METHOD FOR PRODUCING A SHEET METAL OR STRIP AND A SHEET METAL OR STRIP PRODUCED USING SAME

Abstract

A method for producing a sheet metal or strip and a sheet metal or strip produced using this method are described. For a comparatively high gloss level and a comparatively high durability, it is proposed for the sheet metal or strip made of an aluminum alloy of the EN AW-5xxx type to have a cold-rolled structure having a grain structure that is elongated in the rolling direction, with grains whose grain aspect ratio AI.sub.l=l.sub.l(0)/l.sub.l(90) is 10, more particularly 15, measured according to ASTM E112-13.

Claims

1. A method for producing a sheet metal or strip, wherein the method comprises the following steps in the indicated order: Hot rolling a rolling ingot made of an aluminum alloy of EN AW-5xxx type and with an initial thickness to a hot-rolled strip or sheet metal with a hot strip thickness, Intermediate annealing of the hot-rolled strip or sheet metal with a first holding temperature, which is a solvus temperature of Mg-containing precipitates of the aluminum alloy and is<a melting temperature of the aluminum alloy, and subsequent quenching of the intermediate annealed strip or sheet metal, Cold rolling the quenched strip or sheet metal to a final thickness in a plurality of rolling passes, optionally with a pickling step as an intermediate step between the plurality of rolling passes, wherein the cold rolling is carried out with a cold rolling degree of 70% of a hot strip final thickness to the final thickness, and Final annealing of the cold-rolled sheet metal or strip with a second holding temperature<a recrystallization temperature of the aluminum alloy.

2. The method according to claim 1, wherein the first holding temperature is in a range from 400 C. to 600 C.

3. The method according to claim 1, wherein the intermediate annealing has a first holding time in a range from >2 seconds(s) to 6 minutes (min).

4. The method according to claim 1, wherein the second holding temperature is in a range from 200 C. to 280 C.

5. The method according to claim 1, wherein the final annealing has a second holding time of 6 hours (h) and/or 30 h.

6. The method according to claim 1, wherein the final annealing of the sheet metal or strip is carried out under inert gas.

7. The method according to claim 1, wherein the hot rolling is carried out with a hot rolling degree of 95% or greater from the initial thickness to the hot strip thickness.

8. The method according to claim 1, wherein the sheet metal or strip is hot-rolled to the hot strip thickness in a range from 5 to 12 mm.

9. The method according to claim 1, wherein in the cold rolling, the sheet metal or strip is rolled in rolling passes with decreasing roll roughness of the rolls in each rolling pass.

10. The method according to claim 1, wherein the sheet metal or strip is cold-rolled to the final thickness in a range from 0.5 to 1.5 mm.

11. The method according to claim 1, wherein before the hot rolling, the rolling ingot is kept at a heating temperature 400 C. for at least one hour.

12. A sheet metal or strip made of an aluminum alloy of EN AW-5xxx type with a cold-rolled structure that has a grain structure that is elongated in a rolling direction, with grains whose grain aspect ratio AI.sub.l=l.sub.l(0)/l.sub.l(90) is 10, measured according to ASTM E112-13.

13. The sheet metal or strip according to claim 12, wherein l.sub.l(90) is <20 m.

14. The sheet metal or strip according to claim 12, wherein the structure is not recrystallized in an H2X state.

15. The sheet metal or strip according to claim 12, wherein a surface of the strip or sheet metal has a gloss level of 50 GU, measured according to NORM EN ISO 7668 at an angle of 20 and transverse to the rolling direction.

16. The sheet metal or strip according to claim 12, wherein the sheet metal or strip has a surface layer that is polished or is polished and anodized, and wherein a surface of the strip or sheet metal has a gloss level of 60 GU, measured according to NORM EN ISO 7668 at an angle of 20 and transverse to the rolling direction.

17. The sheet metal or strip according to claim 12, wherein the aluminum alloy contains from 0.50 to 1.1 wt % magnesium (Mg), from 0.01 to 0.30 wt % silicon (Si), from 0.01 to 0.7 wt % iron (Fe), and optionally, elements from the following group, either individually or in combination: up to 0.20 wt % manganese (Mn) up to 0.20 wt % copper (Cu) up to 0.10 wt % chromium (Cr) up to 0.25 wt % zinc (Zn) up to 0.01 wt % titanium (Ti) up to 0.03 wt % gallium (Ga) up to 0.05 wt % vanadium (V) and residual aluminum as well as inevitable production-related impurities, each totaling a maximum of 0.05 wt % and all together totaling at most 0.15 wt %.

18. The method according to claim 1, wherein the first holding temperature is greater than or equal to a solvus temperature of Mg.sub.2Si type precipitates.

19. The method according to claim 1, wherein the cold rolling is carried out with a cold rolling degree of 75% of the hot strip final thickness to the final thickness.

20. The sheet metal or strip according to claim 12, wherein the sheet metal or strip is made of an aluminum alloy of the EN AW-5xxx type with a cold-rolled structure that has a grain structure that is elongated in the rolling direction, with grains whose grain aspect ratio AI.sub.l=l.sub.l(0)/l.sub.l(90) is 15 measured according to ASTM E112-13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0043] To demonstrate the effects achieved, several strips (also called metal strips or sheet metal strips) A, B, C, and D with a final thickness of 1.2 mm were produced. Strips A, B, C, and D are of the EN AW-5xxx type with the following chemical composition in wt %: Mg: 0.8%, Si: 0.03%, Fe: 0.03%, and residual aluminum as well as inevitable production-related impurities with a maximum of 0.05 wt % each and all together totaling at most 0.15 wt %.

[0044] Production sequence A: The strip A according to the invention was subjected to the following method steps in the indicated order: [0045] a. Heating of the aluminum alloy rolling ingot to a temperature of 420 C. for 9 hours; [0046] b. Hot rolling of the rolling ingot in several hot-rolling passes to a hot-rolled strip with a hot rolling degree of 98% and a hot strip thickness of 8 mm; [0047] c. Intermediate annealing of the hot-rolled strip in a continuous strip furnace with a first holding temperature of 480 C. (the solvus temperature of Mg-containing precipitates) with a holding time of 3 min. [0048] d. Quenching of the intermediate annealed strip with water to a temperature <100 C. at a cooling rate of 50 C./s. [0049] e. Cold rolling of the quenched strip in several rolling passes with a pickling step as an intermediate step and with decreasing roll roughness and with a cold rolling degree of 85% to a final thickness of 1.2 mm. [0050] f. Final annealing of the cold-rolled strip with a second holding temperature of 240 C. (i.e. <the recrystallization temperature of the aluminum alloy) in a coil furnace with a second holding time of 12 h. [0051] g. Cooling of the final annealed strip to room temperature in still air.

[0052] Production sequence B: The strip B according to the invention was subjected to the following method steps in the indicated order: [0053] a. Heating of the aluminum alloy rolling ingot to a temperature of 420 C. for 9 hours. [0054] b. Hot rolling of the rolling ingot in several hot-rolling passes to a hot-rolled strip with a hot rolling degree of 98% and a hot strip thickness of 8 mm. [0055] c. Intermediate annealing of the hot-rolled strip in a continuous strip furnace with a first holding temperature of 480 C. (the solvus temperature of Mg-containing precipitates) with a holding time of 3 min. [0056] d. Quenching of the intermediate annealed strip with water to a temperature <100 C. at a cooling rate of 50 C./s. [0057] e. Cold rolling of the quenched strip in several rolling passes with a pickling step as an intermediate step and with decreasing roll roughness, wherein a rougher roll is used in the last cold rolling pass by contrast with strip A according to the invention, and with a cold rolling degree of 85% to a final thickness of 1.2 mm. [0058] f. Final annealing of the cold-rolled strip with a second holding temperature of 240 C. in a coil furnace with a second holding time of 12 hours. [0059] g. Cooling of the final annealed strip to room temperature in still air.

[0060] Production sequence C: The strip C not according to the invention was produced with the following method steps: [0061] a. Heating of the aluminum alloy rolling ingot to a heating temperature of 420 C. for 9 hours. [0062] b. Hot rolling of the rolling ingot in several hot-rolling passes to a hot-rolled strip with a hot rolling degree of 98% and a hot strip thickness of 9 mm. [0063] c. Cold rolling of the quenched strip in several rolling passes with a pickling step as an intermediate step, with decreasing roll roughness and with a cold rolling degree of 87% to a final thickness of 1.2 mm [0064] d. Final annealing of the cold-rolled strip with a second holding temperature of 245 C. in a coil furnace with a second holding time of 12 hours. [0065] e. Cooling of the final annealed strip to room temperature in still air.

[0066] Production sequence D: The strip D not according to the invention was produced with the following method steps: [0067] a. Heating of the aluminum alloy rolling ingot to a temperature of 420 C. for 9 hours. [0068] b. Hot rolling of the rolling ingot in several hot-rolling passes to a hot-rolled strip with a hot rolling degree of 98% and a hot strip thickness of 9 mm. [0069] c. Cold rolling of the quenched strip in several cold rolling passes with a pickling step as an intermediate step and with a cold rolling degree of 82% to a material thickness of 1.6 mm. [0070] d. Intermediate annealing of the cold-rolled strip in a continuous strip furnace with a first holding temperature of 450 C. with a holding time of 2 min and immediate quenching to a temperature <100 C. at a cooling rate of 50 C./s. [0071] e. Cold rolling of the quenched strip in several cold rolling passes with a cold rolling degree of 25% to a material thickness of 1.2 mm. [0072] f. Final annealing of the cold-rolled strip in a coil furnace with a second holding temperature of 240 C. and a holding time of 12 hours. [0073] g. Cooling of the final annealed strip to room temperature in still air.

[0074] To compare the gloss levels achieved according to the different production variants A, B, C and D, samples were treated in an acidic brightening bath (consisting of distilled water, sulfuric acid, and phosphoric acid). After subsequent application of an artificial anodizing layer, the gloss levels were compared to one another.

[0075] The determined grain elongation and the corresponding gloss levels (measured according to NORM EN ISO 7668 at an angle of 20 and transverse to the rolling direction) of strips A and B, which were treated according to the invention, and strips C and D, which were not treated according to the invention, are listed in Table 1 below.

TABLE-US-00001 TABLE 1 Characteristic values of strips A to D Grain Gloss level GU Grain elongation Gloss level GU surface thickness ratio surface untreated treated Strip l.sub.l(90)[m] Al (raw surface) (polished + anodized) A 15 20 62 67 B 16 16 57 64 C 32 2 53 62 D 48 2 44 57

[0076] As Table 1 illustrates, the strips A and B, which undergo intermediate annealing in the continuous strip furnace following the hot rolling process according to the invention, have a gloss level that is up to 10 GU higher than strips C and D. This is the case for both the untreated strip and the strip that is surface-treated, i.e. (chemically or electrolytically) polished and then anodized.

[0077] The positive effect of the intermediate annealing of the hot-rolled strip or sheet metal is illustrated by comparing production variants A and B with C.

[0078] In the case of production sequences A and B, the implementation of the intermediate annealing prior to the cold rolling according to the invention can be used to influence the soluble Mg-containing phases. By means of the Mg-containing phases being brought into solution during the intermediate annealing of the hot strip and the associated rapid cooling of the material, the number of scattering centers is minimized in a lasting way. This leads to an increase in the gloss level compared to production variant C, which was carried out without intermediate annealing.

[0079] In addition, the influence of a high cold rolling degree of 70%, 85% in the exemplary embodiments, is illustrated by directly comparing the samples A, B, and C with sample D. The production sequences according to A, B, and C result in highly elongated grain. This can be seen in Table 1.

[0080] The production sequences A, B, and C were cold-rolled with decreasing roll roughness in order to thus reduce the surface roughness. A comparison of the production sequences A and B shows higher gloss levels for sheet metal A than is the case for sheet metal B, for which a rougher roll was used. Sheet metal B according to the invention is nevertheless significantly higher in gloss level than sheet metals C and D that are not according to the invention, sheet metal C of which, for example, was also cold-rolled with a decreasing roll roughness.

[0081] In this case, the grain thickness l.sub.(90) (according to ASTM E112-13) for strips A and B in the H2X state is significantly lower in the structure than that of strips D and C in the H2X state. This difference is also reflected in the grain expansion ratio AI.sub.l=l.sub.l(0)/l.sub.l(90) (measured according to ASTM E112-13), which, at over 15, differs significantly from the grain expansion ratio AI.sub.l of strips C and D.

[0082] Applying such a cold rolling degree of at least 70% influences not only the corrosion resistance but also the predominantly Fe-containing phases that are present in the material after the intermediate annealing. Fragmentation of these phases reduces the number of scattering centers in the size range comparable to the wavelength of visible light. According to the invention, this results in an increase in the gloss level, as can be seen in strips A and B in comparison with strips C and D, which are not according to the invention, according to Table 1, and has already been explained above.

[0083] It should be noted in general that the German expression insbesondere can be translated as more particularly in English. A feature that is preceded by more particularly is to be considered an optional feature, which can be omitted and does not thereby constitute a limitation, for example, of the claims. The same is true for the German expression vorzugsweise, which is translated as preferably in English.