AMS 2771
Heat Treatment of Aluminum Alloy Castings
Solution heat treatment, quenching, ageing and annealing of aluminum alloy castings (sand, permanent mold, investment and die castings such as A356.0, A357.0, C355.0, 319.0, 201.0 and 206.0) to the T5, T6, T7 and related tempers.
What AMS 2771 specifies
AMS 2771 is the casting counterpart of AMS 2770: casting alloys need longer solution times because their silicon and copper phases are coarse, and they distort and crack more readily in a cold quench. Tables give per-alloy solution temperatures — about 1000 °F (540 °C) for A356.0/A357.0 and 950–980 °F (510–525 °C) for copper-bearing 319/355 — with solution times of 6–12 h, quenching in water that may be heated to 150–212 °F (65–100 °C) to limit distortion, or in polymer, and ageing cycles such as 310 °F (155 °C) for 3–5 h to T6 or higher temperatures for the stabilised T7/T71 tempers. Quench delay limits, re-solution limits and furnace uniformity per AMS 2750 apply as for wrought parts. Acceptance is normally by Brinell hardness (ASTM E10) and by tensile test on separately cast or integrally cast test bars per ASTM B557 when the casting specification requires it; conductivity is used where the alloy allows.
Tests and the drawing call-out
Tests the document imposes
- Brinell hardness per ASTM E10 (500 kgf, 10 mm ball) or Rockwell per ASTM E18 on each lot
- Tensile test per ASTM B557 on separately cast, attached or excised specimens when the casting specification requires it
- Eddy-current conductivity when specified
- Radiographic or metallographic check for eutectic melting and blistering when specified
- Quenchant temperature and quench delay record; pyrometry per AMS 2750
How to cite it
Drawing call-out
HEAT TREAT PER AMS 2771 TO A356.0-T6; BRINELL HARDNESS PER ASTM E10 AND TENSILE PER ASTM B557 ON TEST BARSAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
AMS 2771 — frequently asked
Why do castings need 6–12 h at solution temperature when wrought parts need about 1 h?
The eutectic silicon in A356 must spheroidise and the magnesium silicide must dissolve from coarse as-cast particles; that diffusion takes hours, and the rounded silicon is what gives T6 castings their ductility. Modified or permanent-mold castings with a fine structure sit at the short end of the range.
Is a hot-water quench allowed?
Yes. AMS 2771 permits water up to boiling (150–212 °F) for castings, trading a little strength for far less distortion and cracking on thin-walled or complex shapes. Polymer quenchants are used the same way; the drawing may restrict the quenchant if peak properties are required.
What is T7 or T71 for a casting?
Overaged tempers held at a higher temperature so that further ageing in service does not move dimensions; used on pistons, housings and parts machined to tight tolerances that run warm. Strength is lower than T6 by roughly 10–20 %, stability and ductility are better.
How are properties proven?
By hardness on the castings and, when the material specification (for example AMS 4218 for A356.0-T6) calls for it, by tensile tests on separately cast test bars heat treated with the lot or on specimens cut from a designated casting. Separately cast bars can over-represent thin sections; specify excised specimens for critical castings.
AMS 2771 is copyrighted by SAE International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗