Aluminum AC8A-T7
Temper
JIS AC8A
T7 = solution heat treated and overaged (stabilized)
Pick when long-term dimensional stability and creep resistance at elevated engine temperature outrank peak strength.
Values for the T7 condition
Other AC8A tempers and conditions
AC8A is listed in 4 conditions; see the grade overview at AC8A.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As fabricated | Cheapest condition; used where dimensional stability and peak hot strength are not critical. | 140 | 190 | 1.5 | 85 HB | 30 % IACS |
T7This page Solution heat treated and overaged (stabilized) | Pick when long-term dimensional stability and creep resistance at elevated engine temperature outrank peak strength. | 195 | 255 | 1.5 | 95 HB | 30 % IACS |
Cooled from hot working and artificially aged | Low-distortion, low-cost strengthening route for mass-produced pistons where full T6 strength is not needed. | 205 | 255 | 1 | 100 HB | 29 % IACS |
T6Default Solution heat treated and artificially aged | Standard condition for high-performance pistons: highest strength and hardness of the AC8A tempers. | 240 | 285 | 1 | 115 HB | 28 % IACS |
What is AC8A-T7?
AC8A-T7 is AC8A in the T7 temper — pick when long-term dimensional stability and creep resistance at elevated engine temperature outrank peak strength. AC8A-T7 has a yield strength of 195 MPa (28.3 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 51% of aluminum grades. Elongation at break is 1.5% and the elastic modulus is 81 GPa (11.7 Msi). AC8A-T7 has a density of 2.7 g/cm³ (0.0975 lb/in³), lighter than 59% of aluminum grades. It melts at 525°C (977 °F). T6 is the default condition FabDigit quotes; T7 is available on request or by drawing note.
Advantages
- High service temperature — 280°C (536 °F), better than 99% of aluminum grades
- Stiff — 81 GPa (11.7 Msi), better than 96% of aluminum grades
Limitations
- Limited ductility — 1.5%, 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
- Hard to polish — 45/100, worse than 76% of aluminum grades
- Needs corrosion protection — 40/100, worse than 75% of aluminum grades
AC8A-T7 properties
Typical room-temperature values for AC8A-T7; 21 are specific to this condition. Other listed values are AC8A reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
AC8A-T7 has a density of 2.7 g/cm³ (0.0975 lb/in³), lighter than 59% of aluminum grades. It melts at 525°C (977 °F).
Mechanical15
AC8A-T7 has a yield strength of 195 MPa (28.3 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 51% of aluminum grades. Elongation at break is 1.5% and the elastic modulus is 81 GPa (11.7 Msi).
Thermal6
AC8A-T7 is rated for continuous service to 280°C (536 °F). It conducts heat at 140 W/m·K (80.9 BTU/hr·ft·°F), worse than 52% of aluminum grades. Thermal expansion is 19.5 µm/m·K (10.8 µin/in·°F).
Electrical3
AC8A-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 AC8A-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
AC8A-T7's machinability is fair (53/100, worse than 62% 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 AC8A-T7
Is AC8A easy to machine?
Abrasive primary/eutectic silicon demands PCD or diamond-coated carbide tooling, high speed with modest feed and copious coolant; finishes well but tool wear is the cost driver.
Can AC8A be welded?
Essentially not weldable for structural repair — the Cu content promotes hot cracking; local repair only by 4047/4145 filler with preheat and immediate re-ageing.
Can AC8A be formed, bent or molded?
Gravity/permanent-mould casting with controlled Sr/P modification and directional solidification; near-eutectic composition gives good fluidity and low shrinkage but requires melt degassing to avoid porosity.
What surface finishes work on AC8A?
Hard anodising or ferrous ring-groove inserts for wear surfaces, graphite/MoS2 skirt coatings and phosphate/ceramic thermal-barrier crown coatings; decorative anodise looks dark and mottled.
AC8A 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 |
|---|---|---|
| Si | 11 – 13 | 12 |
| Cu | 0.8 – 1.3 | 1 |
| Mg | 0.7 – 1.3 | 1 |
| Niforms thermally stable aluminides | 0.8 – 1.5 | 1.1 |
| Feimpurity limit | ≤ 0.8 | — |
| Mn | ≤ 0.15 | — |
| Zn | ≤ 0.15 | — |
| Ti | ≤ 0.2 | — |
| Cr | ≤ 0.1 | — |
| Pb | ≤ 0.05 | — |
| Sn | ≤ 0.05 | — |
| Al | balance | — |
AC8A-T7 — frequently asked
What is AC8A-T7 used for?
AC8A-T7 is typically used for automotive pistons, small engine pistons and high-temp wear parts. In short: standard JIS piston alloy; 250 °C service temperature; low thermal expansion casting.
What is the yield strength of AC8A-T7?
AC8A-T7 has a typical yield strength of 195 MPa (28.3 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 51% of aluminum grades. Strength varies by condition: see the 4 listed tempers.
Is AC8A-T7 easy to machine?
Reasonably — machinability is rated fair (53/100, worse than 62% of aluminum grades). Abrasive primary/eutectic silicon demands PCD or diamond-coated carbide tooling, high speed with modest feed and copious coolant; finishes well but tool wear is the cost driver.
Can AC8A-T7 be welded?
Not readily — weldability is rated poor (28/100). Essentially not weldable for structural repair — the Cu content promotes hot cracking; local repair only by 4047/4145 filler with preheat and immediate re-ageing.
What surface finishes work on AC8A-T7?
Hard anodising or ferrous ring-groove inserts for wear surfaces, graphite/MoS2 skirt coatings and phosphate/ceramic thermal-barrier crown coatings; decorative anodise looks dark and mottled.
Can AC8A-T7 be formed, bent or molded?
Gravity/permanent-mould casting with controlled Sr/P modification and directional solidification; near-eutectic composition gives good fluidity and low shrinkage but requires melt degassing to avoid porosity.
What is the maximum service temperature of AC8A-T7?
AC8A-T7 is rated for continuous use to about 280°C (536 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AC8A-T6 and AC8A-F?
T6 is the default condition — standard condition for high-performance pistons: highest strength and hardness of the AC8A tempers. F: cheapest condition; used where dimensional stability and peak hot strength are not critical. Yield strength is 240 MPa in T6 versus 140 MPa in F.
Sources
- JIS H5202 Aluminium alloy castings — JSA (2010)
- EN 1706 Aluminium and aluminium alloys — Castings (EN AC-48000 AlSi12CuNiMg) — CEN (2020)
- ASTM B26/B108 & AA designation 332.0/A332.0 — ASTM / Aluminum Association (2018)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- GB/T 1173 (ZL109 comparable piston alloy) — SAC (2013)
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.