6XXX ALUMINUM ALLOYS

Abstract

New 6xxx aluminum alloy products and methods and systems of making the same are disclosed. A method may include heating a billet of a 6xxx aluminum alloy to a preheat temperature, holding the billet at the preheat temperature for a time sufficient to dissolve at least some precipitate hardening phases of the billet, extruding the billet into an extruded product wherein, during the extruding, both the billet and the extruded product are maintained at or above the preheat temperature, discharging the extruded product from the extrusion apparatus while maintaining the extruded product within 100° F. of a solvus temperature of the 6xxx aluminum alloy, and moving the extruded product from the heating shroud to a quenching apparatus.

Claims

1. A 6xxx extruded product comprising: from 0.2 to 2.0 wt. % Si; from 0.2 to 1.5 wt. % Mg; one of either: (i) from 0.07 to 1.0 wt. % Mn; or (ii) less than 0.07 wt. % Mn; up to 1.5 wt. % Bi; up to 1.5 wt. % Sn; up to 1.0 wt. % Cu; up to 1.0 wt. % Zn; up to 0.7 wt. % Pb; up to 0.7 wt. % Fe; up to 0.35 wt. % Cr; up to 0.35 wt. % V; up to 0.25 wt. % Zr; up to 0.20 wt. % Ti; the balance being aluminum, optional incidental elements and impurities; wherein, when the 6xxx extruded product includes from 0.07 to 1.0 wt. % Mn, the 6xxx extruded product comprises an unrecrystallized microstructure as measured from T/10 to 9T/10 of the 6xxx extruded product; wherein the unrecrystallized microstructure comprises at least 50 vol. % unrecrystallized grains; wherein at least 60% of the unrecrystallized grains are fibrous grains; wherein the fibrous grains have an aspect ratio (grain length/diameter) of at least 5:1; wherein the average grain size of the unrecrystallized microstructure is not greater than 200 microns; or wherein, when the 6xxx extruded product includes less than 0.07 wt. % Mn, the 6xxx extruded product comprises a recrystallized microstructure as measured from T/10 to 9T/10 of the 6xxx extruded product; wherein the recrystallized microstructure comprises at least 50 vol. % recrystallized grains; wherein at least 60% of the recrystallized grains are equiaxed grains having as aspect ratio of not greater than 5:1 (L:LT); wherein the average grain size of the recrystallized microstructure is not greater than 200 microns.

2. The 6xxx extruded product of claim 1, wherein the 6xxx extruded product comprises at least 1 vol. % more cube (ED) texture as compared to a conventional 6xxx extruded product; wherein the conventional 6xxx extruded product is conventionally press-quenched and is of a comparable composition, product form, size and temper.

3. The 6xxx extruded product of claim 2, wherein the 6xxx extruded product comprises at least 2 vol. % more cube (ED) texture as compared to the conventional 6xxx extruded product.

4. The 6xxx extruded product of claim 2, wherein the 6xxx extruded product comprises a maximum ODF [001] texture intensity, wherein the maximum ODF [001] texture intensity is at least 10% higher than a maximum ODF [001] texture intensity of a conventional 6xxx extruded product; wherein the conventional 6xxx extruded product is conventionally press-quenched and is of a comparable composition, product form, size and temper.

5. The 6xxx extruded product of claim 4, wherein the extruded 6xxx extruded product realizes a maximum ODF [001] texture intensity that is at least about 20% higher than the conventional 6xxx extruded product.

6. A method comprising: (a) heating a billet of a 6xxx aluminum alloy to a preheat temperature; (b) holding the billet at the preheat temperature for a time sufficient to dissolve at least some precipitate hardening phases of the billet; (c) after the holding step, immediately transferring the billet to an extrusion apparatus; (d) extruding the billet into an extruded product in the extrusion apparatus, wherein, during the extruding, both the billet and the extruded product are maintained at or above the preheat temperature; (e) discharging the extruded product from the extrusion apparatus and into an exit shroud, wherein the exit shroud maintains the extruded product within 100° F. of a solvus temperature of the 6xxx aluminum alloy; (f) moving the extruded product from the heating shroud to a quenching apparatus, wherein the quenching apparatus comprises at least one of a water spray and a water bath, and wherein the quenching apparatus quenches the extruded product to a temperature below 125° F. and at a cooling rate of at least 1° F./second.

7. A system comprising: (a) a furnace adapted to preheat an extrusion billet of a 6xxx aluminum alloy; (b) an extrusion apparatus adjacent to and downstream of the furnace, wherein the extrusion apparatus is adapted to extrude the billet into an extruded product; (c) an exit shroud adjacent to and downstream of the extrusion apparatus, wherein the exit shroud is adapted to maintain the extruded product within 100° F. of a solvus temperature of the 6xxx aluminum alloy; (d) a quenching apparatus located immediately adjacent to and downstream of the extrusion apparatus, wherein the quenching apparatus is adapted to cool the extruded product received from the exit shroud to a temperature below 125° F. and at a cooling rate of at least 1° F./second.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 is a block diagram illustrating one embodiment of a method (100) for producing extruded 6xxx aluminum alloy products.

[0060] FIG. 2 is a block diagram illustrating one embodiment of system (200) for producing extruded 6xxx aluminum alloy products relative to the methods of FIG. 1.

[0061] FIG. 3a is a flowchart illustrating one method for producing extruded 6xxx aluminum alloy products in the T6 or T9 temper.

[0062] FIG. 3b is a flowchart illustrating one method for producing extruded 6xxx aluminum alloy products in the T8 temper.

[0063] FIG. 4 is a top-down schematic view of one embodiment of portions of a system for producing extruded 6xxx aluminum alloy products relative to the methods of FIG. 1.

[0064] FIG. 5a illustrates micrographs of a conventionally press-quenched 6026LF product.

[0065] FIG. 5b illustrates micrographs of a new 6026LF product made by the inventive systems and methods described herein.

[0066] FIG. 6a is a micrograph of a 6026LF product made with a conventional process employing a separate post-extrusion solution heat treatment.

[0067] FIG. 6b is a micrograph of a new 6026LF product made by the inventive systems and methods described herein.

[0068] FIGS. 7a-7b are graphs showing properties of a 6026LF product made by the inventive systems and methods described herein.

[0069] FIG. 8a illustrates micrographs of a new 6020 product made by the inventive systems and methods described herein.

[0070] FIG. 9a is a micrograph of a new 6020 product (50 micrometer scale) made by the inventive systems and methods described herein.

[0071] FIG. 9b is a micrograph of a 6020 product (50 micrometer scale) made with a conventional press-quench process.

[0072] FIGS. 9c-9d illustrate additional micrographs (200 micrometer scale) of a new 6020 product made by the inventive systems and methods described herein.

[0073] FIGS. 10a-10b are graphs showing properties of a 6020 product made by the inventive systems and methods described herein.

[0074] FIGS. 11a-11b illustrate micrographs of a new 6262A product made by the inventive systems and methods described herein.

[0075] FIGS. 12a-12b are graphs showing properties of a 6262A product made by the inventive systems and methods described herein.

[0076] FIG. 13a is a photograph showing machining chips of a 6262A product made with a conventional process employing a separate post-extrusion solution heat treatment.

[0077] FIG. 13b is a photograph showing machining chips of a 6262A product made by the inventive systems and methods described herein.

[0078] FIGS. 14a-14b are graphs showing properties of a 6061 product made by the inventive systems and methods described herein.

DETAILED DESCRIPTION

Example 1

[0079] A conventional 6026LF (lead free) aluminum alloy was produced by two different methods. The basic steps of the two methods are shown in Table 1, below.

TABLE-US-00001 TABLE 1 Method 1 Method 2 (Conventional) (Inventive) Cast Billet Cast Billet Homogenize Billet Homogenize Billet Cool to Ambient Cool to Ambient Preheat to 775-800° F. Preheat above the solvus temperature Hold at preheat temperature Hold at preheat temperature for 3 to 5 minutes for ≈50 minutes Reduce the temperature and Move to extrusion press within move to extrusion press 90 seconds (e.g., to achieve (high heat losses) a heat loss of ≤10° F.) Extrude billet into rod Extrude billet into rod Discharge rod to ambient air Discharge rod to exit shroud (e.g., to maintain the rod above its solvus temperature) Move rod from ambient Move rod from heating shroud to air to water bath water sprays and then water bath Temper to T6, T8 or T9 Temper to T6, T8 or T9
The systems used to conduct the second, inventive method are consistent with those illustrated in FIGS. 2 and 4.

[0080] Micrographs of the extrudates were taken in the longitudinal direction. FIG. 5a illustrates the microstructure of the 6026LF-T9 alloys processed via Method 1, i.e., a conventional press-quench. FIG. 5b illustrates the microstructure of the 6026LF-T9 alloys processed via Method 2, i.e., the inventive method. As shown, Method 1 results in the 6026LF product having large recrystallized grains near the surface. Conversely, Method 2 produces fine fibrous unrecrystallized grains, uniform in the cross-section direction. Moreover, as shown in FIG. 6b, the microstructure of Method 2 results in a uniform distribution of fine and small constituent particles, consistent with that of a conventionally processed rod that has a completely separate furnace solution heat treatment after extrusion (FIG. 6a).

[0081] FIG. 7a illustrates the strength properties achieved by 0.5625 inch extruded 6026LF-T9 rod extruded produced according to Method 2. FIG. 7b illustrates the elongation properties achieved by these same rods. As shown, the strength and elongation of the extruded rod significantly exceed the ASTM requirements for the 6026LF alloy. The measured property values are also shown in Table 2. (All values are relative to the longitudinal direction.)

TABLE-US-00002 TABLE 2 Mechanical Properties of 6026LF Alloy UTS TYS Elong. Item (ksi) (ksi) (%) Billet 1-11 56.6 55.8 10 Billet 2-10 57.0 56.5 9 Billet 3-10 56.8 56.2 9 Billet 6-10 56.9 56.1 8 Billet 10-10 57.3 56.5 8 Billet 13-10 56.2 55.9 9 Billet 14-10 57.1 56.9 8

[0082] The new methods and systems described herein also produce improved microstructures and properties in other 6xxx aluminum alloys. For instance, FIG. 8a shows the microstructure of a 6020 alloy that has been prepared using the methods consistent with those illustrated in FIGS. 1 and 3b (T8 temper) and using systems consistent with those illustrated in FIGS. 2 and 4. As shown, the grains of the extruded 6020 alloy are fibrous and uniform in the cross section direction.

[0083] FIG. 9a illustrates a micrograph of a 6020 alloy product made by the inventive methods and systems described herein. FIG. 9b is a micrograph of a 6020 alloy product made by a conventional press-quench process. The new 6020 product has fewer large tin-bearing constituent particles and the tin-bearing constituent particles are spheroidized. Finer and better distributed tin-bearing phases contribute to improved machinability for the 6xxx free machining alloys. As also shown in FIGS. 9c-9d, the new 6020 product realizes small constituent particles are that are uniformly distributed. Such particle sizes and particle size distribution is consistent with that of a conventionally processed rod that has a completely separate furnace solution heat treatment after extrusion. The mechanical properties of the 6020 alloy in rod form (1.16 inch under 20%, 25% and 30% draw) produced by the inventive methods and systems in the T8 temper are shown in FIGS. 10a-10b. As shown, the strength and elongation values significantly exceed the 6020-T8 ASTM minimums. The measured property values are also shown in Table 3, below. (All values are relative to the longitudinal direction.)

TABLE-US-00003 TABLE 3 Mechanical Properties of 6020 Alloy UTS TYS Elong. Item (ksi) (ksi) (%) R + 10f_20%_B1 45.3 42.9 15 R + 10f_20%_B2 45.5 42.5 15 R + 10f_25%_B1 46.7 43.3 15 R + 10f_25%_B2 46.5 43.8 15 R + 10f_30%_B1 47.3 45.2 15 R + 10f_30%_B2 47.4 44.7 15 R + 22f_20%_B1 45.9 43.2 15 R + 22f_20%_B2 45.0 42.0 15 R + 22f_25%_B1 46.7 43.8 15 R + 22f_25%_B2 45.6 42.6 15 R + 22f_30%_B1 47.6 45.2 15 R + 22f_30%_B2 47.4 45.0 15

[0084] Alloy 6262A was also made by the inventive methods and systems (e.g., consistent with FIGS. 1 and 3a (T9 temper) and FIGS. 2 and 4). Again, as shown in FIGS. 11a-11b, the new 6262A products contain small constituent particles and the particle size distribution is uniform, which is consistent with that of a conventionally processed rod that has a completely separate furnace solution heat treatment after extrusion. The mechanical properties of the 6262A alloy in rod form (0.5626 inch rod) produced by the inventive methods and systems in the T9 temper are shown in FIGS. 12a-12b. As shown, the strength and elongation values significantly exceed the 6262A-T9 ASTM minimums. The measured property values are also shown in Table 4, below. (All values are relative to the longitudinal direction.)

TABLE-US-00004 TABLE 4 Mechanical Properties of 6262A Alloy UTS TYS Elong. Item (ksi) (ksi) (%) 2-2-PQ 54.1 53.1 7 2-13-PQ 54.4 53.3 7 2-7-PQ 54.1 53.1 8 3-1-PQ 54.6 53.6 8 3-6-PQ 54.7 53.7 8 3-7-PQ 54.9 53.8 7 3-14-PQ 54.9 53.8 6 4-7-PQ 54.8 53.7 7 4-10-PQ 54.6 53.6 7 4-12-PQ 55.0 53.8 8 7-1-PQ 55.2 54.1 7 8-7-PQ 55.3 54.2 6 8-12-PQ 54.9 53.8 7 9-1-PQ 54.4 53.3 7 9-6-PQ 54.9 53.8 7 9-13-PQ 54.1 53.0 7 a-PQ 55.0 53.8 6 b-PQ 55.4 54.3 6

[0085] The machinability of the 6262A rods produced by the inventive methods and systems is also significantly improved. As shown in FIG. 13a, 6262A-T9 products made using a conventional post-extrusion solution heat treatment typically exhibit a large amount of extra-long chips. Conversely, as shown in FIG. 13b, the new 6262A-T9 products manufactured using the inventive methods and systems described herein exhibit finer chips, which shows superior machinability.

[0086] Alloy 6061 was also made by the inventive methods and systems (e.g., consistent with FIGS. 1-2a (T6 temper) and FIGS. 3-4). The mechanical properties of the 6061 alloy in rod form (1.50 inch rod) produced by the inventive methods and systems in the T6 temper are shown in FIGS. 14a-14b. As shown, the strength and elongation values again significantly exceed the 6061-T6 ASTM minimums. The measured property values are also shown in Table 5, below. (All values are relative to the longitudinal direction.)

TABLE-US-00005 TABLE 5 Mechanical Properties of 6061 Alloy UTS TYS Elong. Item (ksi) (ksi) (%) 6061-1 TR 53.1 50.1 16 6061-2 TR 54.0 51.2 16 6061-3 TR 52.1 48.9 16 6061-1 TF 55.1 51.9 16 6061-2 TF 55.6 52.4 16 6061-3 TF 55.4 52.2 16

Example 2

[0087] Microstructure data for the alloys was obtained per the EBSD sample procedure shown below. Table 6 provides some illustrative properties of the alloys. The reported maximum ODF texture intensities are in the [001] plane, through the cross section. The cube texture and grain size values are in the transverse direction.

TABLE-US-00006 TABLE 6 Microstructure Data Max. ODF Cube Texture Grain Size Alloy Intensity (ED)(Vol. %) (micrometers) 6020-T8 3.545 15% 52 (Conventional SHT) 6020-T8 3.439 16% 74 (Conventional PQ) 6020-T8 6.982 27% 142 (Inventive Method) 6262A-T9 5.473 22% 192 (Conventional SHT) 6262A-T9 3.864 17% 64 (Conventional PQ) 6262A-T9 6.282 24% 184 (Inventive Method) 6026LF-T9 2.751  4% 1310 (Conventional SHT) 6026LF-T9 9.621 16% 33 (Conventional PQ) 6026LF-T9 11.225 19% 23 (Inventive Method) 6061-T6 1.558  6% 171 (Conventional SHT) 6061-T6 1.995  4% 137 (Conventional PQ) 6061-T6 10.824 17% 51 (Inventive Method)

[0088] As shown in Table 6, the alloys produced by the invention process realize a much higher maximum texture intensity over the conventional press quenched alloys and even the solution heat treated alloys. For instance, the new 6020 extruded alloy has a maximum ODF texture intensity that is 203% higher than the maximum ODF texture intensity of the conventionally extruded and press-quenched 6020 alloy (6.982/3.439=2.03).

[0089] As also shown in Table 6, the alloys produced by the invention process realize more cube ED (extrusion direction) texture as compared to the conventional press quenched alloys and even the solution heat treated alloys. For instance, the new 6020 extruded alloy includes 9 vol. % more cube ED texture than the conventionally extruded and press-quenched 6020 alloy (26 vol. % versus 17 vol. %).

[0090] Textured aluminum alloys have grains whose axes are not randomly distributed. Since the images can vary based on various factors, measured texture intensities are generally normalized by calculating the amount of background intensity, or random intensity, and comparing that background intensity to the intensity of the textures of the image. Thus, the relative intensities of the obtained texture measurements are dimensionless quantities that can be compared to one another to determine the relative amount of the different textures within a polycrystalline material. For example, an OIM analysis may determine a background (random) intensity and use orientation distribution functions (ODFs) to produce ODF intensity values. These ODF intensity values may be representative of the amount of texture within a given aluminum alloy (or other polycrystalline material).

[0091] For the present application, ODF intensities are measured according to the EBSD sample procedure (described below), or a substantially similar OIM procedure (x-ray diffraction is not used), where a series of ODF plots containing intensity (times random) representations may be created. The new 6xxx aluminum alloy products generally have a high maximum ODF intensity, indicating a high amount of texture. It is believed that the high amount of texture in the new 6xxx aluminum alloy products may contribute to their improved properties.

[0092] In one embodiment, the new extruded 6xxx aluminum alloy product realizes a maximum ODF intensity that is at least about 10% higher than a conventionally extruded and press-quenched 6xxx aluminum alloy product of comparable product form, composition and temper. For instance, if a conventionally extruded and press-quenched 6026 alloy realized a maximum ODF intensity of 4.0, then a new 6026 aluminum alloy product made by the new processing disclosed herein may realize a maximum ODF intensity of at least 4.4 (10% higher than the 4.0). In other embodiments, the new extruded 6xxx aluminum alloy product may realize a maximum ODF intensity that is at least about 20% higher, or at least about 40% higher, or at least about 40% higher, or at least about 60% higher, or at least about 80% higher, or at least about 100% higher, or at least about 120% higher, or at least about 140% higher, or at least about 160% higher, or at least about 180% higher, or at least about 200% higher, or at least about 220% higher, or at least about 240% higher, or at least about 260% higher, or at least about 300% higher, or at least about 340% higher, or at least about 360% higher, or at least about 380% higher, or at least about 400%, or at least about 420% higher, or at least about 440% higher, or at least about 460% higher, or at least about 480% higher, or at least about 500% higher, or more, than a conventionally extruded and press-quenched 6xxx aluminum alloy product of comparable product form, composition and temper.

[0093] In one embodiment, the new extruded 6xxx aluminum alloy product realizes at least 1 vol. % more cube ED texture that than a conventionally extruded and press-quenched 6xxx aluminum alloy product of comparable product form, composition and temper. For instance, if a conventionally extruded and press-quenched 6026 alloy realized 15 vol. % cube ED texture, then a new 6026 aluminum alloy product made by the new processing disclosed herein may realize 16 vol. % cube ED texture (1 vol. % more than 15 vol. %). In other embodiments, the new extruded 6xxx aluminum alloy product may realize at least 2 vol. % more, or at least 3 vol. % more, or at least 4 vol. % more, or at least 5 vol. % more, or at least 6 vol. % more, or at least 7 vol. % more, or at least 8 vol. % more, or at least 9 vol. % more, or at least 10 vol. % more, or at least 11 vol. % more, or at least 12 vol. % more, or at least 13 vol. % more than a conventionally extruded and press-quenched 6xxx aluminum alloy product of comparable product form, composition and temper.

[0094] EBSD Sample Procedure [0095] Electron backscatter diffraction (EBSD) is carried out using a Thermo-Scientific Apreo S scanning electron microscope (SEM), or similar. The SEM operating conditions are a spot size of 51 nA at an accelerating voltage 20 kV with the sample tilted at 68° and a working distance of 17 mm. The EBSD patterns are collected using an EDAX Velocity camera with 4×4 binning and EDAX Orientation Image Microscopy software (OIM v. 7.3.1), or similar. The EBSD scans are carried out using a square grid scanning pattern and dimensions of 2.8 mm tall and through thickness. [0096] The collected scan data is processed using OIM TSL Analysis software (v. 8.0). The scan data is cleaned up using two processes. The first clean-up process is a neighbor orientation correlation with a minimum confidence of 0.1 and a grain tolerance angle of 5°. The second clean-up process is a grain dilation which specified a minimum grain size of five data points containing multiple rows. These two processes were carried out with one iteration of clean up. [0097] A grain is defined as have a grain tolerance angle of 5° and a minimum number of 5 points. The grain shape is assumed to be spherical. Grain size charts are then calculated using the grain size diameters. In the charts, grain size diameters were binned and plotted against the area fraction.

[0098] While various embodiments of the new technology described herein 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 presently disclosed technology. Various ones of the unique aspects noted hereinabove may be combined to yield various new 6xxx aluminum alloy products having an improved combination of properties. Additionally, these and other aspects and advantages, and novel features of this new technology are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the following description and figures or may be learned by practicing one or more embodiments of the technology provided for by the present disclosure.