Aluminum flat bar is a rectangular bar product (constant width and thickness) widely used for frames, brackets, base plates, machine components, trailers, architectural trims, and general fabrication. It’s popular because it offers a strong strength-to-weight advantage, good corrosion resistance, and easy machining/welding—depending on the alloy you choose.
This guide explains:
- how aluminum flat bar is produced,
- which standards and tempers matter,
- how to pick the right alloy,
- and what to specify on a purchase order to avoid rework.
1) What Is Aluminum Flat Bar?
Aluminum flat bar is a solid rectangular cross-section bar, usually supplied in stock lengths or cut-to-size pieces. Compared with plate, it’s often used when you need:
consistent edge geometry,
easier handling and cutting for small parts,
and predictable stock for machining or welding.
2) How Aluminum Flat Bar Is Made: Extruded vs Rolled/Cold-Finished
Most aluminum flat bar you’ll see in fabrication is produced by one of two routes:
A) Extruded flat bar (most common)
Extrusion forms the bar by pushing heated aluminum through a die. In ASTM terms, extruded aluminum bars fall under ASTM B221/B221M, which covers aluminum and aluminum-alloy extruded bars, rods, wire, profiles, and tubes.
Why extruded flat bar is popular
cost-effective production for many sizes,
good availability (especially 6061),
consistent geometry for general fabrication.
B) Rolled or cold-finished flat bar
Some bars are produced by rolling and/or cold-finishing (drawing). ASTM distinguishes this route in ASTM B211/B211M, which covers rolled or cold-finished aluminum and aluminum-alloy bar, rod, and wire.
Why cold-finished matters
Cold finishing is done at room temperature and is commonly associated with tighter tolerances and improved surface finish compared with basic extrusion.
Buyer tip: If your job needs tighter dimensional control for machining/fit-up, ask for “cold-finished” (when available) or confirm tolerance expectations explicitly—don’t assume all flat bar is the same.
3) Key Standards You’ll See on Quotes and MTRs
When purchasing aluminum flat bar, the “standard” is often what makes material acceptable for a customer or project.
ASTM B221 / B221M → extruded bars and profiles
ASTM B211 / B211M → rolled or cold-finished bars
(Your purchase order should also specify alloy + temper, which is usually more important than the standard name alone.)
4) Common Alloys for Aluminum Flat Bar (and When to Use Them)
Below is a practical “selection table” for the most common buyer scenarios:
| Alloy | Best for | Why it’s chosen | Watch-outs |
|---|---|---|---|
| 6061 (T6 / T6511) | General structural + machining | Versatile, widely available; strong and easy to fabricate | Not as formable as 5052 for tight bends |
| 6063 | Architectural + anodizing | Often preferred for a clean anodized finish; good for trim | Lower strength than 6061 in many cases |
| 5052 (H32) | Corrosion + forming | Great corrosion resistance and formability (marine-ish environments, enclosures) | Not heat-treatable like 6061 |
| 5083 / 5086 | Marine + high corrosion resistance | Stronger corrosion-focused plate alloys (availability as flat bar varies) | Supply may be less “stock” than 6061 |
| 2024 | High strength (aerospace-type) | Strength-focused | Corrosion resistance and weldability concerns; special handling |
| 7075 | Very high strength | Excellent strength | Generally poor weldability; more expensive |
If you only stock one alloy for broad industrial use, it’s usually 6061 because it’s “do-most-things” material.
5) Typical Properties: 6061-T6 Flat Bar (Reference Numbers)
6061-T6 is commonly used for flat bar. Typical published data shows about:
Yield strength: ~276 MPa (40 ksi)
Ultimate tensile strength: ~310 MPa (45 ksi)
Density: ~2.70 g/cc (0.0975 lb/in³)
These values are widely used as reference points, but always verify your exact lot with the Mill Test Report (MTR) (properties vary by product form, thickness, and temper).
6) Tempers Explained (Why “T6” Isn’t Just a Suffix)
The temper tells you how the alloy was processed, which strongly affects strength and workability.
Common tempers you’ll see for flat bar:
T6: solution heat-treated + artificially aged (high strength in heat-treatable alloys like 6061)
T651 / T6511: similar to T6 but stress-relieved (often preferred for machining stability)
O: annealed (soft, formable)
H tempers (like H32): strain-hardened/stabilized (common for 5052)
Machining note: If tight flatness and dimensional stability matter, stress-relieved tempers can reduce warping during machining (still: setup and tooling matter).
7) Sizes, Tolerances, and Straightness
Because aluminum flat bar is supplied across multiple manufacturing routes, it’s smart to request:
thickness × width × length
tolerance expectation (standard vs tighter)
straightness/flatness expectations for machining or assembly
If your customer requires formal compliance, list the governing standard:
extruded: ASTM B221/B221M
rolled/cold-finished: ASTM B211/B211M
8) Surface Finish Options
Common finishes for aluminum flat bar:
Mill finish (as-produced)
Brushed / polished (decorative)
Anodized (especially common for architectural 6063; also used on 6061)
Powder coated (color + protection)
Protective film (to reduce handling marks)
If appearance matters, specify finish requirements in writing (sample photos help).
9) Fabrication Tips: Cutting, Drilling, Welding, Bending
Cutting & drilling
Aluminum flat bar machines easily with proper tooling and chip evacuation. For repeatable cuts:
use carbide blades/end mills where appropriate,
keep the surface clean to reduce galling,
manage heat (especially on thicker sections).
Welding
Many shops weld 6061 successfully, but welding can reduce strength in the heat-affected zone (HAZ). If your design is strength-critical, coordinate:
alloy/temper choice,
weld process and filler selection,
and post-weld expectations.
Bending/forming
For tight-radius bends, 5052 is often preferred over 6061.
If you must bend 6061-T6, expect larger radii or consider alternative temper/processing.
10) How to Calculate Weight of Aluminum Flat Bar
A simple method:
Volume = thickness × width × length
Weight = volume × density
For 6061, density is commonly referenced around 0.0975 lb/in³ (2.70 g/cc).
Example:
A bar 0.25″ thick × 2″ wide × 72″ long
Volume = 0.25 × 2 × 72 = 36 in³
Weight ≈ 36 × 0.0975 = 3.51 lb
(Always treat as approximate—finishes and tolerances create slight variation.)
11) Purchase Order Checklist
When requesting a quote, include:
Product: Aluminum Flat Bar
Alloy + temper: e.g., 6061-T6 or 5052-H32
Standard: ASTM B221/B221M (extruded) or ASTM B211/B211M (rolled/cold-finished)
Size: thickness × width × length
Quantity: pcs + total weight if needed
Cut-to-size: yes/no; cutting tolerance
Surface finish: mill / brushed / anodized / coated
Documentation: MTR required, heat/lot traceability
Packaging: export packing / protective film if required
FAQs
Is aluminum flat bar the same as aluminum plate?
Not exactly. Plate is typically ordered by plate standards and thickness ranges; flat bar is supplied as bar product (often extruded or cold-finished), usually with different tolerance expectations and availability.
What’s the most common aluminum flat bar alloy?
6061 is one of the most common because it balances strength, corrosion resistance, and machinability—and it’s widely stocked.
Which standard should I specify: ASTM B221 or B211?
Choose B221/B221M for extruded flat bar.
Choose B211/B211M for rolled or cold-finished bar.
Can 6061-T6 flat bar be welded?
Yes, it’s commonly welded, but the weld zone can lose some strength. If your project is strength-critical, coordinate design allowances and WPS details.
Which alloy is best for bending?
For tighter bends and forming, many buyers choose 5052 over 6061 (better formability in typical practice).
If you’re sourcing aluminum flat bar for fabrication or resale, Steel1Stop can quote 6061, 6063, 5052 and other alloys with cut-to-size, MTR documentation, and export-ready packing. Share your required alloy/temper, standard (B221 or B211), and dimensions to get an accurate quote.
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