A method for controlling a 5-series automobile panel material stamping lueders band

Abstract

The application provides a control method of a 5-series automobile covering material stamping lueders strip, which comprises the following steps: heating, rough rolling, hot finish rolling, primary cold rolling, intermediate annealing, secondary cold rolling, roughening, product annealing, surface treatment and stamping of an aluminum alloy ingot. Through material processing process adjustment, the stamping lueders strip defects are systematically improved and eliminated in the premise of guaranteeing material forming performance in the chemical composition, cold deformation, product annealing and stamping process, so that the use requirements of covering materials of different main machine plants, different structural designs and different models are met.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy technology, and in particular relates to a method for controlling the stamping of Lüders strips in 5-series automotive body panel materials. Background Technology

[0002] To reduce painting costs and harmful emissions, automotive body painting processes are increasingly adopting advanced, low-cost, and environmentally friendly intermediate-coat-free processes, resulting in a thinner overall film thickness. However, some interior body panels have exposed areas where surface defects are more visible due to the thinner paint film. The streaks (Lüders bands) after stamping of 5XXX aluminum alloy cannot be masked, constituting an unacceptable surface defect and failing to meet the OEM's surface rating standards. The complex forming structure of interior body panels, with deep drawing depths and significant thinning, necessitates aluminum alloys with good formability. Improving the streaks after stamping of 5XXX aluminum alloy often leads to a decrease in stamping performance and unstable stamping. Previously, to ensure a streak-free surface after stamping and painting, OEMs could only eliminate defects through post-stamping grinding, which was inefficient, costly, and required significant effort. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for controlling Lüders stripe stamping on 5 Series automotive body panel materials, which eliminates Lüders stripe stamping on the surface while ensuring the stamping performance of the material. The method provided by the present invention results in no stripe defects on the surface after stamping.

[0004] This invention provides a method for controlling the stamping of Lüders strips in body panel materials for 5 Series automobiles, comprising:

[0005] The aluminum alloy ingot is heated, rough rolled, hot precision rolled, cold rolled once, intermediate annealed, cold rolled twice, roughened, finished annealed, surface treated, and stamped.

[0006] Preferably, the composition of the aluminum alloy ingot is:

[0007] 0.05–0.15 wt% Si;

[0008] 0.2–0.3 wt% Fe;

[0009] 0.03–0.05 wt% Cu;

[0010] 0.20–0.24 wt% Mn;

[0011] 4.65–4.85 wt% Mg;

[0012] 0.03–0.07 wt% Zn;

[0013] The balance is Al.

[0014] Preferably, the heating temperature is 470–490°C; and the heating holding time is ≥2 hours.

[0015] Preferably, during the rough rolling process, the initial rolling temperature is ≥450℃, the final rolling temperature is ≥410℃, the deformation amount during the microstructure improvement stage is ≤15mm, the deformation amount during the reduction deformation stage is ≥20mm, and the pass deformation rate during the shape control stage is ≥16%.

[0016] Preferably, the rolling speed in the hot finishing rolling process is ≥120m / min, the deformation rate per pass is ≥30%, and the final rolling temperature is ≥320℃.

[0017] Preferably, the cold rolling deformation rate during the primary cold rolling process is ≥70%;

[0018] The cold rolling deformation rate during the secondary cold rolling process is ≤30%.

[0019] Preferably, the intermediate annealing includes:

[0020] Washing, primary heating, and secondary heating;

[0021] The blowing temperature is 200-220℃, the primary heating temperature is 430-470℃, and the secondary heating temperature is 330-370℃.

[0022] Preferably, the annealing temperature of the finished product is 450–550°C.

[0023] Preferably, the blank holder force during the stamping process is 200-220t, and the stamping cycle is 14-18 times / minute.

[0024] Existing 5XXX aluminum alloy processing techniques result in severe Lüders banding after stamping, which is noticeable to the touch and clearly visible after painting, failing to meet the requirements for exposed areas of the inner panels in automotive body panels. This invention, through process adjustments, systematically improves and eliminates the Lüders banding defect in stamping by modifying the chemical composition, cold deformation, finished product annealing, and stamping process, while ensuring material formability. This meets the material requirements of various OEMs for different vehicle models and structural designs. This invention solves the problem of surface striations (Lüders banding) after stamping 5XXX aluminum alloy for automotive interior body panels. Attached Figure Description

[0025] Figure 1 High-magnification image of the grain structure of the product prepared in Example 1;

[0026] Figure 2 Images of Lüders bands on the surface of products prepared before the method improvement;

[0027] Figure 3 This is an image of the product prepared in Example 1 after surface polishing. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a method for controlling the stamping of Lüders strips in body panel materials for 5 Series automobiles, comprising:

[0030] The aluminum alloy ingot is heated, rough rolled, hot precision rolled, cold rolled once, intermediate annealed, cold rolled twice, roughened, finished annealed, surface treated, and stamped.

[0031] In this invention, the aluminum alloy ingot is preferably composed of 5-series aluminum alloy, more preferably 5182 aluminum alloy. In this invention, the preferred composition of the aluminum alloy ingot is:

[0032] 0.05–0.15 wt% Si;

[0033] 0.2–0.3 wt% Fe;

[0034] 0.03–0.05 wt% Cu;

[0035] 0.20–0.24 wt% Mn;

[0036] 4.65–4.85 wt% Mg;

[0037] 0.03–0.07 wt% Zn;

[0038] The balance is Al.

[0039] In this invention, the mass content of Si is preferably 0.08-0.12%, more preferably 0.1%; the mass content of Fe is preferably 0.23-0.27%, more preferably 0.25%; the mass content of Cu is preferably 0.04%; the mass content of Mn is preferably 0.21-0.23%, more preferably 0.22%; the mass content of Mg is preferably 4.70-4.80%, more preferably 4.75%; and the mass content of Zn is preferably 0.04-0.06%, more preferably 0.05%.

[0040] In this invention, the heating method preferably includes:

[0041] First, heat it once, then heat it a second time.

[0042] In this invention, the furnace gas constant temperature for the primary heating is preferably 600-640°C, more preferably 610-630°C, and most preferably 620°C; the metal temperature for the primary heating is preferably 450-470°C, more preferably 455-465°C, and most preferably 460°C.

[0043] In this invention, the furnace gas constant temperature refers to the air temperature during the ingot heating process; the metal temperature refers to the temperature of the ingot; and the metal temperature reached refers to the actual value reached by the measured metal temperature.

[0044] In this invention, the furnace gas temperature for secondary heating is preferably 480-500℃, more preferably 450-495℃, and most preferably 500℃; the metal temperature for secondary heating is preferably 460-480℃, more preferably 465-475℃, and most preferably 470℃; the holding time for secondary heating is preferably ≥2h, more preferably 2-4h, and most preferably 3h.

[0045] In this invention, the heating process raises the temperature of the aluminum alloy ingot to 470–490°C, more preferably 475–485°C, and most preferably 480°C.

[0046] In this invention, the roughing temperature is preferably 460–490°C, more preferably 470–480°C; the initial rolling temperature during the roughing process is preferably ≥450°C, more preferably 470–490°C, and most preferably 480°C; the final rolling temperature is preferably ≥410°C, more preferably 410–430°C, and most preferably 420°C; the deformation amount during the microstructure improvement stage is preferably ≤15mm, more preferably 10–15mm, and most preferably 12–13mm; the deformation amount during the reduction deformation stage is preferably ≥20mm, more preferably 20–30mm, and most preferably 25mm; and the pass deformation rate during the shape control stage is preferably ≥16%, more preferably 16–20%, and most preferably 18%.

[0047] In this invention, during the roughing process, when the thickness of the rolled billet H is preferably 350 mm, the reduction per pass Δh is 5-15 mm, more preferably 8-12 mm, and most preferably 10 mm; the reduction gradually increases; in order to limit the ingot width, the vertical roll mill performs four roll edge rolling operations at billet thicknesses of 300 mm, 260 mm, 220 mm, and 180 mm.

[0048] In this invention, during the roughing process, when the thickness H of the rolled billet is preferably 350-70 mm, the reduction per pass Δh is 17-23 mm, more preferably 19-21 mm, and most preferably 20 mm, and equal reduction rolling is adopted.

[0049] In this invention, during the rough rolling process, it is preferable to cut off the head and tail when the thickness of the rolled billet is 75mm to eliminate the opening during the ingot rolling process.

[0050] In this invention, during the roughing process, when the thickness H of the rolled billet is preferably 75-20mm, five passes of rolling are used, and the reduction per pass is distributed equally with the rolling force. The reduction per pass Δh is preferably 20mm-13mm-10mm-7mm-5mm.

[0051] In this invention, when the thickness of the cold-rolled finished product during the hot finishing rolling process is 0.85–1.0 mm, the thickness of the finished raw material is preferably 4.8–5.2 mm, more preferably 4.9–5.1 mm, and most preferably 5.0 mm; when the thickness of the cold-rolled finished product is 1.5 mm, the thickness of the finished raw material is preferably 5.3–5.7 mm, more preferably 5.4–5.6 mm, and most preferably 5.5 mm.

[0052] In this invention, the rolling speed in the hot finishing rolling process is preferably ≥120m / min, more preferably 120~180m / min, and most preferably 140~160m / min; the deformation rate per pass is preferably ≥30%, more preferably 30~40%, and most preferably 35%; the final rolling temperature is preferably ≥320℃, more preferably 320~340℃, and most preferably 330℃.

[0053] In this invention, the temperature of the hot finishing rolling is preferably 410-320℃, more preferably 400-350℃, and most preferably 380-360℃; the hot finishing rolling process preferably involves 4-6 passes, more preferably 5 passes; the rolling speed of the first pass is preferably 100-140 m / min, more preferably 110-130 m / min, and most preferably 120 m / min; the rolling speed of the other passes is preferably 130-170 m / min, more preferably 140-160 m / min, and most preferably 150 m / min.

[0054] In this invention, when the thickness of the finished stock during the hot finishing rolling process is 5.0 mm, the preferred pass reduction distribution (mm) is 20-13-9.5-7.3-5.8-5.0; the preferred rolling speed ((m / min) ±20) is 120-150-150-150-150; when the thickness of the finished stock is 5.5 mm, the preferred pass reduction distribution (mm) is 20-13.5-10. 0.3-8.0-6.3-5.5; the rolling speed ((m / min)±20) is preferably 120-150-150-150-150; when the thickness of the finished rolled material is 6.0mm, the pass reduction distribution setting value (mm) is preferably 20-14-10.5-8.3-6.8-6.0; the rolling speed ((m / min)±20) is preferably 120-150-150-150-150.

[0055] In this invention, the thickness of the finished product during the first cold rolling process is preferably half the thickness of the cold-rolled semi-finished product; for example, when the finished product thickness is 0.85 mm, the thickness of the cold-rolled semi-finished product is 1.7 mm; when the finished product thickness is 1.0 mm, the thickness of the cold-rolled semi-finished product is 2.0 mm; and when the finished product thickness is 1.5 mm, the thickness of the cold-rolled semi-finished product is 3.0 mm. In this invention, the cold rolling deformation rate during the first cold rolling process is preferably ≥70%, more preferably 70-80%, and most preferably 75%.

[0056] In this invention, the intermediate annealing is preferably non-temperature annealing. The metal temperature can be precisely controlled by constant furnace gas temperature. Considering that the intermediate annealing process parameters have a wide range and are not sensitive to the material microstructure, non-temperature annealing can be used for production.

[0057] In this invention, the intermediate annealing preferably includes:

[0058] Washing, primary heating, and secondary heating.

[0059] In this invention, the blowing temperature is preferably 200–220°C, more preferably 205–215°C, and most preferably 210°C; the blowing time is preferably 15–25 min, more preferably 18–22 min, and most preferably 20 min. In this invention, the blowing refers to the process before material annealing, where a fan operates at high speed, residual oil on the material surface evaporates and is discharged outside the furnace, and fresh air is introduced into the furnace.

[0060] In this invention, the furnace gas temperature for the first heating in the intermediate annealing process is preferably 430-470°C, more preferably 440-460°C, and most preferably 450°C. The holding time for the first heating is preferably 540-580 min, more preferably 550-570 min, and most preferably 560 min.

[0061] In this invention, the furnace gas temperature for the secondary heating during the intermediate annealing process is preferably 330-370°C, more preferably 340-360°C, and most preferably 350°C; the holding time for the secondary heating is preferably 80-100 min, more preferably 85-95 min, and most preferably 90 min.

[0062] In this invention, the secondary cold rolling is preferably rolled to the finished thickness; the finished thickness is preferably 1.0 to 1.5 mm; the cold rolling deformation rate of the secondary cold rolling is preferably ≤30%, more preferably 30 to 20%, and most preferably 25%.

[0063] In this invention, the texturing refers to rolling aluminum strip with a small deformation using specialized high-roughness rolls to improve surface roughness and eliminate the difference in roughness between the transverse and longitudinal directions. In this invention, the roughness of the rolls during the texturing process is preferably 1.5–3.5 μm, more preferably 2–3 μm, and most preferably 2.5 μm; the pass deformation rate is preferably 1–4%, more preferably 2–3%; the speed is preferably 1.5–2.5 m / s, more preferably 2.0 m / s; the bending force is preferably 120–180 t, more preferably 140–160 t, and most preferably 150 t; and the rolling force is preferably ≥400 t.

[0064] In this invention, the finished product annealing is preferably carried out in an air cushion furnace, which is a continuous heat treatment furnace that uses an air cushion to support and heat the metal strip; the independent temperatures of zones one to five during the finished product annealing process are preferably 450-560°C, more preferably 500-560°C, and most preferably 560°C; the running speed of the strip in the air cushion furnace during the finished product annealing process is preferably 10-12 m / min, more preferably 11 m / min; during the finished product annealing process, after the strip passes through the air cushion furnace, bending rollers and straightening rollers are fed into the bending and straightening unit to obtain a better strip shape and appropriately increase the dislocation density.

[0065] In this invention, the surface treatment is preferably carried out on a surface treatment line. After degreasing the surface of the aluminum plate and strip, the surface oxide film is removed, and then the surface is subjected to Ti / Zr passivation treatment before being coated with oil.

[0066] In this invention, the degreasing method is preferably alkaline washing, and the alkaline washing process is preferably operated at 100%. In this invention, the method for removing the surface oxide film is preferably acid washing, and the acid washing is preferably operated at 55-65% nozzle opening, more preferably 60%. In this invention, the passivation treatment is preferably operated at 45-55% nozzle opening, more preferably 50%. In this invention, the oiling is preferably done using stamping oil. In this invention, the reagents for alkaline washing, acid washing, passivation, and oiling can be commercially available products, such as Kemet 7271, 4591, and Quaker 6130. In this invention, the machine speed during the surface treatment process is preferably 25-35 m / min, more preferably 30 m / min; the spray pressure is preferably 1-2 kg, more preferably 1.5 kg.

[0067] In this invention, the dimensions during the stamping process are preferably 1.5mm × 1505mm; the blank holder force during the stamping process is preferably 200-220t, more preferably 205-215t, and most preferably 210t; the stamping cycle time during the stamping process is preferably 14-18 times / min, more preferably 15-17 times / min, and most preferably 16 times / min.

[0068] In this invention, the 5182 aluminum alloy exhibits two drawbacks: the Lüders effect and the PLC effect. The Lüders effect manifests as a yield plateau and upper and lower yield points on the tensile curve, accompanied by the formation and propagation of Lüders bands on the sample surface. The Lüders effect is caused by static strain aging. In the initial stage of deformation, mobile dislocations are pinned by solute atoms. When the stress reaches the upper yield point, the mobile dislocations break free, causing the stress to drop, resulting in the lower yield point. In subsequent deformation, due to the slow diffusion rate of solute atoms, they cannot catch up with the rapidly moving mobile dislocations, failing to form a pinning effect. The stress remains constant to maintain plastic deformation, corresponding to the stress plateau on the curve. Simultaneously, a large number of mobile dislocations slide to the sample surface, forming localized plastic deformation zones, thus creating Lüders bands. The PLC effect manifests as "sawtooth" stress fluctuations (an irregular plastic instability phenomenon) on the curve at a certain temperature and strain rate, producing repeatedly propagating local deformation bands on the sample. The PLC effect significantly increases the non-uniform plastic deformation of the alloy and also forms obvious band-like marks on the material surface.

[0069] In this invention, the Lüders effect and PLC effect can be improved by the following measures: optimizing the chemical composition and controlling the content of main elements such as Mg, Fe, and Mn; increasing the intracrystalline dislocation multiplication rate and reducing the number of grain boundaries; increasing the matrix defect density and increasing the density of dislocation lines and vacancies; and increasing the strain rate, as the PLC effect weakens (Mg does not have enough time to diffuse).

[0070] This invention mainly determines the entire material processing technology by redesigning the chemical composition, cold rolling process, finished product annealing process, and stamping process; through multiple rounds of parameter optimization and exploration, the problem of stamping stripes (Lüders band) is solved, while ensuring the forming performance of the material.

[0071] The ingots used in the following embodiments of the present invention are aluminum alloy ingots with a composition of 5182 provided by Southwest Aluminum (Group) Co., Ltd.

[0072] Example 1

[0073] Aluminum alloy products are prepared according to the following method:

[0074] (1) Ingot heating shall be carried out according to the process in the table below:

[0075]

[0076] (2) Hot rolling

[0077] 1) Rough rolling temperature: 490℃.

[0078] 2) The procedure for pressing down after cutting off the head and tail is as follows:

[0079] thickness 75 52 36 25 18 Deformation per pass / mm 20 16 11 7 Pass deformation rate 30.7％ 30.7％ 30.6％ 28％

[0080] (3) Hot finishing rolling

[0081] 1) Hot finishing rolling temperature 320±10℃.

[0082] 2) The finishing rolling passes are allocated as follows:

[0083] 0.85 5.5 18-13.5-10.3-8.0-6.3-5.5

[0084] (4) Cold rolling, cold rolling is distributed as follows:

[0085] 5182-O 0.85 5.5-1.2-Intermediate annealing-0.85

[0086] (5) Intermediate annealing

[0087] The intermediate annealing process is as follows: blowing temperature 210℃, blowing time 50 minutes; primary heating furnace gas constant temperature 450℃, heating time 550 minutes; secondary heating furnace gas constant temperature (metal temperature) 350℃, holding time 90 minutes.

[0088] (6) Hair-like

[0089] 0.02-0.08 ≥400t 2.0±0.5 150±30

[0090] (7) Annealing of the finished product, with the following process parameters:

[0091]

[0092] (8) Surface treatment, process parameters are as follows:

[0093] 5182 30m / min nozzle fully open 7 sets of nozzles after opening Four sets of nozzles after opening 1.5 kg

[0094] (9) Stamping

[0095] 210 16

[0096] Example 2

[0097] The aluminum alloy product was prepared according to the method of Example 1, except that the finished product thickness was 1.5 mm and the number of finishing rolling passes was as follows:

[0098] 1.5 5.5 18-13.5-10.3-8.0-6.3-5.5

[0099] Cold-rolled components are distributed as follows:

[0100] 5182-O 1.5 5.5-2.0-Intermediate annealing-1.5

[0101] The heat treatment process is as follows:

[0102]

[0103] Performance testing

[0104] The mechanical properties of the aluminum alloy products prepared in the embodiments of this invention were tested according to GB / T 228 "Metallic materials - Tensile testing at room temperature". The test results are as follows:

[0105]

[0106] The aluminum alloy product prepared in Example 1 was subjected to high-magnification grain size detection according to the method specified in GB / T6394 to obtain the grain structure. The detection results are as follows: Figure 1 As shown, the grain size of the material is between 20 and 30 μm, the grains are uniformly distributed, and there are no abnormally large grains.

[0107] The stamped product prepared in Example 1 was partially polished, and the test results are as follows: Figure 3 As shown, it can be seen that Figure 3 No Lüders band; while the detection results before the improved method were as follows Figure 2 As shown, the Lüders bands are severe. The difference between the preparation method before the improvement method and Example 1 is:

[0108] Cold rolling, cold rolling allocation is as follows:

[0109] 5182-O 0.85 5.5-2.0-Intermediate annealing-0.85

[0110] The finished product undergoes annealing, with the following process parameters:

[0111]

[0112] stamping

[0113] 210 12

[0114] The key aspects of this invention are the improvement measures for Lüders strip, including the design of chemical composition, finished product annealing process, and cold rolling deformation, aiming to protect the chemical composition, rolling process, and finished product annealing process parameters. This invention establishes a technical path for improving and eliminating Lüders strip and a complete set of control processes for Lüders strip, achieving stable material output and supply, and meeting the usage requirements of OEMs using inner and outer plates.

[0115] While the invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration are not intended to limit the invention. It will be readily understood by those skilled in the art that various changes may be made to suit particular circumstances, materials, compositions, substances, methods, or processes to the objectives, spirit, and scope of this application without departing from the true spirit and scope of the invention as defined by the appended claims. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a particular order, it should be understood that these operations may be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of the invention. Therefore, unless specifically indicated herein, the order and grouping of operations are not a limitation of this application.

Claims

1. A method for controlling the stamping of Lüders strips for 5 Series automotive body panels, comprising: The aluminum alloy ingot is heated, rough rolled, hot finish rolled, first cold rolled, intermediate annealed, second cold rolled, roughened, finished annealed, surface treated, and stamped. During the hot finish rolling process, the rolling speed is ≥120 m / min, the deformation rate per pass is ≥30%, and the final rolling temperature is ≥320℃. During the first cold rolling process, the cold rolling deformation rate is ≥70%, and during the second cold rolling process, the cold rolling deformation rate is ≤30%. The intermediate annealing includes: Washing, primary heating, and secondary heating; The blowing temperature is 210℃, the furnace gas constant temperature for the first heating is 450℃, and the furnace gas constant temperature for the second heating is 350℃; During the texturing process, the roughness of the rolls is 1.5~3.5μm, the deformation rate per pass is 1~4%, the speed is 1.5~2.5m / s, the bending force is 120~180t, and the rolling force is ≥400t. The blank holder force during the stamping process is 210t, and the stamping cycle is 16 times / minute; The composition of the aluminum alloy ingot is as follows: 0.05~0.15wt% Si; 0.2~0.3wt% Fe; 0.03~0.05wt% Cu; 0.20~0.24wt% Mn; 4.65~4.85wt% Mg; 0.03~0.07wt% Zn; The balance is Al.

2. The method according to claim 1, characterized in that, The heating temperature for heating the aluminum alloy ingot is 470~490℃, and the holding time is ≥4h.

3. The method according to claim 1, characterized in that, During the roughing process, the initial rolling temperature is ≥450℃, the final rolling temperature is ≥410℃, the deformation during the microstructure improvement stage is ≤15mm, the deformation during the reduction deformation stage is ≥20mm, and the pass deformation rate during the shape control stage is ≥16%.

4. The method according to claim 1, characterized in that, The annealing temperature of the finished product is 450~560℃.

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