Novel al-mg-si-cu-v series aluminum alloy having high baking performance and preparation method therefor

Abstract

Disclosed in the present invention are a novel Al-Mg-Si-Cu-V series aluminum alloy having high baking performance and a preparation method therefor. The chemical composition of the Al-Mg-Si-Cu-V series aluminum alloy, in mass percentage, is as follows: Mg: 0.8-1.5 wt.%, Si: 0.70-1.30 wt.%, Cu: 0.50-1.00 wt.%, V: 0.05-0.30 wt.%, Mn: 0.05-0.50 wt.%, Cr: 0.05-0.20 wt.%, Ti: 0.030-0.100 wt.%, Fe: 0.05-0.40 wt.%, with the balance being Al and inevitable impurities, wherein 1.10≤Mg / Si≤1.50 and Mn / Fe≥0.50; in the formulas, each element symbol represents the mass percentage content of the corresponding element. In the present invention, by designing the alloy composition, reasonably optimizing the process, and performing simulated paint baking treatment after cold rolling, solution treatment and water quenching, an Al-Mg-Si-Cu-V series aluminum alloy material having high baking performance is obtained.

Description

A novel Al-Mg-Si-Cu-V aluminum alloy with high baking performance and its preparation method Technical Field

[0001] This invention belongs to the field of aluminum alloy technology, specifically relating to a novel Al-Mg-Si-Cu-V aluminum alloy with high baking performance and its preparation method. Background Technology

[0002] Currently, automobiles have become one of the world's major sources of energy consumption and pollutant emissions. With increasing awareness of energy conservation and emission reduction and the introduction of the "dual-carbon" strategic decision, lightweighting of automobiles is imperative. 6xxx series aluminum alloys, in the T4 state, possess low yield strength and good formability, and their strength can be significantly improved after baking treatment (2% pre-stretching + 185℃ / 20min). They are currently widely used in the preparation of automotive body panels.

[0003] Chinese Patent Application 1 (Publication No. CN 101880805A) discloses an Al-Mg-Si aluminum alloy for automotive body panels and its manufacturing method. The composition and mass percentage of the Al-Mg-Si aluminum alloy are as follows: Si: 0.75–1.5%; Fe: 0.2–0.5%; Cu: 0.2–1.0%; Mn: 0.25–1.0%; Mg: 0.75–1.85%; Zn: 0.15–0.3%; Cr: 0.05%–0.15%; Ti: 0.05–0.15%; Zr: 0.05–0.35%; with the balance being Al. This patent application focuses on 6000 series aluminum alloys, optimizing the content of Mg and Si elements, adjusting the Mg / Si ratio, and adding some Cu element, while adding 0.05–0.35 wt% Zr to the base alloy. In aluminum-magnesium-silicon-aluminum alloys, dispersed, fine coherent second-phase particles (Al3Zr) precipitate. The strengthening mechanism involves extremely strong grain refinement, substructure strengthening, dispersion strengthening, and coherent strengthening within the alloy, preventing the formation of coarse second-phase compounds, thereby refining the material's microstructure and improving its properties. After baking paint treatment, the yield strength of 6xxx series aluminum alloys is 220–230 MPa, with a paint strength increase of approximately 50 MPa.

[0004] Chinese Patent Application 2 (Publication No. CN 103173661A) discloses an aluminum alloy sheet for automobile bodies and its preparation method. The chemical composition and weight percentage content of the aluminum alloy sheet are as follows: Zn: 0.20-1.50 wt%, Mg: 0.30-1.40 wt%, Si: 0.40-1.40 wt%, Cu: 0.05-1.0 wt%, Fe≤0.4 wt%, Mn≤0.4 wt%, Cr≤0.2 wt%, Ti≤0.2 wt%, B≤0.2 wt%, with the balance being Al. This patent application introduces the alloying element Zn, utilizing its high solid solubility in aluminum and its strong interaction with element Mg, thereby influencing the precipitation kinetics of the Mg-Si strengthening phase. Ultimately, this results in a lower yield strength for the aluminum alloy sheet before paint hardening, ensuring excellent processing and forming properties. After paint treatment, the strength of the aluminum alloy sheet is significantly improved, and low-temperature paint hardening treatment can also be implemented.

[0005] Chinese Patent Application No. 3 (Publication No. CN 103509980A) discloses an Al-Mg-Si-Cu-Zn series aluminum alloy, its preparation method, and its application. This application adds Zn to conventional 6xxx series aluminum alloys. The alloy sheet treated with T4P, after low-temperature baking at 175℃ for 20 minutes, exhibits a yield strength increase of approximately 100 MPa, demonstrating good paint hardening properties.

[0006] Chinese Patent Application 4 (Publication No. CN 103757507A) discloses a high-paint-hardening aluminum alloy material for automotive body exterior panels and its preparation method. The chemical composition and mass percentage content of the aluminum alloy material are as follows: Zn: 0.05-4.0 wt%, Mg: 0.5-1.5 wt%, Si: 0.2-1.2 wt%, Cu: 0-1.0 wt%, Fe≤0.35 wt%, Mn≤0.35 wt%, Cr≤0.25 wt%, Ti≤0.25 wt%, with the balance being Al. This application fully utilizes the fact that the solute element Mg can interact simultaneously with the solute elements Si and Zn, thereby rapidly forming multiple reinforcing phases such as Mg2Si and MgZn2 (or their corresponding transition phases) during the paint baking process, ultimately resulting in a significant increase in the paint hardening increment of the alloy.

[0007] Chinese Patent Application 5 (Publication No. CN 113201672A) discloses an Al-Mg-Si-Cu-Zn alloy with high paint hardening increment and its preparation method. The composition range of this Al-Mg-Si-Cu-Zn alloy, by weight percentage, is Mg: 1.2-1.6wt%, Si: 1.2-1.6wt%, Cu: 0.1-0.3wt%, Zn: 3.0wt%, Fe: 0.4wt%, Mn: 0.5-0.8wt%, Ti≤0.03wt%, Ni≤0.04wt%, with the remainder being Al. This application increases the Mg and Si content to levels exceeding the range of 6xxx series alloys while adding a large amount of Zn, thereby improving the strength of the Al-Mg-Si-Cu-Zn alloy after paint baking. Its yield strength is 334-365 MPa, tensile strength is 386-404 MPa, and elongation is 13-17%.

[0008] Chinese Patent Application 6 (Publication No. CN 109722573A) discloses a highly formable Al-Mg-Si-Cu-Zn-Er-Zr alloy and its preparation method. The chemical composition of this Al-Mg-Si-Cu-Zn-Er-Zr alloy is as follows: Mg: 0.75–2.0 wt.%; Si: 0.8–1.0 wt.%; Cu: 0.3–0.65 wt.%; Mn: 0.2–0.4 wt.%; Zn: 0.10–2.0 wt.%; Er: 0.01–0.5 wt.%; Zr: 0.01–0.5 wt.%; Fe ≤ 0.2 wt.%; the remainder is Al. The addition of microalloying elements such as Er and Zr improves the alloy's formability and plasticity, but has no significant effect on increasing its paint hardening ability.

[0009] Currently, the main method for improving the post-baking strength of Al-Mg-Si-Cu aluminum alloys is to increase the content of Mg and Si elements while adding a large amount of Zn, introducing Mg2Si and MgZn2 (or their corresponding transition phases) after short-term baking. Therefore, the maximum strength increase of Al-Mg-Si-Cu-Zn alloys after baking can reach 180 MPa, with a corresponding baked-on yield strength of 360 MPa, tensile strength of 399 MPa, and elongation of 16%. However, most Zn is dissolved in the Al matrix, and its main mechanism of action is to enhance the formation of atomic clusters, without significantly participating in the formation and transformation of precipitated phases. Therefore, adding a large amount of Zn reduces the room-temperature stability after pre-aging and the bake-hardening properties after room-temperature baking. Furthermore, the composition range of existing high-baking-strength Al-Mg-Si-Cu-Zn alloys exceeds the typical 6xxx series aluminum alloy composition range, and existing enterprise production facilities and key preparation processes are difficult to meet the requirements of industrial production, increasing the difficulty of promoting and applying this type of alloy.

[0010] In view of the above, there is an urgent need to develop a new type of high-baking-performance Al-Mg-Si-Cu aluminum alloy material and its preparation method based on traditional Al-Mg-Si-Cu alloys and new design concepts, so as to meet the current demand for lightweight development in transportation. Summary of the Invention

[0011] To meet the current demand for lightweight development in transportation, the present invention aims to provide a novel Al-Mg-Si-Cu-V aluminum alloy with high baking performance and its preparation method. The resulting Al-Mg-Si-Cu-V aluminum alloy exhibits both ultra-high baking performance and good plasticity. The Al-Mg-Si-Cu-V aluminum alloy has a yield strength ≥340 MPa, a tensile strength ≥390 MPa, an elongation after fracture of 18.0%–20.0%, and a paint coating increment of 85–110 MPa.

[0012] The first aspect of the present invention provides an Al-Mg-Si-Cu-V aluminum alloy, wherein the chemical composition of the Al-Mg-Si-Cu-V aluminum alloy, by mass percentage, is: Mg: 0.8–1.5 wt.%, Si: 0.70–1.30 wt.%, Cu: 0.50–1.00 wt.%, V: 0.05–0.30 wt.%, Mn: 0.05–0.50 wt%, preferably 0.10–0.50 wt.%, Cr : 0.05~0.20wt%., preferably 0.10~0.20wt%., Ti: 0.030~0.100wt.%, Fe: 0.05~0.40wt.%, preferably 0.14~0.40wt.%, more preferably 0.15~0.40wt.%, the balance includes Al and unavoidable impurities, wherein 1.10≤Mg / Si≤1.50, Mn / Fe≥0.50, and the symbols of each element are substituted with the corresponding mass percentage content of each element.

[0013] Preferably, the balance is Al and unavoidable impurities.

[0014] Preferably, the microstructure of the Al-Mg-Si-Cu-V aluminum alloy consists of fine equiaxed crystals with a grain size of 15.0–20.0 μm; and the microstructure contains uniformly distributed nano-precipitated phases and dispersed phases, wherein the dispersed phases are α-Al(Fe,Mn)Si and AlFeSiV, and the bulk density of the dispersed phases is 3.00 × 10⁻⁶. 19 ~7.50×10 19 / m 3 The average size is 130–260 nm; the nano-precipitated phases are β″ and Q′ phases, with a bulk density of 9.0 × 10⁻⁶. 23 ~12.0×10 23 / m 3The average length is 10.0–15.0 nm.

[0015] Preferably, the Al-Mg-Si-Cu-V aluminum alloy has a yield strength ≥340MPa, a tensile strength ≥390MPa, an elongation after fracture of 18.0~20.0%, and a paint coating increment of 85~110MPa.

[0016] The composition design principle of the Al-Mg-Si-Cu-V aluminum alloy of the present invention is as follows:

[0017] Mg and Si: Mg and Si are important components of the main strengthening phase (β″ phase) in aluminum alloys. Increasing the content of Mg and Si can enhance the nucleation driving force of the strengthening phase, promote its dispersed precipitation, and improve the mechanical properties of the alloy. Therefore, the Mg content is controlled at 0.8–1.5 wt.% and the Si content is controlled at 0.70–1.30 wt.%. At the same time, by adjusting the Mg / Si ratio of the alloy to 1.10–1.50 (e.g., 1.10–1.41), the situation where excess Mg leads to unfavorable strength improvement can be avoided.

[0018] Adding Cu to Al-Mg-Si aluminum alloys can improve the stability of the GP zones / clusters after pre-aging treatment, increase the nucleation sites of the strengthening phase, promote its rapid precipitation in a short time, and increase the paint yield. Furthermore, Cu can form a new strengthening phase (Q′ phase) with Al, Mg, and Si in the aluminum alloy, achieving synergistic precipitation of the β″ and Q′ phases, thus improving the baked strength of the alloy. Therefore, the Cu content is controlled at 0.50–1.00 wt.%.

[0019] V: This invention involves adding trace amounts of V to Al-Mg-Si-Cu aluminum alloys, resulting in the precipitation of submicron-AlFeSiV dispersed phases within the grains during homogenization treatment or hot rolling, with a bulk density controlled at 3.0 × 10⁻⁶. 19 ~7.5×10 19 / m 3 The average size is controlled between 130 and 260 nm. During hot rolling, it can effectively pin grain boundaries, prevent grain growth and coarsening, refine grain size, and improve the plasticity of the sheet. On the other hand, it can provide nucleation sites for the nucleation and precipitation of the main strengthening phases (β″ and Q′ phases). Combined with the baking process of 6xxx series aluminum alloys, the high-density submicron dispersed phase interacts with dislocations, increasing the dislocation density in the matrix after pre-deformation and breaking through the traditional paint addition of 6xxx series aluminum alloys. However, adding excessive V will form high-melting-point intermetallic compounds in the alloy matrix, consuming effective Mg and damaging the mechanical properties of the sheet. Therefore, the V content is controlled at 0.05–0.30 wt.%.

[0020] Mn: As a trace element in 6xxx series aluminum alloys, adding a small amount of Mn can improve the morphology of the Fe-rich phase, prevent premature formation of microcracks around the Fe-rich phase during deformation, and improve the alloy's plasticity. Simultaneously, Al, Fe, Mn, and Si elements can form the α-Al(Fe,Mn)Si dispersed phase, refining the alloy grain size. However, excessive Mn will form a coarse, hard, and brittle Al6Mn phase. Therefore, the Mn content is controlled at 0.05–0.50 wt.%, preferably 0.10–0.50 wt.%, for example, 0.10–0.44 wt.%.

[0021] Cr: Adding trace amounts of Cr to aluminum alloys will cause them to react with elements such as Fe and Mn to form Al7(Cr,Fe) and Al... 12 Intermetallic compounds such as Cr and Mn inhibit the nucleation and growth processes of recrystallization, thus exerting a certain strengthening effect on the alloy. Therefore, the Cr content is controlled at 0.05–0.20 wt.%, preferably 0.10–0.20 wt.

[0022] Ti: Adding trace amounts of Ti to 6xxx series aluminum alloys can act as a heterogeneous nucleation site, synergistically promoting grain nucleation during solidification with grain refiners, thus refining the grain size in the as-cast state. Therefore, the Ti content should be controlled at 0.030–0.100 wt.%.

[0023] Fe: As an additive element in aluminum alloys, it forms α-Al(Fe,Mn)Si dispersed phase and AlFeSiV dispersed phase in the matrix. Therefore, the Fe content is controlled at 0.05 to 0.40 wt.%, preferably 0.14 to 0.4 wt.%, more preferably 0.15 to 0.40 wt.%, for example 0.15 to 0.38 wt.

[0024] In this invention, by optimizing the content of Mg, Si and Cu elements in Al-Mg-Si-Cu aluminum alloy and controlling it to 1.1≤Mg / Si≤1.5, high-density and stable Mg-Si-Cu clusters can be formed in the matrix of the aluminum alloy after pre-aging treatment. After short-time high-temperature baking treatment, they can be further transformed into β″ phase and Q′ phase, thereby improving the baking strength of the material.

[0025] Based on this, by introducing trace amounts of V and adjusting the Fe, Mn, and V contents to control Mn / Fe ≥ 0.50, in addition to the α-Al(Fe,Mn)Si dispersed phase, a tetragonal AlFeSiV dispersed phase can also be formed in the matrix, with the bulk density of the dispersed phase controlled at 3.00 × 10⁻⁶. 19 ~7.50×10 19 / m 3With an average size controlled between 130 and 260 nm, it serves two purposes: firstly, it pins grain boundary movement during material thermal deformation, inhibiting grain growth and coarsening, refining grain size, and improving material plasticity; secondly, it provides nucleation sites for the β″ and Q′ phases, reducing the nucleation barrier of the nanoprecipitates, promoting precipitation, and controlling the bulk density of the nanoprecipitates at 9.00 × 10⁻⁶. 23 ~12.00×10 23 / m 3 The average length is controlled at 10–15 nm, preferably 12.2–15.0 nm. While ensuring good plasticity, the yield strength of the baked alloy sheet is increased to over 340 MPa, and the paint thickness increase is increased to 85–110 MPa, consistent with the highest reported strength Al-Mg-Si-Cu-Zn aluminum alloys. However, this invention has a lower degree of alloying, achieving both high strength and good plasticity in the aluminum alloy, with an elongation after fracture of 18%–20%, ensuring the formability of the aluminum alloy and facilitating rolling, which is superior to existing Al-Mg-Si-Cu-Zn aluminum alloys (approximately 12.2%–14.8%).

[0026] A second aspect of the present invention provides a method for preparing an Al-Mg-Si-Cu-V aluminum alloy, the method comprising the following steps performed sequentially:

[0027] 1) Smelting and casting:

[0028] Ingots are obtained through smelting and casting;

[0029] 2) Homogenization heat treatment:

[0030] The ingot is subjected to homogenization heat treatment to obtain a homogenized ingot; wherein the temperature of the homogenization heat treatment is 545-565℃, the holding time of the homogenization heat treatment is 16-24h, the heating rate of the homogenization heat treatment is 0.50-1.00℃ / min, and the cooling rate is 0.50-1.00℃ / min.

[0031] 3) Hot rolling:

[0032] A homogenized ingot is hot-rolled to obtain a hot-rolled sheet, wherein the total deformation of the hot rolling is 85% to 95%, and the hot rolling temperature is 545 to 565°C.

[0033] 4) Cold rolling:

[0034] Hot-rolled sheet metal is cold-rolled to obtain cold-rolled sheet metal;

[0035] 5) Solution treatment + quenching:

[0036] The cold-rolled sheet is subjected to solution treatment and quenching in sequence to obtain a solution-treated and quenched sheet. The solution treatment temperature is 560-570℃, the solution treatment holding time is 5-10 min, and the quenching method is water quenching.

[0037] 6) Pre-aging treatment:

[0038] After solution treatment and quenching, the solution-treated and quenched plate is pre-aged and then left to stand naturally for more than 14 days to obtain the T4P plate. The temperature of the pre-aging treatment is 110-130℃ and the holding time of the pre-aging treatment is 8-10h.

[0039] 7) Simulated paint baking process:

[0040] A simulated baking paint treatment was performed on the T4P state sheet material to obtain an Al-Mg-Si-Cu-V series aluminum alloy.

[0041] Preferably, in step 1), the following raw materials are smelted and cast: high-purity aluminum, pure magnesium, pure zinc, and master alloys are used as raw materials, wherein the master alloys are Al-Si master alloys, Al-Cu master alloys, Al-V master alloys, Al-Mn master alloys, Al-Cr master alloys, and Al-Fe master alloys.

[0042] First, high-purity aluminum is completely melted and heated to 740–760°C. A master alloy is added and held at this temperature for 20–30 minutes. After the master alloy is completely melted, the first melt is obtained and cooled to 720–740°C. Pure magnesium and pure zinc are added and held at this temperature for 10–15 minutes to obtain the second melt. Then, a refining agent is added. After the refining agent reacts fully with the second melt, a slag-removing agent is added and held at 720–740°C for 10–15 minutes. Finally, a refining agent is added and the melt is held at this temperature for 2–5 minutes before casting to obtain an ingot.

[0043] The refining agent is a sodium fluoride ionic refining agent, and its addition amount is 0.40 to 0.60 wt.% of the mass of the second melt;

[0044] The refining agent is an Al-5Ti-1B refining agent, and its addition amount is 0.01 to 0.06 wt.% of the mass of the second melt.

[0045] Preferably, in step 1), the casting temperature is 720–740°C.

[0046] Preferably, in step 2), after homogenization heat treatment and before hot rolling, the homogenized ingot is milled. The resulting cast ingot has surface defects; milling can improve the surface quality of the subsequently hot-rolled plate.

[0047] Preferably, in step 4), the total deformation of the cold rolling is ≥65%.

[0048] The process design principle of the preparation method of the Al-Mg-Si-Cu-V aluminum alloy of the present invention is as follows:

[0049] The effects of homogenization heat treatment on aluminum alloys at homogenization heat treatment temperatures of 545–565℃, holding times of 16–24 h, and heating and cooling rates of 0.50–1.00℃ / min are as follows: On the one hand, it promotes the full dissolution of non-equilibrium eutectic phases into the matrix and improves the morphology of Fe-rich phases; on the other hand, it promotes the uniform precipitation of α-Al(Fe,Mn)Si dispersed phases and AlFeSiV dispersed phases during homogenization heat treatment, and inhibits excessive grain growth and coarsening during subsequent hot deformation.

[0050] Milling is performed on the homogeneous ingot obtained after homogenization heat treatment to remove defects on the surface of the homogeneous ingot and improve the quality of the plate.

[0051] The solution treatment temperature is controlled at 560–570℃, and the holding time is controlled at 5–10 min. The purpose is as follows: on the one hand, to ensure that the effective solid solution elements of Mg, Si and Cu can be fully dissolved into the matrix, and to promote the dispersion precipitation of the main strengthening phase; on the other hand, to avoid grain growth caused by prolonged high temperature holding.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] This invention, through synergistic design and optimization of elements such as Mg, Si, Cu, and V, controls 1.10 ≤ Mg / Si ≤ 1.50 and Mn / Fe ≥ 0.50. While ensuring the high-density precipitation of the main reinforcing phases β″ and Q′, it achieves the composite precipitation of α-Al(Fe,Mn)Si dispersed phase and AlFeSiV dispersed phase, with a bulk density of 3.00 × 10⁻⁶. 19 ~7.50×10 19 / m 3 The average size is 130–260 nm; on the one hand, it enhances the dispersion strengthening effect, resulting in a fine equiaxed crystal microstructure in the aluminum alloy with a grain size of 15–20 μm, ensuring good plasticity of the material; on the other hand, it promotes the precipitation of nano-precipitates in the microstructure, with a bulk density of 9.0 × 10⁻⁶. 23 ~12.0×10 23 / m 3The average length is 10-15 nm, increasing the strength of the aluminum alloy under simulated baking paint treatment conditions to over 340 MPa, with the paint addition increasing to 85-110 MPa, consistent with the highest reported strength Al-Mg-Si-Cu-Zn aluminum alloys. However, this invention has a lower degree of alloying, achieving both high strength and good plasticity in the aluminum alloy, with an elongation after fracture of 18%-20%, ensuring the formability of the aluminum alloy and facilitating rolling. In contrast, the elongation of the highest reported strength Al-Mg-Si-Cu-Zn aluminum alloys is typically 12.2%-14.8%.

[0054] Based on chemical composition design, this invention optimizes homogenization heat treatment, rolling process, and solution-quenching-pre-aging treatment process. By controlling the composition and distribution of submicron dispersed phases and nano-reinforcing phases in aluminum alloys, the produced sheet metal has good surface quality and fine grain size, achieving an excellent match between strength and plasticity. This invention has certain guiding significance for the development, processing and application of 6xxx series aluminum alloy automotive body outer panels with high baking performance.

[0055] The high-baking-performance Al-Mg-Si-Cu-V aluminum alloy prepared by this invention provides a new design concept for the development of novel high-baking-performance Al-Mg-Si-Cu aluminum alloys. The obtained Al-Mg-Si-Cu-V aluminum alloy (in the baked state) has a yield strength ≥340MPa, a tensile strength ≥390MPa, an elongation after fracture of 18%–20%, and a paint-baking increment of 85–110MPa, providing a potential industrial alloy sheet for the current lightweight design and safety requirements in the transportation field. Attached Figure Description

[0056] Figure 1 is a macroscopic image of the hot-rolled aluminum alloy sheet and the cold-rolled aluminum alloy sheet obtained in Embodiment 1 of the present invention;

[0057] Figure 2 is a microstructure image of the Al-Mg-Si-Cu-V aluminum alloy material obtained in Example 1 of the present invention;

[0058] Figure 3 is a grain size distribution diagram of the Al-Mg-Si-Cu-V aluminum alloy material obtained in Example 1 of the present invention;

[0059] Figure 4 shows a typical dispersed phase in the homogenized state of the aluminum alloy material obtained in Example 1 of the present invention;

[0060] Figure 5 shows the typical strengthening phase of the Al-Mg-Si-Cu-V aluminum alloy material obtained in Example 1 of the present invention in the painted state;

[0061] Figure 6 is a microstructure image of the Al-Mg-Si-Cu-V aluminum alloy material obtained in Comparative Example 1 of the present invention;

[0062] Figure 7 is a grain size distribution diagram of the Al-Mg-Si-Cu-V aluminum alloy material obtained in Comparative Example 1 of the present invention;

[0063] Figure 8 shows the field emission scanning (FESEM) characterization results of the aluminum alloy material in the homogenized state obtained in Comparative Example 1 of this invention;

[0064] Figure 9 is a comparison of the paint gain and yield strength of the Al-Mg-Si-Cu-V series aluminum alloy material obtained in Example 1 of the present invention with those of the existing typical 6xxx series aluminum alloy sheets (AA6016, AA6022 and AA6111) used in commercial vehicle bodies. Detailed Implementation

[0065] To better understand the above-described technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following embodiments are only used to describe specific implementations of the present invention and do not constitute any limitation on the scope of protection of the present invention.

[0066] Examples 1-8 and Comparative Examples 1-3

[0067] 1) Smelting and casting:

[0068] Ingots are obtained through smelting and casting;

[0069] 2) Homogenization heat treatment:

[0070] The ingot is subjected to homogenization heat treatment to obtain a homogenized ingot.

[0071] 3) Hot rolling:

[0072] The homogenized ingot is milled and hot-rolled to obtain hot-rolled sheet metal.

[0073] 4) Cold rolling:

[0074] Hot-rolled sheet metal is cold-rolled to obtain cold-rolled sheet metal;

[0075] 5) Solution treatment + water quenching:

[0076] Cold-rolled sheet metal is subjected to solution treatment and water quenching to obtain solution-treated sheet metal;

[0077] 6) Pre-aging treatment:

[0078] The solution-treated board was pre-aged (PA) and then left to stand naturally (at room temperature) for 14 days to obtain the T4P board.

[0079] 7) Simulated paint baking process:

[0080] The T4P state sheet was subjected to simulated baking paint treatment to obtain Al-Mg-Si-Cu-V series aluminum alloy sheet (or aluminum alloy sheet after baking paint or in the baking paint state). The T4P state sheet was first subjected to 2% pre-stretch deformation, and then baked under the set baking paint process conditions. The baking temperature was 185℃ and the treatment time was 20min.

[0081] The methods for testing microstructure and performance parameters are as follows:

[0082] The yield strength, tensile strength and elongation after fracture of aluminum alloys were determined by room temperature tensile testing method, with reference to GB / T 228.1-2021.

[0083] The paint addition is defined as the difference between the yield strength after baking and the yield strength of the T4P state specimen.

[0084] Grain size of aluminum alloys was determined using EBSD.

[0085] The composition of uniformly distributed nano-precipitates and dispersed phases in the matrix of aluminum alloy was analyzed using FESEM, TEM and STEM.

[0086] Based on statistical analysis of TEM images, the bulk density and average size of dispersed phases and nano-precipitates in the aluminum alloy matrix were obtained.

[0087] Table 1 shows the chemical composition of the aluminum alloys described in Examples 1-8 and Comparative Examples 1-3 of this invention.

[0088] Table 2 shows the preparation process parameters of the aluminum alloys described in Examples 1-8 and Comparative Examples 1-3 of the present invention. Furthermore, in step 1) of Examples 1-8 and Comparative Examples 1-3, the following raw materials were smelted and cast: high-purity aluminum, pure magnesium, pure zinc, and master alloys were used as raw materials, wherein the master alloys were Al-Si master alloys, Al-Cu master alloys, Al-V master alloys, Al-Mn master alloys, Al-Cr master alloys, and Al-Fe master alloys; first, the high-purity aluminum was completely melted, heated to 740°C, and the master alloy was added and held at that temperature for 30 minutes. After the master alloy was completely melted, a first melt was obtained and cooled to 7... At 40℃, pure magnesium and pure zinc are added and held for 10 minutes to obtain a second melt. Then, a refining agent is added, and after the refining agent has fully reacted with the second melt, a slag-removing agent is added, and the mixture is held at 720℃ for 15 minutes. Finally, a refining agent is added, and after holding for 5 minutes, the mixture is cast (at 720℃) to obtain an ingot. The refining agent is a sodium fluoride ionic refining agent, and its addition amount is 0.40 wt.% of the mass of the second melt. The refining agent is an Al-5Ti-1B refining agent, and its addition amount is 0.01 wt.% of the mass of the second melt. In step 4), the total deformation of the cold rolling is 65%.

[0089] Table 3 shows the performance parameters of the aluminum alloys obtained in Examples 1-8 and Comparative Examples 1-3 of the present invention.

[0090] This invention produces cold-rolled sheets through alloy casting, homogenization treatment, hot rolling, and cold rolling. After the cold-rolled sheets are subjected to simulated baking paint treatment, the resulting aluminum alloy has a yield strength of 340-360 MPa, a tensile strength of 390-410 MPa, and an elongation after fracture of 18%-20%, which is far higher than that of existing commercial AA6111, AA6016, and AA6022 aluminum alloy sheets. It is comparable to the highest baking strength of Al-Mg-Si-Cu-Zn aluminum alloys reported in the present invention, but with better plasticity.

[0091] Figure 1 is a macroscopic image of the hot-rolled aluminum alloy sheet and the cold-rolled aluminum alloy sheet obtained in Embodiment 1 of the present invention. As can be seen from the image, the surface quality of the obtained aluminum alloy material is good.

[0092] Figure 2 is a microstructure image of the aluminum alloy material obtained in Example 1 of the present invention, and Figure 3 is a grain size distribution diagram of the aluminum alloy material obtained in Example 1 of the present invention. As can be seen from the images, the grain size of the material is small, with an average size of 18.6 μm.

[0093] Figure 4 shows the typical dispersed phases of the aluminum alloy material in the homogenized state obtained in Example 1 of the present invention, and Figure 5 shows the typical reinforcing phases of the aluminum alloy material in the baked state obtained in Example 1 of the present invention. As can be seen from the pictures, a large number of submicron dispersed phases (α-Al(Fe,Mn)Si and AlFeSiV) and high-density nano-reinforcing phases (β″ phase and Q′ phase) are precipitated in the baked state substrate, which improves the mechanical properties of the substrate in the baked state. Compared with the existing typical 6xxx series aluminum alloy substrates used in commercial vehicle bodies, the mechanical properties of the material are greatly improved.

[0094] Figures 6 and 7 are microstructure images and grain size distribution diagrams of the aluminum alloy material obtained in Comparative Example 1 of the present invention, respectively. By comparing with Figures 2 and 3, it is found that the grain size in Comparative Example 1 is significantly coarser than that in Example 1 due to the lower density of the dispersed phase, and its average size has increased from 18.6 μm to 29.1 μm.

[0095] Figure 8 shows the FESEM characterization results of the aluminum alloy material obtained in the homogenized state in Comparative Example 1 of this invention. By comparing with Figure 4, it can be seen that after homogenization treatment, the alloy in Comparative Example 1 has almost no dispersed phase precipitated in the crystal.

[0096] Figure 9 is a comparison of the paint coating increment and yield strength of the aluminum alloy material obtained in Embodiment 1 of the present invention with that of the existing typical 6xxx series aluminum alloy sheet used in commercial vehicle bodies. As can be seen from the figure, the strength of the material obtained by the present invention is significantly improved compared with the existing aluminum alloy material.

[0097] In Comparative Example 1, no V element was added, resulting in a microstructure with larger grain size, lower density of dispersed phases, larger average size, lower density of nanoprecipitates, and larger average size. Consequently, the yield strength and paint gain of the alloy in the baked state were significantly lower.

[0098] In Comparative Example 2, with the addition of V, the Mg / Si ratio is low (Mg / Si = 0.53), the density of the nanoprecipitates is low, the average size is large, and the strengthening mechanism is transformed into single-phase strengthening of the β″ phase. Therefore, the yield strength and paint addition are low.

[0099] In Comparative Example 3, with the addition of V, the Mg / Si ratio is relatively high (Mg / Si = 1.7), while the Mn / Fe ratio is relatively low (Mn / Fe = 0.25). The strengthening mechanism is transformed into single-phase strengthening of the Q′ phase, and there is a needle-like β-AlFeSi phase in the alloy. The alloy strength and plasticity are significantly lower, with a yield strength of only 286 MPa and an elongation of only 15.1% in the baked state.

[0100] In summary, this invention, by optimizing the content of elements such as Mg, Si, Cu, and V, and controlling the precipitation of strengthening and dispersed phases, improves the bake-hardening effect while ensuring the plasticity of the alloy. It provides a new solution for improving the bake-hardening strength of existing commercial 6xxx series aluminum alloy sheets, and has certain guiding significance for the development, processing, and application of 6xxx series aluminum alloy automotive sheets for automotive body panels.

[0101] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. An Al-Mg-Si-Cu-V based aluminum alloy, characterized by, The chemical composition of the Al-Mg-Si-Cu-V aluminum alloy, expressed as a percentage by mass, is as follows: Mg: 0.8–1.5 wt.%, Si: 0.70–1.30 wt.%, Cu: 0.50–1.00 wt.%, V: 0.05–0.30 wt.%, Mn: 0.05–0.50 wt.%, preferably 0.10–0.50 wt.%, Cr: 0.05–0.20 wt.%, preferably 0.10–0.50 wt.%, Ti: 0.030–0.100 wt.%, Fe: 0.05–0.40 wt.%, preferably 0.14–0.40 wt.%, more preferably 0.15–0.40 wt.%, with the balance including Al and unavoidable impurities, wherein 1.10 ≤ Mg / Si ≤ 1.50, Mn / Fe ≥ 0.50, where the element symbols are replaced with the corresponding mass percentage content of each element.

2. The Al-Mg-Si-Cu-V aluminum alloy according to claim 1, characterized in that, The balance consists of Al and unavoidable impurities.

3. The Al-Mg-Si-Cu-V aluminum alloy according to claim 1 or 2, characterized in that, The microstructure of the Al-Mg-Si-Cu-V aluminum alloy consists of fine equiaxed crystals with a grain size of 15.0–20.0 μm. Furthermore, the microstructure contains uniformly distributed nano-precipitated phases and dispersed phases, wherein the dispersed phases are α-Al(Fe,Mn)Si and AlFeSiV, and the bulk density of the dispersed phases is 3.00 × 10⁻⁶. 19 ~7.50×10 19 / m 3 The average size is 130–260 nm; the nano-precipitated phases are β″ and Q′ phases, with a bulk density of 9.0 × 10⁻⁶. 23 ~12.0×10 23 / m 3 The average length is 10.0–15.0 nm, preferably 12.2–15.0 nm.

4. The Al-Mg-Si-Cu-V aluminum alloy according to claim 1, 2, or 3, characterized in that, The Al-Mg-Si-Cu-V series aluminum alloy has a yield strength ≥340MPa, a tensile strength ≥390MPa, an elongation after fracture of 18.0%~20.0%, and a paint coating increment of 85~110MPa.

5. The method for preparing the Al-Mg-Si-Cu-V aluminum alloy according to any one of claims 1-4, characterized in that, The preparation method includes the following steps performed sequentially: 1) Smelting and casting: Ingots are obtained through smelting and casting; 2) Homogenization heat treatment: The ingot is subjected to homogenization heat treatment to obtain a homogenized ingot, wherein the homogenization heat treatment temperature is 545-565℃, the holding time of the homogenization heat treatment is 16-24h, the heating rate of the homogenization heat treatment is 0.50-1.00℃ / min, and the cooling rate is 0.50-1.00℃ / min. 3) Hot rolling: A homogenized ingot is hot-rolled to obtain a hot-rolled sheet, wherein the total deformation of the hot rolling is 85% to 95%, and the hot rolling temperature is 545 to 565°C. 4) Cold rolling: Hot-rolled sheet metal is cold-rolled to obtain cold-rolled sheet metal; 5) Solution treatment + quenching: The cold-rolled sheet is subjected to solution treatment and quenching in sequence to obtain a solution-treated and quenched sheet, wherein the solution treatment temperature is 560-570℃, the solution treatment holding time is 5-10 min, and the quenching method is water quenching. 6) Pre-aging treatment: After solution treatment and quenching, the solution-treated and quenched plate is pre-aged and then left to stand naturally for more than 14 days to obtain the T4P plate. The temperature of the pre-aging treatment is 110-130℃ and the holding time of the pre-aging treatment is 8-10h. 7) Simulated paint baking process: A simulated baking paint treatment was performed on the T4P state sheet material to obtain an Al-Mg-Si-Cu-V series aluminum alloy.

6. The preparation method according to claim 5, characterized in that, In step 1), the following raw materials are smelted and cast: high-purity aluminum, pure magnesium, pure zinc, and master alloys are used as raw materials, wherein the master alloys are Al-Si master alloys, Al-Cu master alloys, Al-V master alloys, Al-Mn master alloys, Al-Cr master alloys, and Al-Fe master alloys. First, high-purity aluminum is completely melted and heated to 740–760°C. A master alloy is added and held at this temperature for 20–30 minutes. After the master alloy is completely melted, the first melt is obtained and cooled to 720–740°C. Pure magnesium and pure zinc are added and held at this temperature for 10–15 minutes to obtain the second melt. Then, a refining agent is added. After the refining agent reacts fully with the second melt, a slag-removing agent is added and held at 720–740°C for 10–15 minutes. Finally, a refining agent is added and the melt is held at this temperature for 2–5 minutes before casting to obtain an ingot. The refining agent is a sodium fluoride ionic refining agent, and its addition amount is 0.40 to 0.60 wt.% of the mass of the second melt; The refining agent is an Al-5Ti-1B refining agent, and its addition amount is 0.01 to 0.06 wt.% of the mass of the second melt.

7. The preparation method according to claim 5, characterized in that, In step 1), the casting temperature is 720–740°C.

8. The preparation method according to claim 5, characterized in that, In step 2), after homogenization heat treatment and before hot rolling, the homogenized ingot is milled.

9. The preparation method according to claim 5, characterized in that, In step 4), the total deformation of the cold rolling is ≥65%.

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