High-formability 6-series aluminum alloy pedestrian protection automobile sheet and preparation method thereof

Abstract

The invention provides a high-formability 6-series aluminum alloy pedestrian protection automobile sheet and a preparation method thereof, and belongs to the technical field of aluminum alloy preparation. The 6-series aluminum alloy pedestrian protection automobile sheet comprises the following components in percentage by mass: 0.40-0.75% of Si, 0.20-0.30% of Fe, 0.10-0.20% of Mn, 0.25-0.50% of Mg, less than or equal to 0.1% of Cu, less than or equal to 0.05% of Cr, less than or equal to 0.05% of Zn, less than or equal to 0.03% of Ti, less than or equal to 0.15% of other impurities and the balance of Al, preferably, 0.55-0.65% of Si, 0.20-0.30% of Fe, 0.15-0.20% of Mn, 0.30-0.40% of Mg, less than or equal to 0.1% of Cu, less than or equal to 0.05% of Cr, less than or equal to 0.05% of Zn, less than or equal to 0.03% of Ti, less than or equal to 0.15% of other impurities and the By controlling the element content of the alloy and optimizing the hot rolling coiling temperature, the cold rolling machining rate and the solid solution and pre-aging treatment process parameters, the 6-series aluminum alloy pedestrian protection automobile sheet with low yield strength, high elongation, high formability and low anisotropy can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloys, and in particular to a high-formability 6-series aluminum alloy pedestrian protection automobile plate and a preparation method thereof. Background Art

[0002] With the rapid development of the automobile industry, vehicle safety performance has become one of the important considerations for consumers when buying a car. Among them, pedestrian protection, as an important part of vehicle safety performance, has attracted more and more attention. In traditional automobile manufacturing, steel is mainly used as the body material. However, the high density of steel is not conducive to the lightweight of the car, and its performance in absorbing the impact energy generated during the collision needs to be improved. As a lightweight and high-specific-strength metal material, 6-series aluminum alloy has been used in the automobile manufacturing industry. It has excellent energy absorption and processing properties, and can meet the needs of lightweight and safety of automobiles. By applying 6-series aluminum alloy to the manufacture of automobile coverings, the weight of the car body can be effectively reduced, fuel economy can be improved, and pedestrians can be better protected in the event of a collision.

[0003] However, in order to meet the aesthetic design of automobile exterior, aerodynamic performance and optimization of interior space, automobile plates often have complex curves, surfaces and angles, and even contain many tiny bumps and holes. This requires that the 6 series aluminum alloy be used in the manufacture of automobile plates, which not only requires the aluminum alloy plates to have excellent mechanical properties, but also requires high formability. At the same time, due to the differences in the mechanical properties of aluminum alloy sheets in different orientation directions, that is, the performance of aluminum alloy sheets along the rolling direction, perpendicular to the rolling direction and any angle between the two is different in all directions, which makes the use of aluminum alloy sheets limited to the direction with the worst performance. Therefore, it is also necessary to reduce its anisotropy while ensuring mechanical properties and high formability. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a high-formability 6-series aluminum alloy for pedestrian protection automobile plates and a preparation method thereof. By controlling the element content of the alloy and optimizing the hot rolling coiling temperature, cold rolling processing rate, solid solution and pre-aging treatment process parameters, the low yield strength of the 6-series aluminum alloy automobile plate is achieved, and it is ensured that it has high elongation and low anisotropy, so that the plate can be used for the inner panel of the automobile engine hood with higher formability requirements.

[0005] The technical solution of the present invention is as follows:

[0006] The invention provides a high-formability 6-series aluminum alloy pedestrian protection automobile plate, which comprises the following components in mass percentage: Si 0.40-0.75%, Fe 0.20-0.30%, Mn 0.10-0.20%, Mg 0.25-0.50%, Cu≤0.1%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurity content≤0.15%, and Al as the balance.

[0007] Furthermore, it includes the following components in mass percentage: Si 0.55-0.65%, Fe 0.20-0.30%, Mn0.15-0.20%, Mg 0.30-0.40%, Cu≤0.1%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurities content ≤0.15%, and Al as the balance.

[0008] In the above technical scheme, the present invention mainly adjusts the content of Mg and Si elements. The Mg2Si phase formed by the combination of Mg and Si elements is the main strengthening phase in the alloy. In order to obtain ideal mechanical properties and formability, it is necessary to adjust the mass ratio of Mg and Si. At the same time, the content of Mg and Si elements will also affect the orientation of the 6-series aluminum alloy texture. During the deformation and heat treatment of the aluminum alloy, the presence of Mg and Si elements will promote or inhibit the growth of certain oriented grains, resulting in changes in the texture orientation, thereby affecting the anisotropy of the 6-series aluminum alloy automotive sheet. In this application, Si is limited to 0.40-0.75%, Mg is 0.25-0.50%, preferably Si is 0.55-0.65%, Mg is 0.30-0.40%, which can ensure mechanical properties while also making it have high formability and low anisotropy.

[0009] Furthermore, the mechanical properties of the automobile sheet at room temperature are: along the vertical rolling direction, its Rp 0.2 ≤90Mpa, A 80mm ≥24%, A g ≥20%、Rp 0.2 / R m ≤0.50, n 4-6 ≥0.30, r 2-20 ≥0.68, Δr=(r 0° +r 90° -2r 45° ) / 2≤0.20; the mechanical properties after baking varnish treatment are: R m ≥160Mpa、110MPa≤Rp 0.2 ≤150Mpa, A 80mm ≥16%.

[0010] The present invention also provides a method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate, comprising the following steps:

[0011] According to the alloy composition and proportion, the ingot is obtained by melting and casting → homogenization treatment → hot rolling and coiling → cooling → cold rolling and coiling → solution treatment → pre-aging treatment → room temperature placement → mechanical properties test to see if it meets the requirements.

[0012] Furthermore, in the homogenization process, the homogenization temperature is 530-560° C., and the insulation time is 5-12 hours.

[0013] Furthermore, in the hot rolling process, the hot rolling start temperature is 530-560° C., 1+5 rolling is adopted, the hot rolling coiling temperature is 300-360° C., and the coil thickness after hot rolling is 4.5-7.0 mm.

[0014] In the above technical scheme, the hot rolling coiling temperature has an important influence on the comprehensive properties of the 6 series aluminum alloy. A higher hot rolling coiling temperature will promote the grain growth in the aluminum alloy, which usually leads to a decrease in the yield strength of the material, because the grain growth reduces the grain boundary area, thereby reducing the grain boundary's hindering effect on dislocation movement; however, an appropriate coiling temperature can also promote the occurrence of dynamic recrystallization, which can refine the grains and improve the plasticity and toughness of the material; in addition, the coiling temperature will also affect the formation and distribution of the precipitated phase in the aluminum alloy. At an appropriate coiling temperature, the precipitated phase can be uniformly precipitated and refined, reducing the directional arrangement of the precipitated phase along the rolling direction, thereby facilitating molding. In the present invention, first, the Mg2Si phase will precipitate and grow during the hot rolling process at 530-560°C, and then the hot rolling coiling is carried out at a temperature of 300-360°C, which will increase the size of the precipitated phase, thereby promoting the particle stimulated nucleation effect (PSN effect) during the solid solution heat treatment process of the subsequent process, so that the automotive sheet has more random textures and reduces the anisotropy of the automotive sheet.

[0015] Furthermore, in the cold rolling process, the cold rolling processing rate is 80-85%, and the thickness of the coil after cold rolling is 0.8-1.1 mm.

[0016] Furthermore, in the solution treatment process, the solution treatment temperature is 530-560° C., the solution treatment time is 25-47 s, and after the solution treatment, the quenching method of the coil is water quenching or air quenching.

[0017] Furthermore, in the pre-aging treatment step, the pre-aging temperature is 70-100°C.

[0018] Furthermore, in the pre-aging treatment, the room temperature is ≤40°C, and the room temperature time is ≤7 days ≤180 days.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The present invention proposes a high-formability 6-series aluminum alloy pedestrian protection automobile plate, which is obtained by adjusting the alloy element content and optimizing the hot rolling coiling temperature, cold rolling processing rate, solid solution and pre-aging treatment process parameters to obtain an aluminum alloy plate with low anisotropy, low yield strength, high elongation and high formability;

[0021] (2) The mechanical properties of the pedestrian protection automobile plate prepared by the present invention at room temperature are: along the vertical rolling direction (90° direction), its Rp 0.2 ≤90Mpa, A 80mm ≥24%, A g ≥20%、Rp 0.2 / R m ≤0.50, n 4-6 ≥0.30, r 2-20 ≥0.68, Δr=(r 0° +r 90° -2r 45° ) / 2≤0.20; the mechanical properties after baking varnish treatment are: R m ≥160Mpa、110MPa≤Rp 0.2 ≤150Mpa, A 80mm ≥16%, which has low yield strength, high elongation, high formability and low anisotropy;

[0022] (3) The forming limit (FLC) of the aluminum plate for pedestrian protection vehicles prepared by the present invention can reach the minimum value of the forming limit principal strain ε1 of 80mm, 100mm, 110mm and 120mm in the FLC preparation samples along the 0° direction and the 90° direction under the corresponding thickness requirements, and in the process of transition between uniaxial and biaxial stretching, the minimum value of the forming limit principal strain ε1 is ≥0.170. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 is a process flow chart of the present invention;

[0025] Figure 2 is the forming limit (FLC) diagram of Example 1 of the present invention;

[0026] Figure 3 is the forming limit (FLC) diagram of Example 2 of the present invention;

[0027] Figure 4 is the forming limit (FLC) diagram of Example 3 of the present invention;

[0028] Figure 5 This is the forming limit (FLC) diagram of comparative example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment 1 provides a high-formability 6-series aluminum alloy pedestrian protection automobile plate, which includes the following components in mass percentage: Si 0.64%, Fe 0.25%, Mn 0.15%, Mg 0.36%, Cu 0.1%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurity content ≤0.15%, and Al as the balance.

[0032] Reference Figure 1 The specific preparation process of the high-formability 6-series aluminum alloy pedestrian protection automobile sheet coil of this embodiment is as follows:

[0033] (1) Melting and casting: After mixing the ingredients according to the mass percentage of each element, semi-continuous casting is performed to obtain a high-formability 6 series aluminum alloy pedestrian protection automobile plate ingot;

[0034] (2) Homogenization treatment: The aluminum alloy ingot is subjected to homogenization treatment at 530°C for 5 hours;

[0035] (3) Hot rolling: the ingot after homogenization treatment is directly hot rolled and coiled to obtain hot rolled coils, the hot rolling start temperature is 530°C, the hot rolling coiling temperature is 350°C, and the hot rolling coiling thickness is 5.0 mm;

[0036] (4) Cold rolling: After the hot rolled coil is cooled to room temperature, it is cold rolled and coiled to obtain a cold rolled automotive sheet coil. The cold rolled coiling thickness is 0.95 mm and the cold rolling processing rate is 81%;

[0037] (5) Solution treatment: The cold-rolled automotive sheet coil is subjected to solution treatment at 550°C for 30 seconds. After the solution treatment, the coil is cooled to room temperature by water quenching.

[0038] (6) Pre-aging treatment: The coil after solution quenching is subjected to pre-aging treatment at a temperature of 75°C;

[0039] (7) Room temperature placement: The pre-aged coil is placed at room temperature for 30 days and then tested for room temperature mechanical properties, bake hardening mechanical properties (baking system: 185±2℃ / 20min) and FLC properties.

[0040] Example 2

[0041] This embodiment 2 provides a high-formability 6-series aluminum alloy pedestrian protection automobile plate, which includes the following components in mass percentage: Si 0.65%, Fe 0.25%, Mn 0.17%, Mg 0.35%, Cu 0.08%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurity content ≤0.15%, and Al as the balance.

[0042] The specific preparation process of the high-formability 6-series aluminum alloy pedestrian protection automobile sheet coil of this embodiment is as follows:

[0043] (1) Melting and casting: After mixing the ingredients according to the mass percentage of each element, semi-continuous casting is performed to obtain a high-formability 6 series aluminum alloy pedestrian protection automobile plate ingot;

[0044] (2) Homogenization treatment: The aluminum alloy ingot is subjected to homogenization treatment at 530°C for 5 hours;

[0045] (3) Hot rolling: the ingot after homogenization treatment is directly hot rolled and coiled to obtain a hot rolled coil. The hot rolling start temperature is 530°C, the hot rolling coiling temperature is 350°C, and the difference between Example 1 and Example 2 is water cooling and air cooling after solution treatment. The hot rolling coiling thickness is 5.0 mm.

[0046] (4) Cold rolling: After the hot rolled coil is cooled to room temperature, it is cold rolled and coiled to obtain a cold rolled automotive sheet coil. The cold rolled coiling thickness is 0.95 mm and the cold rolling processing rate is 81%;

[0047] (5) Solution treatment: The cold-rolled automobile sheet coil is subjected to solution treatment at 550°C for 30 seconds. After the solution treatment, the coil is cooled to room temperature by air quenching.

[0048] (6) Pre-aging treatment: The automotive material after solution quenching is subjected to pre-aging treatment at a temperature of 75°C;

[0049] (7) Room temperature placement: The pre-aged coil is placed at room temperature for 30 days and then tested for room temperature mechanical properties, bake hardening mechanical properties (baking system: 185±2℃ / 20min) and FLC properties.

[0050] Example 3

[0051] This embodiment 3 provides a high-formability 6-series aluminum alloy pedestrian protection automobile plate, which includes the following components in mass percentage: Si 0.56%, Fe 0.20%, Mn 0.15%, Mg 0.30%, Cu 0.10%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurity content ≤0.15%, and Al as the balance.

[0052] The specific preparation process of the high-formability 6-series aluminum alloy pedestrian protection automobile sheet coil of this embodiment is as follows:

[0053] (1) Melting and casting: After mixing the ingredients according to the mass percentage of each element, semi-continuous casting is performed to obtain a high-formability 6 series aluminum alloy pedestrian protection automobile plate ingot;

[0054] (2) Homogenization treatment: The aluminum alloy ingot is subjected to homogenization treatment at 530°C for 5 hours;

[0055] (3) Hot rolling: the ingot after homogenization treatment is directly hot rolled and coiled to obtain hot rolled coils, the hot rolling start temperature is 530°C, the hot rolling coiling temperature is 350°C, and the hot rolling coiling thickness is 5.0 mm;

[0056] (4) Cold rolling: After the hot rolled coil is cooled to room temperature, it is cold rolled and coiled to obtain a cold rolled automotive sheet coil. The cold rolled coiling thickness is 0.95 mm and the cold rolling processing rate is 81%;

[0057] (5) Solution treatment: The cold-rolled automotive sheet coil is subjected to solution treatment at 545°C for 30 seconds. After the solution treatment, the coil is cooled to room temperature by air quenching.

[0058] (6) Pre-aging treatment: The automotive material after solution quenching is subjected to pre-aging treatment at a temperature of 85°C;

[0059] (7) Room temperature placement: The pre-aged coil is placed at room temperature for 30 days and then tested for room temperature mechanical properties, bake hardening mechanical properties (baking system: 185±2℃ / 20min) and FLC properties.

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Example 1 is that the weight percentage of Mg element in this comparative example is set to 0.20%.

[0062] Comparative Example 2

[0063] The difference between this comparative example 2 and example 1 is that the hot rolling coiling temperature is set at 290°C in this comparative example.

[0064] The aluminum alloy plates obtained in each embodiment and comparative example were subjected to mechanical property testing. The room temperature mechanical property test method was in accordance with "GB / T 228.1-2021 Metallic Materials Tensile Test Part 1: Room Temperature Test Method", the bake hardening performance test method was in accordance with "GB / T 33227-2016 Automobile Aluminum and Aluminum Alloy Plates and Strips", and the tensile specimen was prepared according to "GB / T 16865-2013 Specimens and Methods for Tensile Test of Deformed Aluminum, Magnesium and Their Alloy Processing Products". The results of the room temperature mechanical property test are shown in Table 1. The statistical results of Δr value are shown in Table 2, and the test results of baking hardening performance are shown in Table 3.

[0065] Table 1 Mechanical properties test results at room temperature

[0066]

[0067] Table 2 Statistical results of Δr value

[0068]

[0069] Table 3 Bake hardening mechanical properties test results

[0070]

[0071] In addition, the FLC performance test was performed on the above-mentioned Examples 1-3 and Comparative Example 1. The forming limit (FLC) test method was in accordance with GB / T 24171.2-2009 Determination of forming curves of metal sheets and strips Part 2: Determination of laboratory forming limit curves. The forming limit (FLC) diagram is shown in the attached figure. Figure 2-5 As shown. Figure 2-5 It can be seen that: in Examples 1-3, under the corresponding thickness requirements, along the 0° direction and the 90° direction, the FLC prepared samples with sizes of 80mm, 100mm, 110mm and 120mm, during the transition process of uniaxial and biaxial stretching, the minimum value of the forming limit principal strain ε1 ≥ 0.170 is required, and Comparative Example 1 does not meet the requirements.

[0072] By comparing the mechanical properties and FLC performance test results of the actual examples and the comparative examples, the embodiments 1-3 of the present invention adjust the chemical composition content of the alloy and optimize the hot rolling, cold rolling, solution and pre-aging processes to obtain a 6 series aluminum alloy sheet with low yield strength, low anisotropy and high formability, and the smaller the Δr value, the lower the anisotropy, and when The larger the value, the smaller the Δr value, the better the formability. The above-mentioned Examples 1-3 have low anisotropy and high formability while ensuring mechanical properties, while Comparative Examples 1 and 2, especially Comparative Example 2, have relatively high anisotropy and relatively low formability. The 6 series aluminum alloy sheet is mainly used for the inner panel of the automobile engine hood, which enables the automobile to better absorb and disperse the impact force during a collision and reduce the degree of injury to pedestrians.

[0073] Although the present invention has been described in detail by reference to the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A high-formability 6-series aluminum alloy pedestrian protection automobile plate, characterized in that: The invention comprises the following components in mass percentage: Si 0.40-0.75%, Fe 0.20-0.30%, Mn 0.10-0.20%, Mg 0.25-0.50%, Cu≤0.1%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurities content ≤0.15%, and Al as the balance.

2. The high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 1, characterized in that: The invention comprises the following components in mass percentage: Si 0.55-0.65%, Fe 0.20-0.30%, Mn 0.15-0.20%, Mg 0.30-0.40%, Cu≤0.1%, Cr≤0.05%, Zn≤0.05%, Ti≤0.03%, other impurities content ≤0.15%, and Al as the balance.

3. A high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 1 or 2, characterized in that: The mechanical properties of the automobile sheet at room temperature are: along the vertical rolling direction, its Rp 0.2 ≤90Mpa, A 80mm ≥24%, A g ≥20%、Rp 0.2 / R m ≤0.50, n 4-6 ≥0.30, r 2-20 ≥0.68, Δr≤0.20; mechanical properties after baking finish: R m ≥160Mpa、110MPa≤Rp 0.2 ≤150Mpa, A 80mm ≥16%.

4. A method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to any one of claims 1 to 3, characterized in that: Including the following processes: According to the alloy composition and proportion, the ingot is obtained by melting and casting → homogenization treatment → hot rolling and coiling → cooling → cold rolling and coiling → solution treatment → pre-aging treatment → room temperature placement → mechanical properties test to see if it meets the requirements.

5. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: In the homogenization process, the homogenization temperature is 530-560° C. and the insulation time is 5-12 hours.

6. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: In the hot rolling process, the hot rolling start temperature is 530-560°C, 1+5 rolling is adopted, the hot rolling coiling temperature is 300-360°C, and the coil thickness after hot rolling is 4.5-7.0 mm.

7. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: In the cold rolling process, the cold rolling processing rate is 80-85%, and the thickness of the coil after cold rolling is 0.8-1.1 mm.

8. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: In the solution treatment process, the solution treatment temperature is 530-560° C., the solution treatment time is 25-47 s, and the cooling method after the solution treatment is water cooling and air cooling.

9. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: In the pre-aging treatment process, the pre-aging temperature is 70 to 100°C.

10. The method for preparing a high-formability 6-series aluminum alloy pedestrian protection automobile plate according to claim 4, characterized in that: During the pre-aging treatment, the room temperature is ≤40°C, and the room temperature placement time is ≤7 days ≤180 days.

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