Aluminum alloy that is not sensitive to quenching, as well as method for the production of a semi-finished product

Abstract

An aluminum alloy that is not sensitive to quenching, for the production of high-strength forged pieces that are low in inherent tension, and high-strength extruded and rolled products, consisting of: 7.0-10.5 wt. % zinc, 1.0-2.5 wt. % magnesium, 0.1-1.15 wt. % copper, 0.06-0.25 wt. % zirconium, 0.02-0.15 wt. % titanium, at most 0.5 wt. % manganese, at most 0.6 wt. % silver, at most 0.10 wt. % silicon, at most 0.10 wt. % iron, at most 0.04 wt. % chrome, and at least one element selected from the group consisting of: hafnium, scandium, strontium and/or vanadium with a summary content of at most 1.0 wt. %. The alloy can also contain contaminants at proportions of at most 0.05 wt. % per element and a total proportion of at most 0.15 wt. %, wherein the remaining component includes aluminum.

Claims

1. A aluminum alloy semi-finished product manufactured from an aluminum alloy that is not sensitive to quenching, the product having a thickness of at least 100 mm said product being manufactured from an aluminum alloy with the following chemical composition comprising: 7.0-10.5 wt. % zinc; 0.06-0.25 wt. % zirconium; 1.0-2.5 wt. % magnesium; 0.1-1.15 wt % copper; 0.02-0.15 wt. % titanium; 0.05-0.4 wt. % manganese; 0.001-0.03 wt. % boron; between 0.2 wt % and 0.6 wt. % silver; at most 0.10 wt. % silicon; at most 0.10 wt. % iron; at most 0.04 wt. % chromium; a plurality of contaminants at proportions of at most 0.05 wt. % per element with a total contaminant proportion of at most 0.15 wt. %; wherein a remaining amount by wt % is aluminum; wherein a sum of the alloy elements zinc and magnesium and copper is at least 9 wt. %; wherein the amount of zinc and magnesium is in the form of a zinc:magnesium ratio that is between 4.4 and 5.3; and which product has been quenched after a solution heat treatment, by which quenching the product has lost less strength than alloys AA7010, AA7050, or AA7075 during the same process.

2. A aluminum alloy semi-finished product manufactured from an aluminum alloy that is not sensitive to quenching, the product having a thickness of at least 150 mm said product being manufactured from an aluminum alloy with the following chemical composition comprising: 7.0-10.5 wt. % zinc; 0.06-0.25 wt. % zirconium; 1.0-2.5 wt. % magnesium; 0.1-1.15 wt % copper; 0.02-0.15 wt. % titanium; 0.05-0.4 wt. % manganese; 0.001-0.03 wt. % boron- between 0.2 wt % and 0.6 wt. % silver; at most 0.10 wt. % silicon; at most 0.10 wt. % iron; at most 0.04 wt. % chromium; a plurality of contaminants at proportions of at most 0.05 wt. % per element with a total contaminant proportion of at most 0.15 wt. %; wherein a remaining amount by wt % is aluminum; wherein a sum of the alloy elements zinc and magnesium and copper is at least 9 wt. %; wherein the amount of zinc and magnesium is in the form of a zinc:magnesium ratio that is between 4.4 and 5.3; and which product has been quenched after a solution heat treatment, by which quenching the product has lost less strength during quenching than alloys AA7010, AA7050, or AA7075 during the same process.

3. The product according to claim 2, wherein the alloy further comprises one or more elements selected from the group consisting of: hafnium, scandium, strontium and vanadium with a summary content of at most 1.0 wt. % and 0.2-0.6 wt % silver.

4. The product according to claim 2, wherein the alloy further comprises 0.001-0.03 percent by weight boron, and wherein said silver is between 0.2-0.4 wt %.

5. The product according to claim 2, wherein the alloy further comprises a maximum of 0.2 percent by weight cerium and a maximum of 0.30 percent by weight scandium.

6. The product according to claim 2, wherein the alloy further comprises a maximum of 0.2 percent by weight cerium.

7. The product according to claim 2, wherein the alloy contains 1.6 to 1.8 wt. % magnesium and 0.8 to 1.1 wt. % copper.

8. The product according to claim 2, wherein the alloy contains 0.8 to 1.1 wt. % copper and 0.3 to 0.4 wt. % manganese.

9. The product according to claim 2, wherein the alloy contains 0.8 to 1.1 wt. % copper.

10. The product according to claim 2, wherein the alloy contains 0.25 to 0.40 wt. % silver.

11. The product according to claim 2, wherein the alloy contains 0.10 to 0.15 wt. % titanium.

12. The product as in claim 2, wherein the iron and silicon content is at most 0.08 wt. %, in each instance.

13. An aluminum alloy semi-finished product configured to be formed as an airplane part having been manufactured by forging, extruding, or rolling, the product being manufactured from an aluminum alloy that is not sensitive to quenching, the product having a thickness of at least 150 mm said product being manufactured from an aluminum alloy has the following chemical composition comprising: 7.0-10.5 wt. % zinc; 0.06-0.25 wt. % zirconium; 1.0-2.5 wt. % magnesium; 0.1-1.15 wt % copper; 0.02-0.15 wt. % titanium; 0.05-0.4 wt. % manganese; 0.001-0.03 wt. % boron- between 0.2 wt % and 0.6 wt. % silver; at most 0.10 wt. % silicon; at most 0.10 wt. % iron; at most 0.04 wt. % chromium; a plurality of contaminants at proportions of at most 0.05 wt. % per element with a total contaminant proportion of at most 0.15 wt %; wherein the remaining amount by wt % is aluminum; wherein the sum of the alloy elements zinc and magnesium and copper is at least 9 wt. %; wherein the amount of zinc and magnesium is in the form of a zinc:magnesium ratio that is between 4.4 and 5.3; and which product has been quenched after a solution heat treatment, by which quenching the product has lost less strength than alloys AA7010, AA7050, or AA7075 during the same process.

14. The product according to claim 12, wherein the alloy further comprises one or more elements selected from the group consisting of: hafnium, scandium, strontium and vanadium with a summary content of at most 1.0 wt. %, and also 0.2-0.7 wt % silver.

15. The product according to claim 13, wherein the alloy further comprises 0.001-0.03 percent by weight boron and wherein said silver is between 0.2-0.4 wt %.

16. The product according to claim 13, wherein the alloy further comprises a maximum of 0.2 percent by weight cerium and a maximum of 0.30 percent by weight scandium.

17. The product according to claim 13, wherein the alloy further comprises a maximum of 0.2 percent by weight cerium.

18. The product as in claim 13, wherein the alloy contains 0.001 to 0.03 wt. % boron.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings, which disclose one embodiment of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.

(2) In the drawings wherein similar reference characters denote similar elements throughout the several views:

(3) FIG. 1 is a graph representing the strength behavior of various AA 7xxx alloys as a function of the average cooling speed during quenching from solution heat treatment temperature; and

(4) FIG. 2 is a flow chart for a process for producing the alloy.

DETAILED DESCRIPTION

(5) The following are examples of different embodiments of the invention.

Examples

(6) To produce sample pieces to carry out the required strength studies, two typical alloy compositions of the claimed aluminum alloy were produced. The two alloys Z1, Z2 have the following composition:

(7) TABLE-US-00001 TABLE 1 Si Fe Cu Mn Mg Cr Zn Ti Zr Ti + Zr Alloy Z1 0.05 0.05 0.95 0.390 1.700 0.002 8.350 0.035 0.120 0.155 Alloy Z2 0.04 0.07 0.90 0.004 1.650 0.001 8.500 0.025 0.120 0.145

(8) The alloys Z1, Z2 were cast to produce extrusion blocks having a diameter of 370 mm, on an industrial scale. The extrusion blocks were homogenized to balance out the micro-segregation resulting from solidification. The blocks were homogenized in two stages, in a temperature range of 465 degrees C.-485 degrees C., and cooled.

Example 1

(9) After the casting skin of the blocks produced in this manner had been lathed off, the homogenized blocks were pre-heated to 370 degrees C. and formed multiple times to produce free-form forged pieces having a thickness of 250 mm and to a width of 500 mm.

(10) Subsequently, the free-form forged pieces of alloy Z1 and Z2 were solution heat treated at 485 degrees C. for at least 4 hours, quenched in water at room temperature, and subsequently artificially aged between 100 degrees C. and 160 degrees C., wherein the artificial aging was carried out in two stages. In the first stage, the semi-finished product was heated to more than 100 degrees C. and held at this temperature for more than eight hours. The second stage, which was carried out immediately after the first stage, took place at a temperature of more than 130 degrees C. for more than five hours.

(11) Drawing samples were taken from the artificially aged free-form forged pieces, on which the strength properties at room temperature were determined in the sample positions long (L), long-transverse (LT), and short-transverse (ST). The average strength properties of the alloy Z1 and Z2 for a thickness of 250 mm with water quenching are shown in the following table:

(12) TABLE-US-00002 TABLE 2 Alloy Stress Direction R.sub.p02 (MPa) R.sub.M (MPa) A.sub.5 (%) Z1 L 504 523 11.2 Z1 LT 502 533 5.2 Z1 ST 498 522 8.0 Z2 L 520 528 8.6 Z2 LT 508 530 4.0 Z2 ST 511 525 5.1

(13) The results show that the R.sub.p02 and R.sub.m.sub._values are almost identical for all three stress directions, and lie above 490 MPa for the stretching limit (R.sub.p02) and above 520 MPa for tensile strength. The A.sub.5 values are highest for the L direction, and reach at least 4% breaking elongation (A.sub.5) for the two transverse directions. The fracture resistance K.sub.IC of the sample positions L-T and T-L was determined using compact drawn samples (W=50 mm) from the same free-form forged pieces, according to ASTM-E 399. The K.sub.IC values are listed as follows:

(14) TABLE-US-00003 Alloy Test Direction Position K.sub.IC (MPa{square root over (M)}) R.sub.P.02 (MPa) Z1 L-T Edge 30.5 529 Z1 L-T Core 32.9 504 Z1 T-L Edge 23.1 516 Z1 T-L Core 20.4 502 Z2 L-T Edge 30.3 514 Z2 L-T Core 35.9 520 Z2 T-L Edge 23.6 514 Z2 T-L Core 21.8 508

(15) The stress crack corrosion resistance was determined on round samples for the LT and the ST position, according to ASTM G47 (alternating immersion test). The results are listed below for the alloy Z1:

(16) TABLE-US-00004 Stress Duration Stress Mpa Duration (Days) Electrical Conductivity LT 320 >30 34.7 LT 320 >30 34.7

(17) For both test directions, lifetimes of more than 30 days are obtained at stresses of 320 MPa. In typical specifications for high-strength Al alloys, such as for AA 7050, for example, these lifetimes are demanded at minimum stresses of 240 MPa. This means that-the new alloy, despite clearly greater strength as compared with the alloy AA 7050, at the same time has a stress crack corrosion resistance that clearly lies above the minimum value for AA 7050.

(18) Analogously, forged pieces having the same parameters were produced from the alloy Z1. In addition, the forged pieces were cold-upset in the short transverse direction (ST) after solution heat treatment and quenching, to reduce the inherent stresses resulting from quenching. After the subsequent hardening, which was performed in two stages, in accordance with the parameters indicated above, the strength properties were determined at room temperature, in the sample positions long (L), long-transverse (LT), and short-transverse (ST). The results for the alloy Z1 are listed in the following table:

(19) TABLE-US-00005 Alloy Stress Direction R.sub.p.02 (MPa) R.sub.m (MPa) A.sub.5 (%) Z1 L 504 523 11.2 Z1 LT 502 533 5.2 Z1 ST 498 522 8.0 Z1 + Cold L 448 501 11.1 Upsetting Z1 + Cold LT 468 516 6.7 Upsetting Z1 + Cold ST 417 498 10.8 Upsetting

(20) The results show that the R.sub.p02 and R.sub.m values for all three stress directions are less, and that the lowest value was found for the short-transverse direction (ST). The A.sub.5 values are highest for the L direction, and reach-at least 6% breaking elongation A.sub.5 for the two-transverse directions. The decrease in strength can be reduced by shortening the second hardening stage. The fracture strength K.sub.IC in sample positions L-T and T-L was determined according to ASTM-E 399, using compact drawn samples (W=50 mm) from the same free-form forged pieces. The K.sub.IC values are listed in the following table:

(21) TABLE-US-00006 Alloy Test Direction Position K.sub.IC (MPa{square root over (M)}) R.sub.P.02 (MPa) Z1 L-T Edge 30.5 529 Z1 L-T Core 32.9 504 Z1 T-L Edge 23.1 516 Z1 T-L Core 20.4 502 Z1 + Cold L-T Edge 38.9 485 Upsetting Z1 + Cold L-T Core 42.2 448 Upsetting Z1 + Cold T-L Edge 23.9 474 Upsetting Z1 + Cold T-L Core 21.9 468 Upsetting

Example 2

(22) In another series of experiments, free-form forged pieces having a thickness of 150 mm and a width of 500 mm were produced from alloy Z1 and, after solution heat treatment, were quenched in water or a water/glycol mixture with approximately 20% and approximately 40%, respectively, and warm settled as described above. One forged piece was additionally cold upset after being quenched in water. The influence of the various cooling media was determined on drawn samples that were taken from the forged pieces in the directions long (L), long-transverse (LT), and short-transverse (ST). The average strength properties of the alloy for a thickness of 150 mm for various cooling treatments are shown as follows:

(23) TABLE-US-00007 Quenching R.sub.m Medium Stress Direction R.sub.p.02 (MPa) (MPa) A.sub.5 (%) Water (RT) L 551 573 10.3 Water (RT) LT 515 544 7.5 Water (RT) ST 505 549 8.0 Water (RT) + L 491 537 12.8 Cold Upsetting Water (RT) + LT 465 520 8.7 Cold Upsetting Water (RT) + Cold ST 430 513 8.5 Upsetting Water/Glycol L 545 566 12.5 (16-20%) Water/Glycol LT 520 547 7.2 (16-20%) Water/Glycol ST 512 548 8.3 (16-20%) Water/Glycol L 503 529 12.2 (38-40%) Water/Glycol LT 493 525 5.0 (38-40%) Water/Glycol ST 487 526 5.6 (38-40%)

(24) The results show that a reduction in the cooling speed by adding glycol has hardly any influence on the strength properties of the alloy. The ductility decreases only minimally with a decreasing cooling speed, i.e. an increasing glycol content.

(25) The fracture resistance K.sub.IC was determined in the sample positions L-T and T-L, according to ASTM-E 399, using compact drawn samples (W=50 mm) from the same free-form forged pieces. The K.sub.IC values are contained in the following table:

(26) TABLE-US-00008 QUENCHING TEST MEDIUM DIRECTION K.sub.IC (MPa{square root over (M)}) R.sub.P.02 (MPa) WATER (RT) L-T 36.8 551 WATER (RT) T-L 23.8 515 WATER (RT) + COLD L-T 39.1 491 UPSETTING ATER (RT) + COLD T-L 24.1 465 UPSETTING WATER/GLYCOL L-T 28.2 545 (16-20%) WATER/GLYCOL T-L 20.7 520 (16-20%) WATER/GLYCOL L-T 35.4 503 (38-40%) WATER/GLYCOL T-L 18.5 493 (38-40%)

(27) No clear dependence on the cooling speed is evident for the L-T position, but for the T-L position, a trend towards slightly lower values with decreasing cooling speed can be seen.

Example 3

(28) To determine the strength properties, the alloy Z1 was also cast in another example, analogous to the first example, and blocks for extrusion were produced.

(29) After the casting skin had been lathed off, the homogenized blocks were pre-heated to over 370 degrees C. and pressed into extrusion profiles having a rectangular cross-section, with a thickness of 40 mm and a width of 100 mm.

(30) Subsequently, the profiles were solution heat treated for at least 4 hours at 485 degrees C., quenched in water at room temperature, and subsequently artificially aged between 100 degrees C. and 160 degrees C., in two stages (first stage: >100 degrees C., >8 h; second stage: >130 degrees C., >5 h).

(31) Drawn samples were taken from the artificially aged extrusion profiles, on which the strength properties were determined at room temperature, in the sample positions long (L), long-transverse (LT), and short-transverse (ST). The average strength properties of the alloy Z1 for an extruded rectangular profile (40*100 mm) for water quenching with subsequent stretching are listed in the following table:

(32) TABLE-US-00009 STRESS DIRECTION R.sub.p.02 (MPa) R.sub.m (MPa) A.sub.5 (%) L 600 609 9.3 LT 554 567 7.1 ST 505 561 7.5

(33) The results show that the R.sub.p02 and R.sub.m values are highest in the L direction, at values of 600 MPa and 609 MPa, respectively, and lowest in the ST direction, at values of 505 MPa and 561 MPa, respectively. The A.sub.5 values are highest for the L direction, and reach at least 7% breaking elongation A.sub.5 for the two transverse directions. The fracture resistance_K.sub.IC in the sample positions L-T and T-L was determined according to ASTM-E 399, using compact drawn samples (W=50 mm) from the same free-form forged pieces. The average fracture mechanics properties of the alloy Z1 and Z2 for a thickness of 250 mm and water quenching are contained in the following table:

(34) TABLE-US-00010 Test Direction K.sub.IC (MPa{square root over (M)}) R.sub.P.02 (MPa) L-T 50.9 50.9 T-L 30.7 30.7

(35) FIG. 1 shows a diagram representing the strength behavior of various AA 7xxx alloys as a function of the average cooling speed during quenching from solution heat treatment temperature. It is clearly evident in this representation that the loss in strength when using the claimed aluminum alloy is significantly less, even at low cooling speeds, than in the case of the comparison alloys AA 7075, AA 7010, and AA 7050.

(36) The strength values of the products/semi-finished products produced with the claimed alloy, determined within the scope of the description of the invention, are significantly improved, in particular with regard to stress crack corrosion resistance, as compared with products of previously known alloys, which represents a result that was not foreseeable in the form that occurred. The results shown are also interesting in that the strength values described can be particularly presented with artificial aging that is carried out in only two stages.

(37) FIG. 2 shows a flow chart for a process for producing the alloy. For example, step 1 comprises providing the alloy which is disclosed in the above examples. In step 2, the alloy is hot formed as described above, and in step 3, the alloy is solution heat treated as described above. In step 4, the alloy is quenched, while in step 5, the alloy is optionally cold formed, while in step 6, the alloy is artificially aged as described above.

(38) Accordingly, while a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.