Overview of 6061 and 6063 Aluminum Alloy
6061 aluminum is the general-purpose structural 6xxx alloy: higher magnesium (0.80–1.20%) and silicon (0.40–0.80%) plus a small copper addition (0.15–0.40%). The copper raises strength but slightly reduces salt-water corrosion resistance. It is the default grade for load-bearing frames, machined parts and welded structures.
6063 aluminum is the "architectural" 6xxx alloy: leaner composition (Si 0.20–0.60%, Mg 0.45–0.90%, copper ≤0.10%). The lower alloy content makes it flow better in the extrusion press and produces a smoother, brighter surface after anodizing - at the cost of lower strength. It is the grade behind window frames, curtain walls, handrails and heat sinks.
Chemical Composition of 6061 and 6063 Aluminum Bars
| Element (wt %) | 6061 | 6063 |
|---|---|---|
| Silicon (Si) | 0.40–0.80 | 0.20–0.60 |
| Iron (Fe), max | 0.70 | 0.35 |
| Copper (Cu) | 0.15–0.40 | ≤0.10 |
| Manganese (Mn), max | 0.15 | 0.10 |
| Magnesium (Mg) | 0.80–1.20 | 0.45–0.90 |
| Chromium (Cr) | 0.04–0.35 | ≤0.10 |
| Zinc (Zn), max | 0.25 | 0.10 |
| Titanium (Ti), max | 0.15 | 0.10 |
| Aluminum (Al) | remainder | remainder |
The extra copper and higher Mg/Si in 6061 are what lift its strength; the copper-free, leaner 6063 is what gives it better extrusion fluidity and a cleaner anodized finish.
Mechanical Properties of 6061 and 6063 Aluminum Bars
| Property (typical) | 6061-T6 | 6063-T6 | 6063-T5 |
|---|---|---|---|
| Tensile strength (MPa) | 310 | 240 | 185 |
| Yield strength, 0.2% (MPa) | 276 | 214 | 145 |
| Elongation at break (%) | 12 | 12 | 12 |
| Brinell hardness (HB) | 95 | 73 | ~60 (typical) |
6061-T6 is roughly 30% stronger in tensile and yield than 6063-T6, and about 65% stronger than 6063-T5. The trade-off is that 6063's lower strength is paired with better formability and surface quality. Values are typical for extruded bar; cold-finished (drawn) 6061 per ASTM B211 reaches the same strength band but with tighter dimensional control.
Physical and Thermal Properties of 6061 and 6063 Aluminum
| Property | 6061 | 6063 |
|---|---|---|
| Density (g/cm³) | 2.70 | 2.70 |
| Modulus of elasticity (GPa) | 68.9 | 68.9 |
| Thermal conductivity (W/m·K) | ~170 | ~200–218 |
| Electrical conductivity (% IACS) | ~43 | ~50 |
| Coefficient of thermal expansion (µm/m·°C) | ~23.6 | ~23.4 |
6063's higher thermal and electrical conductivity makes it the better fit for heat sinks and bus-bar/electrical trim, while 6061's higher strength usually outweighs the small conductivity gap in structural roles.
Extrusion and Dimensional Tolerances of 6061 and 6063 Aluminum Bars
Both grades are supplied as extruded bar (per ANSI H35.2(M) §10) or cold-finished drawn bar (per §9). Note that for extruded round bar the standard allows a slightly tighter band for the "other alloy" group (which includes 6061) than for 6063:
| Diameter (mm) | 6061 extruded, ± (mm) | 6063 extruded, ± (mm) |
|---|---|---|
| 12.50–25.00 | 0.23 | 0.36 |
| 25.00–50.00 | 0.30 | 0.46 |
| 50.00–100.00 | 0.61 | 0.91 |
Cold-finished (drawn) bar is much tighter - for 12.50–25.00 mm diameter, ±0.06 mm; for 40.00–50.00 mm, ±0.15 mm. Length tolerance (extruded, up to 5000 mm) is +4 / +7 mm, and straightness is 1 mm/m for heat-treated bar. Buyer-specified single-side limits always override the standard bilateral values.
Machinability of 6061 and 6063 Aluminum Bars
On the standard aluminum machinability index (2011 = 100), 6061-T6 rates about 50 and 6063 about 30 (indicative). 6061 cuts cleanly with sharp carbide tooling, breaks chips well and holds dimension after machining - it is the grade to pick when the bar needs threads, bores, pockets or tight-tolerance features. 6063 is acceptable to machine but is "gummier," tends to produce longer stringy chips and needs more careful speeds/feeds and coolant.
Weldability of 6061 and 6063 Aluminum Bars
Both weld readily by TIG (GTAW) and MIG (GMAW) using ER4043 (general purpose) or ER5356 (higher joint strength, better anodized color match). The key data point: both lose strength in the heat-affected zone. As-welded 6061-T6 drops toward its naturally-aged (T4) level - yield roughly 150 MPa instead of 276 MPa - and post-weld artificial aging can recover much of the loss. 6063 has lower as-welded strength but also lower hot-cracking sensitivity, so it is common in lighter architectural welded assemblies rather than heavy load-bearing welded frames.
Anodizing and Surface Finish of 6061 and 6063 Aluminum Bars
6063 develops a clearer, more uniform anodized layer - often up to 25 µm - with fewer surface defects (die lines, orange peel) because of its higher purity and lower alloying content. That is why clear, black, bronze and champagne anodized architectural members are almost always 6063. 6061 anodizes acceptably but the layer can show more graininess; for consistent color on structural parts it is more often powder-coated or painted. Both accept mechanical finishing (brushing, polishing) without difficulty.
Corrosion Resistance of 6061 and 6063 Aluminum Bars
Both alloys have excellent atmospheric corrosion resistance thanks to their protective oxide film. 6063 rates marginally better in aggressive outdoor and near-marine exposure because its lower copper content reduces the risk of intergranular attack; 6061 is still rated "good" and is widely used in marine hardware. Neither requires coating for indoor use, though anodizing or powder coating extends service life in splash zones.
Applications of 6061 and 6063 Aluminum Bars
6061 aluminum bar:
Structural frames, machine bases, jigs and fixtures
Load-bearing brackets, supports and gussets
Marine hardware and boat fittings needing strength
Automotive and truck body / chassis components
CNC-machined parts with threads, bores or precise pockets
Welded structural assemblies where HAZ strength matters
6063 aluminum bar:
Architectural sections: window/door frames, curtain-wall mullions
Handrails, trims and decorative visible members
Heat sinks and thermal-management bars (higher conductivity)
Electrical bus-bar trim and conduits
Complex thin-wall extrusions where appearance governs
How to Choose Between 6061 and 6063 Aluminum Bars
Use the decision below, matched to what actually governs your part:
| If your priority is… | Specify | Why |
|---|---|---|
| Load-bearing strength / high stress | 6061-T6 | 310 MPa tensile, 276 MPa yield - ~30% above 6063-T6 |
| Heavy CNC machining, threads, bores | 6061-T6 | Machinability index ~50 vs ~30; cleaner chips |
| Welded structural frame | 6061-T6 | Higher HAZ and post-weld strength |
| Visible / architectural member | 6063-T5/T6 | Brighter, uniform anodized finish |
| Complex thin-wall extrusion | 6063-T5 | Better extrusion fluidity, faster press speed |
| Heat sink / electrical bar | 6063-T5/T6 | Higher thermal (~210 W/m·K) and electrical (~50% IACS) conductivity |
Practical tip: confirm the temper and the tolerance band (extruded vs cold-finished) before ordering. Many "6061 vs 6063" mix-ups are actually T6-vs-T5 or extruded-vs-drawn mismatches - a 6063-T6 bar can outperform a 6061-T4 bar on strength, so match the full designation to the load case.
FAQ
Which is stronger, 6061 or 6063 aluminum bar?
6061-T6 is about 30% stronger than 6063-T6 - roughly 310 MPa tensile / 276 MPa yield versus 240 MPa tensile / 214 MPa yield. 6063-T5 is lower still at about 185 MPa tensile / 145 MPa yield.
Can 6061 and 6063 aluminum bars be welded together?
Yes. Join them with ER4043 or ER5356 filler; the joint is governed by the weaker heat-affected zone, so design for the reduced local strength.
Why is 6063 preferred for anodized architectural aluminum bars?
Its leaner, copper-free composition flows better in extrusion and yields a smoother surface that anodizes to a brighter, more uniform finish - often up to 25 µm with fewer die lines.
What is the difference between T5 and T6 tempers?
T5 is cooled from the extrusion press and artificially aged (no separate solution treatment) - moderate strength, good stability. T6 is a full solution heat treatment (~520–530°C) plus aging (~175–185°C) for peak strength.
Which alloy machines better?
6061, by a clear margin - cleaner chips, better surface finish and more consistent results in turning and milling.
Are 6061 and 6063 aluminum bars freely exportable?
Both are standard commercial 6xxx grades with no special export-control classification as bars. GNEE supplies them to more than 100 countries; confirm any end-use or buyer-country requirements at order time.
About GNEE Aluminum
GNEE Aluminum has supplied aluminum bars, plates, tubes and profiles since 2008, exporting to more than 100 countries and regions. We stock common tempers of 6061 and 6063 bars in frequent sizes, accept both small and large orders (flexible MOQ), and ship within 15–30 days. Every lot ships with an EN 10204 3.1 mill test certificate (3.2 and third-party inspection available on request), and our technical team helps match the alloy, temper and tolerance to your actual service conditions.
Contact us to specify your 6061 / 6063 aluminum bar
Need a data sheet, MTC sample, or a tolerance/price quote for a specific size and temper? Tell us the alloy, diameter/section, temper, quantity and destination - we will confirm the exact specification before production.
