Aluminum AL25-T7
Temper
T7 = solution heat treated and overaged (stabilized)
Select solution treated and stabilised (over-aged) for long-term service up to 300 °C with no further growth; yield drops to 170 MPa but thermal and dimensional stability are best.
Values for the T7 condition
Other AL25 tempers and conditions
AL25 is listed in 6 conditions; see the grade overview at AL25.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Cooled from hot working, cold worked and naturally aged | Choose the stress-relief annealed state when dimensional stability and low residual stress matter more than strength; yield falls to 120 MPa while conductivity rises to 145 W/m·K. | 120 | 160 | 1.2 | 70 HB | 32 % IACS |
As fabricated | Use the untreated as-cast chill or permanent-mould state for lightly loaded parts, or as the starting point before heat treatment; 150 MPa yield with only 0.8% elongation. | 150 | 180 | 0.8 | 85 HB | 29 % IACS |
T7This page Solution heat treated and overaged (stabilized) | Select solution treated and stabilised (over-aged) for long-term service up to 300 °C with no further growth; yield drops to 170 MPa but thermal and dimensional stability are best. | 170 | 195 | 0.9 | 95 HB | 30 % IACS |
T1Default Cooled from hot working and naturally aged | Pick for volume piston production: artificial ageing without a quench keeps distortion and cost low while giving 180 MPa yield, 95 HB and good thermal stability to 250 °C. | 180 | 200 | 0.6 | 95 HB | 27 % IACS |
Cooled from hot working and artificially aged | Use solution treated and partially (short) aged when you need more strength than the aged-only state (190 MPa yield, 100 HB) but must retain some ductility in thermally loaded castings. | 190 | 215 | 0.7 | 100 HB | 25 % IACS |
Solution heat treated and artificially aged | Choose solution treated and fully artificially aged for the highest room- and mid-temperature strength — 205 MPa yield, 110 HB — in highly rated diesel pistons; elongation drops to 0.5%. | 205 | 230 | 0.5 | 110 HB | 24 % IACS |
What is AL25-T7?
AL25-T7 is AL25 in the T7 temper — select solution treated and stabilised (over-aged) for long-term service up to 300 °C with no further growth; yield drops to 170 MPa but thermal and dimensional stability are best. AL25-T7 has a yield strength of 170 MPa (24.7 ksi) and a tensile strength of 195 MPa (28.3 ksi) — weaker than 56% of aluminum grades. Elongation at break is 0.9% and the elastic modulus is 80 GPa (11.6 Msi). AL25-T7 has a density of 2.73 g/cm³ (0.0986 lb/in³), heavier than 61% of aluminum grades. It melts at 510°C (950 °F). T1 is the default condition FabDigit quotes; T7 is available on request or by drawing note.
Advantages
- High service temperature — 300°C (572 °F), better than 99% of aluminum grades
- Stiff — 80 GPa (11.6 Msi), better than 95% of aluminum grades
Limitations
- Limited ductility — 0.9%, worse than 97% of aluminum grades
- Hard to polish — 40/100, worse than 91% of aluminum grades
- Limited formability — 6/100, worse than 89% of aluminum grades
- Low fracture toughness — 17 MPa·√m (15.5 ksi·√in), worse than 83% of aluminum grades
- Needs corrosion protection — 40/100, worse than 75% of aluminum grades
AL25-T7 properties
Typical room-temperature values for AL25-T7; 22 are specific to this condition. Other listed values are AL25 reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
AL25-T7 has a density of 2.73 g/cm³ (0.0986 lb/in³), heavier than 61% of aluminum grades. It melts at 510°C (950 °F).
Mechanical14
AL25-T7 has a yield strength of 170 MPa (24.7 ksi) and a tensile strength of 195 MPa (28.3 ksi) — weaker than 56% of aluminum grades. Elongation at break is 0.9% and the elastic modulus is 80 GPa (11.6 Msi).
Thermal6
AL25-T7 is rated for continuous service to 300°C (572 °F). It conducts heat at 140 W/m·K (80.9 BTU/hr·ft·°F), worse than 52% of aluminum grades. Thermal expansion is 19 µm/m·K (10.6 µin/in·°F).
Electrical3
AL25-T7 conducts electricity at 30 % IACS, worse than 73% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (40/100), worse than 75% of aluminum grades.
Sustainability4
Producing a kilogram of AL25-T7 takes about 200 MJ of energy and emits 12 kg of CO₂ — less than 60% of aluminum grades. Typical recycled content is 60%.
Manufacturability8
AL25-T7's machinability is fair (48/100, worse than 68% of aluminum grades); weldability poor (28/100); formability not recommended (6/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with AL25-T7
Is AL25 easy to machine?
The abrasive high-silicon eutectic structure calls for PCD or diamond-coated tooling with high speed, light feed and ample coolant; dimensional accuracy achieved this way is good.
Can AL25 be welded?
Fusion welding is generally not recommended, as the Cu and Mg content causes hot cracking and property loss; for repair only, TIG with 4047 or 4145 filler after a 200 °C preheat, then re-age.
Can AL25 be formed, bent or molded?
Cast mainly by gravity permanent mould, and also by low-pressure casting; the near-eutectic composition gives good fluidity and low hot-tearing tendency, but requires sound feeding and Sr/P modification to control silicon morphology. Not workable cold.
What surface finishes work on AL25?
Hard anodizing is standard on piston crowns and ring grooves, with phosphating or tin plating as alternatives; decorative anodizing is poor because the high silicon gives a dull grey finish.
AL25 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 |
|---|---|---|
| Sieutectic Si, lowers CTE, raises wear resistance and castability | 11 – 13 | 12 |
| Cu | 1.5 – 3 | 2 |
| Mg | 0.8 – 1.3 | 1 |
| Niforms heat-resistant intermetallics | 0.8 – 1.3 | 1 |
| Mn | 0.3 – 0.6 | 0.45 |
| Tigrain refiner | 0.05 – 0.2 | 0.1 |
| Feimpurity limit | ≤ 0.8 | — |
| Znimpurity limit | ≤ 0.5 | — |
| Crimpurity limit | ≤ 0.2 | — |
| Pbimpurity limit | ≤ 0.1 | — |
| Snimpurity limit | ≤ 0.02 | — |
| Alper GOST 1583 AL25 (AK12M2MgN); ASTM 242.0 matched by use only | balance | — |
AL25-T7 — frequently asked
What is AL25-T7 used for?
AL25-T7 is typically used for diesel engine pistons, turbocharger components, air-cooled cylinder heads, engine crankcases, piston ring carriers and elevated-temperature bearing housings. In short: highest hot strength, 250 °C; classic piston alloy; very low ductility.
What is the yield strength of AL25-T7?
AL25-T7 has a typical yield strength of 170 MPa (24.7 ksi) and a tensile strength of 195 MPa (28.3 ksi) — weaker than 56% of aluminum grades. Strength varies by condition: see the 6 listed tempers.
Is AL25-T7 easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 68% of aluminum grades). The abrasive high-silicon eutectic structure calls for PCD or diamond-coated tooling with high speed, light feed and ample coolant; dimensional accuracy achieved this way is good.
Can AL25-T7 be welded?
Not readily — weldability is rated poor (28/100). Fusion welding is generally not recommended, as the Cu and Mg content causes hot cracking and property loss; for repair only, TIG with 4047 or 4145 filler after a 200 °C preheat, then re-age.
What surface finishes work on AL25-T7?
Hard anodizing is standard on piston crowns and ring grooves, with phosphating or tin plating as alternatives; decorative anodizing is poor because the high silicon gives a dull grey finish.
Can AL25-T7 be formed, bent or molded?
Cast mainly by gravity permanent mould, and also by low-pressure casting; the near-eutectic composition gives good fluidity and low hot-tearing tendency, but requires sound feeding and Sr/P modification to control silicon morphology. Not workable cold.
What is the maximum service temperature of AL25-T7?
AL25-T7 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AL25-T1 and AL25-T2?
T1 is the default condition — pick for volume piston production: artificial ageing without a quench keeps distortion and cost low while giving 180 MPa yield, 95 HB and good thermal stability to 250 °C. T2: choose the stress-relief annealed state when dimensional stability and low residual stress matter more than strength; yield falls to 120 MPa while conductivity rises to 145 W/m·K. Yield strength is 180 MPa in T1 versus 120 MPa in T2.
Sources
- ГОСТ 1583 — Сплавы алюминиевые литейные (АЛ25 / АК12М2МгН) — Госстандарт (1993)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys (cast Al-Si-Cu-Ni piston alloys, 336.0/242.0) — ASM International (1990)
- GB/T 1173 — (ZL109) — SAC (2013)
- ASM Handbook Vol.13B — Corrosion: Materials (aluminum alloys) — ASM International (2005)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.