Method for producing a metal sheet or strip and a metal sheet or strip produced using same

Abstract

The invention relates to a method for producing a metal sheet or strip and to a metal sheet or strip produced using same. According to the invention, for a comparatively high gloss level and comparatively high resistance, the metal sheet or strip, made of an aluminium alloy of the type EN AW-5xxx, has a cold-rolled join with a grain structure extending in the rolling direction and with grains with a grain aspect ratio of AIt = ̅ll ( 0°) / ̅ll (90 °) ≥ 10, in particular ≥ 15, measured according to ASTM E112-13.

Description

[0001] Method for producing a sheet or strip and a sheet or strip produced thereby

[0002] Technical area

[0003] The invention relates to a method for producing a sheet or strip and to a sheet or strip produced thereby.

[0004] State of the art

[0005] It is known that in the production of bright parts from anodized or anodized sheet or strip made of a 5xxx aluminum alloy, optical scattering centers, such as foreign phases in the oxide layer, must be reduced to ensure that the directed light reflection responsible for the gloss level can occur unhindered. This applies particularly to scattering centers whose size is comparable to or larger than the wavelength of visible light (400 to 750 nm).

[0006] Therefore, EP3011067B1 proposes reducing fine Mg2Si precipitates formed during the manufacturing process by applying an intermediate annealing followed by cooling during cold rolling. This intermediate annealing takes place between the solvus temperature of the precipitates and the melting temperature of the aluminum alloy.

[0007] However, this process has no effect on scattering centers of Fe-containing precipitates, which, due to their size and inhomogeneous distribution in the structure, reduce the gloss level of the sheet or strip. Furthermore, sheet or strip heat-treated in this way is comparatively susceptible to corrosion, which has a negative impact on the stability of the gloss level.

[0008] Description of the invention The object of the invention is therefore to modify the method of the type described at the outset in such a way that both the degree of gloss and the durability of a sheet or strip made of a 5xxx aluminum alloy are further improved.

[0009] The invention solves the problem with regard to the method by the features of claim 1.

[0010] By performing the intermediate annealing according to claim 1 (with a first holding temperature > the solvus temperature of Mg-containing precipitates, in particular of the Mg2Si type, of the aluminum alloy, and with the first holding temperature < the melting temperature of the aluminum alloy) and subsequent quenching of the intermediately annealed strip or sheet between hot rolling and cold rolling, Mg-containing precipitates can be acted upon prior to cold rolling, in contrast to the prior art. Preferably, quenching takes place at a temperature below the precipitation temperature of Mg-containing precipitates. For example, quenching takes place at an average cooling rate of at least 10 °C / s, for example at least 50 °C / s.

[0011] If the subsequent cold rolling is carried out with a cold rolling degree of > 70% from the final thickness of the hot strip to the final thickness of the sheet or strip (also referred to as metal strip or sheet strip), this leads to improved fragmentation of those precipitates that cannot be dissolved by intermediate annealing, especially those containing Fe. Such precipitates are therefore more homogeneous and less clustered in the aluminum matrix compared to the state of the art, so their negative impact on the gloss level can also be significantly reduced.

[0012] In addition, the grains of the aluminum matrix are significantly stretched, resulting in higher corrosion resistance due to an increased path length for intergranular corrosion - this in turn can have a positive effect on the stability of the gloss level.

[0013] According to the invention, the intermediate annealing in combination with the comparatively high degree of cold rolling results in an improved and more consistent degree of gloss or improved corrosion resistance on the sheet or strip.

[0014] The above can be further improved if cold rolling is carried out with a cold rolling degree of > 75% from the final hot strip thickness to the final thickness. According to the invention, this is carried out in several passes and can optionally include a pickling step as an intermediate step between these passes.

[0015] In addition, the method according to the invention comprises a final annealing of the cold-rolled sheet or strip with a second holding temperature < the recrystallization temperature of the aluminum alloy. The cold-rolled microstructure is thus finally annealed and is in a non-recrystallized state. The grain structure is elongated in the rolling direction. The state of the sheet or strip produced in this way is, for example, H2X.

[0016] Preferably, the first holding temperature is in the range of > 400 °C to < 600 °C so that essentially all Mg-containing precipitates in the aluminum alloy are dissolved. This is particularly achievable if the first holding temperature of the intermediate annealing is in the range of 450 °C to 560 °C.

[0017] It may prove advantageous for the above-mentioned dissolution of Mg-containing precipitates if the intermediate annealing has an initial holding time in the range of > 2 s (seconds) to 6 min (minutes). Furthermore, this initial holding time range can prevent, among other things, the formation of coarse grains due to excessive grain growth and thus orange peel during forming or bending of the sheet or strip.

[0018] The second holding temperature, i.e., the holding temperature for the final annealing, is, for example, in the range below the recrystallization temperature of the aluminum. The defect density or dislocation density in the aluminum matrix introduced by cold rolling is reduced primarily through recovery processes, preventing new grain formation. This enables the required mechanical properties to be achieved while maintaining the elongated grain structure created during cold rolling and increasing corrosion resistance. This is particularly the case when the second holding temperature is in the range of 200 to 280 °C, preferably in the range of 200 to 250 °C.

[0019] The extent of the reduction in the defect density introduced by cold rolling depends on the level of the thermal load introduced by the final annealing, for example, in addition to the second holding temperature, the second holding time, i.e., the holding time of the final annealing. To even out the mechanical properties across the entire strip length, the second holding time should be > 6 h and / or < 30 h. The second holding time is preferably in the range of 8 to 24 h (hours).

[0020] If the final annealing of the sheet or strip takes place under an inert gas, for example, this can prevent the magnesium from reacting with ambient oxygen, thus preventing clouding of the surface. The gloss level of the sheet or strip can thus be further increased and / or manufactured more reproducibly.

[0021] Hot rolling is preferably carried out with a hot rolling degree of 95% or higher from the initial thickness to the final hot strip thickness. This allows for sufficient work hardening to ensure an elongated grain and fragment Fe-containing phases. This can further improve the gloss level and corrosion resistance, and thus the stability of the gloss level.

[0022] A sufficiently high hot strip thickness to enable a comparatively high degree of deformation during cold rolling can be achieved, for example, if the sheet or strip is hot rolled to a final hot strip thickness in the range of 5 to 12 mm, for example 6 to 12 mm, or in particular 6 to 10 mm.

[0023] During cold rolling, the sheet or strip is preferably rolled in rolling passes with decreasing roll roughness with each pass. This allows, for example, the surface roughness of the strip or sheet to be further reduced, which, according to the state of the art, also has a positive effect on the gloss of the untreated aluminum surface.

[0024] Preferably, the sheet or strip is cold-rolled to a final thickness in the range of 0.5 to 1.5 mm (millimeters), especially 0.8 to 1.3 mm. This thickness range is particularly suitable for applications in decorative components whose geometric design requires high degrees of deformation and small bending radii.

[0025] Hot rolling can be further facilitated if, for example, the rolling ingots are held at a heating temperature > 400 °C for at least one hour prior to hot rolling. In particular, the heating temperature is in the range of 400 °C to 470 °C. A heating temperature of 400 °C is the minimum temperature at which hot rolling should take place, as this temperature enables recrystallization processes and facilitates a reduction in ingot thickness. By keeping the heating temperature < 470 °C, coarsening of phases in the temperature range close to the melting temperature of the aluminum alloy is essentially prevented.

[0026] It is also the object of the invention to further improve the degree of gloss and its durability of a sheet or strip made of a 5xxx aluminum alloy of the type described above.

[0027] The invention solves the stated problem by the features of claim 12. According to the invention, the sheet or strip is made of an aluminum alloy of the type EN AW-5xxx with a cold-rolled structure which has a grain structure elongated in the rolling direction with grains whose grain aspect ratio AI t > 10, measured according to ASTM E112-13. Preferably, AI t = li^ / l > 15.

[0028] This significantly increases, among other things, the path length for intergranular corrosion. Therefore, increased corrosion resistance and stability of the gloss level can be expected. Thus, the sheet (often called metal sheet) or strip (often called metal strip) produced by the inventive process, with its cold-rolled and finally annealed microstructure, can exhibit an increased gloss level and increased durability.

[0029] It may also be advantageous if 1 1(9^< 20 pm, especially < 17 pm.

[0030] Preferably, the microstructure in the H2X temper is non-recrystallized and therefore contains no recrystallized components. This is ensured, for example, by final annealing the cold-rolled sheet or strip with a second holding temperature below the recrystallization temperature of the aluminum alloy. This preserves the cold-rolled microstructure with a grain structure elongated in the rolling direction.

[0031] For this purpose, the surface of the strip or sheet preferably has a gloss level of > 50 gil, measured according to ÖNORM EN ISO 7668 at an angle of 20° and transverse to the rolling direction. This value is preferably > 55 gil. For example, a measuring device called "micro-TRI-gloss S" from BYK-Gardner GmbH can be used for this measurement.

[0032] The sheet or strip preferably has a brightened or a brightened and anodized surface layer, the surface of the strip or sheet having a gloss level of > 60 Gil, measured according to ÖNORM EN ISO 7668 at an angle of 20° and transverse to the rolling direction. The aluminum alloy of the strip or sheet preferably 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 the remainder aluminum as well as unavoidable impurities due to manufacturing, each with a maximum of 0.05 wt.% and a total of no more than 0.15 wt.%.

[0033] Optionally, the aluminum alloy can also be used individually or in combination

[0034] Contain elements from the group: 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)

[0035] Ways to implement the invention

[0036] To demonstrate the achieved effects, several strips (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 type EN AW-5xxx with the following chemical composition in wt.%: Mg: 0.8%, Si: 0.03%, Fe: 0.03%, and the remainder aluminum, as well as unavoidable impurities due to manufacturing, each with a maximum of 0.05 wt.% and a total of no more than 0.15 wt.%.

[0037] Production sequence A: The strip A according to the invention was subjected to the following process steps in the order stated: a. heating of the rolling ingot made of the aluminum alloy to a temperature of 420°C for 9 hours; 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 final hot strip thickness of 8 mm; c. intermediate annealing of the hot-rolled strip in a continuous strip furnace with a first holding temperature of 480°C (> solvus temperature of Mg-containing precipitates) with a holding time of 3 minutes. d. Quenching the intermediately annealed strip with water to a temperature of < 100 °C at a cooling rate of 50 °C / s. Cold rolling of the quenched strip in several passes with an intermediate pickling step and with decreasing roll roughness and with a cold rolling degree of 85% to a final thickness of 1.2 mm. f.Final annealing of the cold-rolled strip with a second holding temperature of 240°C (i.e. < recrystallization temperature of the aluminum alloy) in a coil furnace with a second holding time of 12 hg. Cooling of the finally annealed strip in still air to room temperature.

[0038] Production sequence B: The strip B according to the invention was subjected to the following process steps in the order stated: a. Heating of the aluminum alloy rolling ingot to a temperature of 420°C for 9 hours. b. Hot rolling of the rolling ingot in several hot rolling passes to produce a hot-rolled strip with a hot-rolling degree of 98% and a final hot-rolled strip thickness of 8 mm. c. Intermediate annealing of the hot-rolled strip in a continuous strip furnace with an initial holding temperature of 480°C (> solvus temperature of Mg-containing precipitates) and a holding time of 3 minutes. d. Quenching of the intermediately annealed strip with water to a temperature <100°C at a cooling rate of 50°C / sec.Cold rolling of the quenched strip in several passes with an intermediate pickling step and with decreasing roll roughness, whereby a rougher roll was used in the last cold rolling pass, in contrast to the strip A according to the invention, and with a cold rolling degree of 85% to a final thickness of 1.2 mm. 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 hg. Cooling of the finally annealed strip in still air to room temperature.

[0039] Production sequence C: The non-inventive strip C was manufactured in the following process steps: a. Heating of the rolling ingot made of the aluminum alloy to a heating temperature of 420 °C for 9 hours. 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 final hot strip thickness of 9 mm. c. Cold rolling of the quenched strip in several passes with an intermediate pickling step, with decreasing roll roughness and with a cold rolling degree of 87% to a final thickness of 1.2 mm 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 h. Cooling of the finally annealed strip in still air to room temperature.

[0040] Production sequence D: The non-inventive strip D was manufactured in the following process steps: a. Heating of the rolling ingot made of the aluminum alloy to a temperature of 420°C for 9 hours. 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 final hot strip thickness of 9 mm. 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. d. Intermediate annealing of the cold-rolled strip in a continuous strip furnace with an initial holding temperature of 450°C and a holding time of 2 minutes and immediate quenching to a temperature < 100°C with a cooling rate of 50°C / s. 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. f.Final annealing of the cold-rolled strip in a coil furnace at a second holding temperature of 240°C and a holding time of 12 hg. Cooling of the finally annealed strip in still air to room temperature.

[0041] To compare the gloss levels according to the different production variants A, B, C, and D, samples were treated in an acidic gloss bath (consisting of distilled water, sulfuric acid, and phosphoric acid). After the subsequent application of an artificial anodizing layer, the gloss levels were compared.

[0042] The determined grain elongation and the corresponding gloss levels (measured according to ÖNORM EN ISO 7668 at an angle of 20° and transverse to the rolling direction) of the strips A and B treated according to the invention, as well as the strips C and D not treated according to the invention, are listed in the following Table 1. Table 1 : Characteristics of bands A to D

[0043] As Table 1 illustrates, the strips A and B, which are subjected to intermediate annealing in the strip drawing furnace following hot rolling according to the invention, have a gloss level up to 10 gil higher than the strips C and D. This is the case both for the untreated strip and for the surface-treated strip, namely brightened (chemically or electrolytically) and then anodized.

[0044] The positive effect of intermediate annealing of the hot-rolled strip or sheet is illustrated by comparing the production variants A and B with C.

[0045] In the case of production sequences A and B, the inventive implementation of intermediate annealing before cold rolling allows for the soluble Mg-containing phases to be influenced. By dissolving the Mg-containing phases during the intermediate annealing of the hot strip and the accompanying rapid cooling of the material, the number of scattering centers is sustainably minimized. This leads to an increase in the degree of gloss compared to production variant C, which was carried out without intermediate annealing.

[0046] Additionally, the influence of a high cold rolling degree of > 70%, in the examples 85%, is illustrated by a direct comparison of 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.

[0047] Production sequences A, B, and C were cold-rolled with decreasing roll roughness in order to reduce the surface roughness. A comparison of production sequences A and B shows higher gloss levels for sheet A than for sheet B, which used a rougher roll. Nevertheless, sheet B according to the invention is significantly higher in gloss levels than the non-inventive sheets C and D, of which, for example, sheet C was also cold-rolled with decreasing roll roughness. For the strips A and B in the H2X state, the grain thickness l in the microstructure is (90 ») (according to ASTM E112-13) is significantly lower than in the case of the strips D and C in the H2X state. In addition, this difference is further reflected in the grain aspect ratio AI t = F^o») / ! 1(90°) (measured according to ASTM E112-13), which, above 15, is a significant distance from the grain aspect ratio AI t of bands C and D.

[0048] By applying such a cold rolling degree of at least 70%, not only corrosion resistance but also the predominantly Fe-containing phases present in the material even after intermediate annealing are influenced. By fragmenting these phases, the number of scattering centers in the size range comparable to the wavelength of visible light is reduced. According to the invention, this results in an increase in the degree of gloss, as can be seen for strips A and B in comparison with the non-inventive strips C and D in Table 1, and as already explained above.

[0049] In general, it is noted that "in particular" can be translated into English as "more particularly." A feature preceded by "in particular" is to be considered an optional feature that can be omitted and thus does not constitute a limitation, for example, of the claims. The same applies to "vorzugsweise," translated into English as "preferably."

Claims

Patent claims:

1. A method for producing a sheet or strip, wherein the method comprises the following steps in the specified order: Hot rolling of a rolling ingot made of an aluminum alloy of type EN AW-5xxx and an initial thickness to a hot-rolled strip or sheet to a hot-rolled strip final thickness, Intermediate annealing of the hot-rolled strip or sheet with a first holding temperature that is > solvation temperature of Mg-containing precipitates, in particular of the type Mg2Si, of the aluminium alloy and < the melting temperature of the aluminium alloy, and subsequent quenching of the intermediately annealed strip or sheet, Cold rolling of the quenched strip or sheet to a final thickness in several passes, optionally with a pickling step as an intermediate step between these passes, wherein the cold rolling is carried out with a cold rolling ratio > 70%, in particular > 75%, from the hot strip final thickness to the final thickness, and 1. Final annealing of the cold-rolled sheet or strip with a second holding temperature < the recrystallization temperature of the aluminum alloy.

2. Method according to claim 1, characterized in that the first holding temperature is in the range of > 400 °C to < 600 °C, in particular from 450 °C to 560 °C.

3. Method according to claim 1 or 2, characterized in that the intermediate annealing has a first holding time in the range of > 2 seconds (s) to 6 minutes (min).

4. Method according to one of claims 1 to 3, characterized in that the second holding temperature is in the range of 200 °C to 280 °C, preferably from 200°C to 250°C.

5. Method according to one of claims 1 to 4, characterized in that the final annealing has a second holding time of > 6 hours (h) and / or < 30 h, in particular in the range of 8 to 24 h.

6. Method according to one of claims 1 to 5, characterized in that the final annealing of the sheet or strip is carried out under inert gas.

7. Method according to one of claims 1 to 6, characterized in that the hot rolling is carried out with a hot rolling degree > 95% or higher from the initial thickness to the hot strip final thickness.

8. Method according to one of claims 1 to 7, characterized in that the sheet or strip is hot-rolled to a hot-rolled final strip thickness in the range of 5 to 12 mm, in particular 6 to 10 mm.

9. Method according to one of claims 1 to 8, characterized in that the sheet or strip is rolled in rolling passes with decreasing roller roughness at each pass during cold rolling.

10. Method according to any one of claims 1 to 9, characterized in that the sheet or strip is cold-rolled to a final thickness in the range of 0.5 to 1.5 mm, in particular to 0.8 to 1.3 mm.

11. Method according to one of claims 1 to 10, characterized in that the rolling ingots are held at a preheating temperature > 400 °C, in particular in the range of 400 °C to 470 °C, for at least one hour before hot rolling.

12. Sheet or strip of an aluminium alloy of type EN AW-5xxx with a cold-rolled microstructure having a grain structure elongated in the rolling direction with grains whose grain size distribution ratio AI t = z(90°) - 10> especially > 15, measured according to ASTM E112-13.

13. Sheet or strip according to claim 12, characterized in that 1 1( 90 °)< 20 pm, especially < 17 pm, is.

14. Sheet or strip according to claim 12 or 13, characterized in that the microstructure is not recrystallized in the H2X state.

15. Sheet or strip according to claim 12, 13 or 14, characterized in that the surface of the strip or sheet has a gloss level of > 50 Gil, in particular > 55 Gil, measured according to ÖNORM EN ISO 7668 at an angle of 20° and transverse to the rolling direction.

16. Sheet or strip according to claim 12, 13 or 14, characterized in that the sheet or strip has a polished or a polished and anodized surface layer, wherein the surface of the strip or sheet has a gloss level of > 60 Gil, measured according to ÖNORM EN ISO 7668 at an angle of 20° and transverse to the rolling direction.

17. Sheet or strip according to any one of claims 12 to 16, characterized in that the aluminium alloy comprises 0.50 to 1.1 wt.% magnesium (Mg), 0.01 to 0.30 wt.% silicon (Si), 0.01 to 0.7 wt.% iron (Fe), optionally individually or in combination from the group: 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 as a remainder aluminium, as well as impurities unavoidable due to the manufacturing process, each with a maximum of 0.05 wt.% and a total of no more than 0.15 wt.%.

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