# A356 casting alloy

A356 casting versus remelt-ingot designations, scoped chemistry and properties, and foundry/finished-part acceptance.

Reviewed: 2026-11-01

Tags: materials, aluminum, casting, aluminum-silicon-magnesium

## Identify the casting and the metal supplied

For T6 castings made from A356.2, Rio Tinto lists **275 MPa tensile, 205 MPa yield and 6% elongation** for sand versus **285 MPa, 205 MPa and 12%** for permanent mold. Both are **typical** for separately cast specimens with a **2-inch/50 mm** elongation gauge length. [Rio Tinto A356.2 data, fourth edition](https://www.riotinto.com/can/-/media/content/documents/products/aluminium/rt-aluminium-foundry.pdf)

**A356** is an aluminum–silicon–magnesium casting-alloy family description. Preserve the letter and decimal suffix. The Aluminum Association's **Pink Sheets, revised August 2025**, register **A356.0 as a casting designation** and **A356.1/A356.2 as ingot designations**. The undifferentiated name does not establish whether an order concerns remelt metal or a finished casting. [Aluminum Association casting and ingot registrations](https://www.aluminum.org/sites/default/files/2025-10/Pink%20Sheets%202025.pdf)

Selected registered limits illustrate why the suffix matters. Values are mass percentages; aluminum is the remainder subject to the complete other-element limits. [Pink Sheets, A356 entries](https://www.aluminum.org/sites/default/files/2025-10/Pink%20Sheets%202025.pdf)

| Designation | Silicon | Magnesium | Maximum iron | Maximum copper |
| --- | --- | --- | --- | --- |
| A356.0 casting | 6.5–7.5% | 0.25–0.45% | 0.20% | 0.20% |
| A356.2 ingot | 6.5–7.5% | 0.30–0.45% | 0.12% | 0.10% |

The registry separately lists 356.0 and other lettered variants. Do not remove the **A** or assume identical chemistry because the numeric family matches. A conforming ingot analysis also does not prove the final casting's chemistry, temper, soundness or dimensions after remelting and manufacture.

An adequate casting order identifies **alloy, casting process, final temper, drawing revision, applicable specification/edition, inspection requirements and certification**. For ingot, identify the registered ingot grade and agreed delivery requirements separately. Keep melt/heat and finished-part identity linked through the foundry route.

## Casting process and temper are part of a property claim

Rio Tinto's **Primary aluminium foundry alloys, fourth edition, April 2019**, describes A356.2 for sand and permanent-mold casting. Its A356.2 section labels the following casting data **typical mechanical properties**. PM denotes permanent mold; elongation uses a 2-inch/50 mm gauge length. Its specimen note identifies separately cast, unfinished 0.50-inch/12.5 mm diameter specimens from permanent or green-sand molds. These figures describe the source's casting/temper combinations, not the mechanical strength of an ingot delivered for remelting. [Rio Tinto A356.2 section](https://www.riotinto.com/can/-/media/content/documents/products/aluminium/rt-aluminium-foundry.pdf)

| Condition and casting method | Typical ultimate tensile strength | Typical 0.2%-offset yield strength | Typical elongation |
| --- | --- | --- | --- |
| F, sand | 160 MPa | 85 MPa | 6% |
| F, PM | 185 MPa | 90 MPa | 8% |
| T6, sand | 275 MPa | 205 MPa | 6% |
| T6, PM | 285 MPa | 205 MPa | 12% |

**Reading example:** the two typical T6 rows differ by 10 MPa in ultimate strength, while the listed PM elongation is twice the sand value. That comparison is not a conversion factor for a particular foundry, section thickness or casting geometry. [Rio Tinto typical-property table](https://www.riotinto.com/can/-/media/content/documents/products/aluminium/rt-aluminium-foundry.pdf)

Do not transfer typical values to a purchase acceptance limit or a structural allowable. Retain specimen source, location, orientation, gauge length, casting method, final condition and test requirements. A separately produced coupon and a specimen removed from a particular casting region need an explicit relationship in the applicable acceptance plan.

## Supplier limits and test definitions

St. Paul Foundry's undated A356.0 page labels a different set of **specification minimum** entries: T6 tensile strength **34 ksi**, yield strength **24 ksi**, and elongation **3.5% over 2 inches**. Its yield heading specifies **0.5% extension under load**, which should not silently be relabeled 0.2%-offset proof strength. Confirm the governing product specification and specimen requirements before using the summary for acceptance. [St. Paul Foundry A356.0 specification-property table](https://stpaulfoundry.com/AlloySpecs/alloy_specifications_data_page.aspx?id=A356.0)

The differing sources are not competing numbers from which to choose the highest strength. They describe different evidence and test bases. Record a value as supplier typical data, a specified limit, a batch result or an approved design value; preserve its original units and definition.

ASTM's public scope for **B26/B26M-25** covers general-purpose aluminum-alloy sand castings. It warns that the specification may not address all mechanical-property, integrity-testing and verification needs of highly loaded or safety-critical applications. Identify any additional requirements explicitly rather than assuming that a B26 callout completes every component qualification. [ASTM B26/B26M-25 scope](https://store.astm.org/b0026_b0026m-25.html)

## Define the foundry and machining route

Casting acceptance concerns the actual part, not just a compliant melt or a tensile bar. Agree critical regions, inspection methods and acceptance criteria with the producer. Keep the approved casting process, melt control, tooling revision, heat-treatment batch and inspection evidence in the manufacturing record. A change in process or section geometry should trigger assessment against the qualified part requirements.

For a machined housing, identify datum targets, stock allowance, critical sealing surfaces, threaded features and inspection after machining. Material removal can expose an internal discontinuity that was not visible on the as-cast skin. Define the disposition of such indications before relying on a finished pressure or structural test.

Where leakage matters, specify the fluid or gas, test conditions and acceptance criterion appropriate to the assembly. A tensile certificate does not establish leak tightness. Likewise, a passed leak test does not establish fatigue life or the absence of every internal discontinuity. Agree whether repair, impregnation or local welding is permitted and how it is documented and reaccepted.

## Thermal processing and service boundaries

Retain the complete final temper and controlled heat-treatment route. A proposed heating, straightening or repair operation needs assessment of the resulting material condition and dimensions. Do not derive universal furnace times, quench parameters or postweld restoration claims from a generic A356-T6 property table.

Rio Tinto separately presents elevated-temperature data for **A356.0-T61 permanent-mold castings**, alongside 356.0-T6 entries. Its exposure/test basis and exact temper belong with those values. They should not be relabeled as unqualified A356-T6 continuous-service ratings. [Rio Tinto elevated-temperature tables](https://www.riotinto.com/can/-/media/content/documents/products/aluminium/rt-aluminium-foundry.pdf)

Evaluate the actual load spectrum, temperature/time history, fluid exposure, joints, protective finish and inspection needs. A supplier application list is not approval for an arbitrary wheel, pressure housing or aerospace component. Release against the ordered material and casting specification, drawing and final-part criteria, retaining traceability through machining, finishing and assembly.

Sources were reviewed November 1, 2026. The AA and Rio Tinto editions above come from their printed revision dates; the undated foundry page is not assigned a publication revision from its crawl date.

## Related reference

[Grades, tempers and conditions](../grades-tempers-and-conditions.md)