Preparation method of lightweight aluminum alloy for automobile

Abstract

The application belongs to the technical field of aluminum alloy, and particularly relates to a lightweight aluminum alloy for automobiles, which comprises the following components in percentage by mass: Si: 0.5-1.2%, Fe: <=0.15%, Cu: 0.6-1.2%, Mn: 0.4-0.8%, Mg: 0.8-1.5%, Cr: 0.05-0.25%, Zn: <=0.25%, Ti: 0.01-0.10%, Sr: 0.01-0.03%, and the balance of Al; wherein Cu:Mg=0.6-1.1:1, and the total content of Mn and Cr:Fe >=5.0:1. By means of moderate Cu and Mg content, and strict control of the content range of Si, good casting and extrusion performance is ensured, and sufficient strengthening phase forming elements are provided for subsequent heat treatment. The addition of Mn and Cr forms the dispersed Mn / Cr-containing dispersed phase, effectively inhibits recrystallization and grain growth, refines the grains, and improves the toughness.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy technology, specifically a method for preparing lightweight aluminum alloys for automobiles. Background Technology

[0002] With the global energy crisis and environmental pollution becoming increasingly severe, lightweighting of automobiles has become one of the main directions of development in the world's automotive industry. Aluminum alloys, due to their advantages such as low density, high specific strength, good corrosion resistance, and easy recyclability, are key materials for achieving lightweighting in automobiles.

[0003] Currently, the 6000 series (Al-Mg-Si) aluminum alloys widely used in automobiles have good comprehensive performance, but their strength, especially yield strength, is often difficult to meet the requirements of some key safety structural components (such as A / B pillars, door sill beams, etc.). While the 7000 series (Al-Zn-Mg-Cu) aluminum alloys have extremely high strength, their formability and stress corrosion resistance are poor, and their extrusion and stamping process windows are narrow, resulting in high production costs, which limits their large-scale application in complex vehicle body structures.

[0004] High-strength and high-toughness aluminum alloys can have their strength increased by adding elements such as Cu, Mg, and Zn. However, these alloys have relatively low elongation and are prone to cracking during complex stamping processes. Some aluminum alloys used in automobiles focus on improving their bake hardening properties, but their initial yield strength is insufficient, making them prone to deformation during assembly. Summary of the Invention

[0005] The purpose of this invention is to provide a lightweight aluminum alloy for automobiles, which has high yield strength while possessing excellent formability and corrosion resistance.

[0006] Another objective of this invention is to provide a method for preparing lightweight aluminum alloys for automobiles, which, through homogenization treatment, makes the distribution of each component more uniform; rapid cooling can effectively suppress the re-precipitation of coarse second phases during the cooling process; and through solid solution treatment, the content of solid solution strengthening elements can be maximized, thereby enhancing the potential for subsequent age hardening.

[0007] The technical problem solved by this invention is achieved by the following technical solution.

[0008] On one hand, embodiments of the present invention provide a lightweight aluminum alloy for automobiles, the chemical composition of which, by mass percentage, includes: Si: 0.5-1.2%, Fe: ≤0.15%, Cu: 0.6-1.2%, Mn: 0.4-0.8%, Mg: 0.8-1.5%, Cr: 0.05-0.25%, Zn: ≤0.25%, Ti: 0.01-0.10%, Sr: 0.01-0.03%, with the balance being Al; wherein, Cu:Mg = 0.6-1.1:1, and the total content of Mn and Cr is Fe ≥ 5.0:1.

[0009] In some embodiments of the present invention, its chemical composition, by mass percentage, includes: Si: 0.5%, Fe: 0.10%, Cu: 0.8%, Mn: 0.8%, Mg: 1.5%, Cr: 0.25%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0010] In some embodiments of the present invention, its chemical composition, by mass percentage, includes: Si: 0.5%, Fe: 0.08%, Cu: 0.6%, Mn: 0.4%, Mg: 0.6%, Cr: 0.05%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0011] The alloy material provided in this invention controls the Cu:Mg ratio to be (0.6-1.1):1 by mass percentage, thereby controlling the precipitation kinetics and proportion of the main strengthening phases S(Al2CuMg) and β(MgSi), avoiding the decrease in plasticity and the aggravation of intergranular corrosion caused by Cu / Mg imbalance; and controls the total content of Mn and Cr to be Fe ≥ 5.0:1 by mass percentage, fixing the Fe element with sufficient Mn and Cr elements to form a stable Al(FeMnCr)Si dispersed phase, thereby neutralizing the adverse effects of Fe element (a common impurity) on plasticity and fatigue performance, and transforming the impurity element into a beneficial dispersed strengthening phase.

[0012] Introducing Sr element: Adding trace amounts of Sr (0.01-0.03%) is used to change the morphology of eutectic Si, transforming it from coarse needle-like structures to fine fibrous structures, which significantly improves the toughness and fatigue performance of the alloy.

[0013] In some embodiments of the present invention, Zr: 0.05-0.15% and / or V: 0.01-0.10% are also included. Zr and V are added simultaneously, and the weight ratio of Zr to V, Zr / V, is controlled to be 1.5-4.0.

[0014] This ratio promotes the formation of coherent (Al,Zr,V) composite nanoparticles, which can more effectively pin dislocations and subgrain boundaries compared to single Zr or V additives, resulting in higher stability at high temperatures and thus significantly improving the alloy's creep resistance and over-aging resistance.

[0015] On the other hand, embodiments of the present invention provide a method for preparing a lightweight aluminum alloy for automobiles, comprising the following steps: S1. Smelting and casting: The elemental or alloy raw materials of each element are smelted at 730-750℃ according to the proportion, and then Al-Sr master alloy is added. After thorough stirring, the mixture is refined, degassed, and slag removed, and then cast into aluminum alloy ingots. S2. Homogenization treatment: The aluminum alloy ingot obtained in S1 is held at 480-570℃ for 6-16h and then cooled to room temperature at a rate of 100-150℃ / min. S3. Hot working: The homogenized ingot is heated to 490-510℃ and hot rolled or hot extruded to obtain the profile. S4. Solution treatment: Heat the profile to 530-560℃, hold for 10-60 minutes, and then quench in water. S5. Aging treatment: The quenched profile is placed in an aging furnace at 90-150℃ and subjected to a two-stage aging treatment as the furnace temperature rises, thus obtaining the lightweight aluminum alloy.

[0016] In some embodiments of the present invention, in step S2, the aluminum alloy ingot is first heated to 480-500°C at a rate of 40-50°C / h and held for 2-4 hours, then heated to 555-570°C and held for 8-16 hours.

[0017] The combination of stepped heating homogenization and rapid cooling, compared to traditional single-stage high-temperature homogenization which easily leads to grain coarsening and excessive spheroidization of low-melting-point eutectic phases, employs a stepped process of first holding at medium temperature (480-500℃) to dissolve some unstable phases, and then holding at high temperature (555-565℃) to fully re-dissolve the strengthening phases, resulting in more thorough compositional homogenization. The subsequent rapid cooling (≥150℃ / min) effectively suppresses the re-precipitation of coarse second phases during the cooling process, laying a better foundation for obtaining a supersaturated solid solution in subsequent solid solution treatment.

[0018] In some embodiments of the present invention, in step S4, the profile is first placed in a first solution furnace and heated to 535-545°C for 15-25 minutes, and then transferred to a second solution furnace at 550-560°C for 5-15 minutes, with a transfer time of less than 10 seconds.

[0019] Two-stage solution treatment: A two-stage solution treatment is adopted, from lower temperature to higher temperature. The first stage (535-545℃) allows the Mg2Si, Al2CuMg and other phases to dissolve smoothly and avoid overheating; the second stage (550-560℃) involves a short-term high-temperature holding period, which can dissolve the Cu-enriched phase and the Al(FeMnCr)Si phase, thereby maximizing the content of solid solution strengthening elements and improving the potential for subsequent aging strengthening.

[0020] In step S5, a two-stage aging treatment is performed to replace the traditional single-stage isothermal aging. The quenched profile is immediately placed in an aging furnace at 80-90℃, and the furnace temperature is increased to perform a two-stage aging treatment: the first stage is held at 90-110℃ for 30-60 minutes; the second stage is held at 130-150℃ for 20-40 minutes; after treatment, it is air-cooled to room temperature. This process enables the GP zone (Guinier-Preston zone) to continuously and uniformly form and transform into the β phase at different temperatures, resulting in a finer and more uniform precipitate distribution. This significantly improves the alloy's plasticity, stress corrosion resistance, and paint hardening response while ensuring strength.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The aluminum alloy provided by this invention, through the combination of moderate Cu and Mg content and strict control of Si content range, provides sufficient strengthening phase forming elements for subsequent heat treatment while ensuring good casting and extrusion performance; the addition of Mn and Cr forms a dispersed Mn / Cr-containing dispersed phase, which effectively inhibits recrystallization and grain growth, refines grains, and improves toughness.

[0022] Through Sr modification, Fe element control and optimized heat treatment, the fatigue life of the alloy is significantly extended, and its resistance to intergranular corrosion and stress corrosion cracking is enhanced, making it suitable for automotive structural components with extremely high requirements for safety and durability.

[0023] The preparation method provided by the present invention, through pre-aging, enables the profile to have low yield strength (≤150MPa) and high elongation (≥25%), which is beneficial for cold stamping of complex shaped parts. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0026] On one hand, embodiments of the present invention provide a lightweight aluminum alloy for automobiles, the chemical composition of which, by mass percentage, includes: Si: 0.5-1.2%, Fe: ≤0.15%, Cu: 0.6-1.2%, Mn: 0.4-0.8%, Mg: 0.8-1.5%, Cr: 0.05-0.25%, Zn: ≤0.25%, Ti: 0.01-0.10%, Sr: 0.01-0.03%, with the balance being Al; wherein, Cu:Mg = 0.6-1.1:1, and the total content of Mn and Cr is Fe ≥ 5.0:1.

[0027] In some embodiments of the present invention, its chemical composition, by mass percentage, includes: Si: 0.5%, Fe: 0.10%, Cu: 0.8%, Mn: 0.8%, Mg: 1.5%, Cr: 0.25%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0028] In some embodiments of the present invention, its chemical composition, by mass percentage, includes: Si: 0.5%, Fe: 0.08%, Cu: 0.6%, Mn: 0.4%, Mg: 0.6%, Cr: 0.05%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0029] In some embodiments of the present invention, Zr: 0.05-0.15% and / or V: 0.01-0.10% are also included. When Zr and V are added simultaneously, the weight ratio of Zr to V, Zr / V, is controlled to be 1.5-4.0.

[0030] On the other hand, embodiments of the present invention provide a method for preparing a lightweight aluminum alloy for automobiles, comprising the following steps: S1. Melting and casting: Melt the raw materials at 730-750℃ according to the proportion. Use electromagnetic stirring or mechanical stirring to make the composition uniform. Then add Al-Sr master alloy. Then pass high-purity argon gas to perform rotary degassing treatment to reduce the hydrogen content of the melt to below 0.15ml / 100g Al. Then add refining agent to remove slag. After standing, cast into aluminum alloy ingots. S2. Homogenization treatment: The aluminum alloy ingot obtained in S1 is placed in a homogenization furnace and subjected to a two-stage step homogenization treatment: the aluminum alloy ingot is first heated to 480-500℃ at a rate of 40-50℃ / h and held for 2-4h, then heated to 555-570℃ and held for 8-16h; after treatment, it is cooled to room temperature in the furnace at a rate of 100-150℃ / min. Compared to single-stage homogenization, it can more thoroughly dissolve the soluble phase and promote a finer and more uniformly distributed dispersed phase. These dispersed phases can strongly pin grain boundaries and dislocations, effectively suppressing recrystallization and grain growth during subsequent hot working and solid solution processes, ultimately resulting in finer recrystallized grains and significantly improving the toughness and fatigue resistance of the material.

[0031] S3. Hot working: The homogenized ingot is heated to 490-510℃ and held for 2-4 hours. Then it is hot rolled or hot extruded. The final rolling temperature of hot rolling is not lower than 350℃ and the exit temperature of hot extrusion is not lower than 480℃. After processing, forced air cooling or water mist cooling is used to reduce the material temperature to below 100℃ within 3 minutes. Rapid cooling avoids the precipitation of coarse equilibrium phases at high temperatures, provides a more ideal initial structure for subsequent solution treatment, and ensures the effect of solution treatment.

[0032] S4. Online Solution Treatment and Quenching: The hot-worked material is immediately passed through the online solution treatment and quenching production line. The profile is first placed in the first solution furnace and heated to 535-545℃, held for 15-25 minutes, and then transferred to the second solution furnace at 550-560℃, held for 5-15 minutes, with a transfer time of less than 10 seconds. Then, high-pressure water mist quenching is performed with a quenching cooling rate ≥200℃ / s, so that the material temperature drops to below 80℃ within 5 seconds. S5. Aging treatment: The quenched profile is immediately placed into an aging furnace at 90-150℃ and heated with the furnace to carry out a two-stage aging treatment: the first stage is held at 90-110℃ for 30-60 minutes; the second stage is held at 130-150℃ for 20-40 minutes; after treatment, it is air-cooled to room temperature to obtain a lightweight aluminum alloy in the T4P state.

[0033] This invention employs a two-stage aging process: the first stage (low temperature) forms a high-density GP zone nucleus; the second stage (higher temperature) allows the nucleus to grow moderately and partially transform into a more stable β phase. This structure effectively resists natural aging, ensuring the T4P state properties remain stable for at least 3 months, greatly improving the convenience of material storage and use. Simultaneously, the precipitated phase embryo transforms into a strengthening phase more quickly and uniformly during baking, not only increasing the bake hardening value but also significantly improving the consistency (stability) of the final properties. This meets the stringent requirements of the automotive industry for batch consistency. Compared to traditional single-stage aging, which struggles to completely lock vacancies and solute atoms, resulting in changes in material properties during room temperature storage (natural aging), this approach offers a significant advantage.

[0034] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0035] Example 1 Prepare the raw materials according to the following proportions: Si: 0.5%, Fe: 0.10%, Cu: 0.8%, Mn: 0.8%, Mg: 1.5%, Cr: 0.25%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0036] Aluminum alloys are prepared using the following method: S1. Melting and casting: Melt the raw materials at 750℃ according to the formula, use electromagnetic stirring or mechanical stirring to make the composition uniform, then add Al-Sr master alloy and stir; then pass high-purity argon gas to perform rotary degassing treatment to reduce the hydrogen content of the melt to below 0.15ml / 100g Al; then add refining agent to remove slag, let stand and then cast into aluminum alloy ingots. S2. Homogenization treatment: The aluminum alloy ingot obtained in S1 is placed in a homogenization furnace and subjected to a two-stage step homogenization treatment: the aluminum alloy ingot is first heated to 500℃ at 50℃ / h and held for 4h; then heated to 555℃ and held for 8h; after treatment, it is cooled to room temperature in the furnace at a rate of 150℃ / min. S3. Hot processing: The homogenized ingot is heated to 510℃ and held for 4 hours. Then it is hot rolled or hot extruded. The final rolling temperature of hot rolling is not lower than 350℃ and the exit temperature of hot extrusion is not lower than 480℃. After processing, forced air cooling or water mist cooling is used to reduce the material temperature to below 100℃ within 3 minutes.

[0037] S4. Online Solution Treatment and Quenching: The hot-worked material is immediately passed through the online solution treatment and quenching production line. The profile is first placed in the first solution furnace and heated to 535℃, held for 25 minutes, and then transferred to the second solution furnace at 560℃ and held for 10 minutes. The transfer time is less than 10 seconds. Then, high-pressure water mist quenching is performed with a quenching cooling rate ≥200℃ / s, so that the material temperature drops to below 80℃ within 5 seconds. S5. Aging treatment: The quenched material is sent into an aging furnace within 2 hours for two-stage aging treatment: the first stage is held at 110℃ for 60 minutes; the second stage is held at 130℃ for 40 minutes; after treatment, it is air-cooled to room temperature to obtain a lightweight aluminum alloy in the T4P state.

[0038] Example 2 Prepare the raw materials according to the following proportions: Si: 0.5%, Fe: 0.08%, Cu: 0.6%, Mn: 0.4%, Mg: 0.6%, Cr: 0.05%, Zn: 0.25%, Ti: 0.10%, with the balance being Al.

[0039] Aluminum alloys are prepared using the following method: S1. Melting and casting: Melt the raw materials at 730℃ according to the formula, use electromagnetic stirring or mechanical stirring to make the composition uniform, then add Al-Sr master alloy and stir; then pass high-purity argon gas to perform rotary degassing treatment to reduce the hydrogen content of the melt to below 0.15ml / 100g Al; then add refining agent to remove slag, let stand and then cast into aluminum alloy ingots. S2. Homogenization treatment: The aluminum alloy ingot obtained in S1 is placed in a homogenization furnace and subjected to a two-stage step homogenization treatment: the aluminum alloy ingot is first heated to 480℃ at 40℃ / h and held for 4h; then heated to 570℃ and held for 10h; after treatment, it is cooled to room temperature in the furnace at a rate of 100℃ / min. S3. Hot processing: The homogenized ingot is heated to 490℃ and held for 4 hours. Then it is hot rolled or hot extruded. The final rolling temperature of hot rolling is not lower than 350℃ and the exit temperature of hot extrusion is not lower than 480℃. After processing, forced air cooling or water mist cooling is used to reduce the material temperature to below 100℃ within 3 minutes.

[0040] S4. Online Solution Treatment and Quenching: The hot-worked material is immediately passed through the online solution treatment and quenching production line. The profile is first placed in the first solution furnace and heated to 545℃, held for 15 minutes, and then transferred to the second solution furnace at 550℃ and held for 15 minutes. The transfer time is less than 10 seconds. Then, high-pressure water mist quenching is performed with a quenching cooling rate ≥200℃ / s, so that the material temperature drops to below 80℃ within 5 seconds. S5. Aging treatment: The quenched material is sent into an aging furnace within 2 hours for two-stage aging treatment: the first stage is held at 90℃ for 60 minutes; the second stage is held at 150℃ for 20-40 minutes; after treatment, it is air-cooled to room temperature to obtain a lightweight aluminum alloy in the T4P state.

[0041] Comparative Example The same solution treatment (T4 state) was performed using commercial AA6061 aluminum alloy.

[0042] The performance of the aluminum alloys prepared in Examples 1 and 2 and the comparative example was tested.

[0043] Tensile property test Standard tensile specimens are processed from treated aluminum alloy sheets or profiles along the rolling or extrusion direction, in accordance with the national standard GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature".

[0044] Testing equipment: Universal testing machine. The test is conducted at room temperature (typically 23±5℃) with a constant beam displacement rate set until the specimen breaks.

[0045] The measured parameters are: yield strength (Rp0.2, i.e., the stress when the specified plastic elongation is 0.2%), tensile strength (Rm), and elongation after fracture (A).

[0046] Baking hardening performance test Pretreatment (T4P / T4 state): First, test the initial mechanical properties of the material under pre-aging or T4 state.

[0047] Simulated baking: The tensile specimens were subjected to heat treatment simulating the baking process of automotive painting. They were kept at a constant temperature of 170°C for 30 minutes, and then air-cooled to room temperature.

[0048] Final test: The tensile properties of the samples after the simulated baking treatment were tested again using the same method as above.

[0049] Baking hardening value calculation Baking hardening value (MPa) = Yield strength after baking (MPa) - Yield strength before baking (MPa).

[0050] The results are shown in the table below:

[0051] Among them, the baking state refers to the aluminum alloy being held at 200℃ for 30 minutes before testing.

[0052] In summary, the aluminum alloy of this invention, through the combination of moderate Cu and Mg content and strict control of the Si content range, provides sufficient strengthening phase forming elements for subsequent heat treatment while ensuring good casting and extrusion performance; the addition of Mn and Cr forms a dispersed Mn / Cr-containing dispersed phase, which effectively inhibits recrystallization and grain growth, refines the grains, and improves toughness.

[0053] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a lightweight aluminum alloy for automobiles, characterized in that, The chemical composition of lightweight aluminum alloys for automobiles, expressed as a percentage by mass, includes: Si: 0.5-1.2%, Fe: ≤0.15%, Cu: 0.6-1.2%, Mn: 0.4-0.8%, Mg: 0.8-1.5%, Cr: 0.05-0.25%, Zn: ≤0.25%, Ti: 0.01-0.10%, Sr: 0.01-0.03%, Zr: 0.05-0.15% and / or V: 0.01-0.10%, with the balance being Al; wherein, Cu:Mg = 0.6-1.1:1, and the total content of Mn and Cr is Fe ≥ 5.0:1; Includes the following steps: S1. Smelting and casting: The elemental or alloy raw materials of each element are smelted at 730-750℃ according to the proportion, and then Al-Sr master alloy is added. After thorough stirring, the mixture is refined, degassed, and slag removed, and then cast into aluminum alloy ingots. S2. Homogenization treatment: The aluminum alloy ingot obtained in S1 is held at 480-570℃ for 6-16h and then cooled to room temperature at a rate of 100-150℃ / min. S3. Hot working: The homogenized ingot is heated to 490-510℃ and hot rolled or hot extruded to obtain the profile. S4. Solution treatment: Heat the profile to 530-560℃, hold for 10-60 minutes, and then quench in water. S5. Aging treatment: The quenched profile is placed in an aging furnace at 90-150℃ and subjected to a two-stage aging treatment as the furnace temperature rises, thus obtaining the lightweight aluminum alloy. The two-stage aging treatment includes: the first stage is held at 90-110℃ for 30-60 minutes; the second stage is held at 130-150℃ for 20-40 minutes; and then air-cooled to room temperature.

2. The method for preparing lightweight aluminum alloy for automobiles according to claim 1, characterized in that, The chemical composition of lightweight aluminum alloys for automobiles, expressed as a percentage by mass, includes: Si: 0.5%, Fe: 0.10%, Cu: 0.8%, Mn: 0.8%, Mg: 1.5%, Cr: 0.25%, Zn: 0.25%, Ti: 0.10%, Zr: 0.05-0.15% and / or V: 0.01-0.10%, with the balance being Al.

3. The method for preparing lightweight aluminum alloy for automobiles according to claim 1, characterized in that, The chemical composition of lightweight aluminum alloys for automobiles, expressed as a percentage by mass, includes: Si: 0.5%, Fe: 0.08%, Cu: 0.6%, Mn: 0.4%, Mg: 0.6%, Cr: 0.05%, Zn: 0.25%, Ti: 0.10%, Zr: 0.05-0.15% and / or V: 0.01-0.10%, with the balance being Al.

4. The method for preparing lightweight aluminum alloy for automobiles according to claim 1, characterized in that, In step S2, the aluminum alloy ingot is first heated to 480-500℃ at a rate of 40-50℃ / h and held for 2-4 hours, then heated to 555-570℃ and held for 8-10 hours.

5. The method for preparing lightweight aluminum alloy for automobiles according to claim 1, characterized in that, In step S4, the profile is first placed in the first solution furnace and heated to 535-545℃ for 15-25 minutes. Then it is transferred to the second solution furnace at 550-560℃ and held for 5-15 minutes. The transfer time is less than 10 seconds.

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