ALUMINUM ALLOY 7255-T7751 Very High Strength, Fatigue-Resistant Plate DESCRIPTION APPLICATIONS Alcoa developed aluminum alloy AA 7255 plate for use in aerospace applications requiring very high strength and fatigue resistance. Compared to alloy 7075, 7150 and 7055 plate, alloy 7255 offers higher strength and improved fatigue resistance with similar or better fracture toughness and corrosion resistance. Alloy 7255 plate can replace alloys 7075, 7150 and 7055 and other high strength plate alloys in applications requiring high tensile or compressive strength such as upper wing panels. The machining and fabrication characteristics of 7255 plate are the same or very similar to that of other high strength 7xxx plate products. Alloy 7255 plate is available in the plant-aged T7751 temper and in the W51 temper for user age forming to the T79E01* temper. The available thickness range for 7255 plate is 0.75 to 1.5 inches (19.0 to 38.1 mm). *Alcoa’s internal designation for age formable temper. COMMERCIAL STATUS Alcoa alloy 7255 plate has been supplied commercially to customer and industry specifications since 2003 and is currently used for upper wing panels on commercial aircraft. 7255-T7751 is covered by AMS 4463 and material design allowables are available in the MMPDS Handbook. CHEMICAL COMPOSITION AND MECHANICAL PROPERTIES The following tables and figures show the composition of 7255, and how the plant-aged T7751 and the T79E01 age form temper compare with each other and 7075, 7150 and 7055. Chemical Composition Limits • AA 7255 (Wt.%)* Zn Cu Mg Zr Mn Cr Ti Si Fe Al 7.6 – 8.4 2.0 – 2.6 1.8 – 2.3 0.08 – 0.15 0.05 max 0.04 max 0.06 max 0.06 max 0.09 max Remainder *Other elements: 0.05 wt.% max (each); 0.15 wt.% max (total) Static Properties • 7255 Plate • Minimum Values (S or A-Basis) Alloy/Temper Dir. Thickness, Inch (mm) 7255-T7751 (AMS 4463) 7255-T79E01 (S or A est.*) 7075-T651 (AMS 4045) 7150-T7751 (AMS 4252) 7055-T7751 (AMS 4206) 0.75 – 1.50 (19.0 – 38.1) 0.50 – 1.00 (12.7 – 38.1) 1.00 – 2.00 (25.4 – 50.8) 0.75 – 1.50 (19.0 – 38.1) 0.50 – 1.50 (12.7 – 38.1) Tensile Strength, Ftu, ksi (MPa) L 91 (627) 88 (607) 76 (524) 84 (579) 89 (614) LT 91 (627) 88 (607) 77 (531) 84 (579) 89 (614) Tensile Yield, Fty, ksi (MPa) L 88 (607) 86 (593) 69 (476) 78 (538) 86 (593) LT 86 (593) 84 (579) 67 (462) 77 (531) 85 (586) L 9 8 na 8 7 LT 7 7 6 8 8 L 88 (607) 86 (593) 66 (455) 77 (531) 86 (593) Elongation, %, 4D Comp. Yield, Fcy ksi (MPa) *T79E01 is Alcoa’s internal designation for the age formable temper. Properties obtained from lot release capability tests to demonstrate aging response of W51 temper. Estimated minimum values determined in accordance with MMPDS guidelines, but have not been approved by AMS or MMPDS. User minimums may differ depending on time and temperature capability of age forming equipment. CONTACT AND PROCUREMENT For additional information on 7255 plate, contact your local Alcoa Sales Account Manager. FATIGUE AND DAMAGE TOLERANCE PROPERTIES The fracture toughness and fatigue crack growth resistance of 7255 is similar to 7075, 7150, and 7055. The S-N fatigue resistance of 7255 is improved over these same alloys. The level of improvement will depend on stress concentration factor, (Kt), and specimen and testing details. FCG Curves 1.0E-03 1.0E-04 Fracture Toughness • 7255-T7751 7255-T7751 7055-T7751 7150-T7751 7075-T651 Orient. KIc Minimum ksi√in (MPa√m) KIc Typical ksi√in (MPa√m) L-T 22 (24) 24 (26) T-L 21 (23) 24 (26) L-T 22 (24) 24 (26) T-L 21 (23) 24 (26) L-T 22 (24) na 7055-T7751 T-L 20 (22) na 7255-T7751 L-T na 26 (29) T-L na 22 (24) da/dN (in/cycle) Alloy/Temper L-T Orientation R=0.1, RH>90% Frequency=25 Hz 1.0E-05 7150-T7751 1.0E-06 1.0E-07 1 10 100 K (ksi in) S-N Fatigue, Kt = 2.5 S-N Fatigue, Kt = 2.3 35 7055-T79E01 7255-T79E01 25 20 L Direction Open Hole, Kt=2.3 (net) R=0.1, RH>90% Frequency=25 Hz 15 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 Maximum Net Stress (ksi) Maximum Net Stress (ksi) 30 L, Direction, Open Hole Kt=2.5 (net) R=0.1, Lab Air Frequency: 25-30 Hz 30 25 7055-T7751 7255-T7751 20 1.0E+04 Fatigue Life (Cycles) 1.0E+05 1.0E+06 1.0E+07 Cycles to Failure CORROSION RESISTANCE The exfoliation corrosion and SCC resistance of 7255 in the T7751 and T79E01 tempers is the same as 7055 in the same temper, and superior to 7xxx alloys in T6 tempers. The minimum guaranteed EXCO (ASTM G34) is EB for the T7751 temper and EC for the T79E01 temper. The minimum guaranteed SCC resistance (ASTM G47) of the T79E01 temper in the ST direction is 16 ksi (110 MPa) compared to a typical SCC resistance of < 10 ksi (69 MPa) for 7075 in the T6 temper. ALCOA AEROSPACE AND AUTOMOTIVE PRODUCTS P.O. BOX 8025 • BETTENDORF, IOWA 52722 • 1-800-523-9596 • www.alcoa.com Product specifications are subject to change without notice. ©2016 Alcoa Inc. 1/16