Aluminum 3B21
GB 3B21
A Chinese Al-Mn wrought alloy with slightly higher Mn/Mg content than 3A21, giving improved strength while retaining good corrosion resistance and formability; used mainly in architectural and general sheet/plate stock in the Chinese domestic market.
Reference datasheet — 3B21 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the H14 condition
3B21 tempers and conditions
3B21 is supplied in 16 conditions, soft to hard. H14 is the default FabDigit quotes; the values on this page are for it.
Compare all 16 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Pick for deep drawing, spinning, tight bends and any severe cold forming. | 52 | 130 | 26 | 30 HB | 42 % IACS |
Strain hardened from hot working only | Standard temper for thicker hot-rolled plate that will be welded or machined rather than cold formed. | 65 | 145 | 18 | 33 HB | 42 % IACS |
As fabricated | Mill-supplied hot-worked/extruded stock with no guaranteed mechanicals; buy only if you will heat treat, form or test yourself. | 65 | 140 | 18 | 30 HB | 42 % IACS |
Strain hardened and partially annealed, quarter hard | Same strength class as H12 but with restored ductility — use for tube bending and formed profiles. | 115 | 150 | 15 | 37 HB | 41 % IACS |
Strain hardened and stabilized, quarter hard | Stabilized temper (thermal treatment after rolling) for the Mg-bearing chemistry; use when long-term property stability matters. | 120 | 155 | 14 | 38 HB | 41 % IACS |
Strain hardened, quarter hard | Light work hardening when a little extra stiffness is needed but bending is still frequent. | 125 | 155 | 12 | 38 HB | 41 % IACS |
Strain hardened and partially annealed, half hard | Most common temper for formed architectural sheet and roll-formed panels needing H14 strength with better bend behaviour. | 140 | 170 | 10 | 43 HB | 40 % IACS |
Strain hardened and stabilized, half hard | Stabilized mid-strength sheet/plate for welded tanks and vessels held at mildly elevated temperature. | 145 | 175 | 10 | 44 HB | 40 % IACS |
H14Default Strain hardened, half hard | The default stocked sheet/coil temper: best balance of panel stiffness and roll-forming/bending ability. | 150 | 175 | 8 | 44 HB | 40 % IACS |
Strain hardened and partially annealed, three-quarter hard | High-strength strip that must still take a modest bend, e.g. clip and bracket stampings. | 165 | 195 | 6 | 49 HB | 40 % IACS |
Strain hardened and stabilized, three-quarter hard | Stabilized high-strength strip for lightly formed, dimensionally stable parts. | 170 | 200 | 6 | 50 HB | 40 % IACS |
Strain hardened, three-quarter hard | Use where flat strength and dent resistance dominate and only mild forming is required. | 175 | 200 | 5 | 50 HB | 40 % IACS |
Strain hardened and partially annealed, full hard | Full-hard strip with slightly better ductility than H18; niche stamping/spring-clip use. | 190 | 220 | 4 | 55 HB | 39.5 % IACS |
Strain hardened and stabilized, full hard | Highest stabilized strength; flat parts only, essentially no forming reserve. | 195 | 225 | 4 | 56 HB | 39.5 % IACS |
Strain hardened, full hard | Maximum strain-hardened strength for flat parts, shims and stamped blanks; bending must be generous-radius. | 200 | 225 | 4 | 56 HB | 40 % IACS |
Strain hardened, extra hard | Only for thin strip and foil where maximum as-rolled hardness is wanted; essentially non-formable. | 220 | 245 | 2 | 60 HB | 39 % IACS |
What is 3B21?
A Chinese Al-Mn wrought alloy with slightly higher Mn/Mg content than 3A21, giving improved strength while retaining good corrosion resistance and formability; used mainly in architectural and general sheet/plate stock in the Chinese domestic market. 3B21 has a density of 2.73 g/cm³ (0.0986 lb/in³), heavier than 61% of aluminum grades. It melts at 643°C (1,189 °F). 3B21 has a yield strength of 150 MPa (21.8 ksi) and a tensile strength of 175 MPa (25.4 ksi) — weaker than 65% of aluminum grades. Elongation at break is 8% and the elastic modulus is 69 GPa (10 Msi).
What is 3B21 used for?
- architectural cladding
- roofing and gutter sheet
- general fabrication plate
- corrosion-resistant panels
Advantages
- Forms and bends easily — 75/100, better than 86% of aluminum grades
- Readily welded — 88/100, better than 85% of aluminum grades
- Good corrosion resistance — 70/100, better than 79% of aluminum grades
Limitations
- Difficult to machine — 32/100, worse than 89% of aluminum grades
3B21 properties
Typical room-temperature values for 3B21-H14; bars are the position among aluminum grades.
Physical3
3B21 has a density of 2.73 g/cm³ (0.0986 lb/in³), heavier than 61% of aluminum grades. It melts at 643°C (1,189 °F).
Mechanical10
3B21 has a yield strength of 150 MPa (21.8 ksi) and a tensile strength of 175 MPa (25.4 ksi) — weaker than 65% of aluminum grades. Elongation at break is 8% and the elastic modulus is 69 GPa (10 Msi).
Thermal6
3B21 is rated for continuous service to 150°C (302 °F). It conducts heat at 158 W/m·K (91.3 BTU/hr·ft·°F), better than 74% of aluminum grades. Thermal expansion is 23.2 µm/m·K (12.9 µin/in·°F).
Electrical3
3B21 conducts electricity at 40 % IACS, better than 72% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is very good (70/100), better than 79% of aluminum grades.
Sustainability4
Producing a kilogram of 3B21 takes about 200 MJ of energy and emits 12.5 kg of CO₂ — less than 60% of aluminum grades. Typical recycled content is 35%.
Manufacturability7
3B21's machinability is poor (32/100, worse than 89% of aluminum grades); weldability excellent (88/100); formability very good (75/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the aluminum family
Yield strength against density for every aluminum grade FabDigit runs. 3B21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 3B21
Is 3B21 easy to machine?
Soft and gummy: use sharp polished high-rake carbide, high speed, low feed and flood coolant/lubricant to avoid built-up edge; harder H16–H18 tempers give cleaner chips.
Can 3B21 be welded?
Excellent with GTAW/GMAW using ER4043 or ER5356 filler, and readily resistance-spot welded; the HAZ reverts toward O temper, so design joints for annealed strength.
Can 3B21 be formed, bent or molded?
Very good cold formability — O/H22/H24 tempers deep draw, roll-form and bend tightly; interstage anneal at 340–400 °C if severe multi-stage drawing is needed.
3B21 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Siimpurity limit; Si+Fe often jointly capped | ≤ 0.5 | 0.2 |
| Feimpurity limit | ≤ 0.5 | 0.3 |
| Cukept low for corrosion resistance | ≤ 0.1 | 0.03 |
| Mnprincipal strengthening/dispersoid element | 1 – 1.6 | 1.3 |
| Mgsmall deliberate addition — main difference vs 3A21 | 0.1 – 0.6 | 0.35 |
| Zn | ≤ 0.1 | |
| Tigrain refiner residual | ≤ 0.15 | 0.03 |
| Others (each)total others ≤ 0.15 | ≤ 0.05 | |
| Alremainder; confirm exact limits against the current GB/T 3190 edition and the mill certificate | balance |
What surface finishes work on 3B21?
Takes clear/protective sulphuric anodize, chromate/chrome-free conversion coating, and coil paint/PVDF well; bright decorative anodizing is only fair because Mn dispersoids grey the film.
Surface treatments FabDigit runs on aluminum parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
How much does 3B21 cost?
3B21 is a standard-cost aluminum ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
3B21 — frequently asked
What is 3B21 used for?
3B21 is typically used for architectural cladding, roofing and gutter sheet, general fabrication plate and corrosion-resistant panels. In short: stronger than 3A21 sheet; formable architectural alloy; weldable, non-heat-treatable.
What is the yield strength of 3B21?
3B21 has a typical yield strength of 150 MPa (21.8 ksi) and a tensile strength of 175 MPa (25.4 ksi) — weaker than 65% of aluminum grades. Strength varies by condition: see the 16 listed tempers.
Is 3B21 easy to machine?
Not especially — machinability is rated poor (32/100, worse than 89% of aluminum grades). Soft and gummy: use sharp polished high-rake carbide, high speed, low feed and flood coolant/lubricant to avoid built-up edge; harder H16–H18 tempers give cleaner chips.
Can 3B21 be welded?
Yes — weldability is rated excellent (88/100). Excellent with GTAW/GMAW using ER4043 or ER5356 filler, and readily resistance-spot welded; the HAZ reverts toward O temper, so design joints for annealed strength.
What surface finishes work on 3B21?
Takes clear/protective sulphuric anodize, chromate/chrome-free conversion coating, and coil paint/PVDF well; bright decorative anodizing is only fair because Mn dispersoids grey the film.
Can 3B21 be formed, bent or molded?
Very good cold formability — O/H22/H24 tempers deep draw, roll-form and bend tightly; interstage anneal at 340–400 °C if severe multi-stage drawing is needed.
What is the maximum service temperature of 3B21?
3B21 is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 3B21-H14 and 3B21-O?
H14 is the default condition — the default stocked sheet/coil temper: best balance of panel stiffness and roll-forming/bending ability. O: pick for deep drawing, spinning, tight bends and any severe cold forming. Yield strength is 150 MPa in H14 versus 52 MPa in O.
How much does 3B21 cost?
3B21 is a standard-cost aluminum ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys (3000 series Al-Mn data) — ASM International (1990)
- ASM Handbook Vol.13B — Corrosion: Materials (aluminium alloys) — ASM International (2005)
- Aluminum Association Teal Sheets — Alloy and Temper Designations — The Aluminum Association (2018)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.