Plate made of a rolled aluminium alloy and production of such a plate

Abstract

The invention relates to a plate made of a rolled aluminium alloy and to a method for producing said plate. According to the invention, to achieve high strength values, the plate has a partially recrystallised microstructure with a degree of recrystallisation of less than 25%, wherein the non-recrystallised region of the microstructure is in the recovered state and has an average subgrain size in the rolling direction of less than 10 μm.

Description

Technical field

[0001] The invention relates to a plate made of a rolled aluminium alloy and a method for manufacturing this plate.

[0002] Plates made from rolled EN AW-6082 aluminum alloy are known. Such plates can achieve a yield strength (R p0,2 ) of around 260 MPa in the T6 condition. State of the art

[0003] To create a finer grain structure in the recrystallized state of plates made from a rolled Al-Mg-Si aluminum alloy, it is known (EP1614760A1) to add 0.1 to 0.4% wt.% zirconium (Zr) to the alloy. The yield strengths (Rp0.2) of the plates in the T4 condition with or without Zr content are essentially the same. Furthermore, CN110629075A and US3642542A disclose Al-Mg-Si alloys with added zirconium. Description of the invention

[0004] The invention therefore aims to improve the strength, in particular the yield strength (Rp0.2), of a plate made of an Al-Mg-Si aluminum alloy. Furthermore, the invention aims to provide a reproducible method for achieving this.

[0005] The invention solves the problem stated with regard to the plate by the features of claim 1.

[0006] If the aluminum alloy contains 0.7 to 1.5 wt.% silicon (Si), 0.5 to 1.3 wt.% magnesium (Mg), 0.05 to 0.6 wt.% manganese (Mn), and 0.1 to 0.3 wt.% zirconium (Zr), the conditions for increased strength, particularly at the yield strength (Rp0.2), can be achieved. With this composition, and considering the increased Zr content compared to other rolled 6xxx alloys, a special microstructure can be achieved in the plate—namely, a substantially recovered microstructure, i.e., a microstructure with a low proportion of recrystallized grains. The plate exhibits a partially recrystallized microstructure with a recrystallization degree of less than 25%, which can lead to increased strength if, in addition, the non-recrystallized microstructure is in a recovered state and has a mean subgrain size in the rolling direction of less than 10 µm.It was surprisingly discovered that, due to the composition of the aluminum alloy with Zr, comparatively finely dispersed intermetallic Zr-containing particles, for example (Al,Si)3Zr or Al3Zr particles, form in the microstructure. This leads to pinning of the subgrain boundaries, resulting in a comparatively low degree of recrystallization and relatively small subgrain sizes. This particular microstructure of the plate allows for a significant increase in its yield strength (Rp0,2).

[0007] The aluminum alloy may also optionally contain one or more of the following elements in the following amounts: up to 0.5 wt.% copper (Cu); up to 0.7 wt.% iron (Fe); up to 0.1 wt.% chromium (Cr); up to 0.2 wt.% titanium (Ti); up to 0.5 wt.% zinc (Zn); up to 0.2 wt.% tin (Sn); up to 0.1 wt.% strontium (Sr); up to 0.2 wt.% vanadium (V); up to 0.2 wt.% molybdenum (Mo). Preferably, the plate is made of a rolled aluminum alloy of the 6xxx series.

[0008] Preferably, the degree of recrystallization is lower to achieve a higher proportion of recovered microstructure. This is particularly true when the degree of recrystallization is less than 15%. A degree of recrystallization of less than 5% is advantageous to ensure a high proportion of recovered structure in the microstructure for high strength.

[0009] The above can be further improved if the mean subgrain size in the rolling direction is less than or equal to 5 µm.

[0010] The strength of the plate can be further increased if it is in condition T6, for example condition T651.

[0011] Based on the T6 state, the plate can, among other things, have a yield strength (R p0,2 ) of greater than 350 MPa.

[0012] The plate can be further improved by further refining the aluminum alloy in one or more of the elements listed below: Si: If the aluminum alloy contains 0.9 to 1.3 wt% silicon (Si), this can further increase its strength. This is especially true if the aluminum alloy contains 1.0 to 1.2 wt% silicon (Si). Mg: If the aluminum alloy contains 0.75 to 0.95 wt% magnesium (Mg), an optimum amount of soluble Mg in the aluminum alloy can be achieved, and the strength can also be further increased by Mg- and Si-containing phases. Mn: With a manganese (Mn) content of 0.3 to 0.5 wt% in the aluminum alloy, the proportion of Mn and Zr-containing particles can be increased to further increase the strength of the plate, especially in the T6 condition. Zr: A further increased zirconium content, namely 0.15 to 0.25 wt% zirconium (Zr), can further increase the strength of the plate. For example, Zr improves and inhibits the recrystallization of the microstructure, creating an increased density of particles.The increased Zr content resulted in a comparatively thermally stable subgrain boundary hardening, the activity of which persisted even after heat treatment up to 570 °C. This is further improved if the aluminum alloy contains 0.18 to 0.22 wt.% zirconium (Zr). Cu: If the aluminum alloy contains 0.1 to 0.5 wt.% copper (Cu), this can further increase the plate's strength. The upper limit of 0.5 wt.% copper (Cu) helps to keep the plate's susceptibility to corrosion low. Si+Mg+Cu: Si and Mg (for example, adjusted to their maximum solubility) in combination with Cu can significantly contribute to increasing the volume fraction of precipitates. Fe: An iron (Fe) content of up to 0.7 wt.% can also contribute to a further increase in strength. For example, the Fe content can be at least 0.1 wt.%.

[0013] Preferably, the intermetallic phase of the aluminum alloy contains Zr-containing particles with a mean particle size of no more than 100 nm (nanometers), where the number of Zr-containing particles is greater than or equal to 1 x 10⁶ particles / mm². Based on such a particle size and number, the pinning of the subgrain boundaries can be improved, thus further increasing the proportion of recovered and non-recrystallized microstructure. Furthermore, this can further reduce the mean subgrain size of the recovered microstructure, which can further increase the strength of the plate.

[0014] The above can be further improved if the mean particle size of the Zr-containing particles is in the range of 30 nm to 100 nm.

[0015] It can also prove advantageous if the number of Zr-containing particles is less than or equal to 100 x 10 6 particles / mm 2.

[0016] Furthermore, it can be advantageous if the number of Zr-containing particles is greater than or equal to 5 x 10 6 particles / mm 2.

[0017] According to claim 9, the plate is used for mechanical engineering.

[0018] The invention solves the problem stated with regard to the method by the features of claim 10.

[0019] By applying a multi-stage homogenization of the rolling ingot followed by accelerated cooling (quenching) to room temperature, a substantially recovered microstructure with a comparatively low degree of recrystallization and a comparatively small subgrain size can be reproducibly produced compared to other known methods. This is achieved by first homogenizing at a temperature in the range of 300 °C to 400 °C with a holding time of 0.5 hours or more, followed by a second homogenization at a temperature in the range of 500 °C to 10 °C below the solidus temperature of the aluminum alloy.

[0020] In general, it is mentioned that accelerated cooling (and often referred to as quenching) can be understood as cooling faster than cooling at room temperature and still air (cf. Friedrich Ostermann, Application Technology Aluminium, 3rd edition, publication year 2014: Cooling after solution annealing).

[0021] Preferably, the initial homogenization can be carried out with a holding time of up to 4 days and / or a maximum heating rate of 5 K / min. This allows the number of Zr-containing particles in the microstructure to be further increased.

[0022] Preferably, the second homogenization is carried out with a second holding time of greater than or equal to 0.5 hours and up to 24 hours in order to further reduce concentration differences in the microstructure.

[0023] Hot rolling of the homogenized rolling ingot can be carried out at a temperature that is 5 °C to 100 °C lower than the solidus temperature of the aluminum alloy in order to obtain a preferred deformation structure.

[0024] Solution annealing of the plate can be carried out at a temperature in the range of 460 °C to 580 °C and with a holding time of 1 minute to 10 hours.

[0025] It is generally mentioned that solution annealing can achieve the most complete possible solution of the alloying elements involved in the hardening process (cf. Friedrich Ostermann, Application Technology Aluminium, 3rd edition, publication year 2014, ISBN 987-3-662-43806-0, page 175).

[0026] For example, cold storage at room temperature can be carried out for a holding time of up to 8 weeks. This can further simplify the process.

[0027] Heat aging can be carried out at a temperature in the range of 130 °C to 210 °C and for a holding time of 1 to 24 hours to further increase the strength of the plate.

[0028] The above can be further enhanced if the heat treatment transforms the plate into the T6 state, in particular T651.

[0029] To demonstrate the effects achieved, rolled semi-finished products, namely plates A and B, each with a plate thickness of 6 mm (millimeters) made from a respective rolled aluminum alloy, were used. plate Si wt.% Mg wt.% Cu wt.% Mn wt.% Fe wt.% Zr wt.% Solidus temperature °C A 0,90 0,61 0,07 0,40 0,32 - 594 B 1,07 0,81 0,30 0,41 0,36 0,21 578 and is produced with a residue of aluminum and impurities unavoidable during manufacturing, each with a maximum of 0.05% by weight and a total of no more than 0.15% by weight. Generally, a plate thickness of 4 mm to 150 mm, and in particular 6 mm to 40 mm, is conceivable.

[0030] The alloy of plate A is an EN AW-6082 standard alloy. Starting with this standard alloy EN AW-6082, the alloying elements Si, Mg, and Cu were increased in content. Plate B, in addition to modified Si, Mg, and Cu contents, also has a Zr content and thus represents the embodiment of the invention.

[0031] The manufacturing process is according to Fig. 1 schematically represented, where these steps, in the aforementioned order, constitute homogenization (H) of a previously cast rolling ingot, hot rolling (WW) of the homogenized rolling ingot into a plate, solution annealing (LG), cold aging (KA), cold forming (R), and hot aging (WA) of the plate. The solid line after Fig. 1The diagram partially illustrates the process flow for manufacturing plate A and plate B. It is partially illustrated because, during homogenization (H), plate B is first treated according to the dashed line and then further along the solid line. This represents a significant process improvement.

[0032] Plates A and B were then subjected to the following process steps in the order mentioned, whereby the rolling ingot for plate A undergoes a different homogenization process than the rolling ingot for plate B: a. Homogenizing (H) of a cast rolling ingot: Rolling ingot for plate A: single-stage homogenizing (H2) at a temperature of 550 °C (degrees Celsius) for a holding time of 2 h (hours) and a heating rate of 1 K / min (Kelvin / minute); Rolling ingot for plate B: two-stage homogenizing with a first homogenizing (H1) at 350 °C for a holding time of 16 h and a heating rate of 1 K / min and with a second homogenizing (H2) at 550 °C for a holding time of 2 h, and a heating rate of 1 K / min, wherein the second homogenizing (H2) directly follows the first homogenizing (H1), as in Fig. 1as can be seen. b. Hot rolling (WW) of the homogenized rolling ingot at a temperature of 540 °C to a plate, starting from an initial thickness of 40 mm (millimeters) to 6 mm; c. Solution annealing (LG) of the plate at a temperature of 570 °C for a holding time of 20 min (minutes) with subsequent accelerated cooling under water quenching to room temperature of 20 °C (RT); d. Cold aging (KA) of the plate for a holding time of 14 days and subsequent cold forming by stretching the plate with a degree of deformation of 2%; e. Warm aging (WA) of the plate at a temperature of 160 °C for a holding time of 14 h;

[0033] Plates A and B subjected to this procedure were examined by means of a tensile test (tensile test according to standard DIN EN 10002-1) with regard to mechanical properties 0.2 % yield strength R p0,2 , tensile strength R m , uniform elongation A g and elongation at break A . Table 1: Mechanical properties of plates A and B in state T6, namely T651 (* in rolling direction) R p0.2 [MPa] Δ R p0,2 [MPa] R m [MPa] A [%] Degree of recrystallization [%] Average subgrain size [µm]* Zr-containing particles Number [particles / mm²< ] Medium size [nm] A 289 - 309 19 83,3 - - - B 362 +73 392 15 4,3 5 7,52x10 6< 74

[0034] Furthermore, the degree of recrystallization, the mean subgrain size, and the number and mean size (calculated from the maximum Feret diameters of these Zr-containing particles) of both plates were determined. The degree of recrystallization was determined using a JEOL 7200F FEG-SEM EBSD detector under the following two conditions: (a) grain-averaged misorientation within a third-order kernel with a step size of 0.6 µm of less than 0.5°, and (b) average band contrast of more than 70% of the maximum measured band contrast. The values ​​of the Zr-containing particles in plate B were determined using a scanning transmission electron microscope (HAADF images at 17,000x magnification, Talos F200X G2 S-TEM).

[0035] As can be seen in Table 1, plate B exhibits significantly increased strength values ​​Rp0.2 and Rm in condition T651 compared to plate A. However, this is not solely due to the increased addition of Si, Mg, and Cu, which primarily leads to an increase in precipitate density and thus to an increase in strength. The strength of plate A is essentially based on precipitates, in particular on β"-precipitates (Si, Mg) that form during warm aging, in combination with Fe- and / or Mn-containing particles, which stabilize the microstructure at higher temperatures.

[0036] In contrast, the significant increase in the 0.2% yield strength (Rp0.2) of plate B to 73 MPa compared to 6082 plate A is primarily due to the hardening effect of Zr, or rather its Al3Zr particles. The microstructure contains an increased amount of Zr-containing particles (Al3Zr), which stabilizes the microstructure region with non-recrystallized deformation structures that form in the microstructure due to hot rolling. Subsequent heat treatments, such as solution annealing at a comparatively high temperature of 570 °C, do not lead to recrystallization, but rather to a recovery of this microstructure region. Considering the small average subgrain size of 5 µm in the rolling direction, this results in a significantly increased strength than could be achieved solely by adding Si, Mg, and Cu. The increase in strength of plate B compared to plate A is also evident in the Fig. 2 to recognize.

[0037] Investigations of the particles also reveal significant differences in their structure.

[0038] The intermetallic phase of the aluminum alloy in plate B contains Zr-containing particles with an average particle size of 74 nm. The number of Zr-containing particles is 7.52 x 10⁶ particles / mm².

[0039] In contrast, the intermetallic phase of the aluminum alloy in plate A contains exclusively Al(Fe,Mn,Cr)Si particles. These have an average particle size of 101 nm. The number of these Al(Fe,Mn,Cr)Si particles is 1.2 x 10⁶ particles / mm². These particle counts for plate A were determined using scanning electron microscope images (BSE images at 10,000x magnification, JEOL 7200F FEG-SEM).

[0040] The particles in plate A are therefore not only significantly larger, but their number is also many times lower than that of the Zr-containing particles in plate B, which also contains Al(Fe,Mn,Cr)Si particles. This high quantity of comparatively very small Zr-containing particles in plate B improves subgrain boundaries and can thus increase the proportion of recovered microstructure in the final state, as well as ensure a further reduction in subgrain sizes.

[0041] These effects result in a particularly mechanically stable plate, suitable for use in toolmaking.

[0042] Furthermore, it was found that the Zr content in the alloy prevents the energy introduced during cold forming (stretching with a 2% degree of deformation) from being eliminated by the subsequent warm aging, as the stabilizing effect of the Zr-containing particles is also effective here.

[0043] It is generally accepted that "in particular" can be translated into English as "more particularly". A feature preceded by "in particular" or "if applicable" is to be considered an optional feature that can be omitted and therefore does not constitute a limitation, for example, of claims. The same applies to "preferably", which is translated into English as "preferably".

Claims

1. Plate made of a rolled aluminum alloy having the following alloy components: from 0.7 to 1.5 wt% silicon (Si), from 0.5 to 1.3 wt% magnesium (Mg) from 0.05 to 0.6 wt% manganese (Mn), from 0.1 to 0.3 wt.% zirconium (Zr), each optionally up to 0.5 wt.% copper (Cu), up to 0.7 wt.% iron (Fe), up to 0.1 wt.% chromium (Cr), up to 0.2 wt.% titanium (Ti), up to 0.5% by weight of zinc (Zn), up to 0.2% by weight of tin (Sn), up to 0.1% by weight of strontium (Sr), up to 0.2% by weight of vanadium (V), up to 0.2% by weight of molybdenum (Mo) and the remainder aluminum, as well as unavoidable impurities resulting from the manufacturing process, each with a maximum of 0.05 wt.% and a total of no more than 0.15 wt.%, characterized in that the plate has a partially recrystallized structure with a recrystallization degree of less than 25%, wherein the non-recrystallized area of the structure is in a recovered state and has an average subgrain size in the rolling direction of less than 10 µm, wherein the average subgrain size is determined according to the method specified in the description.

2. Plate according to claim 1, characterized in that the degree of recrystallization is less than 15%, more particularly less than 5%.

3. Plate according to claim 1 or 2, characterized in that the average subgrain size in the rolling direction is less than or equal to 5 µm.

4. Plate according to one of claims 1 to 3, characterized in that the plate has the T6 state, more particularly T651.

5. Plate according to claim 4, characterized in that the plate has a yield strength (Rp0,2) greater than 350 MPa.

6. Plate according to one of claims 1 to 5, characterized in that the rolled aluminum alloy comprises from 0.9 to 1.3 wt.%, more particularly from 1.0 to 1.2 wt.%, silicon (Si) and / or from 0.75 to 0.95 wt.% magnesium (Mg) and / or from 0.3 to 0.5 wt.% manganese (Mn) and / or from 0.15 to 0.25 wt.%, more particularly from 0.18 to 0.22 wt.%, zirconium (Zr) and / or from 0.1 to 0.5 wt.% copper (Cu) and / or up to 0.5 wt.% iron (Fe).

7. Plate according to one of claims 1 to 6, characterized in that the intermetallic phase of the aluminum alloy has Zr-containing particles with a mean particle size of at most 100 nm, wherein the number of Zr-containing particles is greater than or equal to 1 x 106 particles / mm2, more particularly greater than or equal to 5 x 106 particles / mm2, wherein the average particle size and the number of Zr-containing particles are determined according to the method specified in the description.

8. Plate according to claim 7, characterized in that the average particle size of the Zr-containing particles is in the range from 30 nm to 100 nm and / or the number of Zr-containing particles is less than or equal to 100 x 106 particles / mm2 and / or the number of Zr-containing particles is greater than or equal to 5 x 106 particles / mm2.

9. Use of a plate according to one of claims 1 to 8 for mechanical engineering.

10. Method for producing a plate according to one of claims 1 to 8, wherein the method comprises the following steps in the order indicated: casting a rolling ingot with the aluminum alloy, multistage homogenization of the rolling ingot with subsequent accelerated cooling to room temperature, wherein the multi-stage homogenization comprises at least a first homogenization at a first temperature in the range of 300°C to 400°C with a first holding time of greater than or equal to 0.5 hours and a subsequent second homogenization at a second temperature in the range of 500°C to 10°C below a solidus temperature of the aluminum alloy, hot rolling of the homogenized rolling ingot to form the plate and subsequent heat treatment, comprising solution annealing of the plate with subsequent accelerated cooling to room temperature, cold aging of the solution-annealed plate, optionally with cold deformation with a degree of deformation in the range between 0.5 and 10%, and subsequent warm aging of the plate.

11. Method according to claim 10, wherein the first homogenization is carried out with a first holding time of up to 4 days and / or a maximum heating rate of 5 K / min and / or that the second homogenization is carried out with a second holding time of greater than or equal to 0.5 hours and up to 24 hours.

12. Method according to one of claims 10 to 11, wherein the hot rolling of the homogenized rolling ingot takes place at a temperature which is 5°C to 100°C lower than the solidus temperature of the aluminum alloy.

13. Method according to one of claims 10 to 12, wherein the solution annealing of the plate is carried out at a temperature in the range of 460°C to 580°C and with a holding time of 1 minute to 10 hours.

14. Method according to one of claims 10 to 13, wherein the cold aging is carried out at room temperature with a holding time of up to 8 weeks.

15. Method according to one of claims 10 to 14, wherein the warm aging is carried out at a temperature in the range of 130°C to 210°C and with a holding time of 1 to 24 hours.

16. Method according to one of claims 10 to 15, wherein the heat treatment brings the plate into the T6 state, more particularly T651.

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