CONTINUOUSLY CAST BOLT MADE OF AN ALUMINUM-BASED ALLOY, EXTRUDED PROFILE, AND METHOD FOR PRODUCING SAME

Abstract

The invention relates to a continuously cast bolt made of an aluminum-based alloy for an extruded profile that has a yield strength of greater than 260 MPa, preferably greater than 280 MPa, in particular greater than 300 MPa. According to the invention, it is provided that the aluminum-based alloy contains, in percentage by weight, greater than 0.0% to 0.40% iron, 0.40% to 1.2% magnesium, 0.60% to 1.1% silicon, greater than 0.0% to 0.35% copper, greater than 0.0% to 0.35% chromium, 0.40% to 0.95% manganese, up to 0.2% zinc, optionally 0.005% to 0.15% titanium and/or 0.005% to 0.15% titanium diboride, and a remainder of aluminum and production-related impurities, wherein a secondary dendrite arm spacing of the microstructure is less than 100 μm. The invention furthermore relates to an extruded profile created from a continuously cast bolt of this type, and to a method for producing an extruded profile.

Claims

1. A continuously cast bolt made of an aluminum-based alloy for an extruded profile which has a yield strength of greater than 260 MPa, preferably greater than 280 MPa, in particular greater than 300 MPa, containing, in percentage by weight, greater than 0.0% to 0.40% iron, 0.40% to 1.2% magnesium, 0.60% to 0.95% silicon, greater than 0.0% to 0.35% copper, greater than 0.0% to 0.35% chromium, 0.40% to 0.95% manganese, up to 0.2% zinc, optionally 0.005% to 0.15% titanium and/or 0.005% to 0.15% titanium diboride, aluminum and production-related impurities as a remainder, wherein a secondary dendrite arm spacing of the microstructure is less than 100 μm.

2. The continuously cast bolt according to claim 1, containing 0.65% to 1.0%, preferably 0.70% to 0.95%, in particular 0.70% to 0.85%, magnesium.

3. The continuously cast bolt according to claim 1, containing 0.65% to 0.95%, preferably 0.70% to 0.90%, silicon.

4. The continuously cast bolt according to claim 1, wherein a weight ratio of silicon to magnesium is 0.90 to 1.20, preferably 0.95 to 1.15, in particular 1.00 to 1.10.

5. The continuously cast bolt according to claim 1, containing 0.05% to 0.35%, preferably 0.1% to 0.3%, iron.

6. The continuously cast bolt according to claim 1, containing 0.10% to 0.30%, preferably 0.12% to 0.25%, copper.

7. The continuously cast bolt according to claim 1, containing 0.10% to 0.30%, preferably 0.10 to 0.25%, chromium.

8. The continuously cast bolt according to claim 1, containing 0.45% to 0.90%, preferably 0.50% to 0.85%, in particular 0.50% to 0.75%, manganese.

9. The continuously cast bolt according to claim 1, wherein the secondary dendrite arm spacing of the microstructure is less than 90 μm, preferably 20 μm to 80 μm, in particular 30 μm to 70 μm.

10. An extruded profile, in particular a hollow profile such as a double hollow cavity profile, in particular obtainable from a continuously cast bolt according to claim 1, having a yield strength of greater than 260 MPa, preferably greater than 280 MPa, in particular greater than 300 MPa, containing, in percentage by weight, greater than 0.0% to 0.40% iron, 0.40% to 1.2% magnesium, 0.60% to 0.95% silicon, greater than 0.0% to 0.35% copper, greater than 0.0% to 0.35% chromium, 0.40% to 0.95% manganese, up to 0.2% zinc, optionally 0.005% to 0.15% titanium and/or 0.005% to 0.15% titanium diboride, aluminum and production-related impurities as a remainder, wherein a microstructure is recrystallized.

11. The extruded profile according to claim 10, wherein a median grain size of the microstructure is less than 60 μm, preferably 2 μm to 50 μm, in particular 10 μm to 30 μm.

12. The extruded profile according to claim 10, wherein the profile is heat treated.

13. A method for producing an extruded profile, in particular a profile according to claim 10, comprising: a) production of the continuously cast bolt; b) homogenization of the continuously cast bolt; c) extruding of the profile; d) optional heat treatment of the extruded profile.

14. The method according to claim 13, wherein the homogenization is carried out at a temperature of 520° C. to 590° C., in particular 530° C. to 580° C.

15. The method according to claim 13, wherein the homogenization takes place for a duration of 3 to 6 hours.

16. The method according to claim 13, wherein the continuously cast bolt is heated to a temperature above 400° C. prior to the extruding.

Description

[0057] Additional features, advantages and effects of the invention follow from the exemplary embodiments described below. In the drawings which are thereby referenced:

[0058] FIG. 1 shows an exemplary microstructural image of a continuously cast bolt according to the invention;

[0059] FIG. 2 shows a chart relating to the temperature progression during a production of an extruded profile;

[0060] FIG. 3 shows a first distribution of dispersoids;

[0061] FIG. 4 shows a second distribution of dispersoids;

[0062] FIG. 5 shows a third distribution of dispersoids;

[0063] FIG. 6 shows an exemplary cross-section of a profile according to the invention;

[0064] FIG. 7 shows an exemplary longitudinal section of a profile according to the invention;

[0065] FIG. 8 shows a frontal view of an exemplary compression specimen from a double hollow cavity profile;

[0066] FIG. 9 shows an exemplary compression specimen in a side view from a double hollow cavity profile;

[0067] FIG. 10 shows a top view of a die for extruding a profile.

[0068] In FIG. 1, an exemplary and typical structural image is shown of a continuously cast bolt as created according to the invention. This continuously cast bolt has a secondary dendrite arm spacing, measured and determined according to the German Casting Industry Association (BDG) guideline and German Foundrymen's Association (VDG) reference sheet P 220, of roughly 50 μm. The continuously cast bolt is then homogenized, preferably in the temperature range from 530° C. to 580° C. A homogenization duration is roughly three to six hours for continuously cast bolts with a diameter of approximately 10 to 12 inches. During this homogenization, different temperature programs can be run, as are shown by way of example in FIG. 2. Depending on the chemical composition of the continuously cast bolt, the distribution of dispersoids can be set via the homogenization temperature and via the progression of the temperature ramps. This can be seen in FIG. 3 through FIG. 5 for the three homogenization progressions illustrated in FIG. 2. In particular, it can also be seen that, with a decreasing temperature from the first homogenization progression to the second homogenization progression according to FIG. 3 and FIG. 4, a more defined distribution with a smaller average dispersoid diameter is obtained. Finally, according to FIG. 5, a tighter distribution that is even more definitive, with an even smaller average dispersoid diameter, can be obtained via the third homogenization progression, which proceeds in a two-stage manner with a first temperature ramp and a second temperature ramp.

[0069] In addition to the continuously cast bolt as shown in FIG. 1, an extruded profile be created following a homogenization. In particular, hollow cavity profiles, for example double hollow cavity profiles, can be created, such as those required for installation in motor vehicles in particular.

[0070] In Table 1 shown below, exemplary alloys and the accompanying material characteristics are indicated. As can be seen, in the case of extrusion based on the given compositions, crash profiles that have a yield strength of greater than 290 MPa are obtained. A recrystallization of the microstructure thereby occurs during the extrusion. Whereas the microstructure in the continuously cast bolt from FIG. 1 has a secondary dendrite arm spacing of approximately 50 μm, the grain size in the microstructure of the extruded profile is markedly smaller and also homogeneous. This can clearly be seen by reference to FIG. 6 (cross-section) and FIG. 7 (longitudinal section). In particular, the longitudinal section along the extrusion direction shows that the microstructure is recrystallized. If this were not the case, there would have to be what is referred to as a “pancake structure” given the high degrees of deformation upwards of 50-fold, which is not the case.

TABLE-US-00001 TABLE 1 Compositions and material characteristics of profiles according to the invention R.sub.p0.2 R.sub.m A Class Si Fe Cu Mn Mg Cr [MPa] [MPa] [%] C32 0.85 0.18 0.12 0.55 0.80 0.12 334 352 12.6 C32 0.88 0.22 0.2 0.62 0.79 0.17 342 356 11.5 C28 0.79 0.17 0.15 0.6 0.75 0.18 305 330 13.2 C28 0.74 0.2 0.2 0.70 0.72 0.2 290 315 11.3

[0071] In FIG. 8 and FIG. 9, an exemplary compression specimen of one of the alloys according to Table 1 is shown in a frontal view (FIG. 8) and side view (FIG. 9). The compression specimen shows, following a standardized compression text, virtually no cracks and thus satisfies the conditions required by automotive manufacturers.

[0072] According to examinations for intracrystalline corrosion, there were no signs of a corrosive attack in profiles according to Table 1 in an artificially aged condition (heat treatment of the profiles for 3 hours at 215° C. and 8 hours at 180° C.) under exposure to test solutions. The profiles thus also meet the conditions in terms of a highest possible corrosion resistance.

[0073] An extruded profile as discussed above is created using a die such as that illustrated in FIG. 10. The die itself is a typical die for an extrusion of a double hollow cavity profile. In contrast to the prior art, however, additional guiding means are also provided in direct proximity to the profile-shaping passage, which guiding means divert the material being extruded. The guiding means are located in the positions marked by the arrows in FIG. 10. With the guiding means, an even higher degree of deformation is achieved locally, which is highly beneficial to a fine microstructure. Local forming is also drastically increased by the guiding means. Consequently, this local forming causes a greatly increased dislocation density. The increased dislocation density, paired with the potential starting seeds for recrystallization (AlFeSi phases), enables the start of recrystallization. Through the targeted influencing of the dispersoids (size and distribution) during the heating to the homogenization temperature, the recrystallization can be optimally controlled and regulated (see FIG. 6 and FIG. 7 for a perfect end result). Thus, in a further aspect, the invention relates to a die for extruding a hollow profile, in particular a double hollow cavity profile, preferably for carrying out a method as explained above, wherein in the die, in addition to multiple cavities for receiving a continuously cast bolt in a branching manner before a profile-shaping die, additional guiding means are provided for diverting the extruded material. With the additionally provided single or plural guiding means, a dislocation density can be increased so that by providing starting seeds, a regulation of the recrystallized grain size using dispersoids or the distribution and density thereof and the dislocation density, an optimized microstructure can be achieved.