Sheet made of rolled aluminium alloy and method for manufacturing the same

Abstract

The invention shows a sheet made of a rolled aluminum alloy and a method for manufacturing the sheet. The invention proposes a sheet having a partially recrystallized structure with a recrystallization degree less than 25%, wherein the unrecrystallized structure zone of the structure is in a recovery state and the average subgrain size along the rolling direction is less than 10 μm to achieve high strength values.

Description

TECHNICAL FIELD

[0001] The invention relates to a sheet made of a rolled aluminum alloy and to a method for producing the sheet.

[0002] Sheets made of a rolled EN AW-6082 aluminum alloy are known. Such a sheet can achieve a yield strength (R p0.2 ) of 260 MPa in the T6 state. BACKGROUND

[0003] In order to achieve a finer grain structure in a sheet made of a rolled Al-Mg-Si aluminum alloy in the recrystallized state, it is known (EP 1 614 760 A1 ) to incorporate 0.1 to 0.4 wt.-% of zirconium (Zr) in the alloy. The yield strength (R p0.2 ) of the sheet with or without Zr in the T4 state is essentially the same. SUMMARY

[0004] It is the task of the invention to improve the strength, in particular the yield strength (R p0.2 ) of a sheet made of an Al-Mg-Si aluminum alloy. Furthermore, it is the task of the invention to provide a reproducible method for this purpose.

[0005] The invention solves the proposed task relating to the sheet by the sheet made of a rolled aluminum alloy according to the invention.

[0006] If the aluminum alloy has 0.7 to 1.5 wt.-% of silicon (Si), 0.5 to 1.3 wt.-% of magnesium (Mg), 0.05 to 0.6 wt.-% of manganese (Mn), 0.1 to 0.3 wt.-% of zirconium (Zr), an increase in the strength, preferably the yield strength (R p0.2 ) can be achieved under this premise. By such a composition, taking into account the increased Zr content compared to other rolled 6xxx alloys, a special microstructure of the sheet can be adjusted, namely a substantially recovered microstructure, that is to say a microstructure with a low proportion of recrystallized grains. For this purpose, the sheet has a partially recrystallized microstructure with a recrystallization degree of less than 25 %, which, if the unrecrystallized microstructure region of this microstructure is in a recovered state and the average subgrain size in the rolling direction is less than 10 μιη, can increase the strength. It can surprisingly be determined on the basis of the composition of the aluminum alloy with Zr that a relatively fine distribution of intermetallic Zr-containing particles, for example (Al, Si)3Zr or Al3Zr particles, is formed in the microstructure, which leads to a pinning of the subgrain boundaries, so that a relatively low recrystallization degree is obtained, while a relatively small subgrain size is achieved. By these special microstructures or microstructures of the sheet, the yield strength (R p0,2 ) of the sheet can be significantly increased.

[0007] Furthermore, the aluminium alloy can optionally additionally comprise one or more of the following listed elements in the following amounts, respectively: copper (Cu) in an amount of at most 0.5 wt.%, iron (Fe) in an amount of at most 0.7 wt.%, chromium (Cr) in an amount of at most 0.1 wt.%, titanium (Ti) in an amount of at most 0.2 wt.%, zinc (Zn) in an amount of at most 0.5 wt.%, tin (Sn) in an amount of at most 0.2 wt.%, strontium (Sr) in an amount of at most 0.1 wt.%, vanadium (V) in an amount of at most 0.2 wt.%, molybdenum (Mo) in an amount of at most 0.2 wt.%; preferably, the sheet is made of a rolled 6xxx-series aluminium alloy.

[0008] In order to achieve a high proportion of recovered structure, it is preferred that the recrystallisation degree is low. This is especially the case if the recrystallisation degree is less than 15%. In one embodiment, the recrystallisation degree is less than 5% so that the proportion of recovered structure in the structure is high, which can ensure that a high strength is obtained.

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

[0010] If the sheet has a T6 condition, for example a T651 condition, the strength of the sheet can be further improved.

[0011] Based on the T6 condition, the sheet can also have a yield strength (R p0.2 ) of more than 350 MPa.

[0012] The properties of the sheet can be further improved if the aluminium alloy is further adjusted with one or more of the following listed elements:

[0013] Si: If the aluminium alloy has 0.9 wt.% to 1.3 wt.% silicon (Si), its strength can be further improved. This is especially the case if the aluminium alloy has 1.0 wt.% to 1.2 wt.% silicon (Si).

[0014] Mg: If the aluminium alloy has 0.75 wt.% to 0.95 wt.% magnesium (Mg), this can achieve an optimum point of the solubility of magnesium in the aluminium alloy and the strength can be further improved by the phase comprising magnesium and silicon.

[0015] Mn: By having the content of manganese (Mn) in the aluminium alloy be 0.3 wt.% to 0.5 wt.%, the proportion of the microparticles comprising Mn and Zr can be increased to further increase the strength of the sheet, especially in the T6 condition.

[0016] Zr: A further increase of the Zr content, i.e. 0.15 wt.-% to 0.25 wt.-% of Zr, can further increase the strength of the sheet. This is, for example, due to the fact that Zr better hinders the recrystallization of the structure and enables an increase of the density of the grain. Thus, by increasing the content of Zr, a relatively thermally stable subgrain strengthening can be determined, which is still active even after a heat treatment of up to 570°C. If the aluminum alloy has 0.18 wt.-% to 0.22 wt.-% of Zr, the above-mentioned properties are further improved.

[0017] Cu: If the aluminum alloy has 0.1 wt.-% to 0.5 wt.-% of copper (Cu), the strength of the sheet can be further increased. At the same time, an upper limit of 0.5 wt.-% of copper (Cu) helps to keep the sheet low in corrosion sensitivity.

[0018] Si + Mg + Cu: Si and Mg, for example, adjusted to the maximum solubility, in combination with Cu, in particular, help to increase the volume fraction of precipitates.

[0019] Fe: Furthermore, a content of at most 0.7 wt.-% of iron (Fe) can help to further increase the strength. For example, the content of Fe can be at least 0.1 wt.-%.

[0020] Preferably, the intermetallic phase of the aluminum alloy has Zr-containing particles with an average particle size of at most 100 nm (nanometers), wherein the number of Zr-containing particles is greater than or equal to 1 x 10 6 particles / mm 2 Based on such a particle size and the number of particles, the pinning of the subgrains can be improved, whereby the proportion of the recovery and unrecrystallized regions is further increased. Furthermore, these can further reduce the average subgrain size of the recovery structure region, whereby the strength of the sheet can be further increased.

[0021] If the average particle size of the Zr-containing particles is in the range of 30 nm to 100 nm, the above-mentioned case can be further improved.

[0022] If the number of Zr-containing particles is less than or equal to 100 x 10 6 particles / mm 2 can also prove to be advantageous.

[0023] Furthermore, it is advantageous if the number of Zr-containing particles is greater than or equal to 5 x 10 6 particles / mm 2 .

[0024] In particular, the sheet is suitable for use in mechanical engineering.

[0025] The present application solves the proposed method-related tasks by the method for producing a sheet according to the present application.

[0026] wherein the method of applying a multi-stage homogenization of the rolled ingot followed by accelerated cooling (quenching) to room temperature can reproducibly produce a substantially recovered microstructure with a relatively low recrystallization degree and with a relatively small subgrain size compared to other known methods. Therein, a first homogenization in a first temperature range of 300 °C to 400 °C is carried out, followed by a subsequent second homogenization in a second temperature range of 500 °C to 10 °C below the solidus temperature of the aluminum alloy.

[0027] Generally, accelerated cooling (often referred to as quenching) can be understood as a cooling which is faster than cooling in room temperature and still air (see Friedrich Ostermann: Anwendungstechnologie Aluminium, 3rd edition, published in 2014: Cooling after solution annealing).

[0028] Preferably, the first homogenization can be carried out with a first holding time of greater than or equal to 0.5 hours and / or at most 4 days and / or a maximum temperature increase rate of 5 K / min. Thereby, the number of Zr-containing particles in the microstructure can be further increased.

[0029] Preferably, the second homogenization is carried out with a second holding time of greater than or equal to 0.5 hours and / or at most 24 hours to further reduce the concentration differences in the microstructure.

[0030] The hot rolling of the homogenized rolled ingot can be carried out at a temperature of 5 °C to 100 °C below the solidus temperature of the aluminum alloy to obtain a preferred deformed structure.

[0031] The solution annealing of the sheet can be carried out in a temperature range of 460 °C to 580 °C. The solution annealing of the sheet can also be carried out with a holding time of 1 minute to 10 hours.

[0032] Generally, the solution annealing can dissolve the alloying elements participating in hardening as completely as possible (see Friedrich Ostermann: Anwendungstechnologie Aluminium, 3rd edition, published in 2014, ISBN 987-3-662-43806-0, page 175).

[0033] For example, the natural aging treatment can be carried out at room temperature and / or preferably with a holding time of at most 8 weeks. These can contribute to further simplifying the method.

[0034] The artificial aging treatment can be carried out in a temperature range of 130 °C to 210 °C and / or with a holding time of 1 hour to 24 hours to further increase the strength of the sheet.

[0035] The above can be further improved if the heat treatment transforms the sheet into the T6 state, in particular the T651 state. BRIEF DESCRIPTION OF DRAWINGS

[0036] In the drawings:

[0037] Figure 1 A method of manufacturing a sheet is schematically shown.

[0038] Figure 2 The yield strengths of sheet A and sheet B are shown DETAILED DESCRIPTION

[0039] To demonstrate the effects achieved, a rolled semi-finished product, i.e. a sheet A and B, each of a respective sheet thickness of 6 mm (millimetres), made of a respective rolled aluminium alloy, was manufactured,

[0040]

[0041] and the remainder of aluminium and unavoidable impurities due to the manufacture, each having a maximum of 0.05% by weight and together at most 0.15% by weight. Typically, the sheet thickness of the sheet is desirably between 4 mm and 150 mm, in particular between 6 mm and 40 mm.

[0042] The alloy of sheet A is the standard alloy EN AW-6082. On the basis of this standard alloy EN AW-6082, the content of the alloying elements Si, Mg and Cu was increased. Sheet B contains Zr in addition to Si, Mg, Cu with changed content, and is therefore used to describe an embodiment according to the invention.

[0043] The manufacturing method is schematically described in Figure 1 which is described in the above order: homogenisation (H) of a cast rolled ingot, hot rolling (WW) of the homogenised rolled ingot into a sheet, solution annealing (LG) of the sheet, natural ageing treatment (KA), cold deformation (R) and artificial ageing treatment (WA) of the sheet. Figure 1 The flow of the manufacturing method of sheet A and sheet B is shown in part by the solid lines in The following is part of the content: Sheet B is first treated according to the dashed line and then further treated according to the solid line during homogenisation (H). This describes a special method improvement.

[0044] Sheet A and B are now subjected to the following process steps in the above order, wherein the rolled ingot for sheet A is subjected to a different homogenisation than the rolled ingot for sheet B:

[0045] a. Homogenisation (H) of the cast rolled ingot:

[0046] Rolling ingot for sheet A: single stage homogenization (H2) at a temperature of 550°C, a holding time of 2h and a temperature increase rate of 1 K / min;

[0047] Rolling ingot for sheet B: two stage homogenization (H1) and (H2) with a first homogenization (H1) at 350°C, a holding time of 16h and a temperature increase rate of 1 K / min and a second homogenization (H2) at 550°C, a holding time of 2h and a temperature increase rate of 1 K / min, wherein the second homogenization (H2) is directly after the first homogenization (H1). Figure 1 It can be seen that the second homogenization (H2) is directly after the first homogenization (H1).

[0048] b. Hot rolling (WW) of the homogenized rolling ingot into a sheet at a temperature of 540°C from an initial thickness of 40mm to 6mm.

[0049] c. Solution annealing (LG) of the sheet at a temperature of 570°C for 20min, followed by accelerated cooling to room temperature 20°C (RT) by water quenching.

[0050] d. Natural aging treatment (KA) of the sheet by keeping the sheet for 14 days, followed by cold forming by stretching with a deformation of 2%.

[0051] e. Artificial aging treatment (WA) of the sheet by keeping the sheet at a temperature of 160°C for 14h.

[0052] The relevant mechanical property values 0.2% yield strength R p0.2 , tensile strength R m , uniform elongation A g and elongation at break A of the sheets A and B treated according to these processes were examined by tensile testing (tensile test according to DIN EN 10002-1).

[0053] Table 1: Mechanical property values of sheets A and B in state T6, i.e. T651 state (* in rolling direction)

[0054]

[0055] Furthermore, the recrystallization degree, the average subgrain size and the number and average size (calculated from the maximum Feret diameter) of the Zr-containing particles in the microstructure of the two above mentioned sheets were determined. The recrystallization degree was determined by the band contrast measured with a JEOL 7200F FEG-SEM EBSD detector fulfilling two conditions: (a) a grain average misorientation of 0.5° within a third order kernel with a step size of 0.6 pm, (b) an average band contrast exceeding 70% of the maximum band contrast. The Zr-containing particle values of sheet B were determined by scanning transmission electron microscopy (HAADF pictures at a magnification of 17000x, Talos F200XG2 S-TEM).

[0056] As can be seen from table 1, sheet B in the T651 condition has significantly higher strength values R p0.2 and Rmthan sheet A. This is not completely caused by the increase of the Si, Mg and Cu additions, which mainly cause an increase of the precipitate density and thus an increase of the strength. So, the strength of sheet A is basically based on precipitates, especially on the beta”-precipitates (Si, Mg) formed during the artificial ageing process, which in combination with the Fe and / or Mn containing particles make the microstructure stable at higher temperatures.

[0057] In contrast, the 0.2% yield strength R p0.2 of sheet B compared to sheet A of 6082 increases significantly by 73 MPa, which is basically achieved by the hardening effect of Zr or its Al3Zr particles. Therefore, an increased amount of Zr-containing particles (Al3Zr) is found in the microstructure, which makes the microstructural areas with unrecrystallized deformed structure in the microstructure stable, which is formed in the microstructure based on the hot rolling. After the heat treatment, for example a solution annealing at a relatively high temperature of 570°C basically does not cause recrystallization, but a recovery of these microstructural areas, which can achieve a significant increase of the strength compared to the addition of Si, Mg and Cu alone, considering the average subgrain size along the rolling direction of only 5 pm. The increase of the strength of sheet B compared to sheet A can also be seen in Figure 2 .

[0058] The investigation of the particles also shows a significant difference in the microstructure.

[0059] Therefore, the aluminium alloy of sheet B has Zr-containing particles in the intermetallic phase with an average particle size of 74 nm. The number of Zr-containing particles is 7.52 x 101 6 particles / mm 2 .

[0060] In contrast, only Al(Fe,Mn,Cr)Si-containing particles were found in the intermetallic phases of the aluminium alloy of sheet A. The average particle size of these particles was 101 nm. The number of these Al(Fe,Mn,Cr)Si-containing particles was 1.2 x 1010particles / mm2. 6 particles / mm2 2 The particle values of sheet A were determined by scanning electron microscopy (BSE photography at 10,000x magnification, JEOL 7200F FEG-SEM).

[0061] Thus, not only are the particles of sheet A significantly larger, but also the number of particles is considered to be many times less than the Zr-containing particles of sheet B, and in addition, sheet A has these Al(Fe,Mn,Cr)Si-containing particles. This large number of relatively small Zr-containing particles in sheet B improves the pinned subgrain boundaries, whereby the proportion of recovered structure in the final state can be increased and further reduction of the subgrain size is ensured.

[0062] These effects result in a mechanically particularly stable sheet which can be used, for example, for tool making.

[0063] In addition, it can be determined that, as a result of the Zr content in the alloy, the energy introduced in the cold forming (tensile deformation of 2%) does not disappear as a result of the subsequent artificial ageing treatment, since the stabilising effect of the Zr-containing particles is also effective here.

[0064] It is generally indicated that "in particular" can be translated as "more particularly" in English. Features preceded by "in particular" or "where necessary" are to be considered as optional features which can be omitted, and therefore do not limit, for example, the claims. The same applies to the expression "preferably", which is translated as "preferably" in English.

Claims

1. A sheet metal made of rolled aluminum alloy, said aluminum alloy having the following alloy composition: 0.7 wt% to 1.5 wt% silicon (Si), 0.5% to 1.3% by weight of magnesium (Mg), 0.05% to 0.6% by weight of manganese (Mn), Zirconium (Zr) of 0.1 wt% to 0.3 wt%, Each can be optionally, Maximum 0.5% by weight of copper (Cu), Maximum 0.7% by weight of iron (Fe), Maximum 0.1% by weight of chromium (Cr), Maximum 0.2% by weight of titanium (Ti), Maximum 0.5% by weight of zinc (Zn), Maximum 0.2% by weight of tin (Sn), Maximum 0.1% by weight of strontium (Sr), Maximum 0.2% by weight of vanadium (V), Maximum 0.2% by weight of molybdenum (Mo), And the remaining aluminum and impurities, each having a maximum of 0.05% by weight and a total of at most 0.15% by weight, which are unavoidable due to manufacturing. in, The plate has a partially recrystallized structure with a recrystallization degree of less than 25%, wherein the non-recrystallized structure region of the structure is in a recovery state and the average subgrain size along the rolling direction is less than 10 μm.

2. The sheet metal according to claim 1, characterized in that, The degree of recrystallization is less than 15%.

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

4. The sheet metal according to claim 1 or 2, characterized in that, The sheet material is in T6 condition.

5. The sheet metal according to claim 4, characterized in that, The yield strength (R) of the plate p0.2 (Greater than 350MPa) 6. The sheet metal according to claim 1 or 2, characterized in that, The rolled aluminum alloy has the following characteristics: 0.9 wt% to 1.3 wt% silicon (Si), and / or 0.75% to 0.95% by weight of magnesium (Mg), and / or 0.3% to 0.5% by weight of manganese (Mn), and / or 0.15 wt% to 0.25 wt% zirconium (Zr), and / or 0.1% to 0.5% by weight of copper (Cu), and / or Maximum 0.5% by weight of iron (Fe).

7. The sheet metal according to claim 1 or 2, characterized in that, The intermetallic phase of the aluminum alloy contains Zr-containing particles with an average particle size of up to 100 nm, wherein the number of Zr-containing particles is greater than or equal to 1 × 10⁻⁶. 6 Particles / mm 2 .

8. The plate material according to claim 7, characterized in that, The average particle size of the Zr-containing particles ranges from 30 nm to 100 nm, and / or the number of Zr-containing particles is less than or equal to 100 × 10⁻⁶. 6 Particles / mm 2 And / or the number of Zr-containing particles is greater than or equal to 5 × 10⁻⁶. 6 Particles / mm 2 .

9. The plate material according to claim 1, characterized in that, The degree of recrystallization is less than 5%.

10. The plate material according to claim 1 or 2, characterized in that, The plate material is in the T651 state.

11. The sheet metal according to claim 6, characterized in that, The rolled aluminum alloy contains 1.0% to 1.2% silicon (Si).

12. The sheet metal according to claim 6, characterized in that, The rolled aluminum alloy contains 0.18% to 0.22% zirconium (Zr).

13. The plate material according to claim 7, characterized in that, The number of Zr particles is greater than or equal to 5 × 10 6 Particles / mm 2 .

14. The use of sheet metal in mechanical manufacturing according to any one of claims 1 to 13.

15. A method for manufacturing a sheet metal according to any one of claims 1 to 13, wherein, The method includes the steps in the following specified order: Cast and rolled ingots from aluminum alloy; The rolled ingot is subjected to multi-stage homogenization followed by accelerated cooling to room temperature, wherein the multi-stage homogenization includes at least: The first homogenization was carried out at a first temperature ranging from 300°C to 400°C, and A second homogenization was then carried out at a second temperature ranging from 500°C to 10°C below the solidus temperature of the aluminum alloy; The homogenized ingot is hot-rolled into a sheet, and The subsequent heat treatment includes: The plate was solution annealed and then rapidly cooled to room temperature. Natural aging treatment is applied to solution-annealed sheets, and The boards were then subjected to artificial aging treatment.

16. The method according to claim 15, characterized in that, The first homogenization is performed with a first holding time greater than or equal to 0.5 hours and / or a maximum of 4 days, and / or a maximum heating rate of 5 K / min, and / or The second homogenization is performed with a second holding time of greater than or equal to 0.5 hours and / or up to 24 hours.

17. The method according to claim 15 or 16, characterized in that, The hot rolling of the homogenized ingot is carried out at a temperature 5°C to 100°C below the solidus temperature of the aluminum alloy.

18. The method according to claim 15 or 16, characterized in that, The solution annealing of the plate is carried out in a temperature range of 460°C to 580°C, and / or the solution annealing of the plate is carried out with a holding time of 1 minute to 10 hours.

19. The method according to claim 15 or 16, characterized in that, The natural aging treatment was carried out at room temperature.

20. The method according to claim 15 or 16, characterized in that, The artificial aging process is carried out at a temperature range of 130°C to 210°C and / or for a holding time of 1 hour to 24 hours.

21. The method according to claim 15 or 16, characterized in that, The heat treatment transforms the sheet material into a T6 state.

22. The method according to claim 15, characterized in that, After solution annealing, the sheet material is subjected to natural aging treatment, followed by cold deformation with a deformation range between 0.5% and 10%.

23. The method according to claim 15 or 16, characterized in that, The natural aging process is performed with a retention period of up to 8 weeks.

24. The method according to claim 15 or 16, characterized in that, The heat treatment transforms the sheet material into the T651 state.

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