6-series aluminum alloy material suitable for automobile outer covering part and preparation method of 6-series aluminum alloy material

Abstract

The invention relates to the technical field of aluminum alloy material and plate forming processing, in particular to a 6-series aluminum alloy material suitable for an automobile outer covering part and a preparation method of the 6-series aluminum alloy material. The content of Mg is 0.60 to 0.90 percent; the content of Cu is 0.25 to 0.35 percent; the content of Zn is 0.05 to 0.10 percent; the content of Mn is 0.05 to 0.30 percent; the content of Fe is less than or equal to 0.20%; the content of Zr is 0.05 to 0.15 percent; the content of Ce is 0.05 to 0.15 percent; the content of La is 0.05 to 0.15 percent; the content of Ti is less than or equal to 0.10%; the single content of other impurity elements is less than or equal to 0.03%; the total content of other impurity elements is less than or equal to 0.15%; the material has excellent formability, bake hardening response, r value / n value and extreme pressure property.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy materials and sheet forming processing, and particularly relates to a 6-series aluminum alloy material suitable for automobile outer cover parts and a preparation method thereof. BACKGROUND

[0002] With the development trend of automobile lightweighting and new energy, 6-series aluminum alloy sheets have been widely used in outer cover parts such as doors, engine covers and fenders due to their good formability, weldability, corrosion resistance and recyclability. Among them, 6016 aluminum alloy has become one of the mainstream materials for automobile outer panels due to its moderate strength and good stamping performance.

[0003] Conventional 6016 alloys usually adopt Mg-Si strengthening mechanism, supplemented by appropriate Cu elements to improve the baking response, but still have the following technical limitations: It is difficult to balance formability and baking response. Although high Cu content can improve the bake hardening (abbreviated as BH) increase, it will significantly reduce the r value, n value and other formability indicators, so it cannot meet the stamping requirements of complex parts and subsequent mechanical performance requirements at the same time.

[0004] The traditional heat treatment path is single, and the existing solid solution treatment is mostly single heating path (such as 540-560°C x 2-5min) or single-stage tempering strengthening, which is difficult to accurately control the multi-stage precipitation process of Cu, Mg and Si eutectoid system, resulting in limited precipitation strengthening effect and unstable material performance.

[0005] The synergistic elements (such as Zn) are not fully utilized. Some studies point out that Zn can form Q' and η' type precipitates with Cu to improve peak aging strength, but in actual industrialized systems, Zn addition is limited, and there is a lack of systematic development and heat treatment strategy support for Zn-Cu synergistic mechanism.

[0006] The rare earth micro-alloying mechanism is not integrated. Although some documents have reported that rare earth elements such as Ce and La can optimize the grain structure or precipitation distribution, there is no systematic integration of Cu-Zn series precipitation path and heat treatment scheme, and related researches are mostly limited to the improvement of corrosion resistance or casting performance.

[0007] There is a lack of compatibility between lubrication and electrophoresis. Traditional stamping lubrication systems mostly use mineral oil-based (such as 6130 wet oil), which has problems such as the need for degreasing treatment after stamping, heavy pollution and large lubrication fluctuation. The existing technology proposes to use zinc phosphate, zirconium passivation or chromium-free coating as a transition, but there is no composite lubrication coating system suitable for 6-series high-strength aluminum alloy that can directly enter the electrophoresis process.

[0008] Therefore, there is an urgent need to provide a new 6-series aluminum alloy material and a preparation method thereof, which have good formability, baking strengthening performance, r value / n value, extreme pressure performance and simplified processing technology. SUMMARY

[0009] The present application aims to solve the technical problem of how to provide a new 6-series aluminum alloy material and a preparation method thereof, which have good formability, baking strengthening performance, r value / n value, extreme pressure performance and simplified processing technology.

[0010] To achieve the above-mentioned purpose, the first aspect of the present application provides a 6-series aluminum alloy material suitable for automobile outer cover, wherein the components and their weight percentages in the material are as follows: Si content is 0.60-0.85%; Mg content is 0.60-0.90%; Cu content is 0.25-0.35%; Zn content is 0.05-0.10%; Mn content is 0.05-0.30%; Fe content is ≤0.20%; Zr content is 0.05-0.15%; Ce content is 0.05-0.15%; La content is 0.05-0.15%; Ti content is ≤0.10%; The content of other impurity elements is ≤0.03% individually; The total content of other impurity elements is ≤0.15%; The balance is Al.

[0011] The second aspect of the present application provides a preparation method of the above-mentioned 6-series aluminum alloy material suitable for automobile outer cover, wherein the method comprises: melting and casting, homogenization treatment, hot rolling self-annealing, cold rolling, solid solution heat treatment, film coating, electrophoretic coating; The conditions of the solid solution heat treatment include: the first stage heating temperature is 420-440℃, the first stage heating time is 1-2min, the second stage heating temperature is 480-500℃, the second stage heating time is 1-2min, the third stage heating temperature is 540-555℃, the third stage heating time is 1-2min, the quenching adopts spray water cooling, the cooling rate is 15-25℃ / s, the quenching time is 35-45s, and pre-aging is performed after quenching, and the pre-aging system is 100-120℃×5-10h; The conditions of the electrophoretic coating include: using cathodic electrophoresis for electrophoretic deposition, using acrylic modified epoxy electrophoretic paint as the coating, the bath temperature is 26-28 DEG C, the pH is 6.0-7.2, preferably 6.5, the conductivity is 1.2-1.6 mS / cm, the circulation mode is three-stage circulation filtration, and the tank material is PVC lining or stainless steel. The conditions of the electrophoretic deposition include: the voltage is 220-260 V, the deposition time is 180-240 s, the current density is 1.5-2.5 A / dm 2 , the plate spacing is 20-30 cm, and the stirring mode is gas bubbling and mechanical circulation.

[0012] The beneficial effects of the present application are: Compared with the existing 6016 aluminum alloy material, (1) The r / n value is simultaneously improved, through Cu-Zn synergistic alloy design and hot rolling self-annealing path, higher texture optimization degree is realized, and the typical r 10 ≥0.6, n 10 ≥0.27, which meets the requirements of complex drawing / forming process.

[0013] (2) The baking strengthening response is enhanced, multiple types of strengthening phases such as Q' and η' are activated by using multi-stage solid solution annealing, and the yield strength (ΔYS) of T4P to baking can reach 80-110 MPa, which is better than the conventional 6016 (generally ΔYS < 70 MPa).

[0014] (3) Process is simplified and energy consumption is reduced, the intermediate annealing process is cancelled, and the microstructure is regulated by relying on hot rolling self-annealing, which effectively simplifies the process, reduces energy consumption, and improves forming consistency.

[0015] (4) The microstructure stability and forming reliability are improved, the distribution of grains and precipitated phases is improved by adding trace rare earth (La / Ce), the formation of coarse second phase and recrystallized abnormal grains is significantly inhibited, and the residual ductility after stamping is ensured.

[0016] (5) The lubrication system and electrophoresis compatibility are excellent, the matched pre-coating film lubrication system has extreme pressure ≥1000 N and friction coefficient μ ≤0.08, and does not need to be cleaned directly into electrophoresis, avoiding secondary pollution and cost increase.

[0017] (6) The overall manufacturing consistency and mold life are improved, the friction reduction and extreme pressure properties of the coating system ensure stable operation of the mold, compared with the traditional 6130 wet oil lubrication, the mold life is prolonged by about 30%, and the material forming fluctuation is significantly reduced. DETAILED DESCRIPTION

[0018] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0019] In the prior art, the 6 series aluminum alloy materials suitable for automobile exterior covering parts obtained by processing cannot meet the requirements of formability, excellent bake hardening response, and r value / n value, and the processing technology is complicated.

[0020] In the present invention, the inventors found that by controlling the alloy composition and adjusting the processing technology, the performance of the 6 series aluminum alloy material suitable for automotive exterior panels can meet the requirements, and it has excellent formability, bake hardening response, and r value / n value.

[0021] To achieve this goal, the inventors attempted to optimize the composition and processing technology of the aluminum alloy materials. The inventors found that the above objectives can be achieved through the specific composition of each component and rare earth microalloying and hot rolling self-annealing processes. Furthermore, the specific multi-stage continuous annealing control and matching environmentally friendly lubrication system make the performance of the aluminum alloy material even better.

[0022] A first aspect of the present invention provides a 6 series aluminum alloy material suitable for automotive exterior panels, wherein the components and their weight percentages in the material are as follows: Si content is 0.60-0.85%; Mg content is 0.60-0.90%; Cu content is 0.25-0.35%; Zn content is 0.05-0.10%; Mn content is 0.05-0.30%; Fe content ≤ 0.20%; Zr content is 0.05-0.15%; Ce content is 0.05-0.15%; La content is 0.05-0.15%; Ti content ≤ 0.10%; The content of other impurity elements is ≤0.03%; The total content of other impurity elements is ≤0.15%; The balance is Al.

[0023] In the present invention, by controlling the synergistic ratio of Cu and Zn contents, the precipitation strengthening multiplication effect is achieved without significantly improving the T4 state strength. Cu contributes to the formation of Q ’Phase, Zn stabilizes GP zone, promotes η ’ Phase formation, alloy obtains significant strengthening amplitude after baking, Si and Mg constitute strengthening phase β ” , form Mg2Si, provide matrix strengthening, Mn regulates β phase into α phase, promote ductility, Fe controls impurity phase, cooperate with Mn to reduce brittle phase formation, Zr pins the grain boundary, inhibits recrystallization, Ce and La rare earth phase disperses, improves grain and precipitation morphology, Ti is a grain refiner.

[0024] According to the application, the 6 series aluminum alloy material is provided with a pre-coating film on the surface of the aluminum alloy substrate, and the film thickness is 0.2-1.5 μm.

[0025] According to the application, the 6 series aluminum alloy material is provided with a pre-coating film and an electrophoretic film on the surface of the aluminum alloy substrate in sequence, the film thickness of the pre-coating film is 0.2-1.5 μm, and the film thickness of the electrophoretic film is 15-25 μm.

[0026] According to the application, the film thickness of the rare earth passivation base layer is 20-100 nm, and the rare earth passivation base layer is formed by reaction of Ce or La elements with phosphate; or the rare earth passivation base layer is formed by reaction of Ce or La elements with carboxylate compounds.

[0027] According to the application, the film thickness of the extreme pressure slip functional layer is 0.1-0.5 μm, and the extreme pressure slip functional layer comprises organic zinc complexing agent and C8-C18 fatty amide.

[0028] According to the application, the organic zinc complexing agent is any one of zinc fatty acid, zinc aminocarboxylic acid or zinc phosphonate complex.

[0029] According to the application, the film thickness of the film-forming polymer covering layer is 0.1-0.8 μm, and the film-forming polymer covering layer is any one or combination of polyacrylate, polyether or polyurethane.

[0030] According to the application, the polyacrylate is water-soluble polyacrylate, and the weight average molecular weight is 5000-10000.

[0031] According to the application, the coating used by the electrophoretic film is acrylic modified epoxy electrophoretic paint.

[0032] According to the application, the extreme pressure performance of the 6 series aluminum alloy material is ≥1000 N, the friction coefficient μ is ≤0.08, and the adhesion after stamping forming is ≥95%.

[0033] According to the application, the surface potential change of the aluminum alloy substrate is ±0.05 V.

[0034] Compared with the traditional lubricating oil 6130, the pre-coating film system can reduce the forming lubricant dosage by 100%, improve the forming uniformity by 15%, and prolong the mold life by more than 30%.

[0035] The second aspect of the present application provides a preparation method of the above-mentioned 6-series aluminum alloy material suitable for automobile outer cover, wherein the method comprises: melting and casting, homogenization treatment, hot rolling self-annealing, cold rolling, solid solution heat treatment, film coating, and electrophoretic coating; The conditions of the solid solution heat treatment include: the first-stage heating temperature is 420-440 DEG C, the first-stage heating time is 1-2 min, the second-stage heating temperature is 480-500 DEG C, the second-stage heating time is 1-2 min, the third-stage heating temperature is 540-555 DEG C, the third-stage heating time is 1-2 min, the quenching adopts spray water cooling, the cooling rate is 15-25 DEG C / s, the quenching time is 35-45 s, and pre-aging is performed after quenching, and the pre-aging system is 100-120 DEG C*5-10 h.

[0036] In the present application, by means of staged heating, different types of Cu-Zn-Mg-Si system nucleation mechanisms are activated in sequence, the precipitation sequence separation and density superposition are realized, the potential of the bake hardening is maximized, the first-stage heating mainly activates the preliminary diffusion and aggregation of Cu-Zn elements, the stable GP zone and Cu-Zn pre-aggregation structure are formed in the matrix, the second-stage heating activates the beta ” phase nucleation, the main channel of Mg2Si precipitation is constructed, the third-stage heating activates the Q ’ and eta ’ phase nucleation, the Cu-Zn enhanced precipitation network is formed, all the supersaturation states are frozen by quenching, the solid solution strengthening and precipitation potential are maintained, the Cu-Zn stable precipitation nucleus is constructed by pre-aging, and the long-acting stable forming performance is met.

[0037] According to the present application, the conditions of the melting and casting include: the smelting temperature is 730-750 DEG C, slagging and furnace turning are performed after smelting is completed, electromagnetic stirring is adopted during the holding furnace refining, and the refining temperature is 720-750 DEG C.

[0038] In the present application, the 6-series aluminum alloy material does not need the pretreatment steps of degreasing and phosphorization after the film coating treatment, and can directly enter the electrophoretic coating process.

[0039] According to the present application, the conditions of the film coating include: cathodic electrophoresis is adopted, the acrylic modified epoxy electrophoretic paint is used as the coating material, the bath temperature is 26-28 DEG C, the pH is 6.0-7.2, preferably 6.5, the conductivity is 1.2-1.6 mS / cm, the circulation mode is three-stage circulation filtration, and the tank body material is PVC lining or stainless steel.

[0040] The electrophoresis conditions include: voltage of 220-260 V, deposition time of 180-240 s, current density of 1.5-2.5 A / dm 2 , plate spacing of 20-30 cm, and stirring mode of gas bubbling and mechanical circulation.

[0041] In the application, the surface potential of the film is stable, the deposition current is uniformly distributed, and the electrophoretic film with no shrinkage and high adhesion can be obtained.

[0042] According to the application, the electrophoretic coating further comprises post-treatment and drying, the post-treatment is primary water washing and secondary water washing, the primary water washing uses deionized water, the primary water washing time is 15-20 s, the conductivity is < 50 muS / cm, the secondary water washing uses deionized water, the secondary water washing time is 25-30 s, the drying temperature is 160-180 DEG C, the drying time is 20-30 min, and the drying air speed is >= 0.8 m / s.

[0043] According to the application, in the smelting process, Si, Mg and Mn master alloys are added at 730-750 DEG C, Cu master alloy is added at 715-735 DEG C, and Zn master alloy is added at 700-720 DEG C, so as to promote the full dissolution and avoid early precipitation; then rare earth elements Ce and La are added at >= 700 DEG C, and finally magnesium ingot is added at >= 700 DEG C, so as to ensure the uniform distribution and sufficient reaction.

[0044] According to the application, Ti or Al-Ti-B refining agent filaments are placed before casting, and the feeding amount of the Ti or Al-Ti-B refining agent filaments is 0.0060-0.0090% based on the melt mother liquor mass.

[0045] According to the application, on-line degassing is carried out at the aluminum liquid temperature of 700-740 DEG C, SNIF degassing equipment is used, the degassing temperature is 700-740 DEG C, the rotor speed is 430-470 rpm, the argon flow rate is 7-9 m 3 / h, Cl2 is added to the inlet during the degassing process, and the volume ratio of Cl2 in the mixed gas is 0.7%.

[0046] According to the application, deep bed filter box plus plate filter is adopted, specifically, the plate filter is 50 ppi, and the working temperature of the filter box is 700-740 DEG C.

[0047] According to the application, semi-continuous casting and electromagnetic stirring are adopted, the casting height is < 300 mm in the starting casting stage, the dross in the flow channel and the crystallizer is removed, the flow channel temperature is 670-690 DEG C after 1 m, and the outlet temperature is 640-660 DEG C.

[0048] According to the application, the conditions of the homogenization treatment include: the regime of the homogenization treatment is 390-410 DEG C * 2-4h+545-555 DEG C * 6-10 h, and air cooling or forced air cooling is carried out to 280-320 DEG C.

[0049] In the application, the homogenization stabilizes the Cu-Zn distribution state, provides element reserves for subsequent multi-phase precipitation, the first heating in the homogenization regime promotes beta phase transformation, and the second heating promotes complete solid solution of Cu, Zn and rare earth.

[0050] According to the application, the conditions of the hot rolling self-annealing include: the final rolling temperature of the hot rolling is 300-320 DEG C, the coiling temperature is 260-300 DEG C, and the coiled material is self-heat preserved for 5-10 h.

[0051] In the application, partial recrystallization and partial solute aggregation during coiling are beneficial to subsequent precipitation, and the hot rolling self-annealing prevents Cu and Zn from forming coarse phases and preliminarily forms nucleation precursors.

[0052] According to the application, the conditions of the cold rolling include: the hot rolled plate with a thickness of 2.8-3.2 mm is cold rolled to a thickness of 0.9-1.5 mm, and the reduction is 50-70%.

[0053] In the application, the cold rolling makes the structure dense and the dislocation density moderate.

[0054] Rp0.2 is the 0.2% specified non-proportional extension strength (yield strength) indicating the stress when the material undergoes micro-plastic deformation, and the test standard is GB / T 228.1-2021 'Metallic Materials Tensile Test Part 1'.

[0055] Rm is the tensile strength that the material can withstand before breaking, and the test standard is GB / T 228.1-2021 'Metallic Materials Tensile Test Part 1'.

[0056] A50 is the elongation after fracture, which measures the plastic extension capacity within a 50 mm gauge length after the sample breaks, and the test standard is GB / T 228.1-2021 'Metallic Materials Tensile Test Part 1'.

[0057] n10 value is the strain hardening index (at a strain of 10%), which reflects the material's ability to strengthen during deformation, and the test standard is ISO 10275.

[0058] r10 value is the plastic strain ratio (at a strain of 10%), which reflects the anisotropy of the material, and the test standard is ISO 10113.

[0059] The r value (plastic strain ratio) and the n value (hardening index) reflect the processability of the material under complex deformation conditions such as stamping and drawing.

[0060] The higher the n value, the stronger the strain hardening ability of the material, the less likely to be locally necked, and the more conducive to uniform deep drawing forming. The higher the r value, the better the material can maintain thickness, the smaller the wall thickness change during deep drawing, and the more conducive to deep drawing or complex edge forming.

[0061] ΔYS is the increase in bake hardening strength, i.e., the increase in material yield strength after simulated paint baking ΔYS = Rp0.2(after bake)-Rp0.2(T4), test standard GB / T 13239 "Aluminum Alloy Plate Bake Hardening Test Method" conditions: 185℃×20 min.

[0062] μ is the friction coefficient, the degree of sliding friction between the material and the mold surface during forming, the smaller the value, the better the lubrication effect, the test standard is based on ASTM G99 or DIN 51834, steel plate friction test bench.

[0063] Extreme pressure performance is the extreme pressure load performance, which represents the anti-seizure and anti-sticking ability of the lubrication system under high pressure sliding state; the higher the value, the better the wear resistance and pressure resistance, the test standard is four-ball test method (ASTM D2783 or SH / T 0203).

[0064] Adhesion is the bonding strength of the film system to the aluminum alloy substrate after electrophoretic coating, which represents the proportion of the coating that is not peeled off, and the test standard is GB / T 9286 (crosshatch method) or ISO 2409 (0~5 grade).

[0065] Shrinkage / foaming is whether there are pinholes, bubbles and other defects on the surface after coating, which affects the quality of subsequent spraying or electrophoresis process, and the test standard is GB / T 13452.2 "Paint Film Appearance Test" and visual grade standard.

[0066] The pre-coating film and the electrophoretic film thickness are measured by an electromagnetic thickness gauge.

[0067] The salt spray resistance test standard is GB / T 1771-2007.

[0068] The water boiling peeling test standard is ISO 2819 / GMW14729.

[0069] The acrylic-modified epoxy electrophoretic paint is purchased from PPG Industries, Inc., model Powercron® 6100HE.

[0070] T4P state (T4 plus) is an extension of the T4 state, which refers to the state of the material after solid solution treatment, rapid quenching and pre-aging (Pre-aging), which is commonly used to improve the forming stability and bake hardening potential of the material, and is particularly suitable for automotive outer plate aluminum alloy.

[0071] The technical solutions of the present application are described in further detail below in conjunction with examples. Obviously, the examples described here are only some of the examples of the present application and are not intended to limit the present application. Based on the examples in the present application, all other examples implemented by those of ordinary skill in the art without making creative improvements fall within the protection scope of the present application.

[0072] Example 1 The alloy is selected with the chemical composition of Si content of 0.75%; Mg content of 0.75%; Cu content of 0.30%; Zn content of 0.08%; Mn content of 0.12%; Fe content of 0.13%; Zr content of 0.10%; Ce content of 0.10%; La content of 0.08%; Ti content of 0.09%; single content of other impurity elements ≤0.03%; total content of other impurity elements ≤0.15%; and the balance of Al.

[0073] Melting and casting: the smelting temperature is 740℃, Si, Mg and Mn master alloy are added first, then Zn master alloy is added in the middle and later stage, Cu master alloy is finally added, Ce and La are added at 730℃, finally magnesium ingot is added, slagging, pouring is performed after smelting is completed, the temperature is 725℃ during holding furnace refining, and electromagnetic stirring is adopted; An Al-Ti-B refiner wire is placed before casting, and the feeding amount of the Al-Ti-B refiner wire is 0.0075%; Online degassing is performed at the aluminum liquid temperature of 730℃, SNIF degassing equipment is used, the degassing temperature is 720℃, the rotor speed is 450 rpm, the argon flow rate is 8m 3 / h, 0.7% Cl2 can be added to the inlet during the degassing process; A deep bed filter box plus a plate filter (50 ppi) is adopted, and the working temperature of the filter box is 720℃; Semi-continuous casting and electromagnetic stirring are adopted, the casting height is <300 mm in the starting casting stage, the dross in the flow channel and the crystallizer is timely removed, and the casting flow channel temperature is 680℃, and the outlet water temperature is 650℃ after 1 m.

[0074] Homogenization treatment: the system is 400℃×3 h+550℃×8 h, and air cooling is performed to 300℃.

[0075] Hot rolling self-annealing: final rolling 320℃, coiling 290℃, and the coil self-temperature preservation is 6h.

[0076] Cold rolling: the hot-rolled plate of 3 mm is cold-rolled to 1.2 mm, and the reduction is 60%.

[0077] Solution heat treatment: the first stage heating temperature is 420℃, the first stage heating time is 2 min, the second stage heating temperature is 480℃, the second stage heating time is 2 min, the third stage heating temperature is 550℃, the third stage heating time is 2 min, the quenching is performed by spraying water cooling, the cooling rate is 20℃ / s, the quenching time is 40s, and pre-aging is performed after quenching, and the pre-aging system is 110℃×8h.

[0078] Film coating: the pre-coating film thickness is 1.08 μm, which comprises a rare earth passivation base layer, an extreme pressure sliding functional layer and a film-forming polymer covering layer arranged on the surface of the aluminum alloy substrate in sequence, the film thickness of the rare earth passivation base layer is 80 nm, the rare earth passivation base layer is composed of Ce(NO3)3, La(NO3)3 and sodium citrate, the film thickness of the extreme pressure sliding functional layer is 0.4 μm, the extreme pressure sliding functional layer comprises zinc aminocarboxylic acid complexing agent and C16 fatty amide, the film thickness of the film-forming polymer covering layer is 0.6 μm, and the film-forming polymer covering layer is a water-soluble polyacrylate with a weight average molecular weight of 8000.

[0079] The film thickness of the electrophoretic film is 15 μm, cathode electrophoresis is adopted, the coating is an acrylic modified epoxy electrophoretic paint, the bath temperature is 28℃, the pH is 6.5, the conductivity is 1.5 mS / cm, the circulation mode is three-stage circulation filtration, and the tank body material is PVC lining.

[0080] The conditions of electrophoresis include: the voltage is 220 V, the deposition time is 180 s, the current density is 2.2 A / dm 2 , the plate spacing is 15 cm, and the stirring mode is gas bubbling and mechanical circulation.

[0081] First-stage water washing and second-stage water washing are performed, the first-stage water washing uses deionized water, the first-stage water washing time is 30 s, the conductivity is 30 μS / cm, the second-stage water washing uses deionized water, the second-stage water washing time is 60 s, the drying temperature is 110℃, the drying time is 10 min, and the drying air speed is 3 m / s.

[0082] An aluminum alloy material A1 is prepared.

[0083] Example 2 The aluminum alloy material is prepared according to the processing method of Example 1, except that the aluminum alloy components are as follows: the Si content is 0.60%; the Mg content is 0.60%; the Cu content is 0.25%; the Zn content is 0.05%; the Mn content is 0.05%; the Fe content is 0.12%; the Zr content is 0.05%; the Ce content is 0.05%; the La content is 0.05%; and the Ti content is 0.08%.

[0084] An aluminum alloy material A2 is prepared.

[0085] Example 3 An aluminum alloy material was prepared according to the processing method of Example 1, except that the aluminum alloy composition was Si content of 0.85%; Mg content of 0.90%; Cu content of 0.35%; Zn content of 0.10%; Mn content of 0.30%; Fe content of 0.20%; Zr content of 0.15%; Ce content of 0.15%; La content of 0.15%; and Ti content of 0.10%.

[0086] An aluminum alloy material A3 was prepared.

[0087] Example 4 An aluminum alloy material was prepared according to the processing method of Example 1, except that the pre-coating film thickness was 0.22 μm, and included a rare earth passivation base layer, an extreme pressure sliding function layer, and a film-forming polymer cover layer, disposed in that order on the surface of the aluminum alloy base, the rare earth passivation base layer had a thickness of 20 nm, and was composed of La / Ce and a zinc phosphate complex, the extreme pressure sliding function layer had a thickness of 0.1 μm, and included a zinc fatty acid complexing agent and a C8 fatty amide, the film-forming polymer cover layer had a thickness of 0.1 μm, and was a water-soluble polyacrylate with a weight average molecular weight of 5000, and the electrophoretic film had a thickness of 15 μm.

[0088] An aluminum alloy material A4 was prepared.

[0089] Example 5 An aluminum alloy material was prepared according to the processing method of Example 1, except that the pre-coating film thickness was 1.4 μm, and included a rare earth passivation base layer, an extreme pressure sliding function layer, and a film-forming polymer cover layer, disposed in that order on the surface of the aluminum alloy base, the rare earth passivation base layer had a thickness of 100 nm, and was composed of La / Ce and a zinc phosphate complex, the extreme pressure sliding function layer had a thickness of 0.5 μm, and included a zinc phosphonate complexing agent + a C18 fatty amide, the film-forming polymer cover layer had a thickness of 0.8 μm, and was a water-soluble polyacrylate with a weight average molecular weight of 10000, and the electrophoretic film had a thickness of 25 μm.

[0090] An aluminum alloy material A5 was prepared.

[0091] Example 6 The aluminum alloy material was prepared according to the processing method of Example 1, except that the first-stage heating temperature of the solution heat treatment was 420℃, the first-stage heating time was 1 min, the second-stage heating temperature was 480℃, the second-stage heating time was 1 min, the third-stage heating temperature was 540℃, the third-stage heating time was 1 min, the quenching was performed by spraying water cooling, the cooling rate was 15℃ / s, the quenching time was 35s, and the pre-aging was performed after the quenching, and the pre-aging regime was 100℃×5h.

[0092] The aluminum alloy material A6 was prepared.

[0093] Example 7 The aluminum alloy material was prepared according to the processing method of Example 1, except that the first-stage heating temperature of the solution heat treatment was 440℃, the first-stage heating time was 2 min, the second-stage heating temperature was 500℃, the second-stage heating time was 2 min, the third-stage heating temperature was 555℃, the third-stage heating time was 2 min, the quenching was performed by spraying water cooling, the cooling rate was 25℃ / min, the quenching time was 45s, and the pre-aging was performed after the quenching, and the pre-aging regime was 120℃×10h.

[0094] The aluminum alloy material A7 was prepared.

[0095] Example 8 The aluminum alloy material was prepared according to the processing method of Example 1, except that the two-stage homogenization regime was 390℃×2h+545℃×6h, and the air cooling was performed to 280℃.

[0096] The aluminum alloy material A8 was prepared.

[0097] Example 9 The aluminum alloy material was prepared according to the processing method of Example 1, except that the two-stage homogenization regime was 410℃×4h+555℃×10h, and the air cooling was performed to 320℃.

[0098] The aluminum alloy material A9 was prepared.

[0099] Example 10 The aluminum alloy material was prepared according to the processing method of Example 1, except that the hot rolling final rolling temperature was 300℃, the coiling temperature was 260℃, and the self-heat preservation of the coiled material was 5h.

[0100] The aluminum alloy material A10 was prepared.

[0101] Example 11 The aluminum alloy material was prepared according to the processing method of Example 1, except that the hot rolling final rolling temperature was 320℃, the coiling temperature was 300℃, and the self-heat preservation of the coiled material was 10h.

[0102] The aluminum alloy material A11 was prepared.

[0103] Example 12 An aluminum alloy material was prepared according to the processing method of Example 1, except that a hot-rolled plate of 2.8 mm was cold-rolled to 0.9 mm at a reduction ratio of 70%.

[0104] An aluminum alloy material A12 was prepared.

[0105] Example 13 An aluminum alloy material was prepared according to the processing method of Example 1, except that a hot-rolled plate of 3.2 mm was cold-rolled to 1.5 mm at a reduction ratio of 53.1%.

[0106] An aluminum alloy material A13 was prepared.

[0107] Comparative Example 1 An aluminum alloy material was prepared according to the processing method of Example 1, except that the aluminum alloy components were Cu: 0.20%, Zn: 0.02%, Ce: 0.02%, and La: 0.02%.

[0108] An aluminum alloy material DA1 was prepared.

[0109] Comparative Example 2 An aluminum alloy material was prepared according to the processing method of Example 1, except that the aluminum alloy components were Cu: 0.38%, Zn: 0.15%, Ce: 0.18%, and La: 0.18%.

[0110] An aluminum alloy material DA2 was prepared.

[0111] Comparative Example 3 An aluminum alloy material was prepared according to the processing method of Example 1, except that the final rolling temperature was 320°C and the intermediate annealing temperature was 300°C.

[0112] An aluminum alloy material DA3 was prepared.

[0113] Comparative Example 4 An aluminum alloy material was prepared according to the processing method of Example 1, except that the solution heat treatment regime was 550°C x 3 min.

[0114] An aluminum alloy material DA4 was prepared.

[0115] Comparative Example 5 An aluminum alloy material was prepared according to the processing method of Example 1, except that no film was applied and 6130 wet oil was used for lubrication.

[0116] An aluminum alloy material DA5 was prepared.

[0117] Comparative Example 6 The aluminum alloy material was prepared according to the processing method of Example 1, except that Cu: 0.20%, Zn: 0.00%, no rare earth elements Ce and La were added, the solid solution heat treatment system was 550°C x 3 min, no film was coated, and 6130 wet oil was used for lubrication.

[0118] The aluminum alloy material DA6 was prepared.

[0119] The performance tests were conducted on A1-A13 and DA1-DA6, as shown in Table 1. Table 1 Through the comparison of the examples and the comparative examples, it can be seen that Example 1 uses Cu-Zn synergistic strengthening combined with rare earth Ce / La micro-alloying. Cu can participate in the formation of Q ’ phase in aging; Zn helps to stabilize GP zone and promote the precipitation of η ’ phase; Ce / La forms a dispersed rare earth phase, which helps to refine the grains and inhibit the coarse precipitation; therefore, ΔYS reaches 125 MPa, which is significantly higher than that of Comparative Example 1 (95 MPa) and Comparative Example 6 (70 MPa). The contents of Cu, Zn, and rare earth in Comparative Example 1 are all low, lacking sufficient nucleation sites and alloying reserves, and the precipitation strengthening reaction is limited, resulting in a decrease in ΔYS. This indicates that the synergy of Cu-Zn-rare earth is the key to achieving high ΔYS.

[0120] In Comparative Example 2, the contents of Cu, Zn, and rare earth exceed the range. Excessive Cu may lead to coarse Q phase or precipitation saturation, excessive Zn promotes the rapid growth of η phase, which damages the plasticity, and excessive rare earth is not conducive to uniform dispersion, forming a brittle phase, resulting in a decrease in A50 and a low r10 of 0.55, and degradation of formability.

[0121] In Example 1, after hot rolling, direct coiling is used for heat preservation to achieve self-annealing. The coiling temperature is controlled at 260-300°C, and the self-heat preservation is ≥6h, which is beneficial to the formation of fine equiaxed crystals by natural recrystallization, weak texture, and low dislocation density, which is conducive to the improvement of r10 (0.68) and n10 (0.27). In Comparative Example 3, the traditional intermediate annealing process is used, which leads to strong recrystallization conditions, resulting in non-uniform texture and reduced r and n values. This proves that the "hot rolling self-annealing instead of intermediate annealing" path is helpful to the forming performance.

[0122] In Example 1, three-stage heating solid solution (420→480→550°C) is used to control the precipitation reaction in stages, activating GP zone, β", Q' and η' phase in sequence, ensuring high-density fine precipitation, improving the strengthening amplitude without excessively sacrificing plasticity, and achieving ΔYS of 125 MPa, while maintaining high levels of n10 and r10. In Comparative Example 4, single-stage solid solution treatment (550°C x 3 min) is used, which causes the formation of some coarse precipitates due to rapid high-temperature treatment, resulting in non-uniform solid solution, a decrease in r10 to 0.60, and a decrease in n10 Example 1 uses a new functional pre-coating film system, a multi-layer structure forms a low shear stress slip layer during stamping, the friction coefficient μ is reduced to 0.08; the extreme pressure performance reaches 1000 N, the adhesion is high, the die sticking and wear are prevented, Comparative Examples 5 and 6 use traditional 6130 wet oil, the friction coefficient is as high as 0.14, the extreme pressure performance is 600 N, it is not compatible with the rare earth surface passivation layer, it is easy to leave pollution, the lubrication is uneven, the forming consistency is poor, it is shown that the pre-coating film system is obviously superior to the traditional lubrication mode in terms of friction control and forming consistency.

[0123] The Cu-Zn-rare earth alloy composition design, multi-stage solid solution heat treatment, hot rolling self-annealing path and coating system of the application are synergistic, which jointly promotes the improvement of the bake hardening amplitude, the significant optimization of the formability, the good compatibility of lubrication and coating integration, significantly improves the comprehensive performance and manufacturing process adaptability of the 6016 aluminum alloy, and meets the technical requirements of lightweight, high strength, high forming quality and green manufacturing of complex automobile outer plates and structural parts.

[0124] The above is only a preferred embodiment of the application, but the protection scope of the application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical scheme and inventive concept of the application within the disclosed technical scope, which should be covered within the protection scope of the application.

Claims

1. A 6 series aluminum alloy material suitable for automobile exterior covering parts, characterized in that: The components and their weight percentages in the material are: Si content is 0.60-0.85%; Mg content is 0.60-0.90%; Cu content is 0.25-0.35%; Zn content is 0.05-0.10%; Mn content is 0.05-0.30%; Fe content ≤ 0.20%; Zr content is 0.05-0.15%; Ce content is 0.05-0.15%; La content is 0.05-0.15%; Ti content ≤ 0.10%; The individual content of other impurity elements is ≤0.03%; The total content of other impurity elements is ≤0.15%; The balance is Al.

2. The 6 series aluminum alloy material suitable for automobile exterior covering according to claim 1, characterized in that: The 6 series aluminum alloy material is sequentially provided with a pre-coating and an electrophoretic film on the surface of the aluminum alloy substrate, wherein the thickness of the pre-coating is 0.2-1.5 μm, and the thickness of the electrophoretic film is 15-25 μm; The pre-coating comprises a rare earth passivation base layer, an extreme pressure slip functional layer and a film-forming polymer covering layer which are sequentially arranged on the surface of the aluminum alloy substrate.

3. The 6 series aluminum alloy material suitable for automobile exterior panels according to claim 2, characterized in that: The rare earth passivation base layer has a thickness of 20-100 nm, and is formed by the reaction of Ce or La elements with phosphate; Or the rare earth passivation base layer is formed by the reaction of Ce or La elements with carboxylate compounds; The film thickness of the extreme pressure slip functional layer is 0.1-0.5 μm, and the extreme pressure slip functional layer includes an organic zinc complexing agent and a C8-C18 fatty amide; Wherein, the organic zinc complexing agent is any one of fatty acid zinc, aminocarboxylate zinc or phosphonate zinc complex.

4. The film thickness of the film-forming polymer covering layer is 0.1-0.8 μm, and the film-forming polymer covering layer is composed of any one or a combination of polyacrylate, polyether or polyurethane; in, The polyacrylate is a water-soluble polyacrylate with a weight average molecular weight of 5000-10000; The coating used for the electrophoretic film is acrylic modified epoxy electrophoretic paint; The extreme pressure performance of the 6 series aluminum alloy material is ≥1000N, the friction coefficient μ≤0.08, and the adhesion after stamping is ≥95%; The surface potential of the aluminum alloy substrate changes by ±0.05 V.

5. A method for preparing a 6 series aluminum alloy material suitable for automobile exterior panels according to any one of claims 1 to 3, characterized in that: The method comprises: Casting, homogenization treatment, hot rolling and autogenous annealing, cold rolling, solution heat treatment, lamination, and electrophoretic coating; The conditions of the solution heat treatment include: a first stage heating temperature of 420-440°C, a first stage heating time of 1-2 minutes, a second stage heating temperature of 480-500°C, a second stage heating time of 1-2 minutes, a third stage heating temperature of 540-555°C, a third stage heating time of 1-2 minutes, quenching by spray plus water cooling, a cooling rate of 15-25°C / s, a quenching time of 35-45 seconds, and pre-aging after quenching, with a pre-aging system of 100-120°C×5-10 hours; The electrophoretic coating conditions include: cathodic electrophoresis for electrophoretic deposition, acrylic modified epoxy electrophoretic paint as the coating, a bath temperature of 26-28°C, a pH of 6.0-7.2, preferably 6.5, a conductivity of 1.2-1.6 mS / cm, a circulation method of three-stage circulation filtration, and a tank body made of PVC lining or stainless steel; The conditions of the electrophoretic deposition include: voltage of 220-260 V, deposition time of 180-240 s, current density of 1.5-2.5 A / dm 2 The plate spacing is 20-30 cm, and the stirring method is gas bubbling and mechanical circulation.

6. The method according to claim 4, characterized in that The casting conditions include: a smelting temperature of 730-750°C, slagging and pouring after smelting, electromagnetic stirring during refining in a holding furnace, and a refining temperature of 720-750°C; Before casting, Ti or Al-Ti-B refining agent wire is placed, and the feeding amount of the Ti or Al-Ti-B refining agent wire is 0.0060-0.0090% based on the mass of the melt mother liquid; Online degassing was performed at a molten aluminum temperature of 695-760°C, a degassing temperature of 700-740°C, a rotor speed of 430-470rpm, and an argon flow rate of 7-9 m 3 / h, Cl2 is added to the inlet during the degassing process; Adopt deep bed filter box plus plate filtration, the filter box working temperature is 700-740℃; Semi-continuous casting and electromagnetic stirring are used. The casting height in the starting stage is <300 mm. The slag in the launder and crystallizer is removed. After 1m, the casting enters a steady state. The launder temperature is 670-690℃ and the outlet temperature is 640-660℃.

7. The method according to claim 4, characterized in that The homogenization treatment conditions include: homogenization treatment system of 390-410°C×2-4 h+545-555°C×6-10 h, air cooling or forced air cooling to 280-320°C.

8. The method according to claim 4, characterized in that The conditions for hot rolling auto-annealing include: hot rolling finishing temperature of 300-320° C., coiling temperature of 260-300° C., and coil auto-insulation for 5-10 hours.

9. The method according to claim 4, characterized in that The cold rolling conditions include: cold rolling of 2.8-3.2 mm hot rolled plate to 0.9-1.5 mm with a reduction rate of 50-70%; The electrophoretic coating also includes post-treatment and drying. The post-treatment is primary water washing and secondary water washing. Deionized water is used for the primary water washing, the primary water washing time is 15-20 s, and the conductivity is < 50 μS / cm. Deionized water is used for the secondary water washing, the secondary water washing time is 25-30 s, the drying temperature is 160-180°C, the drying time is 20-30 min, and the drying wind speed is ≥ 0.8m / s.

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