METHOD FOR PRODUCING SHEET METAL OR STRIP AND SHEET METAL OR STRIP PRODUCED USING THIS METHOD - Patent application

Abstract

The present invention relates to a method for producing a metal sheet or strip and a metal sheet or strip produced using this method. According to the invention, a metal sheet or strip made of an aluminum alloy of the EN AW-5xxx type for a relatively high gloss and relatively high resistivity has a grain structure elongated in the rolling direction and has a grain size of 0.01 mm or less, measured according to ASTM E112-13. JPEG2025510778000009.jpg1773 has cold roll joints with grains having a grain aspect ratio of 10 or greater, specifically 15 or greater.

Description

[Technical field]

[0001] The present invention relates to a method for producing sheet metal or strip and to the sheet metal or strip produced using this method. [Background technology]

[0002] It is known that in order to produce shiny parts from sheet metal or strip made of 5xxx aluminum alloys that have been anodized, i.e. electrolytically oxidized, it is necessary to reduce the light scattering centers, for example foreign phases in the oxide layer, so that the directional light reflection responsible for the glossiness can occur undiminished. This applies more particularly to those scattering centers whose size is comparable to or larger than the wavelength of visible light (400-750 nm).

[0003] For this reason, EP 3011067 proposes to reduce the fine Mg2Si precipitates formed during the manufacturing process by intermediate annealing and subsequent cooling during cold rolling, which is carried out between the solvus temperature of the precipitates and the melting temperature of the aluminium alloy.

[0004] Unfortunately, however, this method does not affect the scattering centers consisting of Fe-containing precipitates, which, due to their uniform distribution in the size and structure of the sheet metal or strip, reduce the gloss of the sheet metal or strip. Additionally, the sheet metal or strip thus heat treated is relatively susceptible to corrosion, which adversely affects the durability of the gloss. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent No. 3011067 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the invention is therefore to modify a method of the type initially described so as to further improve both the gloss and the durability of sheet metal or strip made of 5xxx aluminium alloys. [Means for solving the problem]

[0007] The present invention achieves the object stated with respect to the method by means of the features of claim 1.

[0008] By carrying out an intermediate annealing according to claim 1 (with a first holding temperature above the solvus temperature of the Mg-containing precipitates, more particularly of Mg2Si type, in the aluminium alloy and the first holding temperature below the melting temperature of the aluminium alloy) and by subsequently quenching the intermediate annealed strip or sheet metal between hot rolling and cold rolling, it is possible, in comparison with the prior art, to act on the Mg-containing precipitates even before cold rolling. Preferably, the quenching is carried out below the precipitation temperature of the Mg-containing precipitates. For example, the quenching is carried out with an average cooling rate of at least 10° C. / s, for example at least 50° C. / s.

[0009] Subsequent cold rolling, carried out from the thickness of the hot rolled strip to the final thickness of the sheet metal or strip (also called metal strip or sheet metal strip) with a cold reduction of 70% or more, leads to an improved breakup of the precipitates that are not broken down by the intermediate annealing, more particularly of the Fe-containing precipitates. In comparison with the prior art, such precipitates are more evenly distributed and less grouped in the aluminum matrix, so that it is also possible to significantly reduce their negative impact on the gloss.

[0010] Additionally, the grains of the aluminum matrix are fairly elongated, which results in higher corrosion resistance due to the extended path length for corrosion between the grains, which in turn has a positive effect on gloss durability.

[0011] According to the present invention, intermediate annealing, in combination with a relatively high degree of cold rolling, results in an improved and more durable gloss in the sheet metal or strip, and improved corrosion resistance.

[0012] This can be further improved if the cold rolling is carried out with a cold reduction of 75% or more from the hot rolled strip thickness to the final thickness.

[0013] According to the invention, this is provided in several rolling passes, which may optionally include a pickling step as an intermediate step between these rolling passes.

[0014] Additionally, the method according to the invention includes a final annealing of the cold rolled sheet metal or strip at a second holding temperature below the recrystallization temperature of the aluminum alloy. This means that the cold rolled structure is subjected to a final annealing and that the cold rolled structure is in a non-regenerated crystallized state, the grain structure of which is elongated in the rolling direction. The sheet metal or strip thus produced is, for example, in the H2X state.

[0015] Preferably, the first holding temperature is 400°C or more and 600°C or less, so that essentially all Mg-containing grains in the aluminum alloy are decomposed. It is more feasible if the first holding temperature in the intermediate annealing is in the range of 450-560°C.

[0016] It can prove to be favorable for the above-mentioned decomposition of Mg-containing precipitates if the intermediate annealing has a first holding time in the range of >2 s (seconds) to 6 min (minutes). A first holding time in this range, inter alia, prevents the formation of coarse grains due to excessive grain growth, and thus also the occurrence of orange peel during forming or bending of the sheet metal or strip.

[0017] The second holding temperature, i.e. the holding temperature in the final annealing, is for example in the range below the recrystallization temperature of aluminum. The defect or dislocation density in the aluminum matrix introduced by cold rolling is mainly reduced by the regeneration process, while avoiding the formation of new grains. This makes it possible to adjust the required mechanical properties while preserving the elongated grain structure created during cold rolling and to improve the corrosion resistance. This is especially true when the second holding temperature is in the range of 200-280°C, preferably in the range of 200-250°C.

[0018] The extent of the reduction in defect density introduced by cold rolling depends on the level of thermal load introduced in the final annealing, for example due to the second hold temperature but also the second hold time, i.e. the hold time of the final annealing. For example, the second hold time is preferably selected to be greater than or equal to 6 hours and / or less than or equal to 30 hours in order to equalize the mechanical properties over the entire length of the strip. Preferably, the second hold time is in the range of 8 to 24 hours.

[0019] If the final annealing of the sheet metal or strip is carried out, for example, under inert gas, it is possible to prevent the reaction of the magnesium with oxygen from the environment and thereby prevent hazing of the surface, which can further improve the gloss of the sheet metal or strip and / or make it more reproducible.

[0020] Preferably, the hot rolling is carried out with a hot rolling reduction of 95% or more from the initial thickness to the thickness of the hot rolled strip, which can then provide a sufficiently high level of cold work hardenability, ensure elongated grains, and decompose the Fe-containing phase. In this way, it is possible to further improve the gloss, as well as the corrosion resistance and therefore the durability of the gloss.

[0021] A sufficiently large hot rolled strip thickness to allow a relatively high degree of forming during cold rolling can be achieved, for example, when sheet metal or strip is hot rolled to a hot rolled strip thickness in the range of 5-12 mm, e.g., 6-12 mm, or more preferably 6-10 mm.

[0022] During cold rolling, the sheet metal or strip is preferably rolled with rolls of reduced roll roughness at each rolling pass, which makes it possible, for example, to further reduce the surface roughness of the strip or sheet metal, which, according to the prior art, also has a positive effect on the gloss of the untreated aluminum surface.

[0023] Preferably, the sheet metal or strip is cold rolled to a final thickness in the range of 0.5 to 1.5 mm (millimeters), more particularly 0.8 to 1.3 mm, this thickness range being particularly suitable for the application of components in decorative parts, where the contour design requires high forming and small bending radii.

[0024] Hot rolling can be further accelerated, for example, if the rolled ingot is maintained at a heating temperature of 400°C or higher for at least 1 hour prior to hot rolling. More specifically, the heating temperature is in the range of 400-470°C. A heating temperature of 400°C is the minimum temperature desired for carrying out hot rolling, since recrystallization processes are possible at this temperature and can facilitate a reduction in the thickness of the ingot. Since the heating temperature is below 470°C, phase coarsening in the temperature range close to the melting temperature of the aluminum alloy is substantially avoided.

[0025] Another object of the invention is to further improve the gloss and durability of sheet metal or strip made from 5xxx aluminum alloys of the type described at the beginning.

[0026] The invention achieves the stated object by means of the features of claim 12.

[0027] According to the present invention, the sheet metal or strip has a grain aspect ratio measured in accordance with ASTEM E112-13:

[0028]

number

[0029]

number

[0030] Among other things, this significantly increases the path length for corrosion between the crystals. It can therefore be assumed that the corrosion resistance and durability of the glossiness are improved. This means that the sheet metal (often called metal sheet) or strip (often called metal strip) produced using the method according to the invention, with its cold rolled and final annealed structure, can have an improved glossiness and improved durability.

[0031] In this regard,

[0032]

number

[0033] Preferably, the structure is not recrystallized in the H2X state and therefore has no recrystallized elements. This is ensured, for example, by a final annealing of the cold rolled sheet metal or strip at a second hold temperature that is below the recrystallization temperature of the aluminum alloy. This preserves the cold rolled structure with an elongated grain structure in the rolling direction.

[0034] Preferably, the surface of the strip or sheet metal has a gloss value of 50 GU or more, measured at an angle of 20° and in the transverse direction to the rolling direction, according to ONORM EN ISO 7668. Preferably, this value is 55 GU or more. For example, a measuring device called "micro-TRI-gloss S" made by the company BYK-Gardner GmbH can be used for this measurement.

[0035] Preferably, the sheet metal or strip has a polished surface layer or a polished and positively oxidized surface layer, the surface of which strip or sheet metal has a gloss, measured at an angle of 20° and transverse to the rolling direction, of 60 GU or more according to ONORM EN ISO 7668.

[0036] Preferably, the aluminum alloy strip or sheet metal is 0.50 to 1.1% by weight of magnesium (Mg); 0.01 to 0.30% by weight of silicon (Si), 0.01 to 0.7% by weight of iron (Fe), and residual aluminium, as well as unavoidable impurities associated with production, each up to a maximum of 0.05% by weight and totalling up to 0.15% by weight.

[0037] Optionally, the aluminum alloys are selected from the group consisting of: up to 0.20% by weight of manganese (Mn); Copper (Cu) up to 0.20% by weight, Up to 0.10% by weight chromium (Cr) up to 0.25% by weight of zinc (Zn), up to 0.01% by weight of titanium (Ti); up to 0.03% by weight of gallium (Ga); 0.05% by weight of vanadium (V), It may also contain elements from the group DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] To demonstrate the effect achieved, several strips (also called metal strips or sheet metal strips) A, B, C and D were produced with a final thickness of 1.2 mm. Strips A, B, C and D are of EN AW-5xxx type with the following chemical composition: 0.8% by weight Mg, 0.03% by weight Si, 0.03% by weight Fe, and a maximum of 0.05% by weight each, all totaling up to 0.15% by weight, residual aluminium, as well as unavoidable impurities linked to production.

[0039] Production sequence A: Strip A according to the invention was produced by the following method steps in the order shown: A rolled ingot of aluminum alloy is heated to a temperature of 420°C for 9 hours. b. The rolling ingot is hot rolled in several hot rolling passes to form a hot rolled strip with a hot rolling reduction of 98% and a thickness of 8 mm. c. Inter-annealing the hot rolled strip in a series of strip furnaces at a first hold temperature of 480° C. (above the solvus temperature of the Mg-bearing precipitates) with a hold time of 3 minutes. d. The intermediate annealed strip is quenched at a temperature below 100°C with a cooling rate of 50°C / s. e. Cold rolling the quenched strip in several passes with an intermediate pickling step to reduce the roll roughness and to a final thickness of 1.2 mm with a cold reduction of 85%. f. Final annealing the cold rolled strip in a coil furnace at a second hold temperature of 240° C. (ie, below the recrystallization temperature of the aluminum alloy) and a second hold time of 12 hours. g. The final annealed strip is cooled in still air to room temperature.

[0040] Production sequence B: Strip B according to the invention was produced by the following method steps in the order shown: A rolled ingot of aluminum alloy is heated to a temperature of 420°C for 9 hours. b. The rolling ingot is hot rolled in several hot rolling passes to form a hot rolled strip with a hot rolling reduction of 98% and a thickness of 8 mm. c. Intermediate annealing the hot rolled strip in a series of strip furnaces at a first hold temperature of 480° C. (above the solvus temperature of the Mg-bearing precipitates) with a hold time of 3 minutes. d. The intermediate annealed strip is quenched at a temperature below 100°C and at a cooling rate of 50°C / s. e. Cold rolling the quenched strip in several passes with an intermediate pickling step to reduce the roll roughness, in contrast to strip A according to the invention, using coarser rolls in the last cold rolling pass and with a cold reduction of 85% to a final thickness of 1.2 mm. f. Final annealing the cold rolled strip in a coil furnace at a second hold temperature of 240° C. and a second hold time of 12 hours. g. The final annealed strip is cooled in still air to room temperature.

[0041] Production sequence C: Strip C not according to the invention was produced by the following method steps: a. Heat a rolled ingot of aluminum alloy at a heating temperature of 420°C for 9 hours. b. The rolling ingot is hot rolled in several hot rolling passes to form a hot rolled strip with a hot rolling reduction of 98% and a thickness of 9 mm. c. Cold rolling the quenched strip in several passes with an intermediate pickling step to reduce the roll roughness and a cold reduction of 87% to a final thickness of 1.2 mm. d. Final annealing the cold rolled strip in a coil furnace at a second hold temperature of 245° C. and a second hold time of 12 hours. e. The final annealed strip is cooled in still air to room temperature.

[0042] Production sequence D: A strip D not according to the invention was produced by the following method steps: A rolled ingot of aluminum alloy is heated to a temperature of 420°C for 9 hours. b. The rolling ingot is hot rolled in several hot rolling passes to form a hot rolled strip with a hot rolling reduction of 98% and a thickness of 9 mm. c. Cold rolling the quenched strip in several cold passes with a cold reduction of 82% to a material thickness of 1.6 mm with an intermediate pickling step. d. Intermediate anneal the cold rolled strip in a series of strip furnaces at a first holding temperature of 450°C and a holding time of 2 minutes, and then intermediate quench at a temperature below 100°C and a cooling rate of 50°C / s. e. Cold roll the quenched strip in several cold rolling passes with a cold reduction of 25% to a material thickness of 1.2 mm. f. Final annealing the cold rolled strip in a coil furnace at a second hold temperature of 240° C. and a hold time of 12 hours. g. The final annealed strip is cooled in still air to room temperature.

[0043] To compare the gloss achieved according to the different production methods A, B, C and D, the samples were treated in a bath of acidic polish (consisting of distilled water, sulfuric acid and phosphoric acid). After the subsequent application of an artificial anodization layer, the gloss was compared with each other.

[0044] The determined grain elongation and the corresponding gloss (measured at an angle of 20° and transverse to the rolling direction according to ONORM EN ISO 7668) of strips A and B treated according to the invention and of strips C and D treated not according to the invention are tabulated below in Table 1.

[0045] [Table 1]

[0046] As Table 1 shows, strips A and B, which have been subjected to the hot rolling process according to the invention followed by intermediate annealing in a series of strip furnaces, have a gloss value up to 10 GU higher than strips C and D. This is the case both for the untreated strip and for the strip which has been surface treated, i.e. polished (chemically or electrolytically) and then anodized.

[0047] The beneficial effect of intermediate annealing on hot rolled strip or sheet metal is shown by comparing production methods A and B with C.

[0048] In the case of production sequences A and B, the implementation of an intermediate annealing prior to cold rolling according to the invention can be utilized to influence the soluble Mg-containing phases. By bringing the Mg-containing phases into solution during the intermediate annealing of the hot rolled strip and the associated rapid cooling of the material, the number of scattering centers is minimized in a sustainable manner. This results in an increase in gloss compared to production method C without intermediate annealing.

[0049] Additionally, the effect of high cold rolling reductions of 70%, 85% or more in the exemplary embodiment is shown by directly comparing Samples A, B, and C with Sample D. The growth sequence according to A, B, and C results in very elongated grains. This can be seen in Table 1.

[0050] The production sequences A, B and C were cold rolled with reduced roll roughness in order to reduce the surface roughness. A comparison of the production sequences A and B shows that the sheet metal A has a higher gloss than the sheet metal B, for which rolls with a higher roughness were used. The sheet metal B according to the invention nevertheless has a significantly higher gloss than the sheet metals C and D, which are not according to the invention. The sheet metal C was also cold rolled with reduced roll roughness, for example.

[0051] In this case, the grain thickness of strips A and B in the H2X state (according to ASTM E112-13)

[0052]

number

[0053]

number

[0054] Applying a cold rolling reduction of at least 70% not only affects the corrosion resistance but also the majority of Fe-containing phases present in the material after intermediate annealing. The disruption of these phases reduces the number of scattering centers in the size range comparable to the wavelength of visible light. According to the invention, it leads to an increase in gloss in strips A and B compared to strips C and D not according to the invention, as can be seen from table 1 and as already explained above.

[0055] It should be noted that in general the German expression "insbesondere" can be translated into English as "more particularly". The aforementioned features with "more particularly" are considered as optional features, which can be omitted and do not, for example, impose limitations on the scope of the claims. The same is true for the German expression "vorzugsweise" which is translated into English as "preferably".

Claims

1. 1. A method for producing sheet metal or strip, comprising the steps of: hot rolling a rolled ingot made of an EN AW-5xxx type aluminum alloy into a hot rolled strip from its original thickness to a thickness of the hot rolled strip; The hot rolled strip or sheet metal is subjected to a process for removing Mg-containing precipitates of the aluminum alloy, more particularly Mg ２ intermediate annealing at a first holding temperature which is equal to or higher than the Si-type solvus temperature and lower than the melting temperature of the aluminum alloy, and then quenching the intermediate annealed strip or sheet metal; cold rolling said quenched strip or sheet metal in multiple rolling passes to a final thickness, optionally with pickling steps as intermediate steps between said rolling passes, the cold rolling being carried out to a final thickness with a cold reduction of at least 70%, more particularly at least 75%, of the final thickness of the hot rolled strip; and final annealing the cold rolled sheet metal or strip at a second holding temperature which is below the recrystallization temperature of the aluminum alloy; in the order listed.

2. 2. The method according to claim 1, wherein the first holding temperature is between 400°C and 600°C, more particularly between 450 and 560°C.

3. 3. The method according to claim 1 or 2, characterized in that the intermediate annealing has a first hold time of more than 2 seconds up to 6 minutes.

4. Method according to any one of claims 1 to 3, characterised in that the second holding temperature is between 200 and 280°C, preferably between 200 and 250°C.

5. A method according to any one of claims 1 to 4, characterized in that the final annealing has a second holding time of at least 6 hours and / or at most 30 hours, more particularly in the range from 8 to 24 hours.

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

7. 7. The method according to claim 1, characterized in that the hot rolling is carried out with a hot rolling reduction of at least 95% from the original thickness to the thickness of the hot rolled strip.

8. A method according to any one of the preceding claims, characterized in that the sheet metal or strip is hot rolled to a hot rolled strip thickness ranging from 5 to 12 mm, more particularly from 6 to 10 mm.

9. A method according to any one of the preceding claims, characterized in that in cold rolling, the sheet metal or strip is rolled in rolling passes with decreasing roll roughness with each rolling pass.

10. A method according to any one of the preceding claims, characterized in that the sheet metal or strip is cold rolled to a final thickness ranging from 0.5 to 1.5 mm, more particularly from 0.8 to 1.3 mm.

11. The method according to claims 1 to 10, characterized in that before hot rolling, the rolled ingot is maintained at a heating temperature of 400°C or higher, more particularly 400-470°C, for at least 1 hour.

12. Grain aspect ratio measured according to ASTEM E112-13; [0010] AW-5xxx type aluminum alloy sheet metal or strip, cold rolled having an elongated grain structure in the rolling direction with grains having a Mn of 10 or more, more particularly 15 or more. 【Request 13】 【Number 2】 13. Sheet metal or strip according to claim 12, characterized in that the thickness is less than 20 μm, more particularly less than 17 μm.

14. 14. Sheet metal or strip according to claim 12 or 13, characterized in that the structure does not recrystallize in the H2X state.

15. 15. Sheet metal or strip according to claim 12, 13 or 14, characterized in that the surface of the strip or sheet metal has a gloss according to ONORM EN ISO 7668, measured at an angle of 20° and in the transverse direction to the rolling direction, of 50 GU or more, more particularly 55 GU or more.

16. 15. The sheet metal or strip according to claim 12, 13 or 14, characterized in that the sheet metal or strip has a polished surface layer or a polished and positively oxidized surface layer, the surface of the strip or sheet metal having a gloss according to ONORM EN ISO 7668 of ≥ 60 GU, measured at an angle of 20° and in the transverse direction to the rolling direction.

17. The aluminum alloy is 0.50 to 1.1% by weight of magnesium (Mg); 0.01 to 0.30 wt.% silicon (Si); 0.01 to 0.7% by weight of iron (Fe), and optionally, up to 0.20% by weight of manganese (Mn); up to 0.20% by weight of copper (Cu); up to 0.10% by weight of chromium (Cr); up to 0.25% by weight of zinc (Zn); up to 0.01% by weight of titanium (Ti); up to 0.03% by weight of gallium (Ga); up to 0.05% by weight of vanadium (V), and residual aluminum, as well as unavoidable impurities associated with production, each up to a maximum of 0.05% by weight and totalling up to 0.15% by weight.

17. Sheet metal or strip according to any one of claims 12 to 16, characterised in that it comprises elements from the group consisting of:

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