Sheet or strip material made of precipitation-hardening aluminum alloy, vehicle parts made from said sheet or strip material, use of said sheet or strip material and method of manufacture

Abstract

A precipitation-hardenable aluminum alloy plate or strip, a vehicle part constructed from the plate or strip, and a method for using and manufacturing the plate or strip are disclosed. To ensure a high degree of paint bake response (PBR), the aluminum alloy is proposed to have 4.0-5.5 wt.% magnesium (Mg) and 2.5-5.5 wt.% zinc (Zn) and be in a T4-FH condition, where the magnesium (Mg) wt.% is greater than the zinc (Zn) wt.%.

Description

[Technical Field]

[0001] The present invention relates to a sheet material or strip material made of precipitation-hardening aluminum alloy, a vehicle part composed of the sheet material or strip material, and a method for using and manufacturing the sheet material or strip material.

[0002] prior art In order to achieve both high formability during deformation processing or sheet deformation processing of aluminum sheets and relatively high strength after the baking cycle (for example, in a cathode dipping coating process), U.S. Patent No. 4,140,556 proposes to transition an Al-Mg aluminum alloy containing 3.5 to 5.5 wt% Mg to the T4 state (solution heat treatment, quenching, and natural aging) by supplementing it with 0.5 to 2 wt% Zn and optionally 0.3 to 1.2 wt% Cu.

[0003] Unfortunately, in the T4 state alloy disclosed in U.S. Patent No. 4,140,556, R is affected by the paint-bake cycle. p0.2 There is no or very slight improvement in strength (for example, Al 4.7 Mg 1.5 Zn 0.6 Regarding Cu, R p0.2 It was found that the strength improvement is approximately 5 MPa, and this is because the heat generated during the heat treatment cycle for strength improvement is disregarded, which leads to a decrease in energy efficiency, for example, in the manufacturing of vehicle parts.

[0004] Furthermore, U.S. Patent Application Publication No. 20170349989 describes an Al-Mg aluminum alloy having 1.75 wt% Mg and 0.78 wt% Cu, which in the T4-FH state, i.e., the T4 state with stabilization heat treatment ("pre-aging"), achieves an R of approximately 60 MPa through a paint-bake cycle. p0.2An improvement in strength is achieved. This paint bake response (PBR) is a PBR of 6xxx alloys in the T4-FH state with a R of 100 to a maximum of 150 MPa. p0.2 Compared to the improvement in strength, the effect is relatively low.

[0005] Given these circumstances, despite having better deformation machinability compared to 6xxx series alloys, Al-Mg aluminum alloys cannot be used in parts that require high strength under operating conditions.

[0006] Description of the Invention Therefore, the object of the present invention is to provide an Al-Mg aluminum alloy that exhibits a high degree of thermosetting reaction, particularly a paint-bake reaction (PBR). Furthermore, it is desirable that this Al-Mg aluminum alloy can achieve relatively high strength.

[0007] The present invention solves the problem with the features of claim 1.

[0008] Aluminum alloys with a balanced alloying element ratio of 4.0–5.5 wt% magnesium (Mg) and 2.5–5.5 wt% zinc (Zn) exhibit a surprisingly high degree of thermosetting reaction in the T4-FH state, i.e., the T4 state with stabilization heat treatment, when magnesium (Mg) wt% > zinc (Zn) wt%. For example, this stabilization heat treatment can be carried out at 95°C–125°C, especially 100°C–120°C, for a maximum of 10 hours with at least 20 minutes, and especially for a maximum of 4 hours with at least 2 hours.

[0009] A paint curing reaction at 185°C for 20 minutes resulted in a plate deformation of 2% and a resistance far exceeding 150 MPa. p0.2 We were able to achieve improved strength. This is not known even for 6xxx series alloys optimized for PBR. Clearly, this Al-Mg-Zn alloy in the T4-FH state, i.e., Al-Mg-Zn alloy treated with solution heat treatment, accelerated cooling (preferably quenching), stabilization heat treatment and natural aging treatment, for example, the stable precursor (Mg) of the T phase during stabilization heat treatment.32 (Al,Zn) 49 Alternatively, through the preferred formation of (Mg3Zn3Al2), it precipitates and hardens particularly rapidly with respect to paint baking. This precursor becomes a precipitate that shows a further enhanced hardening effect during the paint baking process (the "paint-bake cycle"), thereby causing a particularly strong paint bake response (the "Paint Bake Response" or PBR). At the same time, the formation of these phases or clusters with a size of 1 to 10 nm suppresses the precipitation of the S phase and the β phase due to the relatively high Zn content. In contrast to sheets and strips that have not been subjected to stabilization heat treatment, these phases or clusters that are formed can significantly improve the strength during the process of a thermosetting reaction, such as a paint baking reaction at 185 °C for 20 minutes.

[0010] Furthermore, this aluminum alloy according to the invention in the T4-FH state has high energy efficiency in the utilization of available thermal energy in subsequent manufacturing processes due to a relatively high degree of thermosetting reaction.

[0011] Therefore, the aluminum alloy according to the invention is considered to be particularly suitable for the production of formed parts of vehicles, preferably body parts, such as outer panels.

[0012] Optionally, the sheet or strip can have one or more of the following elements: 0 to 0.8 wt% copper (Cu) and / or 0 to 0.2 wt% silver (Ag) and / or 0 to 1.0 wt% manganese (Mn) and / or 0 to 0.45 wt% silicon (Si) and / or 0 to 0.55 wt% iron (Fe) and / or 0 to 0.35 wt% chromium (Cr) and / or 0 to 0.2 wt% titanium (Ti) and / or  0 to 0.8 wt% zirconium (Zr) and / or 0 to 1.0 wt% hafnium (Hf) and / or 0 to 0.3 wt% niobium (Nb) and / or 0 to 0.25 wt% tantalum (Ta) and / or 0 to 0.2 wt% vanadium (V).

[0013] The remainder of the aluminum alloy consists of aluminum and unavoidable impurities from the manufacturing process, each up to 0.05% by weight, for a total of up to 0.15% by weight.

[0014] Generally, it is mentioned that "vehicle" refers to, for example, land vehicles, water vehicles, and / or aircraft.

[0015] To reach the T4-FH state, it is known that in addition to T4 treatment (=solution heat treatment and natural aging or cold precipitation hardening), the alloy is subjected to heat treatment, such as thermal shock, after solution heat treatment and accelerated cooling, and then undergoes natural aging.

[0016] Further examples of such stabilization heat treatments are known from the literature (see Friedrich Ostermann: Anwendungstechnologie Aluminium, 3. Auflage, Erscheinungsjahr 2014, ISBN 987-3-662-43806-0, p.138), German Patent Application Publication No. 112011103667, which is also known as pre-aging.

[0017] According to Friedrich Ostermann, *Anwendungstechnologie Aluminium*, 3rd Edition, 2014, ISBN 987-3-662-43806-0, p.175, solution heat treatment is also known, and according to this method, the most complete solution treatment possible of the alloying elements involved in precipitation hardening is achieved during solution heat treatment.

[0018] When an aluminum alloy contains 3.0-4.0 wt% of Zn, particularly 3.3-3.7 wt%, it is possible to achieve a relatively very favorable precipitation hardening ability, especially when combined with magnesium, thus enabling high PBR (Precipitation-Based Hardening). Furthermore, alloys in the T4-FH state have relatively higher yield strength compared to alloys without Zn, which is significantly increased after subsequent deformation processing and paint curing.

[0019] When the aluminum alloy has 4.5 to 5.0 wt% of Mg, the above matters can be further improved. Thereby, on the one hand, favorable precipitation hardening ability, i.e., PBR, can be realized by combining with Zn, and on the other hand, since Mg is forced to dissolve in the Al solid solution, very good deformation workability can be realized.

[0020] Particularly, when the aluminum alloy has 0.3 to 0.6 wt%, particularly 0.4 to 0.6 wt%, for example 0.5 to 0.6 wt% of Cu, this tendency is remarkable. By doing so, for example, an increase in precipitation density in the process of stabilization heat treatment can be realized, and further improvement of PBR can be made possible. Preferably, if the Cu content is more than 0.5 wt%, the Zn content satisfies the following condition: Zn = 7.2 - 3.4 * Cu [wt%].

[0021] Preferably, the aluminum alloy can have 0.1 to 0.3 wt% of silver (Ag). This presented Ag content, similar to Cu, can bring about a higher precipitation density in the process of stabilization heat treatment and can further improve PBR.

[0022] Preferably, the aluminum alloy can have 0.05 to 0.25 wt% of iron (Fe) in order to enable an increase in the proportion of secondary aluminum in the alloy.

[0023] Preferably, the aluminum alloy can have 0.3 to 1.0 wt% of manganese (Mn). Preferably, the aluminum alloy has 0.3 to 0.5 wt% of manganese (Mn). By setting the presented Mn content, particularly the morphology of the phase containing iron can be changed, thereby reducing the ductility reduction effect. Also, by increasing the Mn content, the particle size can be reduced, which can be advantageous for deformation workability. Also, the inclusion of Mn can contribute to the adjustment of the main phase suitable for suppressing the Lüder's band.

[0024] Preferably, the aluminum alloy may contain, for example, 0.05 to 0.15 wt% titanium (Ti) to adjust the grain size in a controlled manner.

[0025] The sheet material or strip material according to the present invention, having a thickness of 0.5 to 4 mm, and particularly 0.8 to 2.5 mm, may be especially suitable for the manufacture of molded parts for vehicles, such as automobiles.

[0026] Preferably, for aluminum alloy sheets or strips, when data obtained by atom probe tomography (LEAP 3000HR atom probe) with Zn as the core atom for the Guinier-Preston-I-zone (GPI zone) of Cu-free Al alloys, and with Zn+Cu as the core atom for Cu-containing Al alloys, is measured using Felfer's evaluation method (see P. Felfer, et al., Detecting and extracting clusters in atom probe data: a simple, automated method using Voronoi cells, Ultramicroscopy 150 (2015) 30-36), the data shows at least 700 atoms per Guinier-Preston-I-zone (GPI zone), with at least 0.25 × 10⁻¹⁶ atoms. 23 GPI zones / m 3 It has a GPI zone density of [value].

[0027] This allows for the growth or generation of a T-phase precursor (Mg 32 (Al,Zn) 49 Alternatively, it can be ensured that Mg3Zn3Al2 is present in sufficient density and size, and that R in the process of the bake cycle ("paint-bake cycle") p0.2 Strength improvement is guaranteed or enhanced. In particular, the aluminum alloy of the sheet or strip material has at least 1.5 × 10¹⁶ atoms per Guinier-Preston-I zone (GPI zone). 23 GPI zones / m 3This applies when the GPI zone density is such that it is high.

[0028] Furthermore, the aluminum alloy sheet or strip material has at least 700 atoms per Guinier-Preston-I zone (GPI zone), with a maximum density of 5.0 × 10⁻¹⁶ 23 GPI zones / m 3 In some cases, having a GPI zone density of a certain value may be sufficient.

[0029] In particular, the plate material or strip material according to the present invention may be suitable for vehicle parts, preferably vehicle body parts.

[0030] By implementing the following process steps, complex shapes and high yield strength R can be achieved. p0.2 It is possible to manufacture sheet or strip materials that enable molded parts having the following characteristics: A process step of hot-rolling an ingot for rolling to obtain a hot-rolled sheet or strip. A process step in which a hot-rolled sheet or strip is cold-rolled to its final thickness, and an intermediate heat treatment is optionally performed on the sheet or strip. A process step for heat-treating a sheet or strip material that has been cold-rolled to its final thickness, wherein the heat treatment is: Solution heat treatment, followed by accelerated cooling. Stabilization heat treatment of accelerated-cooled plate or strip material, and Natural aging of heat-treated plate or strip materials A process step that includes the following:

[0031] According to the present invention, the stabilizing heat treatment of the alloy according to the present invention makes it possible to guarantee its rapid precipitation hardening kinetics, which result from the formation of a stable nucleus responsible for a strong thermosetting reaction, particularly a paint curing reaction.

[0032] Preferably, the stabilization heat treatment is carried out at 95°C to 125°C for at least 20 minutes and up to 10 hours, and this temperature control prepares the sheet or strip material for a relatively high degree of thermosetting reaction, particularly paint bake response (PBR), with reproducibility. This thermosetting reaction, such as PBR, can be further enhanced by carrying out the stabilization heat treatment at 100°C to 120°C and / or for at least 2 hours and up to 4 hours.

[0033] It may be found that performing solution heat treatment at 450°C to 500°C, and especially at, for example, 460°C to 490°C, are favorable process conditions. Recrystallization may also occur during the solution heat treatment process.

[0034] To ensure relatively high precipitation hardening ability, accelerated cooling is performed at a cooling rate of at least 10°C / s for the plate or strip material. Preferably, accelerated cooling is performed at a cooling rate of at least 20°C / s. In particular, if the plate or strip material has a temperature of less than 300°C during cooling, it is advantageous to perform accelerated cooling of the plate or strip material at a cooling rate of at least 10°C / s.

[0035] Generally, accelerated cooling refers to cooling that is faster than cooling at room temperature or in still air (see Friedrich Ostermann, Anwendungstechnologie Aluminium, 3. Auflage, Erscheinungsjahr 2014: Abkuehlen nach dem Loesungsgluehen).

[0036] Preferably, to reliably avoid, for example, edge cracking or double-layering during hot rolling, the hot rolling is performed at a temperature of 310°C to a maximum of 440°C for the sheet or strip material. Therefore, the method according to the present invention can exhibit particularly high process safety.

[0037] High moldability and high yield strength R for complex shapes p0.2The advantages of the present invention in relation to this may prove particularly advantageous when using the aluminum sheet or strip material for cold deformation processing, particularly sheet deformation processing, and subsequent precipitation hardening, particularly baking, preferably paint baking, to form molded parts, particularly vehicle parts, preferably body parts, such as exterior panels.

[0038] Favorable process conditions may be obtained when the paint is baked at 150°C to 200°C for at least 10 minutes and up to 30 minutes, and especially at 170°C to 190°C for at least 15 minutes and up to 25 minutes. [Brief explanation of the drawing]

[0039] [Figure 1] A graph showing the relationship between Rp0.2 and A.

[0040] To demonstrate the effects obtained, for example, rolled semi-finished products, i.e., thin sheets (which can also be wound into coils), were manufactured from various aluminum alloys using the following method: a. Hot-roll the rolling ingot at 370°C to 430°C to obtain hot-rolled sheet material or strip material. b. The hot-rolled sheet or strip is cold-rolled to a final thickness of 1.2 mm, subjected to intermediate heat treatment at 370°C for 1 hour, and then cooled to room temperature. c. The sheet or strip material, cold-rolled to its final thickness, is heat-treated in the order described below: i. Solution heat treatment at 465°C ii. Subsequent accelerated cooling at at least 15°C / s (i.e., rapid cooling using water) iii. Stabilization heat treatment of accelerated-cooled plate or strip material at 100°C for 3 hours. iv. Natural aging of heat-treated plate or strip material at room temperature (20°C) for 3 weeks.

[0041] After subjecting this sheet material to natural aging in the T4-FH state, it was deformed by cold sheet material deformation processing with a deformation degree of 2% to obtain molded parts, i.e., body parts for the outer panels. After deformation processing, these molded parts were subjected to cathode dipping coating (CDP) with a baking cycle of 20 minutes at a baking temperature of 185°C.

[0042] [Table 1]

[0043] Alloy 1 is the AA5182 alloy, which is known as a reference alloy. Alloys 2 to 4 are alloys according to the present invention, and contain Zn, Zn+Cu, or Zn+Cu+Ag in a well-balanced manner.

[0044] Each alloy consists of aluminum as the remainder, with a maximum of 0.05% by weight of impurities each, totaling a maximum of 0.15% by weight, which are unavoidable during manufacturing. On the other hand, alloys 1-4 may contain an additional 0.1% by weight of chromium (Cr).

[0045] The alloys shown in Table 1 were subjected to tensile tests to determine their mechanical properties R p0.2 The elongation at break A was also investigated. The tests were performed in the T4-FH state after a paint-baking cycle (PB) with a preceding 2% deformation process. Furthermore, as described above, the GPI zone density, with at least 700 atoms per Guinier-Preston-I zone (GPI zone), was measured using Felfer's evaluation method with atom probe tomography (LEAP 3000HR atom probe).

[0046] [Table 2]

[0047] As shown in Table 2, aluminum alloys 2 to 4 according to the present invention achieve an unexpectedly high paint bake response (PBR) of up to 195 MPa compared to alloy 1, without significantly degrading the deformability (or elongation) in the T4-FH state. For this reason, the combination of the alloy according to the present invention and the manufacturing method according to the present invention shows particularly good suitability for molded parts of vehicle bodies.

[0048] In Figure 1, the formability of alloy 4 in the T4-FH state according to the present invention, shown as L4(T4-FH) in Figure 1, is almost the same as that of alloy 1 (AA5182) in the T4-FH state, shown as L1(T4-FH) in Figure 1, and the strength R p0.2 Tensile tests show that it is higher.

[0049] In Figure 1, alloy 1, shown as L1(PB), and alloy 4, shown as L4(PB), have different strengths after paint curing. p0.2 What is even more surprising is the indication of a higher altitude increase.

[0050] These properties described for alloy 4 also apply to the other alloys 2 and 3 according to the present invention.

[0051] Furthermore, the alloy according to the present invention exhibits a delayed onset of the PLC effect, resulting in a reduction in type B tensile wrinkles.

[0052] Furthermore, in Table 2, it can be seen that alloys 2-4 in the T4-FH state show an increased GPI zone density, with at least 700 atoms per Guinier-Preston-I zone (GPI zone). Here, the GPI zone density with at least 700 atoms per Guinier-Preston-I zone (GPI zone) is shown in Table 2 as the GPI zone density * It is referred to as such.

[0053] As seen in alloy 3, GPI zone density * 1.6 × 10 23 GPI zones / m3 And already, R after PB p0.2 The improvement in strength was remarkably high, exceeding 400 MPa, and even higher results were achieved with alloy 4.

[0054] For alloys 2-4, the maximum density of the Guinier-Preston-I zone (GPI zone) is 5 × 10¹⁶ atoms, with at least 700 atoms per GPI zone. 23 GPI zones / m 3 That would be perfectly sufficient.

Claims

1. A sheet or strip made of a precipitation-hardening aluminum alloy, wherein the alloy is 4.0 to 5.5% by weight of magnesium (Mg) and 2.5–5.5% by weight of zinc (Zn) This includes, where magnesium (Mg) weight% > zinc (Zn) weight%. Optionally, Copper (Cu) up to 0.8% by weight Silver (Ag) up to 0.2% by weight Manganese (Mn) up to 1.0 wt% Silicon (Si) up to 0.45% by weight Iron (Fe) up to 0.55% by weight Chromium (Cr) up to 0.35% by weight Titanium (Ti) up to 0.2% by weight Zirconium (Zr) up to 0.8% by weight Hafnium (Hf) up to 1.0 wt% Niobium (Nb) up to 0.3% by weight up to 0.25% by weight of tantalum (Ta) and / or up to 0.2% by weight of vanadium (V) It contains, and impurities that are unavoidable in the manufacturing process, each at a maximum of 0.05% by weight, for a total of up to 0.15% by weight, with the remainder being aluminum, and the sheet or strip material has a T4-FH state, The aluminum alloy is a sheet or strip material having a GPI zone density of at least 0.25 × 10²³ GPI zones / m³, with at least 700 atoms per Guinier-Preston-I zone (GPI zone).

2. The aluminum alloy comprises 3.0 to 4.0% by weight of Zn, as described in claim 1, for the plate or strip material.

3. The aluminum alloy comprises 3.3 to 3.7% by weight of Zn, as described in claim 2, for a plate or strip material.

4. The aluminum alloy comprises 4.5 to 5.0% by weight of Mg, as described in any one of claims 1 to 3, for a plate or strip material.

5. The aluminum alloy comprises 0.3 to 0.6% by weight of Cu, as described in any one of claims 1 to 4, a plate or strip material.

6. The aluminum alloy comprises 0.4 to 0.6% by weight of Cu, as described in claim 5, for the plate or strip material.

7. The aforementioned aluminum alloy is 0.05 to 0.25 wt% iron (Fe) and / or 0.3–1.0 wt% manganese (Mn) and / or 0.05–0.15% by weight of titanium (Ti) A plate or strip material according to any one of claims 1 to 6, having the following characteristics.

8. The aforementioned aluminum alloy is 0.1–0.3% by weight of silver (Ag) A plate or strip material according to any one of claims 1 to 7, having the following characteristics.

9. A plate or strip material according to any one of claims 1 to 8, having a thickness of 0.5 to 4 mm.

10. The aforementioned aluminum alloy has at least 700 atoms per Guinier-Preston-I zone (GPI zone), with a maximum of 5.0 × 10⁻¹⁶ atoms. ２３ GPI zone / m ３ A plate or strip material according to claim 1, having the GPI zone density.

11. A vehicle part comprising a plate or strip material according to any one of claims 1 to 10.

12. A method for manufacturing a plate or strip according to any one of claims 1 to 10, A process step of hot-rolling an ingot for rolling to obtain a hot-rolled sheet or strip. A process step of cold-rolling the hot-rolled sheet or strip material to its final thickness, and optionally performing intermediate heat treatment on the sheet or strip material. A process step for heat-treating a sheet or strip material that has been cold-rolled to the aforementioned final thickness, wherein the heat treatment is: Solution heat treatment, followed by accelerated cooling. Stabilization heat treatment of the accelerated-cooled plate or strip material at 95°C to 125°C for at least 20 minutes and up to 10 hours. The natural aging of the aforementioned heat-treated plate or strip material Process steps that include Methods that include...

13. The method according to claim 12, wherein the stabilization heat treatment is performed at 100°C to 120°C for at least 2 hours and a maximum of 4 hours.

14. The method according to claim 12 or 13, wherein the solution heat treatment is performed at 450°C to 500°C.

15. The method according to any one of claims 12 to 14, wherein the accelerated cooling is performed at a cooling rate of at least 10°C / s for the plate or strip material.

16. The method according to any one of claims 12 to 15, wherein the hot rolling is performed at a temperature of 310°C to a maximum of 440°C for the sheet or strip material.

17. The use of a sheet material or strip material according to any one of claims 1 to 10 for obtaining a molded part by cold deformation processing, deformation processing of a sheet material, and subsequent precipitation hardening.

18. The use according to claim 17, wherein the precipitation hardening is performed by paint baking, and the paint baking is performed at 150°C to 200°C for at least 10 minutes and a maximum of 30 minutes.

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