Aluminum 7178 · temper
Aluminum 7178-O
Properties of the O condition, compared with the other 7178 tempers.
Soft annealed stock for severe forming or machining before solution heat treatment and aging.
What is 7178-O?
7178-O is 7178 in the O temper — soft annealed stock for severe forming or machining before solution heat treatment and aging. 7178-O has a yield strength of 103 MPa (14.9 ksi) and a tensile strength of 228 MPa (33.1 ksi) — weaker than 84% of aluminum grades. Elongation at break is 15% and the elastic modulus is 71.7 GPa (10.4 Msi). 7178-O has a density of 2.83 g/cm³ (0.102 lb/in³), heavier than 91% of aluminum grades. It melts at 477°C (891 °F).
Advantages
- High service temperature — 200°C (392 °F), better than 90% of aluminum grades
- Ductile — tolerates forming and impact — 15%, better than 82% of aluminum grades
- Forms and bends easily — 65/100, better than 80% of aluminum grades
Limitations
- Difficult to weld — 12/100, worse than 98% of aluminum grades
- Low strength — 103 MPa (14.9 ksi), worse than 84% of aluminum grades
- Needs corrosion protection — 40/100, worse than 75% of aluminum grades
7178-O properties
Typical room-temperature values for 7178-O — 11 properties are specific to this condition; the rest are grade-level values shared by every 7178 temper. Each bar shows where the value sits among the aluminum grades in FabDigit's library — further right is higher.
Physical3
7178-O has a density of 2.83 g/cm³ (0.102 lb/in³), heavier than 91% of aluminum grades. It melts at 477°C (891 °F).
Mechanical13
7178-O has a yield strength of 103 MPa (14.9 ksi) and a tensile strength of 228 MPa (33.1 ksi) — weaker than 84% of aluminum grades. Elongation at break is 15% and the elastic modulus is 71.7 GPa (10.4 Msi).
Thermal6
7178-O is rated for continuous service to 200°C (392 °F). It conducts heat at 152 W/m·K (87.8 BTU/hr·ft·°F), better than 66% of aluminum grades. Thermal expansion is 23.4 µm/m·K (13 µin/in·°F).
Electrical3
7178-O conducts electricity at 38 % IACS, better than 61% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (40/100), worse than 75% of aluminum grades.
Sustainability4
Producing a kilogram of 7178-O takes about 205 MJ of energy and emits 12.5 kg of CO₂ — more than 75% of aluminum grades. Typical recycled content is 15%.
Manufacturability7
7178-O's machinability is fair (45/100, worse than 72% of aluminum grades); weldability not recommended (12/100); formability good (65/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 7178 tempers and conditions
7178 is also supplied in 7 other conditions. The full side-by-side table is on the 7178 overview.
- T6510Extruded stringer/section temper with controlled stretch and no subsequent straightening.570 MPa yield · 165 HB
- T6511Most common high-strength extrusion temper — straightness-corrected version of T6510.570 MPa yield · 165 HB
- T6Peak-strength condition — pick it for maximum static and compressive strength in sheet, clad sheet and simple sections.538 MPa yield · 160 HB
- T627178 re-solution-treated from O/F temper and artificially aged by the fabricator; strength essentially equals T6 with no stretch stress relief.530 MPa yield · 160 HB
- T651Standard plate temper — same peak strength as T6 but low residual stress for stable machining of thick parts.530 MPa yield · 160 HB
- T7651Over-aged plate with low residual stress — for machined skins needing exfoliation resistance and dimensional stability.510 MPa yield · 150 HB
- T76Choose when exfoliation-corrosion resistance matters more than the last 5 % of strength.505 MPa yield · 150 HB
- OSoft annealed stock for severe forming or machining before solution heat treatment and aging.103 MPa yield · 60 HB
Working with 7178-O
Is 7178 easy to machine?
Machines well in T6/T76 with sharp carbide, high speed and flood coolant; relieve stresses (T651/T7651) before heavy pocket milling to control distortion.
Can 7178 be welded?
Not fusion weldable — hot cracking and severe HAZ SCC; join by riveting, bolting or adhesive bonding (friction-stir only with qualified procedures).
Can 7178 be formed, bent or molded?
Form in O or freshly quenched W temper and age afterwards; T6 sheet tolerates only large-radius bends and is prone to cracking.
What surface finishes work on 7178?
Clad or anodize (chromic/sulfuric) plus chromate conversion and primer for corrosion protection; avoid sustained short-transverse tensile stress and use T76 tempers in exfoliation-prone areas.
7178 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 | ≤ 0.4 | — |
| Fe | ≤ 0.5 | — |
| Cu | 1.6 – 2.4 | 2 |
| Mn | ≤ 0.3 | — |
| Mg | 2.4 – 3.1 | 2.7 |
| Cr | 0.18 – 0.28 | 0.23 |
| Zn | 6.3 – 7.3 | 6.8 |
| Ti | ≤ 0.2 | — |
| Others (each)each | ≤ 0.05 | — |
| Others (total)total | ≤ 0.15 | — |
| Al | balance | — |
7178-O — frequently asked
What is 7178-O used for?
7178-O is typically used for aircraft upper wing skins, wing stringers, compression-loaded airframe panels, extruded stiffeners and spar caps, alclad aerospace sheet components and legacy airframe replacement parts. In short: compression aerospace alloy.
What is the yield strength of 7178-O?
7178-O has a typical yield strength of 103 MPa (14.9 ksi) and a tensile strength of 228 MPa (33.1 ksi) — weaker than 84% of aluminum grades. Strength varies by condition: see the 8 listed tempers.
Is 7178-O easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 72% of aluminum grades). Machines well in T6/T76 with sharp carbide, high speed and flood coolant; relieve stresses (T651/T7651) before heavy pocket milling to control distortion.
Can 7178-O be welded?
Not readily — weldability is rated not recommended (12/100). Not fusion weldable — hot cracking and severe HAZ SCC; join by riveting, bolting or adhesive bonding (friction-stir only with qualified procedures).
What surface finishes work on 7178-O?
Clad or anodize (chromic/sulfuric) plus chromate conversion and primer for corrosion protection; avoid sustained short-transverse tensile stress and use T76 tempers in exfoliation-prone areas.
Can 7178-O be formed, bent or molded?
Form in O or freshly quenched W temper and age afterwards; T6 sheet tolerates only large-radius bends and is prone to cracking.
What is the maximum service temperature of 7178-O?
7178-O is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 7178-O?
Yes — 7178-O is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum (Teal Sheets) — The Aluminum Association (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- MMPDS-17 Metallic Materials Properties Development and Standardization — Battelle/FAA (2022)
- ASTM B209 / B221 — Aluminum Sheet, Plate and Extruded Products — ASTM International (2021)
- ASM Handbook Vol. 13B — Corrosion: Materials — 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.