A compound deformation heat treatment method for inhibiting natural aging and improving artificial aging response of an aluminum alloy for automobiles

Abstract

The present application belongs to the technical field of aluminum alloy heat treatment, and discloses a composite deformation heat treatment method for inhibiting natural aging of aluminum alloy for automobiles and improving artificial aging response. The method comprises the following steps: 1) heat preservation, rapid cooling, cold rolling, and completion of pre-deformation of the rolled deformed aluminum alloy plate; 2) heat preservation and completion of intermediate pre-aging of the alloy plate after the pre-deformation; 3) cold rolling and completion of post-deformation of the alloy plate after the intermediate pre-aging; and 4) placing the alloy plate after the post-deformation at room temperature, heat preservation, and completion of final aging. The method of the present application inhibits the formation of atom clusters at room temperature in the natural aging process, promotes the precipitation of strengthening phase in the artificial aging process, fully plays the dispersion strengthening effect, realizes significant artificial aging response, and maintains a high response amount after the natural aging, especially the tensile strength is significantly improved, and excellent plasticity is exhibited. The present application is easy to mass produce.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy heat treatment technology, specifically relating to a composite deformation heat treatment method that suppresses the adverse effects of natural aging of 6xxx series aluminum alloys and improves the response of artificial aging. Background Technology

[0002] With increasing carbon emissions and worsening air pollution and climate conditions, people are becoming increasingly aware of the importance of energy conservation and emission reduction. In the automotive industry, achieving "lightweighting" has become a key focus. It is estimated that a 10% reduction in vehicle body weight can reduce fuel emissions by 8-10%, and since the body weight accounts for approximately 30-40% of the total vehicle weight, achieving lightweighting of the vehicle body plays a crucial role in overall vehicle weight reduction. Aluminum alloys, due to their low density, corrosion resistance, and high strength, have gradually become the first choice to replace steel. Among the various aluminum alloy series, the 6xxx series (Al-Mg-Si alloys) has more significant advantages compared to other series, such as: heat-treatable strengthening, good weldability, good formability, and ease of surface treatment; in addition, this series of alloys also has high paint hardening characteristics, representing an optimal combination of excellent formability and high strength and toughness. 6xxx series alloys are mostly supplied in the T4 condition (solution state). During stamping, they maintain good formability due to their low yield strength. In the painting process, the relatively high temperature (generally between 160 and 200°C) causes artificial aging, resulting in significant precipitation hardening and a substantial increase in yield strength. Several grades of 6xxx series aluminum alloys, such as AA6111, AA6022, and AA6013, are already widely used in automotive sheet metal manufacturing.

[0003] During production and transportation, 6xxx series aluminum alloys inevitably undergo slow natural aging at room temperature, exhibiting natural aging properties. Specifically, this manifests as age hardening after solution quenching, occurring over several days or months of storage and transportation at room temperature. This increases the alloy's strength but reduces its stamping formability. Simultaneously, it significantly reduces the artificial aging response during subsequent painting processes, making it difficult for painting to significantly improve the alloy's strength, ultimately resulting in a strength that does not meet actual production requirements.

[0004] Extensive experimental and applied research has been conducted to mitigate the adverse effects of natural aging on 6xxx series aluminum alloys and improve their artificial aging response for paint hardening. This research primarily focuses on controlling the pre-aging or pre-deformation of 6xxx series alloy sheets after solution quenching. Patent application CN115141990A discloses a pretreatment method to improve the paint hardening performance of automotive 6xxx series aluminum alloys. This method involves high-temperature pre-deformation of the alloy after solution quenching. After solution quenching, the alloy sheet is held at 165℃–180℃ for 4–6 minutes, while simultaneously undergoing pre-stretch deformation (1–10%). This is followed by natural aging and then artificial aging. The treated alloy exhibits lower T4 hardness and higher paint hardness. Patent CN108884524A discloses a processing method to improve the paint-baking performance of 6xxx series aluminum alloy sheets. The method involves pre-aging the solution-treated aluminum alloy sheet at a high temperature of 100℃~300℃ for a short period of 5~300s, then maintaining it at a low temperature of 30℃~50℃ for a long period of 5~500h, followed by natural aging and then artificial aging. The treated alloy exhibits high paint-baking hardening strength, with a maximum paint-baking increase of 92MPa.

[0005] The above patents all involve deformation heat treatment processes for aluminum alloys. Pre-aging or pre-deformation can reduce the adverse effects of natural aging of 6xxx series aluminum alloys and improve the response capability of artificial aging. However, the low-temperature pre-aging holding time is relatively long, which leads to high energy consumption and low production efficiency in actual production. At the same time, the strength increase of the developed sheet material after baking is limited, and the strength improvement obtained by short-time paint baking artificial aging cannot meet the requirements of high formability and high paint strength for automotive aluminum alloys. The synchronous high-temperature pre-deformation method is difficult to control in production. The high-temperature holding time is relatively short, and the alloy is difficult to rise to the corresponding temperature, especially the surface and core are difficult to achieve isothermal quickly. The pretreatment cycle of high-temperature short-time pre-aging and low-temperature long-time pre-aging methods is long, resulting in high energy consumption and low production efficiency in actual production.

[0006] The pretreatment process in the method of this invention is compact, easy to operate and control, and conducive to improving production efficiency. Moreover, the alloy obtained by the method of this invention exhibits a high increase in tensile strength during natural aging and artificial aging after baking, with a maximum hardness of 119.5 HV after baking, while maintaining good plasticity and an elongation at break of over 20%, demonstrating significant performance improvement advantages. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the present invention aims to provide a composite deformation heat treatment method that suppresses natural aging of automotive aluminum alloys and improves the response of artificial aging. The method of the present invention can significantly reduce the adverse effects of natural aging and significantly improve the artificial aging response of paint, while also improving production efficiency and significantly reducing energy consumption. The present invention optimizes and determines the deformation heat treatment process flow and obtains an optimal range of process parameters. This process does not require additional production equipment; it is simply a combination of deformation and heat treatment, and can be implemented using existing mature production lines.

[0008] This invention is achieved through the following technical solution:

[0009] A composite deformation heat treatment method for suppressing natural aging and improving the response of artificial aging in automotive aluminum alloys includes the following steps:

[0010] 1) The rolled aluminum alloy sheet is placed in a heat preservation device for heat preservation, and then rapidly cooled to obtain a supersaturated solid solution sheet.

[0011] 2) The supersaturated solid solution plate is cold-rolled to complete the pre-deformation;

[0012] 3) Insulate the alloy plates that have completed pre-deformation to complete intermediate pre-aging;

[0013] 4) The alloy sheet that has completed intermediate pre-aging is cold rolled and then pre-deformed.

[0014] 5) Place the pre-deformed alloy sheet at room temperature and then heat it to complete the final aging.

[0015] The aluminum alloy sheet that is rolled and deformed in step 1) refers to the aluminum alloy sheet that has been homogenized and then subjected to hot rolling and cold rolling deformation to obtain a cold-rolled sheet.

[0016] The aluminum alloy is a 6xxx series aluminum alloy;

[0017] The homogenization treatment involves placing the 6xxx series wrought aluminum alloy casting billet in a heat preservation device for heat preservation at a temperature of 550–580°C for 7–9 hours; the hot rolling temperature is 450–480°C with a total reduction of 50%; the cold rolling is performed after the hot rolling is completed and the plate is cooled to room temperature with a total reduction of 50%.

[0018] The hot rolling and cold rolling are each multi-pass rolling processes, with a reduction of 5-15% per pass; the number of rolling passes is 10-25. When the reduction per pass is controlled at 10%, the number of rolling passes is 13-17.

[0019] The temperature for heat preservation in step 1) is 510–530℃, and the heat preservation time is 20–40 min.

[0020] The rapid cooling refers to cooling with room temperature water. Specifically, it means immersing the insulated board in water for cooling or spraying water mist to cool the board.

[0021] The total reduction in cold rolling described in step 2) is 2-5%, and it is a single rolling process.

[0022] In step 3), the temperature for heat preservation is 140-170℃ (preferably 150-170℃), and the heat preservation time is 5-20 minutes (preferably 5-15 minutes).

[0023] The total reduction in cold rolling described in step 4) is 2-5%, and it is a single rolling process.

[0024] The time to place the product at room temperature as described in step 5) is 14 days to 1 month, the temperature is 170℃~190℃, and the holding time is 20~60 minutes.

[0025] The aluminum alloy is a 6xxx series aluminum alloy.

[0026] The alloy prepared in this invention is an aluminum alloy for the casing of automotive power batteries.

[0027] This invention combines pre-deformation and pre-aging. It utilizes dislocations generated during deformation to increase internal defects in the alloy, providing nucleation sites for the formation of the GP zone. This accelerates the transformation of the GP zone to the β” phase during the artificial aging process, leading to the accelerated precipitation of the main strengthening phase, the β” phase, and providing activation energy for the precipitated phase. Pre-aging inhibits the formation of atomic clusters during natural aging, reducing the impact of natural aging on the alloy's mechanical properties. The atomic clusters formed during pre-aging can serve as nucleation sites for the β” phase or directly transform into the β” phase, accelerating the precipitation of the artificially aged phase and improving the response capability of the artificial aging process. The combined effect of these factors helps reduce heat treatment time and improve heat treatment efficiency. The alloy can maintain a high aging response capability even after short-term artificial aging following a period of time at room temperature.

[0028] Excessive pre-deformation is equivalent to applying significant work hardening to the alloy, resulting in a substantial increase in the T4 hardness. This reduces the alloy's stamping performance during production. If the pre-aging temperature is too low, pre-aging clusters are difficult to form, making it difficult to suppress the formation of naturally aged clusters. Conversely, if the pre-aging temperature is too high, the alloy undergoes direct artificial aging, leading to the precipitation of strengthening phases and the loss of the ability to undergo artificial aging through baking paint after natural aging. If the pre-aging time is too short, pre-aging clusters are difficult to form; if the time is too long, the alloy will directly undergo the artificial aging process.

[0029] Compared with the existing manufacturing process of 6xxx series aluminum alloys for automotive body panels, it has the following outstanding advantages:

[0030] (1) The present invention provides a 6xxx series aluminum alloy preparation process technology. The mechanical properties of the prepared alloy are significantly delayed during the natural aging process at room temperature, while still having high plasticity to ensure stamping performance. After being left at room temperature for a period of time, it undergoes short-term artificial aging and has significant response capability.

[0031] (2) The present invention achieves that the strength and hardness of the alloy do not change significantly during the natural aging process, the natural aging is effectively suppressed, and the increase in artificial aging of the paint does not decrease as the natural aging experiment is prolonged.

[0032] (3) For 6111 aluminum alloy, which is widely used in automotive sheet materials, the alloy treated by this invention has a T4 hardness increase of ΔH≤5HV within 2 to 4 weeks of natural aging. After long-term natural aging, the hardening effect of short-term artificial aging and baking paint is significant, with an increase of ΔH≥20HV.

[0033] (4) The tensile mechanical property increment ΔRm after natural aging for 2 weeks and short-term artificial aging is above 57MPa, and the elongation at break is still above 20%. It has high artificial aging increment while maintaining good plasticity.

[0034] (5) Compared with traditional pre-aging or pre-deformation processes, the present invention reduces the pre-aging time and the total pre-deformation reduction, resulting in significant cost reduction advantages in production.

[0035] (6) The process of the present invention does not require the addition of new equipment. It only requires the adjustment of the production steps of the existing production line to produce 6xxx series aluminum alloys for automotive sheet metal that reduce the adverse effects of natural aging and improve the response capability of artificial aging, and is easy to achieve mass production. Attached Figure Description

[0036] Figure 1 This is a flow chart of the traditional production process for 6xxx series aluminum alloys.

[0037] Figure 2 The hardness of the alloy in Comparative Example 1 in the T4 state at different natural aging times and the corresponding increase in hardness after short-time baking paint artificial aging.

[0038] Figure 3 The mechanical property curves of the alloy in Comparative Example 1 after 14 days of natural aging in the T4 state and the corresponding mechanical property curves after short-time baking paint artificial aging are shown.

[0039] Figure 4 This is a flowchart of the composite pretreatment process of the present invention;

[0040] Figure 5 The changes in hardness (i.e., hardness increment) of the alloy under natural aging for different times in Example 1 and under the corresponding short-time artificial aging with baked paint are shown.

[0041] Figure 6 The mechanical property curves of the alloy in Example 1 after 14 days of natural aging in the T4 state and the corresponding mechanical property curves after short-time baking paint artificial aging are shown. Detailed Implementation

[0042] The present invention will be described in further detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0043] To better illustrate the implementation effect of the present invention, the solution aging and pre-aging process of 6111 aluminum alloy used in the production of power battery shells for new energy vehicles is used as Comparative Example 1.

[0044] Comparative Example 1

[0045] 6111 aluminum alloy is a common wrought aluminum alloy used in the manufacture of automotive body panels. In mass production, its manufacturing process includes smelting, water-cooled crystallizer ingot production, homogenization annealing, high-temperature hot rolling, and cold rolling to obtain the sheet material. In the comparative example, the composition of the 6111 alloy is 0.72% Mg, 0.86% Si, 0.72% Cu, 0.30% Mn, 0.21% Fe, with the balance being Al.

[0046] The wrought aluminum alloy used in this invention is first processed through casting ingot equipment, homogenization heat treatment, high-temperature hot rolling, and cold rolling to obtain sheet metal. The homogenization treatment involves holding at 560℃ for 8 hours, followed by furnace cooling to room temperature to dissolve the alloy phases as much as possible and ensure sufficient compositional homogeneity. After homogenization annealing, the ingot is heated to 460℃ and hot-rolled to a 10mm sheet metal, with a rolling deformation exceeding 50%. The hot-rolled sheet metal is then cooled to room temperature and cold-rolled to a 5mm sheet metal, with a rolling deformation exceeding 50%. The resulting cold-rolled sheet metal undergoes solution aging treatment to obtain the desired properties. This comparative example uses a traditional solution aging process, which is currently the most widely used production process for manufacturing 6111 alloy automotive body sheet metal.

[0047] Solution aging treatment: First, the plate material cooled to room temperature undergoes solution treatment at 530℃ for 30 minutes, followed by quenching in room temperature water to obtain a supersaturated solid solution. Then, it is placed at room temperature for 0–14 days. The T4 state alloy is tested for hardness daily, followed by short-term artificial aging with paint baking at 180℃ for 30 minutes. Finally, the hardness of the aged alloy (T61 state) is tested. It should be noted that in actual production, the artificial aging temperature for paint baking is around 180℃, and the baking time is controlled within 30–60 minutes to ensure production efficiency.

[0048] This comparative example describes the treatment of homogenized rolled sheets using traditional heat treatment processes, the process flow diagram of which is shown below. Figure 1 As shown.

[0049] The hardness of the alloy in the T4 state after daily natural aging and the corresponding hardness in the T61 state after short-time baking were measured using a Vickers hardness tester (model: HVS-10A, standard: GB / T 4340.1-2009). The mechanical properties of the alloy under different conditions and times were measured using an electronic multi-material testing machine (model: AG-X-100KN, standard: BG / T 228-2010), and the corresponding tensile strength, yield strength, and elongation at break were obtained.

[0050] Figure 2 To compare the hardness of the alloy in Example 1 at different aging times in the T4 state and the corresponding hardness increase in the T61 state after short-term baking paint, it can be seen that the hardness of the alloy is very low immediately after solution treatment. However, as natural aging progresses, the hardness of the T4 state gradually increases from 55.7 HV to 72.7 HV, with a hardness increase ΔH of 17 HV brought about by natural aging. From the hardness change of the T61 state after artificial aging with baking paint, it can be seen that as natural aging progresses, the daily hardness increase from baking paint gradually decreases, and on the 14th day, the hardness increase brought about by baking paint is only 4.9 HV, with almost no improvement in hardness compared to before baking paint.

[0051] The mechanical properties of the alloy were tested under different conditions of natural aging (0 days and 14 days), with a focus on comparing the changes in tensile strength before and after painting. Figure 3 The mechanical property curves of the alloy in Example 1 after natural aging for 14 days and after artificial aging with paint are shown. From the tensile mechanical properties, it can be seen that the tensile strength of the alloy after solution treatment is 190.2 MPa, and the elongation at break is 38.6%. After painting, the tensile strength of the T61 alloy increases to 220.3 MPa, an increase of 30.1 MPa, while the elongation at break is 34.5%, a decrease of 4.2%. The tensile strength of the T4 state after 14 days of natural aging is 214.0 MPa, an increase of 23.8 MPa compared to after solution quenching, and the elongation at break is 35.7%. The tensile strength of the alloy after painting is 219.6 MPa, an increase of only 5.6 MPa.

[0052] To further illustrate the effects of the present invention, the present invention will be described below in conjunction with embodiments.

[0053] Example 1

[0054] The alloy used in this embodiment is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, and hot and cold rolling process parameters are the same as those in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet. This embodiment uses rolled sheet as raw material (sheet that has undergone homogenization treatment, hot rolling, and cold rolling), and processes it using the composite pretreatment process provided by this invention. The process flow is as follows: Figure 4 As shown.

[0055] In this embodiment, the composite pretreatment process refers to the process where the rolled plate is solution treated, then continuously quenched and subjected to pre-deformation treatment, followed by short-time pre-aging, cooled to room temperature and then subjected to post-deformation treatment. After the treatment is completed, the alloy is left at room temperature for a period of time and then subjected to short-time baking paint artificial aging to obtain the final product.

[0056] The composite pretreatment process in this embodiment specifically includes the following steps:

[0057] (1) Pre-deformation

[0058] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 2%.

[0059] (2) Intermediate pre-aging

[0060] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0061] (3) Post-deformation

[0062] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 2%.

[0063] (4) Store at room temperature

[0064] The pre-deformed alloy is left to age naturally at room temperature.

[0065] (5) Final Validity Period

[0066] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0067] To better understand the design basis of the process flow of this invention and the determination range of its process parameters, the basic principles for realizing this invention are explained as follows:

[0068] 6111 alloy is an Al-Mg-Si based wrought aluminum alloy. Its strengthening mechanisms mainly include solid solution strengthening, deformation strengthening, and second-phase strengthening. Among these, the formation of finely dispersed precipitates during aging is the primary strengthening mechanism. The aging precipitation sequence of 6111 alloy progresses with increasing temperature from solute atom clusters to the GP region, then to the β” phase, then to the β' phase, and finally to the Q' phase. The main strengthening phases, the β” and Q' phases, are coherent with the matrix. The resulting coherent distortion generates a continuous strain field around the precipitates, hindering dislocation movement and thus achieving a strengthening effect.

[0069] During the production of 6111 alloy, due to storage or transportation processes, it inevitably undergoes a period of rest at room temperature after solution quenching, during which natural aging occurs. During natural aging, Mg and Si atoms in the solute combine with quenching vacancies and gradually grow into atomic clusters through diffusion. These clusters gradually grow and stabilize with natural aging, but their size remains very small and coherent with the matrix, increasing the hardness and strength of the T4 state alloy while reducing its stamping formability. In the artificial aging stage for baking paint, these clusters hinder the formation of the β” phase, reducing the alloy's paint hardening ability. Furthermore, because artificial aging for baking paint involves a short aging period at a relatively low temperature, the alloy is usually in an under-aged stage, making it difficult to achieve considerable strength.

[0070] After the first pre-deformation cold rolling, defects such as dislocations introduced into the solid solution alloy accelerate the annihilation of quenching vacancies and inhibit the formation of naturally aged clusters. Dislocations also serve as atomic channels for subsequent artificial aging, promoting the precipitation of Mg and Si atoms and accelerating the transformation of the GP zone to the β” phase. After applying intermediate pre-aging, pre-aged clusters are formed in the alloy, inhibiting the formation of naturally aged clusters. During the baking process, these pre-aged clusters also serve as nucleation sites for the β” phase or directly transform into the β” phase, accelerating aging precipitation. In the alloy after pre-deformation, the increase in defects such as dislocations provides channels for atomic diffusion, accelerating the transformation of pre-aged clusters to the β” phase. At the same time, the GP zone and β” phase in the alloy are fragmented under external force, becoming more finely dispersed. A large number of dislocations also provide nucleation sites for the aging precipitates, reducing the activation energy of the β” phase and causing the strengthening phase to precipitate more abundantly and finely. It can not only reduce the adverse effects of natural aging, but also improve the response capability of short-time baking paint artificial aging, shorten the time required for alloy peak aging, and improve production efficiency.

[0071] Figure 5The figures show the hardness of the alloy in the T4 state at different natural aging times in Example 1, and the corresponding hardness increment in the T61 state after short-term baking paint. It can be seen that after pretreatment, the initial hardness of the alloy is relatively high, reaching 80.8 HV. This is because the pretreatment applies work hardening to the alloy, increasing the material's hardness. After baking paint, the alloy's hardness increases to 115.3 HV, with a hardness increase ΔH of 34.5 HV. After 14 days of natural aging, the hardness of the alloy in the T4 state increases to 83.0 HV, an increase of 2.2 HV. After baking paint, the alloy's hardness increases to 119.5 HV, with a hardness increase ΔH of 36.5 HV. Even after 14 days of natural aging, the alloy still exhibits a high response to artificial aging with baking paint.

[0072] Similar to Comparative Example 1, the mechanical properties of the alloy were tested under different conditions of natural aging (0 days and 14 days), with a focus on comparing the changes in tensile strength before and after painting. Figure 6 The figures show the mechanical property curves of the alloy in Example 1 after 14 days of natural aging in the T4 state and the corresponding mechanical property curves after short-term artificial aging with paint. After solution pretreatment, the tensile strength of the alloy in the T4 state is 233.8 MPa, and the elongation at break is 24.2%. After painting, the tensile strength of the alloy in the T61 state is 307.5 MPa, an increase of 73.7 MPa, and the elongation at break is 21.9%. After 14 days of natural aging, the tensile strength of the alloy in the T4 state is 238.0 MPa, and the elongation at break is 22.3%. After painting, the tensile strength of the alloy in the T61 state is 308.1 MPa, an increase of 70.1 MPa, and the elongation at break is 21.2%. After 14 days of natural aging, the alloy still maintains excellent response to artificial aging with paint, and the alloy treated by this process still maintains an elongation at break of over 20% after painting, retaining good plasticity.

[0073] Compared to Comparative Example 1, in this embodiment, under the same natural aging time (0–14 days), the hardness increment of the alloy in the T4 state decreased significantly during natural aging, from 17.0 HV in the comparative example to 2.2 HV. On the 14th day of natural aging, artificial aging with paint baking was performed, and the hardness increment increased from 4.9 HV in the comparative example to 36.5 HV. The hardness increment during artificial aging with paint baking was also significantly increased. Furthermore, in Example 1, the hardness increment hardly decreased during natural aging, demonstrating significant stability against natural aging and rapid response to artificial aging. Simultaneously, the alloy exhibited excellent strength before and after paint baking. After 14 days of natural aging, the hardness increment of Example 1 with paint baking was 70.1 MPa, a significant improvement compared to the 5.6 MPa hardness increment of Comparative Example 1.

[0074] Example 2

[0075] The alloy used in this embodiment is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, and cold rolling process parameters are exactly the same as those in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet. This embodiment uses rolled sheet as raw material (sheet that has undergone homogenization treatment, hot rolling, and cold rolling), and processes it using the composite pretreatment process provided by this invention. The process flow is exactly the same as in Example 1. The difference lies in the process parameters.

[0076] The composite pretreatment process in this embodiment specifically includes the following steps:

[0077] (1) Pre-deformation

[0078] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 5%.

[0079] (2) Intermediate pre-aging

[0080] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0081] (3) Post-deformation

[0082] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 2%.

[0083] (4) Store at room temperature

[0084] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0085] (5) Final Validity Period

[0086] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0087] The hardness of the alloy in the T4 state at different natural aging times and the corresponding hardness in the T61 state after short-time painting were tested. The influence trend of natural aging on the hardness of the alloy in the T4 state and the corresponding hardness in the T61 state after short-time painting is similar to that in Example 1, except that the specific performance data are different. After pretreatment, the initial hardness of the alloy was 81 HV. After painting, the hardness of the alloy increased to 113.6 HV, and the painting increase ΔH was 32.6 HV. After 14 days of natural aging, the hardness of the alloy in the T4 state increased to 84.1 HV, an increase of 3.1 HV; after painting, the hardness of the alloy increased to 118.6 HV, and the painting increase ΔH = 34.5 HV. After 14 days of natural aging, the alloy still has a high response capability to artificial aging with painting.

[0088] The variation in tensile strength is similar to that of Example 1. After solution pretreatment, the tensile strength of the alloy in the T4 state is 240.1 MPa, with an elongation at break of 18.0%. After baking paint treatment, the tensile strength of the alloy in the T61 state is 304.5 MPa, an increase of 63.4 MPa, with an elongation at break of 22.9%. Compared to Example 1, the initial strength is higher, but the elongation at break is lower. This is actually related to the 5% cold rolling deformation applied before pre-deformation, resulting in a larger rolling amount and a greater degree of work hardening. After 14 days of natural aging, the tensile strength of the alloy in the T4 state is 241.5 MPa, with an elongation at break of 18.3%. After baking paint treatment, the tensile strength of the alloy in the T61 state is 306.7 MPa, an increase of 65.2 MPa, with an elongation at break of 23.2%. Even after 14 days of natural aging, the alloy still maintains excellent response to artificial aging after baking paint treatment. After 14 days of natural aging, the alloy underwent short-time artificial aging with paint baking. The fracture elongation of the aged alloy was increased compared to the naturally aged T4 state. This is presumably because the overall pre-deformation applied was larger, and the alloy underwent a recovery process during the short-time artificial aging, which improved the alloy's plasticity.

[0089] Compared to Comparative Example 1, this embodiment maintains a lower hardness change in the T4 state and a higher hardening response in the T61 state under the same natural aging time. The hardness decreased from 17.0 HV in the Comparative Example to 3.1 HV. After 14 days of natural aging, artificial aging with paint resulted in a hardness increase from 4.9 HV in the Comparative Example to 34.5 HV, with a significantly improved increase in the artificial aging increment. Furthermore, in Example 1, the hardness hardly decreased during natural aging, demonstrating significant stability against natural aging and a rapid artificial aging response. Simultaneously, the alloy exhibited excellent strength before and after paint application. After 14 days of natural aging, the paint application increment in Example 2 was 65.2 MPa, a significant improvement compared to the 5.6 MPa increase in Comparative Example 1.

[0090] Example 3

[0091] The alloy used in this embodiment is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, and cold rolling process parameters are exactly the same as those in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet. This embodiment uses rolled sheet as raw material (sheet that has undergone homogenization treatment, hot rolling, and cold rolling), and processes it using the composite pretreatment process provided by this invention. The process flow is exactly the same as in Example 1. The difference lies in the process parameters.

[0092] The composite pretreatment process in this embodiment specifically includes the following steps:

[0093] (1) Pre-deformation

[0094] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 2%.

[0095] (2) Intermediate pre-aging

[0096] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 140℃ for 20 minutes.

[0097] (3) Post-deformation

[0098] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 2%.

[0099] (4) Store at room temperature

[0100] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0101] (5) Final Validity Period

[0102] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0103] The hardness of the alloy in the T4 state at different natural aging times and the corresponding hardness in the T61 state after short-term painting were tested. The influence of natural aging on the hardness of the alloy in the T4 state and the corresponding hardness in the T61 state after short-term painting showed a similar trend to that in Example 1, except that the specific performance data differed. After solution treatment, the initial hardness of the alloy was 77.0 HV. After painting, the hardness of the alloy increased to 109.3 HV, with a painting increase of ΔH of 32.3 HV. After 14 days of natural aging, the hardness of the alloy in the T4 state was 81.4 HV. After painting, the hardness of the alloy increased to 111.6 HV, with a painting increase of ΔH of 30.2 HV. With the progress of natural aging, the hardness change of the T4 state was ΔH = 4.4 HV, while the paint increase did not change significantly with the progress of natural aging.

[0104] The mechanical properties of the alloys under different conditions after natural aging (0 days and 14 days) were tested, and the variation pattern of tensile strength was similar to that in Example 1. After solution pretreatment, the tensile strength of the alloy in the T4 state was 229.2 MPa, and the elongation at break was 25.7%. After baking paint treatment, the tensile strength of the alloy in the T61 state was 297.2 MPa, an increase of 68.0 MPa, and the elongation at break was 23.9%. After 14 days of natural aging, the tensile strength of the alloy in the T4 state was 234.8 MPa, and the elongation at break was 24.1%. After baking paint treatment, the tensile strength of the alloy in the T61 state was 301.0 MPa, an increase of 66.2 MPa, and the elongation at break was 23.9%.

[0105] Compared to Comparative Example 1, this embodiment also maintains a lower hardness change in the T4 state and a higher hardening response in the T61 state under the same natural aging time. The hardness decreased from 17.0 HV in the Comparative Example to 4.4 HV. After 14 days of natural aging, artificial aging with paint resulted in a hardness increase from 4.9 HV in the Comparative Example to 30.2 HV, with a significant increase in the artificial aging hardness. Furthermore, in Example 1, the hardness hardly decreased during natural aging, demonstrating significant stability against natural aging and a rapid artificial aging response. Simultaneously, the alloy exhibited good strength before and after paint application. After 14 days of natural aging, the paint hardness increase in Example 4 was 66.2 MPa, a significant improvement compared to the 5.6 MPa increase in Comparative Example 1.

[0106] Example 4

[0107] The alloy used in this embodiment is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, and cold rolling process parameters are exactly the same as those in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet. This embodiment uses rolled sheet as raw material (sheet that has undergone homogenization treatment, hot rolling, and cold rolling), and processes it using the composite pretreatment process provided by this invention. The process flow is exactly the same as in Example 1. The difference lies in the process parameters.

[0108] The composite pretreatment process in this embodiment specifically includes the following steps:

[0109] (1) Pre-deformation

[0110] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 2%.

[0111] (2) Intermediate pre-aging

[0112] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0113] (3) Post-deformation

[0114] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 5%.

[0115] (4) Store at room temperature

[0116] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0117] (5) Final Validity Period

[0118] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0119] The hardness of the alloy in the T4 state at different natural aging times and the corresponding hardness in the T61 state after short-term painting were tested. The influence of natural aging on the hardness of the alloy in the T4 state and the corresponding hardness in the T61 state after short-term painting showed a similar trend to that in Example 1, except that the specific performance data differed. After solution treatment, the initial hardness of the alloy was 84.5 HV. After painting, the hardness of the alloy increased to 114.1 HV, with a painting increase of ΔH of 29.6 HV. After 14 days of natural aging, the hardness of the alloy in the T4 state was 85.2 HV. After painting, the hardness of the alloy increased to 113.5 HV, with a painting increase of ΔH of 28.3 HV. With the progress of natural aging, the hardness change of the T4 state was ΔH = 0.7 HV, while the paint increase did not change significantly with the progress of natural aging.

[0120] The mechanical properties of the alloys under different conditions after natural aging (0 days and 14 days) were tested, and the variation pattern of tensile strength was similar to that in Example 1. After solution pretreatment, the tensile strength of the alloy in the T4 state was 242.6 MPa, and the elongation at break was 20.6%. After baking paint treatment, the tensile strength of the alloy in the T61 state was 304.5 MPa, an increase of 61.9 MPa, and the elongation at break was 22.7%. After 14 days of natural aging, the tensile strength of the alloy in the T4 state was 245.3 MPa, and the elongation at break was 19.9%. After baking paint treatment, the tensile strength of the alloy in the T61 state was 303.0 MPa, an increase of 57.7 MPa, and the elongation at break was 22.5%.

[0121] Compared to Comparative Example 1, this embodiment also maintains a lower hardness change in the T4 state and a higher hardening response in the T61 state under the same natural aging time. The hardness decreased from 17.0 HV in the Comparative Example to 0.7 HV. Artificial aging with paint baking was performed on the 14th day of natural aging, and the hardness increment increased from 4.9 HV in the Comparative Example to 28.3 HV. The increment during artificial aging with paint baking was also significantly improved. Furthermore, in Example 1, the hardness hardly decreased during natural aging, demonstrating significant stability against natural aging and rapid response to artificial aging. Simultaneously, the alloy exhibited good strength before and after paint baking. After 14 days of natural aging, the paint baking increment in Example 3 was 57.7 MPa, a significant improvement compared to the 5.6 MPa increment in Comparative Example 1. Similar to Example 2, the elongation at break of the alloy after paint baking was higher than in the T4 state. This is presumably because the overall pre-deformation applied was larger, and the alloy underwent a recovery process during the short-term artificial aging, improving the alloy's plasticity.

[0122] To better compare the implementation effects of the present invention, the key performance parameters of the alloys prepared in Comparative Example 1 and Examples 1-4, and their performance improvement data compared with the traditional process, are summarized in Table 1. It should be noted that the comparative improvement ratio and comparative increase value in this table are based on the hardness data and tensile mechanical property data of Comparative Example 1 after 14 days of natural aging.

[0123] Obviously, the alloys prepared by the process of this invention show a hardness increase of less than 5 HV in the T4 state during 14 days of natural aging. Compared with the hardness increase in the T4 state during 14 days of natural aging in Comparative Example 1, the hardness increase in the T4 state caused by natural aging is much smaller than that of the alloys prepared by the traditional process, which significantly reduces the adverse effects of natural aging. After 14 days of natural aging, the hardness increase after short-term artificial aging is more than 25 HV, which is much greater than the hardness increase of the alloys prepared by the traditional process after 14 days of natural aging followed by short-term artificial aging. The alloys still maintain good paint hardening response.

[0124] Table 1. Key performance parameters and improvement data statistics of alloys prepared in Comparative Examples 1 and Examples 1-4

[0125]

[0126] Explanation: The artificial aging response ΔH of the naturally aged paint on day 14 = Hardness of the T61 state after paint baking - Hardness of the T4 state before paint baking. ΔRm = Tensile strength of the T61 state after paint baking - Tensile strength of the T4 state before paint baking.

[0127] Based on the above embodiments, the key to the composite deformation heat treatment process of the present invention lies in the pre-deformation, intermediate pre-aging, and post-deformation applied before room temperature storage after solution treatment. This effectively reduces the adverse effects of natural aging and improves the artificial aging response capability for short-term paint baking after natural aging. After artificial aging, the material not only exhibits high hardness but also outstanding tensile strength and good plastic deformation capability, which can well meet the requirements of new energy vehicle power battery shells and other automotive sheet metal structural components. Furthermore, compared to traditional processes, the material maintains good aging response characteristics even after pretreatment.

[0128] To better illustrate the effects of this invention, the present invention further modifies the process flow or process sequence, processes the 6111 alloy homogenized rolled sheet, and provides a comparative explanation.

[0129] Comparative Example 2

[0130] The alloy used in this comparative example is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, cold rolling, and solution quenching process parameters are exactly the same as in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet after alloy homogenization. The main difference is that the post-pre-deformation rolling reduction is 0%, i.e., the post-pre-deformation process is omitted. The detailed process flow and parameters are as follows:

[0131] The composite pretreatment process in this comparative example specifically includes the following steps:

[0132] (1) Pre-deformation

[0133] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 2%.

[0134] (2) Intermediate pre-aging

[0135] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0136] (3) Post-deformation

[0137] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 0%.

[0138] (4) Store at room temperature

[0139] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0140] (5) Final Validity Period

[0141] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0142] The change in hardness in the T4 state during the natural aging process of the alloy was tested. The hardness of the alloy in the T4 state after solution pretreatment was 75.7 HV, and the hardness in the T4 state after 14 days of natural aging was 77.1 HV. After short-time artificial aging with paint baking, the hardness of the alloy was 98.5 HV, and the hardening increment ΔH after paint baking was 21.4 HV. The corresponding tensile strength in the T4 state after 14 days of natural aging was 203.7 MPa, and the tensile strength after paint baking increased to 258.2 MPa, an increase of 54.5 MPa. Compared with Comparative Example 1, the increase in hardness during natural aging was reduced, but the paint baking performance was not as good as that of this invention, mainly reflected in the fact that the hardness and tensile strength of the alloy after paint baking were lower than the corresponding parameters of this invention.

[0143] Comparative Example 3

[0144] The alloy used in this comparative example is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, cold rolling, and solution quenching process parameters are exactly the same as in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet after alloy homogenization. The main difference is that the pre-deformation rolling reduction is 0%, i.e., the pre-deformation process is omitted. The detailed process flow and parameters are as follows:

[0145] The composite pretreatment process in this comparative example specifically includes the following steps:

[0146] (1) Pre-deformation

[0147] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 0%.

[0148] (2) Intermediate pre-aging

[0149] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0150] (3) Post-deformation

[0151] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 2%.

[0152] (4) Store at room temperature

[0153] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0154] (5) Final Validity Period

[0155] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0156] The change in hardness in the T4 state during the natural aging process of the alloy was tested. After solution pretreatment, the hardness of the alloy in the T4 state was 80.5 HV. On day 14 of natural aging, the hardness of the T4 state was 83.2 HV. After short-time artificial aging with paint baking, the hardness of the alloy was 105.3 HV, and the paint baking hardening increment ΔH was 22.1 HV. The corresponding tensile strength in the T4 state on day 14 of natural aging was 234.5 MPa, which increased to 280.1 MPa after paint baking, an increase of 55.5 MPa. Compared with Comparative Example 1, the increase in hardness during natural aging was reduced, but the paint baking performance was inferior to that of this invention, mainly reflected in the fact that the hardness and tensile strength of the alloy after paint baking were lower than the corresponding parameters of this invention.

[0157] Comparative Example 4

[0158] The alloy used in this comparative example is 6111 alloy. The alloy composition, ingot preparation, homogenization annealing, hot rolling, cold rolling, and solution quenching process parameters are exactly the same as in Comparative Example 1. The difference lies in the subsequent heat treatment process for the rolled sheet after alloy homogenization. The main difference is that the pre-deformation and post-deformation rolling reduction is 0%, i.e., the pre-deformation and post-deformation processes are omitted. The detailed process flow and parameters are as follows:

[0159] The composite pretreatment process in this comparative example specifically includes the following steps:

[0160] (1) Pre-deformation

[0161] The alloy sheet after solution quenching is subjected to cold rolling deformation with a reduction of 0%.

[0162] (2) Intermediate pre-aging

[0163] The pre-deformed alloy sheet was placed in a heat-preserving furnace for intermediate pre-aging at a temperature of 160℃ for 10 minutes.

[0164] (3) Post-deformation

[0165] After the intermediate pre-aged alloy is cooled to room temperature after being taken out of the furnace, it is subjected to cold rolling deformation with a reduction of 0%.

[0166] (4) Store at room temperature

[0167] The pre-deformed alloy is left at room temperature for a period of time to allow it to age naturally.

[0168] (5) Final Validity Period

[0169] The alloys that have been left at room temperature for 14 days to 1 month are subjected to final aging, namely short-time baking paint artificial aging, with an aging temperature of 180℃ and an aging time of 30 minutes.

[0170] The change in hardness in the T4 state during the natural aging process of the alloy was tested. After solution pretreatment, the hardness of the alloy in the T4 state was 62.3 HV. After 14 days of natural aging, the hardness of the T4 state was 70.5 HV. After short-time artificial aging with paint baking, the hardness of the alloy was 83.1 HV, with a paint hardening increment ΔH of 12.6 HV. The corresponding tensile strength in the T4 state after 14 days of natural aging was 220.5 MPa, which increased to 251.3 MPa after paint baking, an increase of 30.8 MPa. Compared with this invention, the overall performance of this comparative example after 14 days of natural aging with paint baking is significantly lower in both hardness and tensile strength, mainly because the pre-deformation process was removed. It can be seen that applying pre-deformation has a significant impact on the final strength of the alloy after paint baking.

[0171] The implementation of the present invention is not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite deformation heat treatment method for suppressing natural aging and improving the artificial aging response of aluminum alloys for automobiles, characterized in that: Includes the following steps: 1) The rolled aluminum alloy sheet is placed in a heat preservation device for heat preservation, and then rapidly cooled to obtain a supersaturated solid solution sheet. 2) The supersaturated solid solution plate is cold-rolled to complete the pre-deformation; 3) Insulate the alloy plates that have completed pre-deformation to complete intermediate pre-aging; 4) The alloy sheet that has completed intermediate pre-aging is cold rolled and then pre-deformed. 5) Place the pre-deformed alloy sheet at room temperature and then heat-insulate it to complete the final aging process; The temperature for heat preservation in step 1) is 510~530℃, and the heat preservation time is 20~40min; The total reduction in cold rolling described in step 2) is 2-5%, and it is a single rolling process; In step 3), the temperature for heat preservation is 140℃~170℃, and the heat preservation time is 5~20 minutes; The total reduction in cold rolling described in step 4) is 2-5%, and it is a single rolling process; In step 5), the heat preservation temperature is 170℃~190℃, and the heat preservation time is 20~60min; The time to place the product at room temperature as described in step 5) is 14 days to 1 month; The rapid cooling mentioned in step 1) refers to cooling with room temperature water; specifically, it means placing the insulated board in water for cooling or spraying water mist to cool the board. The rolled aluminum alloy sheet mentioned in step 1) is obtained by hot rolling and cold rolling of the homogenized aluminum alloy sheet; the aluminum alloy is a 6xxx series aluminum alloy; the homogenization treatment is obtained by placing the deformed aluminum alloy casting billet in a heat preservation device for heat preservation and cooling it in the furnace; The heat preservation temperature is 550~580℃ and the time is 7~9h; the hot rolling temperature is 450~480℃ and the total reduction is 48~55%; the cold rolling is carried out after the plate is cooled to room temperature after hot rolling, and the total reduction is 48~55%.

2. The composite deformation heat treatment method for suppressing natural aging and improving artificial aging response of automotive aluminum alloys according to claim 1, characterized in that: The hot rolling and cold rolling are each multi-pass rolling processes, with a reduction of 5-15% per pass; the number of rolling passes is 10-25; when the reduction per pass is controlled at 10%, the number of rolling passes is 13-17.

3. An aluminum alloy obtained by the method according to any one of claims 1 to 2.

4. The application of the aluminum alloy according to claim 3, characterized in that: The aluminum alloy is used in automobiles.

5. The application of the aluminum alloy according to claim 4, characterized in that: The aluminum alloy is used to manufacture the battery casing for electric vehicles.

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