Reading Yield Strength, Tensile Strength and Elongation on an Aluminum Coil Datasheet.
A datasheet row for an aluminum alloy gives three numbers that matter in forming and design: tensile strength, yield strength and elongation. They mean something only when you know the alloy, the temper, the thickness, and whether the number is a requirement or a typical value.
Key takeaways
- Tensile strength is the maximum stress the specimen carries, yield strength is the stress at a specified small permanent deformation, and elongation is how far the specimen stretches before it breaks.
- Read each row by alloy, temper and thickness. Standards such as ASTM B209 publish requirements in tables organized by alloy and temper.
- A minimum requirement in a standard and a typical value on a producer datasheet are different things.
- Annealed (O) temper gives lower strength and more elongation. H tempers raise strength and lower elongation as the second digit rises.
- This post gives no numeric values. Values for a given alloy, temper and thickness belong to the standard's own tables and to your specification.
What do tensile strength, yield strength and elongation each measure?
All three come from a tension test, in which a specimen is pulled until it breaks. ASTM B557/B557M is the test method for wrought and cast aluminum- and magnesium-alloy products, and it gives information on strength and ductility under uniaxial loading.
Tensile strength is the maximum engineering stress the specimen carries, meaning the maximum load divided by the original cross-section. Yield strength is the stress at which a small, specified amount of permanent deformation is reached. Because aluminum alloys generally do not show a sharp yield point, it is reported at a defined offset on the stress-strain curve, conventionally 0.2 percent. Elongation is how far the specimen stretches before it fractures, reported as a percentage of its gauge length. Elongation can be stated on different gauge-length bases, for example A50mm in EN or 2 in. in ASTM, so confirm the basis before comparing across standards.
How do I read a row on a datasheet?
Find the alloy and temper first, then the thickness range, then the units. The remaining checks are quick:
- Units: megapascals or ksi
- Alloy and temper: both must match the order
- Thickness range: your gauge must fall inside the range the row covers
- Direction: some datasheets state whether the test was along or across the rolling direction
- Gauge length: the basis the datasheet states for elongation
- Status: a requirement, or a typical value
A row that leaves any of these out is harder to compare, since some details may be fixed by the cited test standard. Ask for the missing item before comparing the number with another.
What is the difference between a requirement and a typical value?
A standard's table states what the material must meet for each alloy and temper, as a minimum and in some cases a maximum. A producer datasheet may instead list typical values, which describe what the material is expected to reach and are not a guarantee.
Acceptance should rely on the requirement in the standard named on the order, not on a typical figure, and design values come from your design code. ASTM B209/B209M covers flat sheet, coiled sheet and plate in the alloys and tempers shown in its tables, and those tables are where the requirements are stated.
How does temper change the numbers?
Within one alloy, annealed (O) temper gives lower strength and more elongation. H tempers trade elongation for strength, and a higher second digit generally means more strength and less formability. A strength value without its temper is incomplete, since the same alloy appears in several tempers with different values.
The comparison of tempers, and the reason the temper letter belongs on every line item, is in the alloy and temper guide.
Does thickness change the row I should read?
It can. Requirement tables in standards such as ASTM B209 are organized by alloy and temper, and a table may divide a temper into thickness ranges. Read the row for the range that contains your gauge, and take the requirement from the standard itself, not from a general chart.
Orbit rolls coil from 0.20 to 2.00 mm thick, so the range that applies depends on the gauge you order.
How does elongation relate to forming?
Higher elongation indicates more ductility, which generally gives more margin before a bend cracks. But elongation from a tension test does not by itself give a safe bend radius. That depends on alloy, temper, gauge and, for coated coil, the coating and whether the coil is coated before forming.
The alloy and temper guide covers the interaction with bend radius. When a profile is demanding, give the supplier the bend radius and let the alloy and temper be confirmed against it.
How does this connect to the mill test certificate?
The certificate reports test results for the lot supplied, and the standard's table states the requirement. Compare them row by row: alloy, temper, thickness range, then each of the three values. The post on reading a mill test certificate covers the rest of that check.
What can I get from Orbit?
Test reports and ASTM or EN references are available on request, and temper is available on request. Orbit rolls 1xxx (1050, 1100), 3xxx (3003, 3105) and 5xxx (5005, 5052, 5754) coil from 0.20 to 2.00 mm thick, as described on the rolled aluminum coil page. Send the alloy, temper and gauge you are considering, and the standard your order cites, and we will confirm what is provided for your order.
Common questions
Should I design to yield strength or tensile strength?
That is set by your design code or engineering basis, not by the datasheet. Yield strength is the stress at a specified small permanent deformation, and tensile strength is the maximum stress the specimen carries.
Can Orbit provide mechanical test results for my order?
Test reports and ASTM or EN references are available on request. Tell us the alloy, temper and gauge in the RFQ and we will confirm what is provided for your order.
Why does my certificate show different numbers from the datasheet?
A certificate reports test results for the lot supplied, while a datasheet may list requirements or typical values. They answer different questions, so compare certificate results with the requirement in the standard named on your order.
Which temper gives more elongation?
Annealed (O) temper gives more elongation than the H tempers of the same alloy, at the cost of strength.
Where do I find the values for a specific alloy and temper?
In the tables of the standard named on your order, such as ASTM B209, and in the mill test certificate for the lot supplied.
References
- ASTM International: B209/B209M, Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate: the requirement tables for sheet, coiled sheet and plate.
- ASTM International: B557/B557M, Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products: the tension test method behind strength and elongation values.
Need mechanical property values for an order?
Send your alloy, temper, gauge and the standard your order cites. We respond to RFQs within one business day.