ALUMINUM ALLOYS HAVING SILICON, MAGNESIUM, COPPER AND ZINC

Abstract

New aluminum alloys are disclosed. The new aluminum alloys may include from 0.70 to 1.4 wt. % Si, from 0.70 to 1.3 wt. % Mg, wherein (wt. % Mg)/(wt. % Si) is not greater than 1.40, from 0.70 - 3.0 wt. % Zn, from 0.55 to 1.3 wt. % Cu, wherein the total amount of Si+Mg+Zn+Cu is not greater than 4.25 wt. %, from 0.01 to 0.30 wt. % Fe, up to 0.70 wt. % Mn, up to 0.15 wt. % Cr, up to 0.20 wt. % Zr, up to 0.20 wt. % V, and up to 0.25 wt. % Ti, the balance being aluminum, optional incidental elements and impurities. The new aluminum alloys may realize an improved combination of properties, such as an improved combination of strength, formability and/or corrosion resistance.

Claims

1. A aluminum alloy sheet product comprising: from 0.70 to 1.4 wt. % Si; from 0.70 to 1.3 wt. % Mg; wherein (wt. % Mg)/(wt. % Si) is not greater than 1.4:1; from 0.70 to 3.0 wt. % Zn; from 0.55 to 1.3 wt. % Cu; wherein the total amount of Si+Mg+Zn+Cu is not greater than 4.25 wt. %; from 0.01 to 0.30 wt. % Fe; up to 0.70 wt. % Mn; up to 0.15 wt. % Cr; up to 0.20 wt. % Zr; up to 0.20 wt. % V; up to 0.25 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 at least one of the following properties: (i) a TYS-LT of not greater than 155 MPa at 7 days of natural aging (“TYS-7NA”); (ii) a TYS-LT of not greater than 175 MPa at 90 days of natural aging (“TYS-90NA”); (iii) a (TYS-90NA) minus (TYS-7NA) of not greater than 20 MPa; (iv) a TYS-LT of at least 235 MPa when naturally aged for 30 days and then paint baked at 180° C. for 20 minutes; (v) a TYS-LT of at least 230 MPa when naturally aged for 90 days and then paint baked at 180° C. for 20 minutes; and (vi) a TYS-LT of at least 350 MPa when naturally aged for 30 days and then artificially aged at 180° C. for 8 hours.

2. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.75 wt. % Si.

3. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes not greater than 1.35 wt. % Si.

4. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.75 wt. % Mg.

5. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes not greater than 1.25 wt. % Mg.

6. The aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Si) is not greater than 1.3:1.

7. The aluminum alloy sheet product of claim 1, 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 1.0 wt. % Zn.

9. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes not greater than 2.8 wt. % Zn.

10. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.60 wt. % Cu.

11. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes not greater than 1.25 wt. % Cu.

12. The aluminum alloy sheet product of claim 1, wherein the aluminum alloy includes at least 0.05 wt. % Mn.

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

14. An aluminum alloy sheet product comprising: from 0.85 to 1.05 wt. % Si; from 0.80 to 1.10 wt. % Mg; from 0.70 to 1.8 wt. % Zn; from 0.70 to 1.05 wt. % Cu; wherein the total amount of Si+Mg+Zn+Cu is not greater than 4.25 wt. %; from 0.01 to 0.30 wt. % Fe; up to 0.50 wt. % Mn; up to 0.15 wt. % Cr; up to 0.20 wt. % Zr; up to 0.20 wt. % V; up to 0.25 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.

Description

DETAILED DESCRIPTION

EXAMPLE 1

[0121] Thirty alloys were cast as 6″×18″ ingots. The compositions of those ingots are provided in Table 1, below.

TABLE-US-00001 TABLE 1 Composition of Ex. 1 Alloys (in wt. %)* Si + Mg + Alloy Si Fe Cu Mn Mg Cr Zn Cu + Zn  1 0.11 0.17 0.06 0.20 3.75 0.03 3.62 7.54  2 0.10 0.14 0.05 0.19 4.65 0.04 3.49 8.283  3 0.09 0.14 0.05 0.19 3.69 0.02 4.45 8.281  4 0.10 0.18 0.05 0.21 4.74 0.02 4.48 9.37  5 0.10 0.17 0.05 0.20 4.38 0.02 4.03 8.557  6 0.10 0.17 0.06 0.79 4.31 0.03 3.96 8.429  7 0.20 0.17 0.06 0.20 4.12 0.03 4.06 8.438  8 0.11 0.17 0.06 0.78 4.61 0.03 4.63 9.406  9 0.85 0.12 0.49 0.20 0.81 0.03 0.01 2.161 10 1.10 0.12 0.99 0.17 0.82 0.03 — 2.913 11 1.10 0.12 0.49 0.20 1.05 0.02 0.03 2.672 12 1.10 0.13 0.74 0.20 1.16 0.02 0.04 3.039 13 0.73 0.14 0.75 0.20 0.80 0.03 0.01 2.286 14 0.71 0.15 0.97 0.21 0.94 0.03 0.01 2.626 15 0.68 0.15 0.51 0.20 1.20 0.03 — 2.393 16 0.88 0.16 0.99 0.20 1.19 0.03 — 3.064 17 0.86 0.12 0.22 0.19 1.00 0.03 0.75 2.83 18 0.89 0.15 0.74 0.20 0.95 0.03 0.74 3.32 19 1.13 0.13 0.48 0.21 1.19 0.03 0.78 3.58 20 1.07 0.13 0.52 0.19 0.80 0.03 1.53 3.92 21 0.89 0.14 0.75 0.20 1.02 0.03 0.79 3.45 22 0.87 0.14 0.73 0.40 0.97 0.03 0.76 3.33 23 0.68 0.13 0.48 0.19 0.81 0.03 1.51 3.48 24 0.89 0.13 0.51 0.21 1.20 0.03 1.55 4.15 25 0.70 0.13 0.97 0.20 1.16 0.03 1.55 4.38 26 1.09 0.12 0.99 0.18 1.21 0.03 1.52 4.81 27 0.89 0.12 1.00 0.20 0.81 0.03 1.49 4.19 28 0.90 0.12 0.74 0.21 1.00 0.03 2.59 5.23 29** 0.88 0.12 0.76 0.04 0.93 0.25 0.71 3.28 30 1.06 0.13 0.75 0.05 1.20 0.25 0.74 3.75 *The balance of each alloy was 0.02-0.03 wt. % Ti, aluminum, 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. **Alloy 29 is an AA6055-style alloy as per U.S. Pat. No. 6,537,392. The Aluminum Association composition limits on the AA6055 alloy are as follows: 0.6-1.2 wt. % Si, 0.30 (max) wt. % Fe, 0.50-1.0 wt. % Cu, 0.10 (max) wt. % Mn, 0.7-1.1 wt. % Mg, 0.20-0.30 wt. % Cr, 0.55-0.9 wt. % Zn, 0.10 (max) wt. % Ti, 0.05 (max) wt. % impurities, 0.15 (max) wt. %, in total, of the other impurities, balance aluminum. (“International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys,” January 2015, page 10, The Aluminum Association, 1525 Wilson Boulevard, Arlington, VA 22209.)
Alloys 18, 21-22 and 27 are invention alloys. Alloys 1-17, 19-20 and 23-26 and 28-30 are non-invention alloys and are highlighted in gray.

[0122] After casting, the ingots were homogenized and then rolled to final gauge sheet products. The final gauge sheet products had a thickness of 2 mm. The final gauge sheet products were then solution heat treated, quenched to room temperature, and then re-heated to a pre-aging temperature of 82° C. (179.6° F.), and then subject to a simulated coil cool by holding in a furnace programmed to cool at a prescribed cooling rate (consistent with Newtonian cooling) to bring the alloys to a T43 temper. The natural aging response of the alloys was then evaluated by measuring each alloy's mechanical properties at 7 and 90 days of natural aging (as measured from the time the alloys were quenched after solution heat treatment). The paint bake response of the T43 tempered alloys was also tested by heating to 180° C. for 20 minutes. The artificial aging response of the alloys was also tested by aging the T43 tempered alloy at 180° C. for 8 hours (a T6-type temper). The results of the experiments are provided in Table 2, below, where all indicated values are TYS-LT (tensile yield strength values from the long-transverse direction) and in MPa units, NA=natural aging, PB=paint baked as per above, and T6=artificial aged as per above.

TABLE-US-00002 TABLE 2 Mechanical Properties of Example 1 Alloys 7 Days 90 Days (90-7 30 days 90 days 30 days Alloy of NA of NA days NA) post PB post PB post T6 1 212 231 19 N/A N/A N/A 2 230  246*  16* N/A N/A N/A 3 260  270*  10* N/A N/A N/A 4 281  294*  13* N/A N/A N/A 5 239 259 20 N/A N/A N/A 6 268 285 17 N/A N/A N/A 7 235 254 20 N/A N/A N/A 8 288 308 21 N/A N/A N/A 9 131 150 19 231 219 342 10 166 171  5 246 238 349 11 150 162 12 237 229 355 12 150 153  3 244 236 352 13 129 150 21 231 223 342 14 151 155  4 232 232 346 15 132 142 10 224 213 322 16 157 164  7 245 242 365 17 138 163 26 240 222 355 18 147 163 16 252 244 360 19 151 165 14 249 242 357 20 134 157 23 235 225 333 21 151 162 10 249 234 362 22 N/A N/A N/A 268 231 364 23 133 152 19 236 221 341 24 151 166 15 261 243 359 25 150 157  8 225 220 337 26 164 173  9 266 248 363 27 148 160 13 245 240 350 28 157 170 13 261 248 360 29 153 167 15 259 249 364 30 137 163 26 259 237 344 *Values for alloys 2-4 are after 60 days of natural aging.

[0123] Natural Aging Properties: As shown, non-invention alloys 1-8, 10, 16, 26, and 28 fail to meet the parameter of a TYS-LT of not greater than 155 MPa at 7 days of natural aging and/or not greater than 175 MPa at 90 days of natural aging. Further, the strength of non-invention alloys 8, 13, 17, 20, and 30 increased too much (more than 20 MPa) between 7 days of natural aging and 90 days of natural aging. Achieving strengths of not greater than 155 MPa at 7 days of natural aging, not greater than 175 MPa at 90 days of natural aging, and with not greater than a 20 MPa increase in strength from 7 days of natural aging to 90 days of natural aging is important for formability purposes. [0124] Note: Natural aging test data for invention alloy 22 are not included as the B557 test specimens for this alloy were inappropriate for other non-relevant reasons. However, based on additional testing, it is believed that alloy 22 would meet the requirements of a TYS-LT of not greater than 155 at 7 days of natural aging, a TYS-LT of not greater than 175 at 90 days of natural aging, and not greater than a 20 MPa increase in TYS-LT from 7 to 90 days of natural aging.

[0125] Paint Bake Properties: As shown, non-invention alloys 9, 11, 13-15, 17, 20, 23 and 25 realized insufficient post paint baking strengths, having a TYS-LT of less than 235 MPa 30 days after paint baking and/or having a TYS-LT of less than 230 MPa 90 days after paint baking. Low post paint baking strength and loss of strength over time after paint baking is not acceptable for most automotive applications.

[0126] Artificial Aging Properties: As shown, non-invention alloys 9-10, 13-15, 20, 23, 25 and 30 all realized insufficient artificial aging strengths, having a TYS-LT of less than 350 MPa after artificial aging. Low artificial aging strength may make the alloys inapplicable for some automotive applications.

[0127] Aside from mechanical properties, the corrosion resistance of several alloys was also tested, the results of which are provided in Tables 3-4 below.

TABLE-US-00003 TABLE 3 Intergranular Corrosion Results (ASTM G110) Corrosion Depth Measurement (μm) Max. Ave. Alloy 1 2 3 4 5 (μm) (μm) Notes 10 177 97.3 94.2 160.3 133.5 177 132 IG + pitting 10 178.7 168 122.7 98.3 79.8 179 130 IG + pitting 14 111 93.5 70.7 103.9 63 111 88 IG + pitting 14 170.3 150.6 140.2 152.6 142.2 170 151 IG + pitting 22 131.8 149 96.6 118 220.6 221 143 IG + pitting 22 142.4 145.7 145 74.7 85.4 146 119 IG + pitting 23 99.8 145.7 87.8 139 128.3 146 120 IG + pitting 23 162.8 116.6 132.7 138 173.5 174 145 IG + pitting 24 180.2 138.7 121.3 162.8 138.7 180 148 IG + pitting 24 172.9 170.9 159.5 162.8 164.2 173 166 IG + pitting

TABLE-US-00004 TABLE 4 Filiform Corrosion Results (ASTM DG85-A2) Maximum Track measurements along the scribe AVG MAX Alloy #tracks/cm 1 2 3 4 5 Length Length Alloy 6 >20 0.78 0.78 0.76 0.76 0.75 0.766 0.78 >20 0.6 0.58 0.6 0.6 0.6 0.596 0.60 >20 0.75 0.7 0.65 0.65 0.7 0.690 0.75 Alloy 7 6 0.49 0.49 0.49 0.48 0.45 0.480 0.49 8 0.60 0.58 0.55 0.53 0.50 0.552 0.60 6 0.52 0.48 0.48 0.48 0.40 0.472 0.52 Alloy 10 4 0.30 0.30 0.26 0.25 0.25 0.272 0.30 5 0.38 0.18 0.22 0.19 0.18 0.230 0.38 5 0.36 0.26 0.24 0.23 0.35 0.288 0.36 Alloy 14 5 0.33 0.27 0.25 0.25 0.25 0.270 0.33 7 0.30 0.30 0.34 0.27 0.27 0.296 0.34 6 0.37 0.30 0.33 0.36 0.28 0.328 0.37 Alloy 22 8 0.29 0.24 0.30 0.22 0.24 0.258 0.30 9 0.30 0.25 0.25 0.25 0.25 0.260 0.30 8 0.30 0.30 0.29 0.26 0.25 0.280 0.30 Alloy 23 7 0.21 0.20 0.20 0.20 0.20 0.202 0.21 6 0.26 0.25 0.25 0.25 0.24 0.250 0.26 8 0.26 0.25 0.24 0.24 0.20 0.238 0.26 Alloy 24 5 0.42 0.38 0.37 0.40 0.35 0.384 0.42 6 0.30 0.25 0.30 0.24 0.23 0.264 0.30 6 0.45 0.42 0.50 0.45 0.40 0.444 0.50

[0128] As shown, the intergranular corrosion resistance of the alloys is generally acceptable. However, the filiform corrosion of alloys 6-7, 10, 14 and 24 is too high on a maximum length basis, being greater than 0.30 inch. It is expected alloy 12 would behave similar to alloys 10 and 14 as it relates to filiform corrosion, so alloy 12 is considered a non-invention alloy. It is expected alloy 19 would behave similar to alloy 24 as it relates to filiform corrosion, so alloy 19 is considered a non-invention alloy.

[0129] These results indicate a specific combination of alloying elements must be used to achieve a combination of properties that may be important for aluminum alloy sheet products.

[0130] Specifically, alloys with too much solute (e.g., alloys 1-8, 25-26, 28) may realize unacceptable strength and/or corrosion resistance. Thus, the amount of Si+Mg+Cu+Zn is limited to not greater than 4.25 wt. %. The specific amounts of silicon and magnesium are also important. Too little silicon (e.g., alloys 15 and 23) results in poor properties. Further, the Mg:Si ratio should be not greater than 1.4 as shown by alloys 15 and 25, whose high Mg:Si ratios were at least partially responsible for their poor strengths. High amounts of both copper and zinc should be used to successfully achieve good strength and corrosion resistance. This is shown by contrasting invention alloys 18, 21-22 and 27 versus various non-invention alloys. Finally, chromium should be avoided, as it negatively impacts potential properties (per alloy 30) and also potentially affects the recyclability of the alloys.

[0131] 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.