.
Frequently Asked Questions
Q: What does the national standard cover for 6063 square rod?
Composition is set by GB/T 3190, extruded bar and rod requirements by GB/T 3191, and tolerances and surface condition by the product standard referenced on the drawing, with EN and ISO equivalents available for export orders.
Q: Should T5 or T6 be specified?
T5 suits cost-sensitive profiles with moderate loads, while T6 gives about 30% more yield strength and is chosen for machined or highly stressed parts.
Q: Is 6063 as strong as 6061?
No. 6063-T6 reaches 214 MPa yield against 276 MPa for 6061-T6, but 6063 extrudes and anodizes more easily.
Q: Can square rod be anodized to a specific colour?
Yes. The low copper content allows consistent dyeing, and finishes are normally specified to a national architectural standard or to ISO 7599.
Q: How is square rod supplied for machining?
It is supplied cut to length with saw cut ends, and T6 temper is preferred where threads, slots and tight bores are machined after delivery.
Q: Does the alloy resist corrosion outdoors?
It performs well in rural and urban atmospheres, and anodizing or powder coating is recommended for coastal and heavily polluted sites.