NEW 6XXX ALUMINUM ALLOYS

Abstract

New 6xxx aluminum alloys are disclosed. In one embodiment, a new 6xxx aluminum alloy sheet product includes from 0.75 to 1.05 wt. % Si, from 0.65 to 0.95 wt. % Mg, wherein (wt. % Mg)/(wt. % Si) is not greater than 0.99:1, from 0.50 to 0.75 wt. % Cu, from 0.02 to 0.40 wt. % Mn, from 0.06 to 0.26 wt. % Cr, wherein (wt. % Mn)+(wt. % Cr) is at least 0.22 wt. %, from 0.01 to 0.30 wt. % Fe, up to 0.25 wt. % Zn, up to 0.20 wt. % Zr, up to 0.20 wt. % V, and up to 0.15 wt. % Ti, the balance being aluminum, optional incidental elements and impurities.

Claims

1. A aluminum alloy sheet product comprising: from 0.75 to 1.05 wt. % Si; from 0.65 to 0.95 wt. % Mg; wherein (wt. % Mg)/(wt. % Si) is not greater than 0.99:1; from 0.50 to 0.75 wt. % Cu; from 0.02 to 0.40 wt. % Mn; from 0.06 to 0.26 wt. % Cr; wherein (wt. % Mn)+(wt. % Cr) is at least 0.22 wt. %; from 0.01 to 0.30 wt. % Fe; up to 0.25 wt. % Zn; up to 0.20 wt. % Zr; up to 0.20 wt. % V; up to 0.15 wt. % Ti; the balance being aluminum, optional incidental elements and impurities; wherein the aluminum alloy sheet product has a thickness of from 1.0 to 4.0 mm; wherein the aluminum sheet product realizes a tensile yield strength (LT) of at least 315 MPa in a T6 temper, wherein the artificial aging of the T6 temper is 30 minutes at 225° C. (437° F.).

2. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.80 wt. % Si.

3. The aluminum alloy sheet product of claim 2, wherein the aluminum alloy includes not greater than 1.0 wt. % Si.

4. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.70 wt. % Mg.

5. The aluminum alloy sheet product of claim 4, wherein the aluminum alloy includes not greater than 0.90 wt. % Mg.

6. The aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Si) is not greater than 0.95:1.

7. The aluminum alloy sheet product of claim 6, wherein (wt. % Mg)/(wt. % Si) is at least 0.7:1.

8. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.55 wt. % Cu.

9. The aluminum alloy sheet product of claim 8, wherein the aluminum alloy includes not greater than 0.73 wt. % Cu.

10. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.04 wt. % Mn.

11. The aluminum alloy sheet product of claim 10, wherein the aluminum alloy includes not greater than 0.35 wt. % Mn.

12. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.08 wt. % Cr.

13. The aluminum alloy sheet product of claim 12, wherein the aluminum alloy includes not greater than 0.24 wt. % Cr.

14. The aluminum alloy sheet product of claim 1, wherein (wt. % Mn)+(wt. % Cr) is at least 0.24 wt. %.

15. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy sheet product realizes at least one of: a three-point bend extension of at least 10.0 mm in the T6 temper; a three-point bend extension of at least 16.0 mm in the T4 temper; a maximum depth of attack of not greater than 200 micrometers when tested in accordance with ASTM G110-92(2015) for 6 hours; and an f/r of at least 0.05.

16. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy sheet product is fully recrystallized.

17. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy sheet product realizes at least one of: an area weighted average grain size of not greater than 50 micrometers; at least 10 vol. % cube texture; and a dispersoid area fraction of at least 0.5%.

18. The aluminum alloy sheet product of claim 1, wherein, in the T4 or T43 temper, the aluminum alloy sheet product realizes an increase of not greater than 15 MPa in tensile yield strength (LT) over the period of 2 weeks of natural aging to 6 months of natural aging.

19. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy sheet product realizes not greater than 21 MPa strength loss in tensile yield strength (LT) over the period of 2 weeks of natural aging to 6 months of natural aging relative to the T6 temper.

20. An automotive sheet product made from the aluminum alloy sheet product of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] FIG. 1 is a graph illustrating properties of the Example 1 alloys versus conventional 6111 and 6013 alloys.

[0084] FIG. 2 is a graph illustrating properties of the Example 2 alloys.

[0085] FIGS. 3-8 are tables illustrating the results of Example 3.

DETAILED DESCRIPTION

Example 1

[0086] Four DC ingots of the aluminum alloy shown in Table 1 were homogenized and then conventionally scalped/peeled.

TABLE-US-00002 TABLE 1 Composition of Ex. 1 Alloy (in wt. %)* Si Fe Cu Mn Mg Cr Zn Ti 0.91 0.23 0.69 0.21 0.80 0.08 0.02 0.03 *The balance of each alloy was incidental elements and impurities, where each alloy contained not greater than 0.03 wt. % of any one impurity, and where each alloy contained not greater than 0.10 wt. %, in total, of all impurities.
Some of the homogenized ingots were hot rolled to 5.842 mm (0.230 inch) followed by cold rolling (without any intermediate anneal) by 66% to a final gauge of 2.007 mm (0.079 inch). Other ingots were hot rolled to 3.531 mm (0.139 inch) followed by cold rolling (without any intermediate anneal) by 43% to a final gauge of 2.007 mm (0.079 inch). The final gauge materials were then solution heat treated in-line at various conditions, as per Table 2, below. The materials were water spray quenched in-line after solution heat treatment.

TABLE-US-00003 TABLE 2 Solution Heat Treatment (SHT) Conditions Approx. SHT Residence Temp. ° C. Condition Time (Sec.)_ (° F.) 1 ~ 150 s 521.1-560   (970-1040) 2 ~ 110 s 521.1-560   (970-1040) 3 ~ 45 s 521.1-548.9 (970-1020) 4 ~ 30 s 521.1-543.3 (970-1010) 5 ~ 2 s 521.1-523.9 (970-975)

[0087] Some of the materials were pre-aged in-line at about 66.7° C. or 72.2° C. (152° F. or 162° F.) for the 43% and 66% cold worked materials, respectively, after the quenching step so as to produce a T43 temper. Other materials were simply naturally aged after quenching to produce a T4 temper. For both the T4 and T43 tempers, all materials were naturally aged for about 1-month. The mechanical properties of the materials are shown in Table 3, below. All properties are relative to the LT (long transverse) direction.

TABLE-US-00004 TABLE 3 Mechanical Properties (LT) of Naturally Aged Alloys Sam- HR SHT Elong. ple Gauge CR Condi- TYS UTS (%) No. (mm) Amount tion Temper (MPa) (MPa) (Total) 1 3.53 43% 1 T4 186 314 26.3 2 3.53 43% 2 T4 185 313 24.0 3 5.84 66% 1 T4 183 313 26.4 4 5.84 66% 2 T4 183 313 26.2 5 3.53 43% 3 T4 174 312 27.2 6 3.53 43% 5 T4 164 301 26.6 7 5.84 66% 3 T4 172 310 27.6 8 5.84 66% 5 T4 164 300 28.2 9 3.53 43% 3 T43 161 299 26.3 10 3.53 43% 4 T43 159 298 28.2 11 3.53 43% 5 T43 147 281 21.4 12 5.84 66% 3 T43 159 297 27.9 13 5.84 66% 4 T43 155 295 25.8 14 5.84 66% 5 T43 148 286 26.0

[0088] Next, the alloys were artificially aged both with and without pre-strain (stretching) prior to the age. Specifically, the alloys were (i) aged at 185° C. (365° F.) for 20 minutes without any pre-strain (“Age1”), (ii) stretched 2% (pre-strained) and then aged at 185° C. (365° F.) for 20 minutes (“Age2”), and (iii) aged at 225° C. (437° F.) for 30 minutes without any pre-strain (“Age3”). The mechanical property results are shown in Tables 4-6, below. All properties are relative to the LT (long transverse) direction.

TABLE-US-00005 TABLE 4 Tensile Yield Strength Properties (LT) of Artificially Aged Alloys T4/T43 Age1 Age2 Age3 Sample SHT TYS TYS TYS TYS No. Condition (MPa) (MPa) (MPa) (MPa)  1 1 186 243 279 340  2 2 185 242 276 347  3 1 183 235 273 339  4 2 183 238 274 339  5 3 174 218 262 339  6 5 164 213 254 325  7 3 172 218 259 335  8 5 164 212 247 323  9 3 161 256 288 340 10 4 159 249 286 337 11 5 147 240 271 319 12 3 159 256 293 338 13 4 155 251 288 333 14 5 148 248 279 322

TABLE-US-00006 TABLE 5 Ultimate Tensile Strength Properties (LT) of Artificially Aged Alloys T4/T43 Age1 Age2 Age3 Sample SHT UTS UTS UTS UTS No. Condition (MPa) (MPa) (MPa) (MPa)  1 1 314 341 347 364  2 2 313 340 345 373  3 1 313 336 343 363  4 2 313 338 344 363  5 3 312 327 337 364  6 5 301 319 328 351  7 3 310 326 335 361  8 5 300 319 324 350  9 3 299 353 357 369 10 4 298 348 355 366 11 5 281 336 341 349 12 3 297 353 361 368 13 4 295 350 357 363 14 5 286 344 347 354

TABLE-US-00007 TABLE 6 Total Elongation Properties (LT) of Artificially Aged Alloys T4/T43 Age1 Age2 Age3 Sample SHT Elong. Elong. Elong. Elong. No. Condition (%) (%) (%) (%)  1 1 26.3 23.0 22.6 10.6  2 2 24.0 24.0 22.1 10.8  3 1 26.4 23.4 22.4 11.2  4 2 26.2 21.8 22.2 10.7  5 3 27.2 24.8 21.8 10.9  6 5 26.6 22.0 20.4 10.6  7 3 27.6 24.8 23.2 10.2  8 5 28.2 23.2 23.0 12.0  9 3 26.3 23.8 22.6 11.7 10 4 28.2 23.4 22.3 11.0 11 5 21.4 21.8 19.0 9.9 12 3 27.8 22.8 21.8 11.6 13 4 25.8 22.6 22.4 11.4 14 5 26.0 23.2 20.6 12.4

[0089] Fracture behavior was also evaluated using three-point bending tests (as defined in the Definitions section), the test results of which are provided in Tables 7-8, below. These tests are used to assess, inter alia, a material's (a) ability to be riveted without cracking and (b) behavior in crash situations. The tests were conducted relative to the transverse orientation (LT), and the reported values are based on the average of ten specimens used for each alloy tested. The properties are in relation to 1-month naturally aged materials.

[0090] In the case of Table 7, three-point bend testing was conducted in the T43 condition after 1-month of natural aging, i.e. no artificial aging was applied because material is riveted in a naturally aged condition. The same materials were also aged to Age condition 2, after which the mechanical properties (strength, elongation) were measured, as this represents the material's condition after a typical paint bake.

[0091] In the case of Table 8, both the three-point bend test results and the mechanical property measurements were taken from samples in the Age3 condition because some materials may be riveted in this condition.

TABLE-US-00008 TABLE 7 Three-point bend testing results for T43 materials plus Age2 strength results Average TYS Extension SHT (LT) (MPa) @70% (mm) CR % Condition (Age 2) (T43 temper) 43% CW 3 288 17.8 43% CW 5 271 17.3 43% CW 4 286 17.4 66% CW 3 293 17.4 66% CW 5 279 17.2 66% CW 4 288 17.3

TABLE-US-00009 TABLE 8 Three-point bend and strength results in Age3 condition Average SHT TYS Extension CR % Condition (LT) (MPa) @70% (mm) 43% CW 3 339 11.1 43% CW 5 325 12.4 66% CW 3 335 11.6 66% CW 5 323 12.7 43% CW 1 340 11.8 43% CW 2 347 12.1 66% CW 1 339 11.7 66% CW 2 339 11.8

[0092] The corrosion resistance of the artificially aged alloys was also tested, the results of which are provided in Table 9, below.

TABLE-US-00010 TABLE 9 Intergranular Corrosion Results (ASTM G110) CR SHT Age Depth of corrosive attack (μm) Max. Ave. Amount Cond. Cond. Surface 1 2 3 4 5 (μm) (μm) 66% 3 Age3 1 72.9 91.8 76.8 80.3 73.6 91.8 71.5 2 81.5 84.4 51.5 43.2 58.8 66% 5 Age3 1 78.3 56.5 52.5 82.2 77.6 82.2 60.3 2 52.9 44.9 42.7 57.6 57.7 43% 3 Age3 1 76.7 62 49.3 59.5 38.4 79 65.8 2 79 72.4 69.9 74 76.7 43% 5 Age3 1 77.7 75.9 68.8 79.7 58.4 79.7 64.5 2 50.4 49.1 56.5 58.3 70.4 66% 1 Age3 1 65.6 58.4 74.7 87.6 X 87.6 64 2 56.5 58.4 70.4 58.5 46.3 66% 2 Age3 1 77.9 79.7 48.1 63.2 56.5 85.1 67.2 2 57.7 57.2 63.8 82.7 85.1 43% 1 Age3 1 58.8 67.4 58.4 70.4 45.7 70.4 60.3 2 68.6 60.2 54.2 54 65.2 43% 2 Age3 1 62 58.9 73.6 60 62.5 77.2 60.8 2 77.2 62.02 59.1 45.5 47.1 66% 3 Age1 1 57.2 55.8 83.4 93.8 87 93.8 65.6 2 54.7 63.8 50.4 46.1 63.4 66% 4 Age1 1 79 103.3 62.7 40 37 103.3 64.4 2 73 59 62 64.5 63.8 66% 5 Age1 1 91.8 80.4 82.7 85.2 103.3 103.3 78.9 2 84 67.9 57.3 74.7 62 43% 3 Age1 1 89.9 78.3 75.3 94 79.5 94.2 84.5 2 77.2 91 82.6 94.2 82.8 43% 4 Age1 1 90.3 84 70.6 69.3 63.3 90.3 74.8 2 88.1 67 67.4 71.1 77.2 43% 5 Age1 1 79 95.6 96 87.4 78.5 96 82.4 2 80.8 81.5 74.7 66.1 84.4

[0093] Conventional 6111 and 6013 alloys were produced similar to the above, i.e., cast as ingots, hot rolled to an intermediate gauge, cold rolled to final gauge, solution heat treated and then quenched, and then naturally aged for at least two weeks. The compositions of the alloys are shown in Table 10, below.

TABLE-US-00011 TABLE 10 Compositions of the 6111 and 6013 Alloys (wt. %) Alloy Si Fe Cu Mn Mg Cr Zn Ti Al 6111 0.75 0.24 0.67 0.20 0.58 0.04 0.01 0.03 Bal. 6013 0.68 0.23 0.85 0.31 0.92 0.03 0.02 0.03 Bal.

[0094] The 6111 and 6013 materials were naturally aged for at least 1.5 months and then aged per Age3. The mechanical properties were then tested, the results of which are shown in Table 11, below. All properties are relative to the LT (long transverse) direction.

TABLE-US-00012 TABLE 11 Mechanical Property Data for 6111 and 6013 Alloys UTS TYS Elong. Average Age (LT) (LT) (LT) Extension Alloy CR % Condition (MPa) (MPa) (%) @70% (mm) 6111 43 Age3 329.9 299.6 10.6 15.4 6013 55 Age3 367.1 328.9 12.3 10.6

[0095] As shown in FIG. 1 the 6111 alloy is unable to achieve the strengths achieved by the invention alloys. As also shown in FIG. 1 the 6013 alloy is unable to achieve the high three-point bend properties achieved by the invention alloys.

[0096] The microstructure of the invention alloy materials and the 6111 and 6013 materials were also assessed. Specifically, grain size, texture, dispersoid fraction, and percent recrystallization were determined in accordance with the Microstructure Assessment Procedure, included herein. The invention alloy has a higher area fraction of dispersoids than both 6111 and 6013, and both the invention alloy and 6111 have finer dispersoids than 6013, as shown in Table 12. The invention alloys also have a notably higher f/r value than the 6013 and 6111 alloys. In the f/r ratio, f is the fraction of dispersoids (Area %/100) and r is the average dispersoid radius (Diameter/2). A higher f/r tends to result in greater grain boundary pinning, also called Zener drag, which will tend to promote fine grain size.

TABLE-US-00013 TABLE 12 Recrystallization and Grain Size Data Dispersoid ave. diameter, Grain Size, Dispersoid micro- % micro- Alloy Area % meters f/r ReX meters Invention 0.77 0.18 0.083 98% 31.4 6111 0.53 0.17 0.061 99% 30.4 6013 0.63 0.21 0.061 99% 34.6

[0097] Texture measurements were also conducted in accordance with the Microstructure Assessment Procedure, the results of which are shown in Table 13. As shown, the invention alloy and 6111 both contain notably higher levels of the cube texture, which is the most desirable component for formability and fracture behavior, compared to 6013.

TABLE-US-00014 TABLE 13 Texture Data Texture (%) Alloy Cube Goss P Brass Copper S Invention 14 12 4 3 6 16 6111 12 11 5 3 7 15 6013 7 10 8 4 6 17

Example 2

[0098] Six pilot scale aluminum alloy ingots (6-inch by 18-inch cross section) were DC cast, then homogenized and then conventionally scalped/peeled. The compositions of the six aluminum alloys are shown in Table 14, below. The alloys generally seek to vary the amount of manganese and chromium while keeping silicon, iron, copper, magnesium, zinc and titanium relatively constant.

TABLE-US-00015 TABLE 14 Composition of Ex. 2 Alloys (in wt. %)* Alloy Si Fe Cu Mn Mg Cr Zn Ti XA08 0.87 0.22 0.69 0.21 0.79 0.07 <0.005 0.02 XA09 0.87 0.26 0.68 0.05 0.78 0.03 0.03 0.02 XA10 0.91 0.25 0.68 0.05 0.81 0.20 0.01 0.02 XA11 0.91 0.26 0.68 0.20 0.82 0.03 0.02 0.02 XA12 0.90 0.27 0.68 0.22 0.81 0.20 0.01 0.02 XA13 0.92 0.24 0.69 0.13 0.80 0.11 0.01 0.02 *The balance of each alloy was incidental elements and impurities, where each alloy contained not greater than 0.03 wt. % of any one impurity, and where each alloy contained not greater than 0.10 wt. %, in total, of all impurities.

[0099] The homogenized ingots were then hot rolled to 3.531 mm (0.139 inch) followed by cold rolling (without any intermediate anneal) by 43% to a final gauge of 2.007 mm (0.079 inch). The final gauge materials were then solution heat treated at 1040° F., water quenched, stretched for flatness, and then naturally aged for 7 days. The alloys were then either aged (i) according to “Age 3” per Example 1 (i.e., at 437° F. (225° C.) for 30 minutes) or (ii) at 356° F. (180° C.) for 8 hours (“Age 4”).

[0100] The mechanical properties and microstructures of the alloys were then evaluated, the results of which are shown in Tables 15a-15b and 16-17, below, and FIG. 2. The provided mechanical properties are from the LT direction. The grain size, texture, dispersoid fraction, and percent recrystallization were determined in accordance with the Microstructure Assessment Procedure included herein, except as noted below.

TABLE-US-00016 TABLE 15a Mechanical Properties (LT) of the Example 2 Alloys in Age 3 Condition Total Average TYS UTS Elong. Extension Alloy (MPa) (MPa) (%) @70% (mm) XA08 337 360 9.7 13.2 XA09 352 373 9.3 10.3 XA10 345 370 8.5 13.9 XA11 360 381 9.6 9.0 XA12 339 364 10.6 12.4 XA13 345 368 9.0 13.0

TABLE-US-00017 TABLE 15b Mechanical Properties (LT) of the Example 2 Alloys in Age 4 Condition Total Average TYS UTS Elong. Extension Alloy (MPa) (MPa) (%) @70% (mm) XA08 358 386 11.5 12.0 XA09 366 394 10.0 9.5 XA10 360 390 10.3 12.3 XA11 375 402 9.9 8.7 XA12 359 390 11.9 11.3 XA13 364 391 11.0 11.1

TABLE-US-00018 TABLE 16 Microstructure Data of the Example 2 Alloys Dispersoid Constituent Area Wt. Dispersoid Ave. Dia., Constituent Diameter, % G.S. Alloy Area %* Micrometers* f/r Area % micrometers Rex (μm) All XA08 0.866 0.177 0.098 0.644 1.10 100 49.3 XA09 0.403 0.162 0.050 0.631 1.14 99 59.8 XA10 0.995 0.166 0.120 0.49 1.03 100 53.4 XA11 0.646 0.178 0.073 0.714 1.13 99 50.0 XA12 1.165 0.165 0.141 0.732 1.41 99 35.5 XA13 0.907 0.173 0.105 0.623 1.05 99 50.1 *Average values measured at t/2 location only.

TABLE-US-00019 TABLE 17 Texture Data of the Example 2 Alloys Texture (%) Alloy Cube Goss P Brass Copper S XA08 15.9 1.9 4.6 3.8 5.2 11.7 XA09 15.2 1.7 4.4 3.4 5.2 8.5 XA10 12.6 3.7 4.4 4.1 5.6 10.7 XA11 16.6 2.6 4.5 3.9 5.5 10.3 XA12 11.5 2.6 7.6 4.5 4.6 12.7 XA13 15.6 1.6 4.7 3.7 4.9 11.3

[0101] As the data shows, although all alloys realize high strength and suitable fracture behavior, the XA10 alloy realizes a very high combination of strength and fracture behavior (e.g., as shown in FIG. 2), which may be due to its manganese plus chromium content. For instance, the XA10 alloy realized a significantly lower amount of constituent particles (0.49%) compared to the other alloys (0.623 to 0.732%). This is especially noteworthy considering XA08, XA10, XA11 and XA13 contain similar total amounts of Fe, Si, Cr and Mn, the elements which are incorporated in the constituent particles. As also shown, the Example 2 alloys realize a similar texture to that of the invention alloy of Example 1, i.e., they contain notably high levels of the cube texture, which is the most desirable component for formability and fracture behavior.

Example 3

[0102] The natural aging and artificial aging response of the alloy of Example 1 was evaluated over a period of several weeks to several months across various conditions. FIGS. 3-5 show the natural aging results and FIGS. 6-8 show the artificial aging results. The artificial aging condition was Age1, i.e., aged at 185° C. (365° F.) for 20 minutes without any pre-strain. The artificial aging occurred after the specified weeks or months of natural aging. (Note: the data for 1 month of natural aging in FIGS. 3-8 are those already reported above in Example 1.)

[0103] As shown, the inventive alloy's properties are highly stable over the Time Test Period, which is important for automotive manufacturers because they can stock/store the invention alloys with confidence in shelf life. For the naturally aged materials, increases in tensile yield strength were less than 13 MPa for all lots over the Test Time Period, i.e., as measured from the period starting after 2 weeks of natural aging (+/−12 hours) and ending after 6 months of natural aging (+/−24 hours). For most lots, the increase was much less (see FIG. 3). Thus, good forming capabilities should be realized over the Test Time Period. Furthermore, the response to a simulated paint bake, i.e. aged at 185° C. (365° F.) for 20 minutes without any pre-strain (“Age1”) was very good. FIG. 6 shows that the tensile yield strength after paint bake is expected to be no less than 21 MPa lower after 6 months of natural aging as compared to values after 2 weeks of natural aging.

[0104] While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.