24 July 2021 7000 Series Aluminum Alloy
7178 Aluminum Alloy Plate
Aluminum Alloy 7178, comprised of copper and magnesium as its primary alloying elements, offers uncompromising strength and accommodates a number of different metalworking processes. These processes include machining, welding, and heat treating. Aluminum 7178 is stocked by 2 North American distributors and produced by 11 large mills.
Alloy 7178 offers good machinability and also responds well to resistance welding. Heat treatment should be performed at 875 °F with a subsequent water quenching. After treatment, this alloy gains precipitation hardening which improves its mechanical properties. Heavier thicknesses are formable.This alloy is preferred for many applications in the marine, construction and aerospace industries. Aluminum Alloy 7178 from Continental Steel and Tube Company meets or exceeds all relevant industry standards. These standards include all appropriate ASTM, QQ, SAE, and UNS specifications. 7178 aluminum alloy is wrought alloy. It has high zinc content. After annealing, aluminum alloy 7178 has high machinability. Resistance welding can be used.
Chemical Composition:
| Chemical Elements | Metric | English |
|---|---|---|
| Aluminum, Al | 85.3 - 89.5 % | 85.3 - 89.5 % |
| Chromium, Cr | 0.18 - 0.28 % | 0.18 - 0.28 % |
| Copper, Cu | 1.6 - 2.4 % | 1.6 - 2.4 % |
| Iron, Fe | <= 0.50 % | <= 0.50 % |
| Magnesium, Mg | 2.4 - 3.1 % | 2.4 - 3.1 % |
| Manganese, Mn | <= 0.30 % | <= 0.30 % |
| Other, each | <= 0.05 % | <= 0.05 % |
| Other, total | <= 0.15 % | <= 0.15 % |
| Silicon, Si | <= 0.40 % | <= 0.40 % |
| Titanium, Ti | <= 0.20 % | <= 0.20 % |
| Zinc, Zn | 6.3 - 7.3 % | 6.3 - 7.3 % |
Mechanical Properties:
| Mechanical Properties | Metric | English | Comments |
|---|---|---|---|
| Hardness, Brinell | 160 | 160 | 500 kg load with 10 mm ball |
| Hardness, Knoop | 205 | 205 | Converted from Brinell Hardness Value |
| Hardness, Rockwell A | 55.3 | 55.3 | Converted from Brinell Hardness Value |
| Hardness, Rockwell B | 90 | 90 | Converted from Brinell Hardness Value |
| Hardness, Vickers | 189 | 189 | Converted from Brinell Hardness Value |
| Tensile Strength, Ultimate | 607 MPa | 88000 psi | AA; Typical |
| 45.0 MPa @Temperature 371 °C | 6530 psi @Temperature 700 °F | ||
| 59.0 MPa @Temperature 316 °C | 8560 psi @Temperature 601 °F | ||
| 76.0 MPa @Temperature 260 °C | 11000 psi @Temperature 500 °F | ||
| 105 MPa @Temperature 204 °C | 15200 psi @Temperature 399 °F | ||
| 215 MPa @Temperature 149 °C | 31200 psi @Temperature 300 °F | ||
| 505 MPa @Temperature 100 °C | 73200 psi @Temperature 212 °F | ||
| 605 MPa @Temperature 24.0 °C | 87700 psi @Temperature 75.2 °F | ||
| 625 MPa @Temperature -28.0 °C | 90600 psi @Temperature -18.4 °F | ||
| 650 MPa @Temperature -80.0 °C | 94300 psi @Temperature -112 °F | ||
| 730 MPa @Temperature -196 °C | 106000 psi @Temperature -321 °F | ||
| Tensile Strength, Yield | 538 MPa | 78000 psi | AA; Typical |
| 38.0 MPa @Strain 0.200 %, Temperature 271 °C | 5510 psi @Strain 0.200 %, Temperature 520 °F | ||
| 48.0 MPa @Strain 0.200 %, Temperature 316 °C | 6960 psi @Strain 0.200 %, Temperature 601 °F | ||
| 62.0 MPa @Strain 0.200 %, Temperature 260 °C | 8990 psi @Strain 0.200 %, Temperature 500 °F | ||
| 83.0 MPa @Strain 0.200 %, Temperature 204 °C | 12000 psi @Strain 0.200 %, Temperature 399 °F | ||
| 185 MPa @Strain 0.200 %, Temperature 149 °C | 26800 psi @Strain 0.200 %, Temperature 300 °F | ||
| 470 MPa @Strain 0.200 %, Temperature 100 °C | 68200 psi @Strain 0.200 %, Temperature 212 °F | ||
| 540 MPa @Strain 0.200 %, Temperature 24.0 °C | 78300 psi @Strain 0.200 %, Temperature 75.2 °F | ||
| 560 MPa @Strain 0.200 %, Temperature -28.0 °C | 81200 psi @Strain 0.200 %, Temperature -18.4 °F | ||
| 580 MPa @Strain 0.200 %, Temperature -80.0 °C | 84100 psi @Strain 0.200 %, Temperature -112 °F | ||
| 650 MPa @Strain 0.200 %, Temperature -196 °C | 94300 psi @Strain 0.200 %, Temperature -321 °F | ||
| Elongation at Break | 5.0 % @Temperature -196 °C | 5.0 % @Temperature -321 °F | |
| 8.0 % @Temperature -80.0 °C | 8.0 % @Temperature -112 °F | ||
| 9.0 % @Temperature -28.0 °C | 9.0 % @Temperature -18.4 °F | ||
| 11 % @Temperature 24.0 °C | 11 % @Temperature 75.2 °F | ||
| 14 % @Temperature 100 °C | 14 % @Temperature 212 °F | ||
| 40 % @Temperature 149 °C | 40 % @Temperature 300 °F | ||
| 70 % @Temperature 204 °C | 70 % @Temperature 399 °F | ||
| 76 % @Temperature 260 °C | 76 % @Temperature 500 °F | ||
| 80 % @Temperature 316 °C | 80 % @Temperature 601 °F | ||
| 80 % @Temperature 371 °C | 80 % @Temperature 700 °F | ||
| 10 % @Thickness 1.59 mm | 10 % @Thickness 0.0625 in | AA; Typical | |
| 11 % @Diameter 12.7 mm | 11 % @Diameter 0.500 in | AA; Typical | |
| Modulus of Elasticity | 71.7 GPa | 10400 ksi | AA; Typical; Average of tension and compression. Compression modulus is about 2% greater than tensile modulus. |
| Compressive Yield Strength | 530 MPa | 76900 psi | 0.1% Permanent Set |
| Notched Tensile Strength | 386 MPa | 56000 psi | 2.5 cm width x 0.16 cm thick side-notched specimen, Kt = 17. |
| Ultimate Bearing Strength | 1089 MPa | 157900 psi | Edge distance/pin diameter = 2.0 |
| Bearing Yield Strength | 807 MPa | 117000 psi | Edge distance/pin diameter = 2.0 |
| Poissons Ratio | 0.33 | 0.33 | Estimated from trends in similar Al alloys. |
| Fatigue Strength | 150 MPa @# of Cycles 5.00e+8 | 21800 psi @# of Cycles 5.00e+8 | |
| Machinability | 70 % | 70 % | 0-100 Scale of Aluminum Alloys |
| Shear Modulus | 27.0 GPa | 3920 ksi | Estimated from similar Al alloys. |
| Shear Strength | 360 MPa | 52200 psi |
Thermal Properties:
| Thermal Properties | Metric | English | Comments |
|---|---|---|---|
| CTE, linear | 21.7 µm/m-°C @Temperature -50.0 - 20.0 °C | 12.1 µin/in-°F @Temperature -58.0 - 68.0 °F | |
| 23.4 µm/m-°C @Temperature 20.0 - 100 °C | 13.0 µin/in-°F @Temperature 68.0 - 212 °F | AA; Typical; average over range | |
| 23.5 µm/m-°C @Temperature 20.0 - 100 °C | 13.1 µin/in-°F @Temperature 68.0 - 212 °F | ||
| 24.4 µm/m-°C @Temperature 20.0 - 200 °C | 13.6 µin/in-°F @Temperature 68.0 - 392 °F | ||
| 25.4 µm/m-°C @Temperature 20.0 - 300 °C | 14.1 µin/in-°F @Temperature 68.0 - 572 °F | ||
| Specific Heat Capacity | 0.856 J/g-°C | 0.205 BTU/lb-°F | |
| Thermal Conductivity | 125 W/m-K | 870 BTU-in/hr-ft²-°F | AA; Typical at 77°F |
| Melting Point | 477 - 629.4 °C | 890 - 1165 °F | AA; Typical range based on typical composition for wrought products >= 1/4 in. thickness. Homogenization may raise eutectic melting temperature 20-40°F but usually does not eliminate it. |
| Solidus | 477 °C | 890 °F | AA; Typical |
| Liquidus | 629.4 °C | 1165 °F | AA; Typical |
Process Properties:
| Processing Properties | Metric | English | Comments |
|---|---|---|---|
| Annealing Temperature | 413 °C | 775 °F | |
| Solution Temperature | 468 °C | 875 °F | |
| Aging Temperature | 121 °C | 250 °F | for 24 hr |
Applications:
Petroleum refineries,
Boilers
Heat exchangers
Condensers
Pipelines
Cooling towers
Steam exhausts
Electric generation plants
Machinability
Machinability of this alloy is good, especially in the annealed condition. Use of oil lubrication during machining is recommended.
Forming
The 7178 alloy is difficult to work, or form, in any of the T tempers. Bend radii must be generous, as 4 or 5 times material thickness for sheet product form in T6 condition.
Welding
Resistance welding methods should be used for this alloy. Approved methods for the fusion welding of the alloy are not available.
Heat Treatment
The alloy is solution heat treated at 875 F (W temper) and water quenched. It may subsequently be given a precipitation hardening treatment - see "Aging"
Forging
No data available. Product forms are usually rolled or extruded shapes.
Cold Working
Cold working is considerably more difficult for this alloy than for many of the other aluminum alloys. Bend radii must be generous, for example 4 times thickness for 0.063" thick sheet in the T6 temper.
Annealing
Anneal at 775 F for 3 hours, cool (at any rate) to 400 F or less then heat to 450 F and hold there for 4 hours. Air cool. This will remove the solution heat treatment condition and produce O temper. For annealing during cold working a 650 F soak followed by air cooling will suffice.
Aging
Precipitation heat treatment (Aging) is done at 250 F for 24 hours to obtain T6 and T651 tempers. Foe the T76 and T7651 temper heat to 250 f for 3 hours, followed by 350 F for 20 hours and air cool.
Hardening
This alloy precipitation hardens. See "Aging".