MXPA06012243A

MXPA06012243A - Heat treatable al-zn-mg-cu alloy for aerospace and automotive castings.

Info

Publication number: MXPA06012243A
Application number: MXPA06012243A
Authority: MX
Inventors: Jen C Lin; Cagatay Yanar; Michael K Brandt; Xinyan Yan; Wenping Zhang
Original assignee: Alcoa Inc
Priority date: 2004-04-22
Filing date: 2005-04-22
Publication date: 2007-01-31
Also published as: AU2005238479A1; US20050238528A1; WO2005106058A2; JP2007534840A; KR20070004987A; CA2564080A1; EP1759027A4; WO2005106058A3; EP1759027A2; NO20065387L

Abstract

A heat treatable aluminum alloy for shaped castings includes from about 3.5-5.5% Zn, from about 1-3% Mg, about 0.05-0.5% Cu, and less than about 1% Si.

Description

Alloy of Al-Zn-Mg-Cu THERMOTRATABLE FOR AEROSPACE AND AUTOMOTIVE PARTS MOLDED BY EMPTYING Field of the Invention This invention relates to an aluminum alloy for casting aerospace and automotive parts, casting parts comprised of the alloy, and methods for making cast components of the alloy.

BACKGROUND OF THE INVENTION The cast aluminum parts are used in structural applications in automotive suspensions to reduce weight. The most commonly used group of alloys, Al-Si7-Mg, have well-established resistance limits.

In order to obtain lighter weight parts, a higher strength material with established properties of material for design is needed. Currently, the cast materials made from A356.0, the most commonly used Al-Si7-Mg alloy, can reliably guarantee a final tensile strength of 290 MPa (42060 lb / in2), and the tensile yield strength of 220 MPa (31908 lb / in2) with elongation of 8% or greater. There are a variety of alternative alloys and they are registered as exhibiting greater strength than the REF: 176993 alloys of Al-Si7-Mg. However, these exhibit problems in molding ability, potential for corrosion or fluidity that are not easily overcome. Therefore, alternative alloys are less suitable for use. When high strength is required, forged products are often used. These are usually more expensive than emptied products. There is the potential for considerable cost savings if the cast products could be used to replace the forged products without loss of strength, elongation, corrosion resistance, fatigue resistance, etc. This is true in both automotive and aerospace applications. Casting casting alloys that exhibit higher tensile strength and greater fatigue resistance than the Al-Si7-Mg material are desirable. These improvements can be used to reduce the weight on new parts or on existing parts that can be redesigned to use the improved material properties for greater benefit.

BRIEF DESCRIPTION OF THE INVENTION The alloy of the present invention is an Al-Zn-Mg alloy for tipping, high pressure nozzle, pressure or gravity, semi-permanent or permanent low pressure mold, investment casting, to the lost foam, cast in V-mold, or in sand mold with the following composition ranges (all in percent by weight): Zn: approximately 3.5-5.5%, Mg: approximately 1-3%, Cu: approximately 0.05-0.5%, Yes: less than about 1.0%, Fe and other incidental impurities: less than about 0.30%, Mn: less than about 0.30%. Silicon can be used up to about 1.0% to improve the molding capacity. Lower levels of silicon can be used to increase strength. For some applications, manganese can be used up to about 0.3% to improve molding capacity. In other alloys, manganese will be avoided. The alloy may also contain grain refiners such as titanium diboride, TiB2 or titanium carbide, Tic and / or anti-recrystallization agents such as zirconium or scandium. If titanium diboride is used as a grain refiner, the concentration of boron in the alloy may be in a range of 0.0025% to 0.05%. Likewise, if titanium carbide is employed as a grain refiner, the concentration of boron in the alloy may be in the range of 0.0025% to 0.05%. Typical grain refiners are aluminum alloys that contain Tic or TiB2. Zirconium, if used to prevent grain growth during heat treatment in solution, is generally employed in a range below 0.2%.

Scandium can also be used in a range below 0. 3 %. In the tempered T6, the alloy showed 50% higher yield strength than what can be obtained from A356.0-T6, while maintaining similar elongations. This will allow for designs of parts that require greater strength than alloys that are readily available at present in Al-Si-Mg alloys such as A356.0-T6 or A357.0-T6. The fatigue performance in the tempered T6 is increased with respect to the material A356.0-T6 by 30%. In one aspect, the present invention is an aluminum alloy that includes from about 3.5-5.5% Zn, from about 1-3% Mg, about 0.05-0.5% Cu and contains less than about 1% Si. In another aspect, the present invention is an aluminum alloy heat-set casting component that includes from about 3.5-5.5% Zn, from about 1-3% Mg, from about 0.05-0.5% Cu, and less of about 1% Si.

In another aspect, the present invention is a method for preparing a molded part by casting heat-treatable aluminum alloy. The method includes preparing a melt of an aluminum alloy which includes from about 3.5-5.5% Zn, from about 1-3% Mg, from about 0.05-0.5% Cu, and less than about 1% Si. The method further includes casting at least a portion of the melt in a mold configured to produce the cast part, allow the melt to solidify, and remove the molded part by casting the mold.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a photograph of a cut surface of a one-piece cast sample cast by casting of the A356.0 alloy into a shrink mold showing the tendency of shrinkage cracking of the A356.0 alloy. of the prior art; Fig. 2 is a photograph, similar to Fig. 1, of a cut surface of a second sample of the cast-molded part of A356.0 of the prior art in a shrinking mold showing the tendency of shrinkage by shrinkage of the A356.0 alloy of the prior art; Figure 3 is a photograph of a cut surface of an alloy sample of the cast-molded part of the present invention in a shrink mold showing a lack of shrinkage cracking; Figure 4 is a photograph, similar to Figure 3, of a cut surface of a second sample of the cast cast alloy of the present invention in a shrink mold showing an appearance of shrinkage cracking; Figure 5 presents the elongation and resistance data for directionally solidified samples of the present invention in condition T6; Figure 6 is a photograph of a front-end casting part of an alloy according to the present invention, showing locations from which the samples of the tensile test were obtained; Figure 7 is a plot of strength and elongation data for tensile test specimens cut from the cast part shown in FIG.

Figure 6 after the thermal treatments T5 and also after T6; Figure 8 is a graph showing the fatigue response S-N (ASTM test E 466, R = -l) of the present alloy in condition T6 compared to the response of A356.0-T6 of the prior art; Figure 9 is a graph showing the stair fatigue test of the present alloy in condition T6 compared to the response of A356.0-T6 of the prior art with the average fatigue strength for A356.0- T6; Figure 10 is a graph showing the depth of attack after an intergranular corrosion test of the alloy of the present invention compared to the A356 alloy of the prior art, - Figure 11 is a microphotograph of an alloy according to the present invention after an intergranular corrosion test, on the side as it is molded by emptying the sample; Figure 12 is a microphotograph of an alloy according to the present invention after an intergranular corrosion test, on a machined side of the sample; Figure 13 is a microphotograph of the alloy A356 of the prior art after an intergranular corrosion test; Figure 14 is a graph showing the results of a stress corrosion test on alloys of the present invention, with varying levels of copper; and Figure 15 is a graph showing the effect of copper and magnesium levels on stress corrosion cracking for the alloys of the present invention.

Detailed Description of the Invention When referring to any numerical range of values herein, these ranges are understood to include each and every number and / or fraction between the stated minimum and maximum of the interval. A range of about 3.5 to 5.5% by weight of zinc, for example, will expressly include all intermediate values from about 3.6, 3.7, 3.8 and 3.9%, to the end and including 5.3, 5.35, 5.4, 5.475 and 5.499% of Zn . The same applies to each numerical property and / or elementary range set forth herein. Table I presents composition data for the alloys that were tested. The first and third lines that show compositions are for directionally solidified, cast molded parts. The second line is for the composition used in a cast-for-cast part. The cast piece was the front head shown in Figure 6.

Table I: Composition of the Alloy Table II presents the mechanical properties at room temperature of directionally solidified alloys having the compositions shown in the first and third data lines of Table I. The first data line in Table II is for a directionally solidified cast casting comprised of the alloy of the first data line in Table I, after five weeks of natural aging. The second data line in Table 2 is for the same alloy after the heat treatment T5, and the third data line is for the alloy after the heat treatment T6. The fourth and fifth data lines in Table II are for the alloy in the bottom line of Table I, which is an alloy with high copper content. This alloy, too, was subjected to a heat treatment T6.

Table II: Mechanical properties at room temperature of cast part DS The development of the mechanical properties of directionally solidified samples of the present invention during the heat treatment is presented in Figure 5. The composition of these samples was presented in the first row of data in Table 1. The heat treatment in solution was at 554 ° C (1030 ° F) for 8 hours, which was followed by the quenching with cold water, and then artificial aging. Samples were removed from the furnace and mechanically tested after various amounts of artificial aging. The - measured properties were TYS, UTS and percent elongation. The duration of artificial aging was 15 hours. After the first 6 hours, the temperature was 121 ° C (250 ° F).

For the next 9 hours, the temperature was 160 ° C (320 ° F). The values for the TYS and UTS refer to the scale on the left; the values of the percent for elongation refer to the scale on the right. Table III presents data for cast parts by frontal patella casting as shown in Figure 6. This is an alloy according to the present invention, and has the composition presented in the second row of data in Table I. of samples 1, 2 and 3 of the tensile test are indicated in Figure 6. The tests were carried out on a molded part by casting subjected to a heat treatment T5 consisting of 160 ° C for 6 hours, and a piece molded by casting subjected to a heat treatment T6 consisting of thermal treatment in solution at 554 ° C for 8 hours followed by extension with cold water, then by artificial aging at 121 ° C for 6 hours and 160 ° C for 6 hours.

Table III: Mechanical properties at CS head frontal temperature It is noted that in Table III, extremely high values of the tensile strength and good elongation are obtained for the alloy to both the T5 and T6 tempers. Again it is pointed out that the composition was as presented in the second data line in Table I. The data presented in Table III is plotted in Figure 7. The graph in Figure 8 shows the fatigue response of SN of the alloy of the present invention compared to the response of alloy A356.0-T6 of the previous technique. This test was ASTM E466, R = -l. It can be seen that after 100,000 cycles, the alloy of the present invention is markedly superior to the alloy of the prior art. Figure 9 is a graph showing the stair fatigue test of the alloy of the present invention in condition T6 compared to the response of the alloy A356.0-T6 of the prior art with a mean value calculated for A356. 0-T6. The composition of the alloy of the present invention was as presented in the second row of data in Table I. The samples were thermally treated in solution at 526 ° C or 554 ° C, extinguished and artificially aged at 160 ° C during 6 hours. As seen above, the fatigue response of these samples is appreciably improved compared to material A356.0-T6. The average fatigue strength of the alloy of the present invention was 109.33 MPa with a standard deviation of 9.02 MPa. The standard deviation of the average resistance to fatigue was 3.01 MPa. The average resistance calculated at fatigue at 107 cycles of A356.0 T6 is 70 MPa. The corrosion resistance of the alloy of the present invention was tested using the corrosion test ASTM G110, which is the "Normal Practice for Evaluating Intergranular Corrosion Resistance of Thermotratable Aluminum Alloys by Immersion in Sodium Chloride Solution + Hydrogen peroxide" . In this test, specimens are immersed in a solution containing 57 g / L of NaCl and 10 mL / L of H202 (30%) for 6-24 hours. The specimens were then cross-sectioned and examined under optical microscopy for type (intergranular corrosion or pitting) and depth of corrosion attack. Figure 10 is a graph showing the depth of attack after the ASTM G110 corrosion test after 6 hours and 24 hours for an alloy according to the present invention and for the alloy A356.0. Figures 11 and 12 are microphotographs of an alloy according to the present invention after 24 hours of exposure to the ASTM G110 corrosion test. You can see very little intergranular corrosion in these microphotographs. Figure 13 is a microphotograph of the A356.0 alloy after 24 hours of exposure to the ASTM G110 corrosion test. Considerable intergranular corrosion can be seen in this photomicrograph. Corrosion tests were also carried out using the ASTM G44 test, which is the "Normal Practice for Exposure of Metals and Alloys by Alternate Immersion in Neutral Solution of 3.5% Sodium Chloride". In this test, the subjected specimens are subjected to a one-hour cycle that includes immersion in 3.5% NaCl solution for 10 minutes and then in laboratory air for 50 minutes. This 1-hour cycle is repeated continuously. During the test, specimens are inspected regularly for cracking and failure. Table IV presents the compositions of various alloys according to the present invention, which were employed in the ASTM G44 tests.

Table IV Table V presents the test results for the alloy compositions presented in Table IV.

Table V: ASTM Test G44 for alloys with various Mg and Cu contents Figure 14 is a graph that presents the results of these tests. You can see that, for the alloys of the present invention, and at these high magnesium levels, the copper increase provides increased resistance to stress corrosion cracking. Figure 15 is a graph showing the effect of copper and magnesium levels on stress corrosion cracking for the alloys of the present invention. This shows that for the alloys according to the present invention having magnesium in the range of 1.5-2%, it is desirable to include copper in the range of 0.25-0.3%. Tables VI and VII present the results of plant tests in which repeated shots were made from an individual liquid metal deposit. One trial was conducted on April 4; one was held on June 4 and one on September 4. In each day, the composition for all the molded parts by casting, elaborated, varied very little. Table VI presents the intervals of the compositions of the samples taken on each of the test days. The compositions contained high levels of magnesium and copper, which were expected to provide exceptionally high levels of resistance. Table VI: Test alloy composition interval in MCC plant Table VII presents the data of stress, ultimate tensile strength, tensile yield strength, and elongation for four different locations in each cast piece by casting. The column for the sample numbers marks the cast, individual castings. The column for location defines the individual mechanical test specimens cut from the molded parts by casting.

Table VII: Mechanical properties of plant test Teacher Location ÜTS YTS Alarg. Shows location ÜTS YTS Alarg. (MPa) (MPa) (%) (MPa) (MPa) (%) Tests for April 2004 Tests for June 2004 1-019 1 337 269 9.9 86 1 268 216 9.3 1-019 2 386 349 9.5 86 2 359 321 9.2 1-019 3 375 357 3.1 86 3 319 294 6.7 1-019 4 405 365 10.6 86 4 366 339 6.7 1-024 1 345 301 8.1 117 1 238 193 12.3 1-024 2 384 355 8.2 117 2 305 254 14.6 1-024 3 388 359 6.3 117 3 291 244 8.5 1-024 4 406 370 9.7 117 4 331 286 8.4 2-007 1 371 330 4.7 138 1 264 198 8.9 2. 007 2 382 340 8.2 138 2 367 320 8.8 2-007 3 381 352 5.5 138 3 343 308 7.5 2-007 4 419 378 9.25 138 4 375 341 8.9 2-024 1 349 301 8.5 138 1 373 334 6.6 2-024 2 381 340 9.25 138 lü 356 333 6.4 2-024 3 369 342 3.7 159 326 265 9.7 2-024 4 408 370 11.7 159 392 352 11.7 3-165 1 331 268 10.1 159 368 339 7.2 3-165 4 436 382 8.85 159 404 369 9.3 1-014 371 335 6.1 159 1L 407 359 9.2 1-014 392 352 8.4 159 l 413 375 7.9 1-014 348 318 5.1 166 393 354 7.2 1-014 392 357 7.5 Tests September 2004 Sample Location ÜTS YTS ALarg. Sample Location UTS YTS ALarg. (MPa) (MPa) (%) (MPa) (MPa) (%) 79 1 326 267 12.4 129 1 330.5 270.5 11 79 2 385 338 9 129 2 351.5 296.5 5 79 3 401 356 9.8 129 3 369 316 11 79 4 387 357 5.6 129 4 387.5 352.5 6 53 1 355 303 12.9 151 1 284 269 4 53 2 396 343 10.8 151 2 349 302 10 53 3 396 349 9.5 151 3 380.5 334.5 10 53 4 404 371 5.7 151 4 378 365.5 4 48 1 361 305 11.6 152 1 364.5 311.5 10 48 2 393 342 11.1 152 2 386 349 6 48 3 395 350 8.85 152 3 351 320 3 48 4 373 332 6.8 152 4 382 347 6 It is pointed out that at these high levels of magnesium and copper, excellent levels of resistance are obtained, with good elongation. Having described the presently preferred embodiments of the invention, it is to be understood that the invention may be otherwise incorporated within the scope of the appended claims. It is noted that in relation to this date, the best method known by the applicant to carry out the present invention is that which is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Heat-treatable aluminum alloy for castings by casting, characterized in that it comprises, in percent by weight, alloying ingredients as follows: Zn: approximately 3.5-5.5%, Mg: about 1-3%, Cu: about 0.05-0.5%, Si: less than about 1%, 2. Aluminum alloy according to claim 1, characterized in that it also comprises at least one refiner of grain selected from the group consisting of boron, carbon and combinations thereof. 3. Aluminum alloy according to claim 2, characterized in that the at least one grain refiner includes boron in a range of about 0.0025 to about 0.05%. 4. Aluminum alloy according to claim 2, characterized in that the at least one grain refiner includes carbon in a range from about 0.0025 to about 0.05%. 5. Aluminum alloy according to claim 1, characterized in that it further comprises at least one anti-recrystallization agent selected from the group consisting of zirconium, scandium and combinations thereof. 6. Aluminum alloy according to claim 5, characterized in that the at least one anti-recrystallization agent includes zirconium in a v range below 0.2%. 7. Aluminum alloy according to claim 5, characterized in that the at least one anti-recrystallization agent includes scandium in a range below 0.3%. 8. Aluminum alloy according to claim 1, characterized in that the zinc is at a concentration of about 4.2 to 4.8%. 9. Aluminum alloy according to claim 1, characterized in that magnesium is at a concentration of about 1.7 to 2.3%. 10. Aluminum alloy according to claim 8, characterized in that the copper is at a concentration of about 0.25-0.3%. 11. Aluminum alloy according to claim 10, characterized in that the copper is at a concentration of approximately 0.27-0.28%. 12. Aluminum alloy according to claim 1, characterized in that a concentration of iron in alloy is less than about 0.3%. Aluminum alloy according to claim 1, characterized in that a concentration of manganese in the alloy is less than about 0.3%. 1 . Cast part by casting an aluminum alloy, characterized in that the alloy comprises alloying ingredients as follows: Zn: about 3.5-5.5%, Mg: about 1-3%, Cu: about 0.05-0.5%, Si: less than about 1%, 15. Cast molded part according to claim 14, characterized in that it is after heat treatment T5. 16. Cast part cast according to claim 14, characterized in that it is after heat treatment T6. 17. Cast molded part according to claim 14, characterized in that the zinc is at a concentration of approximately 4.2-4.8%. 18. Cast molded part according to claim 14, characterized in that the magnesium is at a concentration of approximately 1.8-2.2%. 19. Casting part according to claim 14, characterized in that the copper is at a concentration of approximately 0.25-0.3%. 20. Cast molded part according to claim 14, characterized in that the copper is at a concentration of approximately 0.27-0.28%. Method for producing an aluminum alloy casting, characterized in that it comprises: preparing a melt of an aluminum alloy, the alloy comprising alloying ingredients as follows: Zn: about 3.5-5.5%, Mg: about 1-3%, Cu: approximately 0.05-0.5%, Si: less than about 1%, cast by casting at least a portion of the melt in a mold configured to produce the molded part by casting; allow the melt in the mold to solidify; Remove the molded part by emptying the mold. 22. Method according to claim 21, characterized in that it also comprises subjecting the molded part by casting to a heat treatment T5. 23. Method according to claim 21, characterized in that it also comprises subjecting the molded part by casting to a heat treatment T6. 24. Method according to claim 21, characterized in that the zinc is at a concentration of about 4.2-4.8%. 25. Method according to claim 21, characterized in that the magnesium is at a concentration of about 1.8-2.2%. 26. Method according to claim 21, characterized in that the copper is at a concentration of approximately 0.25-0.3%. 27. Method according to claim 26, characterized in that the copper is at a concentration of approximately 0.27-0.28%.