Can an aluminum casting be specified in T5 or T6?
Yes, when the alloy responds to the treatment and the manufacturing route has shown the required results on representative parts. A temper designation alone is not evidence. Before approving production, connect alloy, casting process, thermal cycle, specimen location and final component checks in one qualification record. The practical question is whether this combination meets your drawing consistently.
T5 vs T6: two different thermal routes
| T5 | T6 | |
|---|---|---|
| Steps | Cooled from casting, then artificially aged | Solution treated, quenched, artificially aged |
| Solution treatment | None | Yes: the step that blisters gas-bearing castings |
| Typical use | Stability, moderate strength gain | Highest strength in heat-treatable alloys such as A356 |
| Parameters from | The alloy and the governing specification, not a generic recipe | |
Rheinfelden's Silafont-36 guidance, for example, describes direct quenching after die removal for its T5 route and a separate solution treatment for T6. That is alloy-specific guidance; do not transfer a cycle from a different material. Start from the required outcome (strength, ductility, dimensional condition, functional tests) and ask which route can demonstrate it. T6 is not a quality grade.
The process name is a starting point
ASTM B917/B917M covers heat treatment of aluminum castings from permanent-mold and other processes; applicability still depends on the material specification or order. High-pressure die castings need a specific discussion: a 2024 study of vacuum-assisted AlSi10MnMg and AlSi10Mg(Fe) parts found blistering under the solution treatment investigated, while the tested T5 avoided visible blisters. That supports qualification on actual parts; it does not prove every vacuum die casting fails T6 or that T5 is defect-free.
Squeeze casting fills at low velocity and solidifies under pressure, which is why it is our route for A356-T6. For any route, ask for the evidence for your application; a process label is not an acceptance report.
Agree the trial before making samples
A planning tool, not limits from a standard.
| Item | Agree before the trial | Examine afterward |
|---|---|---|
| Material identity | Designation, specification, permitted substitutions | Material identification linked to the trial parts |
| Casting route | Production process, tooling, configuration | Record of how trial parts were made |
| Thermal route | Sequence, controlling document, processor | Cycle record per trial batch |
| Component condition | Machining, inspection and finishing stage | Results in the drawing's condition |
| Mechanical | Requirements, specimen source, method | Results with specimen and batch ID |
| Component acceptance | Dimensional, integrity, functional checks | Results for identified parts, including failures |
| Approval | Reviewer and decision | Signed decision covering the qualified scope |
Ask for the complete result set, including rejected parts. If the trial route differs from production, record the difference and decide what further demonstration is needed.
Connect mechanical results to the component
ASTM B557 notes that specimens from selected portions may not represent the whole product or its service behaviour, and a test method does not supply acceptance limits. Ask for a specimen map: cut from production parts, cast-on, or separately cast. If two quotations use different specimen sources, resolve that before comparing their numbers.
Make the production decision explicit
- Approve the demonstrated route. Results complete and acceptable; production scope identified.
- Request another trial. A requirement unmet, a result missing, or the trial not representative.
- Revise the design or proposal. Reconsider alloy, process, temper or requirement.
Do not release a batch with "T6 capability to be confirmed" open. Changing an acceptance criterion after a failure needs the design authority. Put the qualified thermal route into the inspection plan and the change-notification list: alloy source, tooling, casting route, heat-treatment processor and cycle.