EP3294917B2

EP3294917B2 - Improved thick wrought 7xxx aluminum alloys, and methods for making the same

Info

Publication number: EP3294917B2
Application number: EP16793338.1A
Authority: EP
Inventors: Julien Boselli; Jen C. Lin; Mark A. James; Gary H. Bray; John R. Brockenbrough
Original assignee: Arconic Technologies LLC
Current assignee: Arconic Technologies LLC
Priority date: 2015-05-11
Filing date: 2016-05-09
Publication date: 2025-09-24
Anticipated expiration: 2036-05-09
Also published as: EP4074851A1; RU2017142718A; KR20180004736A; CN107592887A; EP3294917B1; CN107592887B; WO2016183030A1; RU2017142718A3; EP3294917A1; RU2752487C2; CA2982482C; EP3294917A4; US20170088920A1; KR102610549B1; CA2982482A1

Description

BACKGROUND

Aluminum alloys are useful in a variety of applications. However, improving one property of an aluminum alloy without degrading another property is elusive. For example, it is difficult to increase the strength of a wrought aluminum alloy without affecting other properties such as fracture toughness or corrosion resistance. Another property of interest is "crack deviation", where a crack abruptly changes direction from the intended or expected fracture plane under fatigue loading (e.g., Mode I loading). Crack deviation can be a problem for aircraft manufacturers in some applications because it is difficult to take into account during design. FIG. 13 shows crack deviation of a constant load amplitude fatigue crack growth test specimen.
CN 103233148 discloses: an aluminum alloy product comprising, by weight, 5.5-10.0 % Zn, 1.5-2.8 % Mg, 1.5-2.5 % Cu, 0.01-0.50 % Cr, 0.05-0.50 % Mn, and 0.01-0.20 % Zr; and a method of preparing said aluminum alloy product.

SUMMARY OF THE DISCLOSURE

Broadly, the present patent application relates to improved thick wrought 7xxx aluminum alloy products. The new thick wrought 7xxx aluminum alloy products may realize an improved combination of crack deviation resistance and at least one of strength, elongation, fracture toughness, and corrosion resistance, among other properties.
The new thick wrought 7xxx aluminum alloy products comprise 0.080 - 0.250 wt. % Cr and have a nominal thickness of from 10.16-30.48 cm (4.0 to 12.0 inches). The new thick wrought 7xxx aluminum alloys also contain 6.0 - 10.0 wt. % Zn, 1.3 - 2.3 wt. % Mg, and 1.2 - 2.6 wt. % Cu. The new thick wrought 7xxx aluminum alloys contain 0.15 to 0.50 wt. % Mn. The new thick wrought 7xxx aluminum alloys may contain up to 0.15 wt. % Zr, up to 0.15 wt. % Ti, up to 0.15 wt. % Si, and up to 0.15 wt. % Fe, the balance being aluminum and impurities, wherein the wrought 7xxx aluminum alloy product includes not greater than 0.05 wt. % of any one of the impurities, and wherein the wrought 7xxx aluminum alloy product includes not greater than 0.15 wt. % in total of the impurities. In one embodiment, a new wrought 7xxx aluminum alloy product includes 0.080 - 0.250 wt. % Cr, 0.15 - 0.50 wt. % Mn, and 0.07 - 0.15 wt. % Zr.
As shown by the below examples, the use of chromium in combination with manganese and optionally zirconium, facilitates achievement of improved crack deviation resistance properties. Thus, the new thick wrought 7xxx aluminum alloy products generally contain a sufficient amount of chromium to obtain improved crack deviation resistance properties as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. As used herein, an "equivalent 7xxx aluminum alloy product" is of an equivalent composition, form, thickness and temper as the new thick wrought 7xxx aluminum alloy product, but contains not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. For instance, if a conventional 7085 aluminum alloy plate product, having a nominal thickness of 12.7 cm (5.00 inches), is artificially aged to achieve a typical tensile yield strength (L) of about 483 MPa (70 ksi), then an improved new thick wrought 7xxx aluminum alloy according to the invention would have an equivalent composition to the conventional 7085 aluminum alloy plate product, but would also include 0.080 - 0.250 wt. % Cr and 0.15-0.50 wt. % Mn optionally with 0.07 - 0.15 wt. % Zr, as provided below. Such an improved new thick wrought 7xxx aluminum alloy accordingly would also be a plate product, would have a nominal thickness of 12.7 cm (5.00 inches), and would also be artificially aged to achieve a typical tensile yield strength (L) of about 483 MPa (70 ksi). The improved new thick wrought 7xxx aluminum alloy, however, would achieve at least 5% better (higher) typical L-S crack deviation resistance K_max-dev at a strength of 483 MPa (70 ksi) as compared to the conventional 7085 aluminum alloy plate product, and at least partially due to the use of chromium and manganese optionally with zirconium.
During fatigue crack growth testing of C(T) specimens in the L-S orientation, there is a strong driving force for cracks to abruptly deviate at approximately 90 degrees (typically 70-110 degrees) primarily along grain boundaries aligned in the preferred microstructural direction (i.e. longitudinal direction). In the new alloys described herein, Cr-containing and Mn-containing dispersoid phases (fine intermetallic phases typically between ~20 and ~200 nm in size) form in a relatively homogeneous manner across the grain structure during processing of 7xxx aluminum alloys. The likely Cr-containing dispersoid phase in 7xxx alloys is E phase (Al₁₈Mg₂Cr₃). Mn can partially substitute for Cr in E phase but will also likely form separate dispersoid phases (e.g., Al₆Mn, Al₁₂(Mn,Fe)₃Si). Such dispersoids are believed to help keep the fatigue crack stay in plane through void initiation and growth ahead of the crack-tip. Zirconium forms Al₃Zr, which, in combination with the E phase and/or Mn-containing dispersoids, may further facilitate improved crack deviation resistance.
In one embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 10% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 12% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 14% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 16% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 18% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 20% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 22% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 24% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 26% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 28% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product realizes at least a 30% improvement in typical L-S crack deviation resistance K_max-dev as compared to an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In any of these embodiments, a new thick wrought 7xxx aluminum alloy product may realize at least equivalent L-T plane strain fracture toughness to the equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength. In any of these embodiments, a new thick wrought 7xxx aluminum alloy product may realize at least equivalent corrosion resistance (e.g., stress corrosion cracking resistance, exfoliation corrosion resistance) to the equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn, at equivalent strength.
As described above, chromium may facilitate improved crack deviation resistance properties. However, too much chromium may result in unnecessary degradation of strength and/or fracture toughness. Thus, the amount of chromium in the new thick wrought 7xxx aluminum alloy products may be limited to facilitate achievement of the improved combination of properties described herein. Further, the amount of chromium required to achieve the improved combination of properties may vary over the different types of 7xxx alloys described herein (e.g., due to magnesium content), but the amount of chromium required generally falls within the range of 0.080 to 0.250 wt. % Cr, keeping in mind to limit the amount of chromium so as to avoid coarse chromium particles.
The new thick wrought 7xxx aluminum alloy product includes an amount of chromium (in weight percent) falling within the scope of the following equations: ${Cr}_{(\min)} = 0.251 - 0.082 (Mg),$ wherein Cr_(min) ≥ 0.080; and ${Cr}_{(\max)} = 0.351 - 0.082 (Mg),$ wherein Cr_(max) ≤ 0.25;
where Mg is the amount of magnesium (in weight percent) in a new thick wrought 7xxx aluminum alloy product, and where the amount of chromium (in weight percent) in the new thick wrought 7xxx aluminum alloy product is at least as high as Cr_(min), but the amount of chromium in the new thick wrought 7xxx aluminum alloy product does not exceed Cr_(max). For instance, if a new thick wrought 7xxx aluminum alloy product includes 1.65 wt. % Mg, then this new thick wrought 7xxx aluminum alloy product may contain from 0.116 to 0.216 wt. % Cr per the above equations.
As noted above, the wrought 7xxx aluminum alloy product may include up to 0.15 wt. % Zr (e.g., 0.07 - 0.15 wt. % Zr). In one embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.09 to 0.13 wt. % Zr. In another embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.09 to 0.11 wt. % Zr. In another embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.10 to 0.12 wt. % Zr. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.07 to 0.09 wt. % Zr. In another embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.11 to 0.13 wt. % Zr. In some embodiments, the new thick wrought 7xxx aluminum alloy products are essentially free of zirconium, containing not greater than 0.03 wt. % Zr, or not greater than 0.01 wt. % Zr, or not greater than 0.005 wt. % Zr, or not greater than 0.001 wt. % Zr.
As noted above, the new thick wrought 7xxx aluminum alloy product includes 0.15 to 0.50 wt. % Mn. The amount of Mn should be limited so as to avoid detrimentally impacting the combination of strength, fracture toughness and crack deviation resistance. As shown by the below examples, some manganese is included in the new thick wrought 7xxx aluminum alloy product. In one embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.20 to 0.50 wt. % Mn. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product includes from 0.25 to 0.45 wt. % Mn.
The new thick wrought 7xxx aluminum alloy products generally contain an amount of chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 37 MPa√m (34 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In one embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 38 MPa√m (35 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 40 MPa√m (36 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 41 MPa√m (37 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In yet another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 42 MPa√m (38 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 43 MPa√m (39 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In yet another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 44MPa√m (40 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 45 MPa√m (41 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In yet another embodiment, the new thick wrought 7xxx aluminum alloy products contain an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 46 MPa√m (42 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, a new thick wrought 7xxx aluminum alloy product contains an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 47 MPa√m (43 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product contains an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 48 MPa√m (44 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn. In another embodiment, a new thick wrought 7xxx aluminum alloy product contains an amount of the chromium sufficient to obtain a typical L-S crack deviation resistance K_max-dev of at least 49 MPa√m (45 ksi√in.) as measured on a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, and at least equivalent strength to that of an equivalent 7xxx aluminum alloy product having not greater than 0.01 wt. % Cr and not greater than 0.02 wt. % Mn.
The new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize all of (a) a typical L-S crack deviation resistance K_max-dev of at least 37 MPa√m (34 ksi√in.), (b) a typical L tensile yield strength of at least 434 MPa (63 ksi), and (c) a typical L-T plane strain K_IC fracture toughness of at least 23 MPa√m (21 ksi√in.) relative to (as measured on) a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper. In one embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 92.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 93.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 93.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 94.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 94.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 95.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 95.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 96.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ - 0.8184x + 96.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 97.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 97.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 98.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ - 0.8184x + 98.61, where x is the TYS(L) and y is the L-S K_max-dev. In another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 99.11, where x is the TYS(L) and y is the L-S K_max-dev. In yet another embodiment, this new thick wrought 7xxx aluminum alloy product contains an amount of the Zn, Mg, Cu and Cr sufficient to realize the above strength and crack deviation properties and such that the realized L-S K_max-dev and TYS(L) satisfy the expression y ≥ -0.8184x + 99.61, where x is the TYS(L) and y is the L-S K_max-dev. In the above expressions, x is in units of ksi and y is in units of ksi√in.
Relating to achievement of a typical L tensile yield strength (TYS(L)) of at least 434 MPa (63 ksi) and a typical L-T plane strain K_IC fracture toughness of at least 23 MPa√m (21 ksi√in.) relative to (as measured on) a rolled 12.7 cm (5.00 inch) version of the wrought 7xxx aluminum alloy product in the T7451 or T7651 temper, as provided above, the amount of Zn, Mg and Cu in the new thick wrought 7xxx aluminum alloy product is selected to comply with (and does contain / comply with) the boundaries of equations (5) and (6), below.
Equation (5) is: $Mg \geq \frac{(A 5 * Cu + B 5 * Zn + C 5 * (Cu - 1.9) * (Zn - 8) + D 5 * {(Cu - 1.9)}^{2} + E 5 * {(Zn - 8)}^{2} + F 5)}{(G 5 * Cu + H 5 * Zn + I 5 * (Cu - 1.9) * (Zn - 8) + J 5 * {(Cu - 1.9)}^{2} + K 5 * {(Zn - 8)}^{2} + 1)}$ wherein Zn, Mg, and Cu are the amount of the Zn, the Mg and the Cu contained in the new thick wrought 7xxx aluminum alloy product, and wherein the equation (5) coefficients are:

Coefficient Value Coefficient Value

A5 -2.676 G5 -0.2805

B5 0.014 H5 0.2631

C5 -0.2327 I5 -0.017

D5 3.2411 J5 -0.5005

E5 0.1016 K5 -0.0148

F5 5.9836

Equation (6) is: Mg ≤ (A6 + B6*Zn + C6*(Zn-8)² + D6*(Zn-8)³ + E6*(Zn-8)⁴ + F6*Cu + G6*Cu*Zn + H6*Cu*(Zn-8)² + I6*Cu*(Zn-8)³ +J6*Cu*(Zn-8)⁴) wherein Zn, Mg, and Cu are the amount of the Zn, the Mg and the Cu contained in the new thick wrought 7xxx aluminum alloy product, and wherein the equation (6) coefficients are:

Coefficient Value Coefficient Value

A6 2.0238 F6 0.5835

B6 0.0905 G6 -0.121

C6 -0.0072 H6 0.0029

D6 0.0058 I6 -0.0023

E6 -0.0021 J6 0.0008
As noted above, the new thick wrought 7xxx aluminum alloy product may include up to 0.15 wt. % Ti. Titanium may be used to facilitate grain refining during casting, such as by using TiB₂ or TiC. Elemental titanium may also or alternatively be used. In one embodiment, the new thick wrought 7xxx aluminum alloy product includes from 0.005 to 0.025 wt. % Ti.
As noted above, the new thick wrought 7xxx aluminum alloy product may include up to 0.15 wt. % Si and up to 0.15 wt. % Fe as impurities. The amount of silicon and iron may be limited so as to avoid detrimentally impacting the combination of strength, fracture toughness and crack deviation resistance. In one embodiment, the new thick wrought 7xxx aluminum alloy product may include up to 0.10 wt. % Si and up to 0.12 wt. % Fe as impurities. In another embodiment, the new thick wrought 7xxx aluminum alloy product may include up to 0.08 wt. % Si and up to 0.10 wt. % Fe as impurities. In yet another embodiment, the new thick wrought 7xxx aluminum alloy product may include up to 0.06 wt. % Si and up to 0.08 wt. % Fe as impurities. In yet another embodiment, the new thick wrought 7xxx aluminum alloy product may include up to 0.04 wt. % Si and up to 0.06 wt. % Fe as impurities. In another embodiment, the new thick wrought 7xxx aluminum alloy product may include up to 0.03 wt. % Si and up to 0.05 wt. % Fe as impurities.
As noted above, the new thick wrought 7xxx aluminum alloy product has a thickness of from 10.16 - 30.48 cm (4.0 to 12.0 inches). In one embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 10.16 - 25.4 cm (4.0 to 10.0 inches). In another embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 10.16 - 20.3 cm (4.0 to 8.0 inches). In yet another embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 10.16-15.24 cm (4.0 to 6.0 inches). In another embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 10.16-12.7 cm (4.0 to 5.0 inches).
In one embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 12.7 - 30.48 cm (5.0 to 12.0 inches). In one embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 12.7 - 25.4 cm (5.0 to 10.0 inches). In another embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 12.7 - 20.3 cm (5.0 to 8.0 inches). In yet another embodiment, the new thick wrought 7xxx aluminum alloy product has a thickness of from 12.7 - 15.24 cm (5.0 to 6.0 inches).
The wrought 7xxx aluminum alloy product is in the form of a rolled product, an extruded product, or a forged product. In one embodiment, a new thick wrought 7xxx aluminum alloy product is a rolled product. In another embodiment, a new thick wrought 7xxx aluminum alloy product is an extruded product. In yet another embodiment, a new thick wrought 7xxx aluminum alloy product is a forged product (e.g., a hand forged product, a die forged product).

Definitions

As used herein, "typical longitudinal (L) tensile yield strength" or TYS(L) is determined in accordance with ASTM B557-10 and by measuring the tensile yield strength (TYS) in the longitudinal direction (L) at the T/4 location from at least three different lots of material, and with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, with the typical TYS(L) being the average of the at least 6 different measured specimen values.
As used herein, typical plane strain fracture toughness (K_IC) (L-T)" or L-T K_IC is determined in accordance with ASTM E399-12, by measuring the plane strain fracture toughness in the L-T direction at the T/4 location from at least three different lots of material using a C(T) specimen, where "W" is 10.16 cm (4.0 inches) and "B" is 5.08 cm (2.0 inches), with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, and with the typical plane strain fracture toughness (K_IC) (L-T) being the average of the at least 6 different valid K_IC measured specimen values.
As used herein, "typical L-S crack deviation resistance K_max-dev" is determined by preparing at least triplicate C(T) specimens in accordance with ASTM E647-13e01, entitled "Standard Test Method for Measurement of Fatigue Crack Growth Rates" ("ASTM E647"). The at least triplicate C(T) specimens are taken in the L-S direction from between width/3 and 2width/3 of the material, where the "B" dimension of the specimen is 6.35 mm (0.25 inch) and the "W" dimension of the specimen is 7.62 cm (3.0 inches), and with the notch tip at T/2. The test specimens are tested per the constant load amplitude test method of ASTM E647, with R = 0.1 (equal to P_min/P_max), high humidity air (relative humidity of > 90%), at room temperature. The pre-crack must meet all validity requirements of ASTM E647, and the pre-cracking must be performed at the same loading conditions as the test. The test is started using a K_max > 11.1 MPa√m (10 ksi√in.), and the starting force must be large enough that crack deviation occurs before the ASTM E647 C(T) specimen validity requirement ((W-a) ≥ (4/π)*(K_max-dev/TYS)²) is no longer met for the test. The test must be valid per ASTM E647 up to the point of crack deviation. A crack "deviates" when the crack of the C(T) specimen substantially deviates from the intended fracture plane (e.g., by 70-110°) in any direction, and the deviation leads to specimen separation along an unintended fracture plane. The average crack length at deviation (a_dev) is derived by using the weighted average of (i) the two surface values (front and back values) and (ii) one mid-thickness value (center value); weighted average (a_dev) = (front + back + 2* center)/4). K_max-dev is the maximum stress-intensity factor calculated by using the average crack length at deviation (a_dev), maximum applied force (P_max), and the stress-intensity factor expression per ASTM E647 A1.5.1.1 for the C(T) specimen (Note: ΔK and ΔP should be replaced by K_max-dev and P_max, respectively, per the stress ratio relationship R = K_min/K_max and ΔK = K_max - K_min as defined in ASTM E647 3.2.14).
In order to set a baseline to determine whether an aluminum alloy contains an amount of Zn, Mg, Cu, Cr and Mn, optionally supplementing the Cr and Mn with Zr, sufficient to achieve the above-noted properties, the typical TYS(L), the typical L-T K_IC, and/or the typical L-S K_max-dev are generally required to be determined on a rolled 12.7 cm (5.00 inch) version of the 7xxx aluminum alloy product in the T7451 and the T7651 tempers. Thus, even though an actual product may not be 12.7 cm (5.00 inches) thick, or may not be rolled, this actual product would still have a sufficient amount of Zn, Mg, Cu, Cr and Mn, optionally with Zr, as per this patent application, if that actual product would meet the property requirements when in the form of a rolled 12.7 cm (5.00 inch) version of the 7xxx aluminum alloy product in either the T7451 or the T7651 temper. As used herein, a "rolled 12.7 cm (5.00 inch) version of the 7xxx aluminum alloy product" means a 7xxx aluminum alloy product, having a composition within the scope of the Zn, Mg and Cu limits described herein, that has been conventionally rolled to a nominal thickness of 12.7 cm (5.00 inches), within thickness tolerance limits per ANSI H35.2-2001, table 7.7b.
All references to specific aluminum alloys (e.g., 7085, 7050, 7040) means the alloys described in the document "International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys", by The Aluminum Association (2015, and subsequent versions), A.K.A., the "Teal Sheets".
As used herein, "T76 temper" means the T76 temper described in ANSI H35.1-2009, and further requiring SCC resistance (stress corrosion cracking resistance), wherein the SCC resistance is tested in accordance with ASTM G47(2011) using three specimens, wherein all three specimens survive the alternate immersion test for a period of 20 days at a net stress of 172 MPa (25 ksi) in the short-transverse (ST) direction. As used herein, the "T7651" temper means the T76 temper where the plate is stress-relieved 1.5 - 3.0% by stretching prior to artificial aging.
As used herein, "T74 temper" means the T74 temper described in ANSI H35.1-2009, and further requiring SCC resistance (stress corrosion cracking resistance), wherein the SCC resistance is tested in accordance with ASTM G47(2011) using three specimens, wherein all three specimens survive the alternate immersion test for a period of 20 days at a net stress of 241 MPa (35 ksi) in the short-transverse (ST) direction. As used herein, the "T7451" temper means the T74 temper where the plate is stress-relieved 1.5 - 3.0% by stretching prior to artificial aging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are graphs illustrating properties of Example 1 alloys. Example 1 alloys do not fall within the scope of the claims.
FIG. 4 is a graph illustrating one embodiment of a property boundary requirement for tensile yield strength (L) and crack deviation resistance L-S K_max-dev.
FIGS. 5-6 are graphs illustrating properties of plant produced 13.4 cm (5.3 inch) (approx.) gauge plate.
FIGS. 7-8 are graphs illustrating properties of plant produced 16.5 cm (6.5 inch) (approx.) gauge plate.
FIGS. 9-10 are graphs illustrating properties of the alloys of Example 3.
FIGS. 11-12 are graphs illustrating properties of the alloys of Example 4.
FIG. 13 is a photograph showing a C(T) specimen having a crack deviating from the intended crack plane.

DETAILED DESCRIPTION

Example alloys 8, 9 and 30 are alloys according to the invention as defined by the claims.

Example 1

Various 7xxx aluminum alloys were cast as 15.24 cm (six inch) thick ingots (nominal). The actual compositions of the cast ingots are shown in Table 1, below. Alloy 1 is a conventional aluminum alloy, registered with the Aluminum Association as aluminum alloy 7085. The registered version of the 7085 alloy requires, among other things, 0.08 - 0.15 wt. % Zr, not greater than 0.04 wt. % Mn and not greater than 0.04 wt. % Cr, as shown by the document "International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys", The Aluminum Association (2009), page 12. Commonly-owned U.S. Patent No. 6,972,110 (among others) also relates to the 7085 alloy. Alloys 2-3 are new variants of the 7085 alloy having manganese (Mn) and/or low or no zirconium (Zr).

Table 1 - Composition of Example 1 Alloys (wt. %) - Lab Scale Materials

Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr
1	0.02	0.05	1.65	0.04	1.44	0	7.35	0.03	0.11
2	0.02	0.05	1.68	*0.25*	1.46	0	7.52	0.02	*0.07*
3	0.02	0.06	1.70	*0.50*	1.42	0	7.47	0.04	0

The balance of each alloy was aluminum and unavoidable impurities (≤ 0.03 wt. % each, ≤ 0.10 wt. % total). After casting, the ingots were stress-relieved, sawed into multiple sections, scalped, homogenized, and then hot rolled to plate having a final gauge of about 4.445 cm (1.75 inches). The alloy plates were then solution heat treated and then hot water quenched in 87.8 °C (190°F) water to simulate cooling conditions at T/2 (mid-thickness) for 12.7 cm (5 inch) plate relative to cold water (ambient) quenching. The plates were then stretched about 2.25% and then artificially aged in accordance with a standard T7651-type aging practice (see, ANSI H35.1 and AMS 4329A).
Various properties of the aluminum alloy plates were then tested. Specifically, the strength and elongation properties were tested in accordance with ASTM E8 and B557 at the T/2 location of the material. Plane strain fracture toughness properties were tested in the L-T direction and in accordance with ASTM E399 using a C(T) specimen taken from the T/2 location of the material, where the "B" dimension of the specimen was 6.35 mm (0.25 inch) and the "W" dimension of the specimen was 63.5 mm (2.5 inches). The typical L-S crack deviation resistance properties (K_max-dev) were determined per the test procedure described above, except the "W" dimension of the specimen was 33.02 mm (1.3 inches). The test is started using a K_max of approximately 22 MPa√m (20 ksi√in.)

The test results are shown in Tables 2-3, below. Table 2 provides the measured values in standard metric units, and Table 3 provides the measured values in English units. The shown strength and elongation values are averages of duplicate specimens. The fracture toughness values are taken from a single specimen. The crack deviation values are averages of triplicate specimens.

Table 2 - Measured Properties (metric units)

Alloy	TYS (L) (MPa)	UTS (L) (MPa)	Elong (L) (%)	Fracture Toughness L-T K_Q (MPa√m)	K_max-dev (MPa√m)
1	505	541	14.0	40.9	33.0
2	503	542	14.0	40	37.0
3	484	529	12.5	41.1	37.0

Table 3 - Measured Properties (English units)

Alloy	TYS (L) (ksi)	UTS (L) (ksi)	Elong (L) (%)	Fracture Toughness L-T K_Q (ksi√in)	K_max-dev (ksi√in)
1	73.2	78.5	14.0	37.2	30.0
2	73.0	78.7	14.0	36.4	33.7
3	70.3	76.7	12.5	37.4	33.6

Properties of various plant produced materials were also tested. The compositions of these plant materials are shown in Table 4, below. Table 4 - Composition of Example 1 Alloys (wt. %) - Plant Materials

Alloy Si Fe Cu Mn Mg Cr Zn Ti Zr

4 0.024 0.032 1.63 0 1.52 0 7.44 0.018 0.11

5 0.020 0.036 1.643 0 1.51 0 7.28 0.020 0.10

The balance of each alloy was aluminum and unavoidable impurities (≤ 0.03 wt. % each, ≤ 0.10 wt. % total). After casting, the plant-scale ingots were scalped, homogenized, and then hot rolled to final gauge. The alloy plates were then solution heat treated and then cold water quenched. The plates were then stretched about 2.25% and then artificially aged. Alloy 4 is a conventional 7085-style plate product rolled to a final gauge of 137.2 mm (5.4 inches). Alloy 5 is a conventional 7085-style plate product rolled to a final gauge of 132.1 mm (5.2 inches). Alloy 4 was aged to a T7651-style temper. Alloy 5 was aged to two different aging conditions, (a) a T7451-style temper (see, ANSI H35.1 and AMS 4470A) and (b) an aging condition overaged relative to the T7451-style temper. After artificial aging, the mechanical properties of Alloys 4-5 were tested as per the testing of the lab-scale materials, except the strength and elongation properties were measured at T/4, the L-S K_max-dev C(T) specimen "W" dimension was 7.62 cm (3.0 inches), and the tests were started using a K_max of approximately 11 MPa√m (10 ksi√in.) The test results are shown in Tables 5-6, below. Table 5 provides the measured values in standard metric units, and Table 6 provides the measured values in English units.

Table 5 - Measured Properties (metric units)

Alloy	TYS (L) (MPa)	UTS (L) (MPa)	Elong (L) (%)	Fracture Toughness L-T K_Q (MPa√m)	K_max-dev (MPa√m)
4	516	536	10.5	41.3	30.9
5a	492	522	13.0	N/A	34.6
5b	432	479	14.5	N/A	41.7

Table 6 - Measured Properties (English units)

Alloy	TYS (L) (ksi)	UTS (L) (ksi)	Elong (L) (%)	Fracture Toughness L-T K_Q (ksi√in)	K_max-dev (ksi√in)
4	74.8	77.7	10.5	37.6	28.1
5a	71.3	75.7	13.0	N/A	31.5
5b	62.7	69.5	14.5	N/A	38.0

FIGS. 1-3 are graphs illustrating the properties of the alloys based on the above data. As shown in FIGS. 1-3, the plant and lab-scale 7085 T7651-style materials have generally similar properties, indicating that the slow quench conditions for the lab-scale materials appropriately model the behavior of the plant produced thick gauge products. Furthermore, the addition of manganese in alloys 2-3 appears to have a limited impact on improving the combination of crack deviation resistance and tensile yield strength.

Example 2

Additional plant materials were produced and tested. The compositions of these plant materials are shown in Table 7, below.

Table 7 - Composition of Example 2 Alloys (wt. %) - Plant Materials

Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr
6	0.02	0.03	1.65	0	1.52	0	7.48	0.02	0.10
7	0.03	0.04	1.75	0	1.53	*0.14*	7.54	0.02	*0.07*
8	0.03	0.05	1.65	*0.26*	1.50	*0.15*	7.48	0.02	*0.07*
9	0.03	0.05	1.65	*0.26*	1.50	*0.15*	7.48	0.02	*0.07*

The balance of each alloy was aluminum and unavoidable impurities (≤ 0.03 wt. % each, ≤ 0.10 wt. % total). After casting, the plant-scale ingots were scalped, homogenized, and then hot rolled to final gauge. The alloy plates were then solution heat treated and then cold water quenched. The plates were then stretched about 2.25% and then artificially aged in accordance with a T7651-type aging practice (see, ANSI H35.1 and AMS 4329A).
Alloy 6 is a conventional 7085-style plate product rolled to a final gauge of 165.1 mm (6.5 inches). Alloys 7-9 are new variants of the 7085 alloy having manganese (Mn), chromium (Cr), and/or low zirconium (Zr). Alloys 7-8 were rolled to a final gauge of 137.2 mm (5.4 inches). Alloy 9 was rolled to a final gauge of 165.1 mm (6.5 inches).

After artificial aging, various properties of the aluminum alloy plates were then tested. Specifically, the strength and elongation properties were tested in accordance with ASTM E8 and B557 at the T/4 location of the material. Plane strain fracture toughness properties were tested in the S-L direction and in accordance with ASTM E399 using a C(T) specimen taken from the T/2 location of the material, where the "B" dimension of the specimen was 5.08 cm (2.0 inch) and the "W" dimension of the specimen was 10.16 cm (4.0 inches). Triplicate C(T) specimens were samples between width/3 and 2*width/3 except for alloys 8-9, where specimens were sampled two thicknesses away from the plate edge. The typical L-S crack deviation resistance properties (K_max-dev) were determined per the test procedure described above, except the "W" dimension of the specimen was 5.08 cm (2.0 inches). The test is started using a K_max of approximately 16.5 MPa√m (15 ksi√in.) The test results are shown in Tables 8-9, below. Table 8 provides the measured values in standard metric units, and Table 9 provides the measured values in English units.

Table 8 - Measured Properties (metric units)

Alloy	TYS (L) (MPa)	UTS (L) (MPa)	Elong (L) (%)	Fracture Toughness S-L K_IC (MPa√m)	K_max-dev (MPa√m)
6	516	536	8.2	29.5	30.5
7	469	507	13.0	36.4	36.8
8	467	506	13.5	36.3	47.2
9	454	498	13.5	39.8	44.7

Table 9 - Measured Properties (English units)

Alloy	TYS (L) (ksi)	UTS (L) (ksi)	Elong (L) (%)	Fracture Toughness S-L K_IC (ksi√in)	K_max-dev (ksi√in)
6	74.9	77.8	8.2	26.8	27.7
7	68.1	73.6	13.0	33.1	33.5
8	67.8	73.5	13.5	33.05	42.9
9	65.9	72.2	13.5	36.2	40.7

FIGS. 5-8 are graphs illustrating the properties of the plant based materials. As shown, the new materials having chromium, manganese, and zirconium realize a large improvement in crack deviation resistance relative to the conventional material. The new materials also realize a similar or improved strength-toughness trade-off. FIG. 4 illustrates one embodiment of a property requirement boundary for the new thick wrought 7xxx alloys based on data herein.

Example 3

Additional lab-scale materials were produced and tested. The compositions of these plant materials are shown in Table 10, below.

Table 10 - Composition of Example 3 Alloys (wt. %) - Lab-Scale

Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr
10	0.02	0.04	1.67	0	1.51	0	7.64	0.02	0.11
11	0.03	0.03	1.65	0	1.57	*0.15*	7.46	0.02	0
12	0.02	0.04	1.63	*0.45*	1.49	*0.15*	7.47	0.02	0
13	0.02	0.05	1.74	*0.46*	1.40	*0.16*	7.48	0.02	0.12
14	0.02	0.04	1.65	0	*2.11*	0	7.65	0.02	0.11
15	0.03	0.03	1.64	0	*2.05*	*0.14*	7.40	0.02	0
16	0.03	0.03	1.69	0	*2.03*	*0.15*	7.57	0.02	0
17	0.03	0.03	1.67	0	*2.02*	*0.17*	7.56	0.02	0
18	0.02	0.04	1.66	0	1.47	0	*6.32*	0.02	0.11
19	0.03	0.02	1.63	0	1.48	*0.15*	*6.39*	0.02	0
20	0.03	0.02	1.70	0	1.56	*0.21*	*6.25*	0.02	0
21	0.02	0.04	1.68	0	1.45	0	*9.68*	0.02	0.11
22	0.02	0.04	1.66	0	1.53	*0.15*	*9.32*	0.02	0
23	0.02	0.05	1.64	0	1.48	*0.21*	*9.46*	0.02	0
24	0.02	0.04	*2.48*	0	1.49	0	7.36	0.02	0.11
25	0.03	0.04	*2.39*	0	1.46	*0.17*	7.45	0.02	0
26	0.02	0.04	*2.42*	0	1.54	*0.21*	7.56	0.02	0

The balance of each alloy was aluminum and unavoidable impurities (≤ 0.03 wt. % each, ≤ 0.10 wt. % total). Alloy 10 is a conventional 7085-style alloy. Alloys 11-26 are new alloys having varying amounts of zinc (Zn), magnesium (Mg), copper (Cu), manganese (Mn), chromium (Cr), and/or zirconium (Zr).
After casting, the lab-scale ingot were stress-relieved, sawed into multiple sections, scalped, homogenized, and then hot rolled to plate having a final gauge of about 4.445 cm (1.75 inches). The alloy plates were then solution heat treated and then hot water quenched in 82.2°C (180°F) water to simulate cooling conditions at T/2 (mid-thickness) for 7.62 cm (3 inch) plate relative to cold water (ambient) quenching. The plates were then stretched about 2.25% and then artificially aged in accordance with a standard T7X51-type aging practice, expected to fall between T7651 and T7451.

After artificial aging, various properties of the aluminum alloy plates were tested. Specifically, the strength and elongation properties were tested in accordance with ASTM E8 and B557 at the T/2 location of the material. Plane strain fracture toughness properties were tested in the L-T direction and in accordance with ASTM E399 using a C(T) specimen taken from the T/2 location of the material, where the "B" dimension of the specimen was 6.35 mm (0.25 inch) and the "W" dimension of the specimen was 63.5 mm (2.5 inches). The typical L-S crack deviation resistance properties (K_max-dev) were determined per the test procedure described above, except the "W" dimension of the specimen was 33.02 mm (1.3 inches). The test is started using a K_max of approximately 22 MPa√m (20 ksi√in.) The test results are shown in Tables 11-12, below. Table 11 provides the measured values in standard metric units, and Table 12 provides the measured values in English units.

Table 11 - Measured Properties (metric units)

Alloy	TYS (L) (MPa)	UTS (L) (MPa)	Elong (L) (%)	Fracture Toughness L-T K_Q (MPa√m)	K_max-dev (MPa√m)
10	488	533	17.0	50.1	48.2
11	486	535	14.0	46.7	45.5
12	484	535	14.5	45.1	47.5
13	490	540	14.0	49.2	53.4
14	485	540	14.0	36.8	32.9
15	483	537	13.0	38.5	37.2
16	485	539	13.0	40.8	42.6
17	492	547	14.5	43.7	39.8
18	477	523	17.0	50.8	48.4
19	494	540	13.5	35.4	33.7
20	479	528	16.0	51.3	53.6
21	476	513	16.5	41.8	44.9
22	485	527	14.0	43.3	44.4
23	485	529	14.0	45.4	43.8
24	482	529	14.0	47.4	41.4
25	483	529	13.5	42.5	35.7
26	484	532	13.0	42.2	36.0

Table 12 - Measured Properties (English units)

Alloy	TYS (L) (ksi)	UTS (L) (ksi)	Elong (L) (%)	Fracture Toughness L-T K_Q (ksi√in)	K_max-dev (ksi√in)
10	70.8	77.4	17.0	45.6	43.8
11	70.6	77.6	14.0	42.5	41.4
12	70.3	77.6	14.5	41	43.2
13	71.1	78.3	14.0	44.8	48.6
14	70.3	78.4	14.0	33.5	29.9
15	70.1	77.9	13.0	35	33.9
16	70.3	78.2	13.0	37.1	38.7
17	71.4	79.4	14.5	39.8	36.2
18	69.2	75.9	17.0	46.2	44.1
19	71.6	78.4	13.5	32.2	30.7
20	69.4	76.6	16.0	46.7	48.7
21	69.1	74.5	16.5	38	40.8
22	70.4	76.4	14.0	39.4	40.4
23	70.4	76.7	14.0	41.3	39.8
24	69.9	76.8	14.0	43.1	37.7
25	70.1	76.7	13.5	38.7	32.5
26	70.3	77.2	13.0	38.4	32.8

FIGS. 9-10 are graphs illustrating properties of the Example 3 alloys. As shown, the materials respond differently to additions of Cr as a function of Zn, Mg and Cu levels. For a 7085-type alloy (alloys 10-13), the presence of Cr, Mn and Zr facilitates a K_max-dev improvement over the conventional 7085 material (alloy 10). For alloys with increased Mg content (alloys 14-17), the addition of Cr in and of itself without the need for Zr facilitates significant increases in K_max-dev at equivalent strength levels over an alloy with Zr but no Cr (alloy 14). For alloys with either lower or higher Zn (alloys 18-23), the addition of Cr in and of itself without Zr also appears to show some improvement in either strength or K_max-dev over the respective alloys with Zr but no Cr. Finally, for alloys with increased Cu content (alloys 24-26), the addition of Cr in and of itself without Zr also appears to decrease K_max-dev over an alloy with Zr but no Cr (alloy 24). Further, FIG. 10 shows that a similar trade-off between fracture toughness and tensile yield strength is achieved for a 7085-type alloy containing Cr, Mn and Zr (alloy 13) over the conventional 7085 material (alloy 10). Similarly, alloys with increased Mg, reduced or increased Zn content with additions of Cr realize similar or improved trade-offs between fracture toughness and tensile yield strength over their Cr-free and Zr-containing base alloys.

Example 4

Additional lab-scale materials were produced and tested. The compositions of these plant materials are shown in Table 13, below.

Table 13 - Composition of Example 4 Alloys (wt. %) - Lab-Scale

Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr
27	0.02	0.04	1.68	*0.23*	1.55	0	7.42	0.03	0.11
28	0.02	0.04	1.65	*0.45*	1.50	0	7.48	0.02	0.11
29	0.02	0.04	1.67	*0.24*	1.52	*0.12*	7.37	0.02	0.11
30	0.02	0.05	1.70	*0.45*	1.52	*0.13*	7.40	0.02	0.11
31	0.02	0.04	1.67	0	1.51	0	7.64	0.02	0.11
32	0.02	0.04	1.67	0	1.51	0	7.64	0.02	0.11

The balance of each alloy was aluminum and unavoidable impurities (≤ 0.03 wt. % each, ≤ 0.10 wt. % total). Alloys 31-32 are conventional 7085-style alloy. Alloys 27-30 are new alloys having varying amounts of manganese (Mn), chromium (Cr), and/or zirconium (Zr).
After casting, the lab-scale ingots were stress-relieved, sawed into multiple sections, scalped, homogenized, and then hot rolled to plate having a final gauge of about 4.445 cm (1.75 inches). The alloy plates were then solution heat treated and then hot water quenched in 87.8°C (190°F water) to simulate cooling conditions at T/2 (mid-thickness) for 12.7 (5 inch) plate relative to cold water (ambient) quenching. The plates were then stretched about 2.25% and then artificially aged in accordance with a standard T7651-type or T7451-type aging practice.

After artificial aging, various properties of the aluminum alloy plates were tested. Specifically, the strength and elongation properties were tested in accordance with ASTM E8 and B557 at the T/2 location of the material. Plane strain fracture toughness properties were tested in the L-T direction and in accordance with ASTM E399 using a C(T) specimen taken from the T/2 location of the material, where the "B" dimension of the specimen was 6.35 mm (0.25 inch) and the "W" dimension of the specimen was 63.5 mm (2.5 inches). The typical L-S crack deviation resistance properties (K_max-dev) were determined per the test procedure described above, except the "W" dimension of the specimen was 33.02 mm (1.3 inches). The test is started using a K_max of approximately 22 MPa√m (20 ksi√in). The test results are shown in Tables 14-15, below. Table 14 provides the measured values in standard metric units, and Table 15 provides the measured values in English units.

Table 14 - Measured Properties (metric units)

Alloy	Temper	TYS (L) (MPa)	UTS (L) (MPa)	Elong (L) (%)	Fracture Toughness L-T K_Q (MPa√m)	K_max-dev (MPa√m)
27	T7451	491	537	13.5	35.2	32.3
28	T7451	484	535	13.0	38.1	35.6
29	T7651	483	534	13.0	44.9	38.5
30	T7651	474	528	12.5	42.4	35.8
31	T7651	511	551	14.0	33.2	29.7
32	T7451	480	528	15.5	39.8	36.8

Table 15 - Measured Properties (English units)

Alloy	Temper	TYS (L) (ksi)	UTS (L) (ksi)	Elong (L) (%)	Fracture Toughness L-T K_Q (ksi√in.)	K_max-dev (ksi√in.)
27	T7451	71.2	78.0	13.5	32	29.4
28	T7451	70.2	77.6	13.0	34.7	32.4
29	T7651	70.1	77.4	13.0	40.9	35.0
30	T7651	68.7	76.6	12.5	38.6	32.6
31	T7651	74.1	79.9	14.0	30.2	27.0
32	T7451	69.7	76.6	15.5	36.2	33.5

FIGS. 11-12 are graphs illustrating properties of the Example 4 alloys. As shown, the addition of manganese in alloys 27 & 28 appears to have a limited impact on improving the trade-off between crack deviation resistance and tensile yield strength. Furthermore, the addition of only low levels of Cr (0.12-0.13) in alloys 29 & 30 appears to be insufficient to provide a significant impact on K_max-dev relative to conventional 7085 materials (alloys 31 & 32).

Claims

A wrought 7xxx aluminum alloy product comprising:
0.080 - 0.250 wt. % Cr;

6.0 - 10.0 wt. % Zn;

1.3 - 2.3 wt. % Mg;

1.2 - 2.6 wt. % Cu;

0.15 - 0.50 wt. % Mn;

up to 0.15 wt. % Zr;

up to 0.15 wt. % Ti;

up to 0.15 wt. % Si; and

up to 0.15 wt. % Fe,

the balance being aluminum and impurities, wherein the wrought 7xxx aluminum alloy product includes not greater than 0.05 wt. % of any one of the impurities, and wherein the wrought 7xxx aluminum alloy product includes not greater than 0.15 wt. % in total of the impurities;

wherein Cr_(min) ≤ Cr ≤ Cr_(max), wherein:
Cr_(min) = 0.251 - 0.082(Mg), wherein Cr_(min) ≥ 0.080; and

Cr_(max) = 0.351 - 0.082(Mg), wherein Cr_(max) ≤ 0.25;

wherein $Mg \geq \frac{(A 5 * Cu + B 5 * Zn + C 5 * (Cu - 1.9) * (Zn - 8) + D 5 * {(Cu - 1.9)}^{2} + E 5 * {(Zn - 8)}^{2} + F 5)}{(G 5 * Cu + H 5 * Zn + I 5 * (Cu - 1.9) * (Zn - 8) + J 5 * {(Cu - 1.9)}^{2} + K 5 * {(Zn - 8)}^{2} + 1)}$

wherein Mg ≤ (A6 + B6*Zn + C6*(Zn-8)² + D6*(Zn-8)³ + E6*(Zn-8)⁴ + F6*Cu + G6*Cu*Zn + H6*Cu*(Zn-8)² + I6*Cu*(Zn-8)³ +J6*Cu*(Zn-8)⁴)

wherein A5 = -2.676, B5 = 0.014, C5 = -0.2327, D5 = 3.2411, E5 = 0.1016, F5 = 5.9836, G5 = -0.2805, H5 = 0.2631, I5 = -0.017, J5 = -0.5005, K5 = -0.0148; and A6 = 2.0238, B6 = 0.0905, C6 = -0.0072, D6 = 0.0058, E6 = -0.0021, F6 = 0.5835, G6 = -0.121, H6 = 0.0029, I6 = -0.0023, J6 = 0.0008;

wherein wrought 7xxx aluminum alloy product is in the form of a rolled product, an extruded product, or a forged product; and

wherein a nominal thickness of the rolled product, the extruded product, or the forged product is from (4.0-12.0 inches) 101.6 to 304.8 mm.
The wrought 7xxx aluminum alloy product of claim 1, comprising 0.07 - 0.15 wt. % Zr.
The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought aluminum alloy product is essentially free of zirconium having not greater than 0.03 wt. % Zr.
The wrought 7xxx aluminum alloy products of claim 1, wherein the wrought aluminum alloy product has a nominal thickness of at least (5.0 inches) 127 mm.