Aluminum AC8B-T7
Temper
JIS AC8B
T7 = solution heat treated and overaged (stabilized)
Choose for best dimensional and property stability at sustained high temperature, trading some room-temperature strength.
Values for the T7 condition
Other AC8B tempers and conditions
AC8B is listed in 4 conditions; see the grade overview at AC8B.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As fabricated | Cheapest condition; use where dimensional stability and peak hot strength are not required. | 130 | 180 | 1.5 | 85 HB | 28 % IACS |
Cooled from hot working and artificially aged | Pick when dimensional stability and moderate strength matter more than peak strength — the common production piston condition. | 180 | 210 | 1 | 95 HB | 27 % IACS |
T7This page Solution heat treated and overaged (stabilized) | Choose for best dimensional and property stability at sustained high temperature, trading some room-temperature strength. | 205 | 250 | 1.5 | 100 HB | 28 % IACS |
T6Default Solution heat treated and artificially aged | Default specified condition for maximum strength and hardness in highly loaded pistons and heads. | 235 | 280 | 1 | 110 HB | 25 % IACS |
What is AC8B-T7?
AC8B-T7 is AC8B in the T7 temper — choose for best dimensional and property stability at sustained high temperature, trading some room-temperature strength. AC8B-T7 has a yield strength of 205 MPa (29.7 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 54% of aluminum grades. Elongation at break is 1.5% and the elastic modulus is 82 GPa (11.9 Msi). AC8B-T7 has a density of 2.76 g/cm³ (0.0997 lb/in³), heavier than 70% of aluminum grades. It melts at 521°C (970 °F). T6 is the default condition FabDigit quotes; T7 is available on request or by drawing note.
Advantages
- High service temperature — 260°C (500 °F), better than 99% of aluminum grades
- Stiff — 82 GPa (11.9 Msi), better than 97% of aluminum grades
Limitations
- Low fracture toughness — 15 MPa·√m (13.7 ksi·√in), worse than 93% of aluminum grades
- Limited ductility — 1.5%, worse than 91% of aluminum grades
- Hard to polish — 40/100, worse than 91% of aluminum grades
- Poor heat conductor — 106 W/m·K (61.2 BTU/hr·ft·°F), worse than 90% of aluminum grades
- Difficult to weld — 22/100, worse than 83% of aluminum grades
AC8B-T7 properties
Typical room-temperature values for AC8B-T7; 10 are specific to this condition. Other listed values are AC8B reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
AC8B-T7 has a density of 2.76 g/cm³ (0.0997 lb/in³), heavier than 70% of aluminum grades. It melts at 521°C (970 °F).
Mechanical13
AC8B-T7 has a yield strength of 205 MPa (29.7 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 54% of aluminum grades. Elongation at break is 1.5% and the elastic modulus is 82 GPa (11.9 Msi).
Thermal6
AC8B-T7 is rated for continuous service to 260°C (500 °F). It conducts heat at 106 W/m·K (61.2 BTU/hr·ft·°F), worse than 90% of aluminum grades. Thermal expansion is 20.7 µm/m·K (11.5 µin/in·°F).
Electrical3
AC8B-T7 conducts electricity at 28 % IACS, worse than 82% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (38/100), worse than 79% of aluminum grades.
Sustainability4
Producing a kilogram of AC8B-T7 takes about 200 MJ of energy and emits 12 kg of CO₂ — less than 60% of aluminum grades. Typical recycled content is 75%.
Manufacturability7
AC8B-T7's machinability is fair (53/100, worse than 62% of aluminum grades); weldability poor (22/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with AC8B-T7
Is AC8B easy to machine?
Machines cleanly but the primary Si and Cu/Ni intermetallics abrade tools — use PCD or fine-grain carbide, high speed, low feed, and flood coolant; finish ring grooves after ageing.
Can AC8B be welded?
Poor fusion weldability because of the 2–4% Cu (hot cracking, loss of ageing response); repairs only by TIG with 4145/4047-type filler followed by re-ageing.
Can AC8B be formed, bent or molded?
Gravity/permanent-mold or squeeze casting alloy with good fluidity and low shrink porosity; degas and grain refine, control Fe below 1% and use controlled solidification for piston crown soundness. Not a wrought/formable alloy.
What surface finishes work on AC8B?
Take chemical conversion coating or functional hard anodizing (crown, ring groove) rather than decorative anodizing; tin or graphite skirt coatings and phosphate/paint systems are common; polishing is limited by Si particles.
AC8B 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 | 8.5 – 10.5 | 9.5 |
| Cu | 2 – 4 | 3 |
| Mg | 0.5 – 1.5 | 1 |
| Ni | 0.1 – 1 | 0.5 |
| Feimpurity limit | ≤ 1 | — |
| Mnimpurity limit | ≤ 0.5 | — |
| Znimpurity limit | ≤ 0.5 | — |
| Tigrain refiner / impurity limit | ≤ 0.2 | — |
| Crimpurity limit | ≤ 0.1 | — |
| Pbimpurity limit | ≤ 0.05 | — |
| Snimpurity limit | ≤ 0.05 | — |
| Al | balance | — |
AC8B-T7 — frequently asked
What is AC8B-T7 used for?
AC8B-T7 is typically used for automotive pistons, compressor pistons, air-conditioning compressor components, motorcycle and small-engine pistons, high-temperature wear bushings and ring-groove-carrying piston crowns. In short: tuned-expansion piston variant; wear-resistant Cu-Ni casting; lowest conductivity in AC8.
What is the yield strength of AC8B-T7?
AC8B-T7 has a typical yield strength of 205 MPa (29.7 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 54% of aluminum grades. Strength varies by condition: see the 4 listed tempers.
Is AC8B-T7 easy to machine?
Reasonably — machinability is rated fair (53/100, worse than 62% of aluminum grades). Machines cleanly but the primary Si and Cu/Ni intermetallics abrade tools — use PCD or fine-grain carbide, high speed, low feed, and flood coolant; finish ring grooves after ageing.
Can AC8B-T7 be welded?
Not readily — weldability is rated poor (22/100). Poor fusion weldability because of the 2–4% Cu (hot cracking, loss of ageing response); repairs only by TIG with 4145/4047-type filler followed by re-ageing.
What surface finishes work on AC8B-T7?
Take chemical conversion coating or functional hard anodizing (crown, ring groove) rather than decorative anodizing; tin or graphite skirt coatings and phosphate/paint systems are common; polishing is limited by Si particles.
Can AC8B-T7 be formed, bent or molded?
Gravity/permanent-mold or squeeze casting alloy with good fluidity and low shrink porosity; degas and grain refine, control Fe below 1% and use controlled solidification for piston crown soundness. Not a wrought/formable alloy.
What is the maximum service temperature of AC8B-T7?
AC8B-T7 is rated for continuous use to about 260°C (500 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AC8B-T6 and AC8B-F?
T6 is the default condition — default specified condition for maximum strength and hardness in highly loaded pistons and heads. F: cheapest condition; use where dimensional stability and peak hot strength are not required. Yield strength is 235 MPa in T6 versus 130 MPa in F.
Sources
- JIS H 5202 Aluminium alloy castings — JSA (2010)
- ASM Handbook Vol. 2: Properties and Selection — Nonferrous Alloys (332.0 / SAE 332) — ASM International (1990)
- ASTM B108 / Aluminum Association Designations for Cast Alloys — ASTM / Aluminum Association (2018)
- 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.