Al-Zn-Mg-Cu Series High-Strength Aluminum Alloy and Forming Method

Abstract

The present invention provides an Al-Zn-Mg-Cu series high-strength aluminum alloy and a forming method, belonging to the technical field of metal material processing. The Al-Zn-Mg-Cu series high-strength aluminum alloy consists of the following components and mass percentages: 0.38% Si, 0.47% Fe, 1.8% Cu, 0.26% Mn, 2.2% Mg, 5.5% Zn, 0.20% Ti, and the balance is Al. By applying an electric pulse during the forming stage and adopting pre-aging (120°C / 5 min) + air cooling + simulated baking (180°C / 30 min) or peak aging process (120°C / 24 h) during the heat treatment strengthening stage, while ensuring a certain amount of fine and dispersed strengthening phases, the corrosion rate of the alloy is reduced, and thus the problems of poor strength-plasticity matching, low corrosion resistance, and low production efficiency of the formed products of high-strength aluminum alloys are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material processing, and particularly relates to a high-strength Al-Zn-Mg-Cu series aluminum alloy and a forming method thereof. Background Art

[0002] In recent years, 7000 series (Al-Zn-Mg-Cu) aluminum alloys have been widely used in the industrial production of automotive structural parts due to their high strength and low density. However, low production efficiency and poor corrosion resistance are still serious problems, which limit the wider application of the alloys.

[0003] In the prior art, aluminum alloys with good corrosion resistance have large precipitate phase sizes, resulting in low strength and plasticity and poor comprehensive properties. Therefore, how to obtain good strength and plasticity while improving the corrosion resistance of the alloy and significantly increasing the production efficiency is a technical problem that urgently needs to be solved in the forming process of high-strength aluminum alloys. Summary of the Invention

[0004] Based on the above technical problems, the present invention provides a high-strength Al-Zn-Mg-Cu series aluminum alloy and a forming method thereof, which solve the problems of poor strength-plasticity matching, low corrosion resistance, and low production efficiency of the formed products of high-strength aluminum alloys.

[0005] The specific technical solutions are as follows:

[0006] A high-strength Al-Zn-Mg-Cu series aluminum alloy consists of the following components and mass percentages: 0.38% Si, 0.47% Fe, 1.8% Cu, 0.26% Mn, 2.2% Mg, 5.5% Zn, 0.20% Ti, and the balance is Al.

[0007] A forming method of a high-strength Al-Zn-Mg-Cu series aluminum alloy includes the following steps:

[0008] S1: Cut the aluminum alloy sheet and place it in a heat treatment furnace for solution treatment;

[0009] S2: After solution treatment, quickly transfer the sheet to a servo press for hot stamping forming. The transfer time is 10 s, the target shape is U-shaped, forming and quenching are carried out simultaneously, the stamping speed is 800 mm / s, and the pressure holding time is 15 s;

[0010] S3: Apply an electric pulse synchronously during forming. The electric pulse device uses an electric pulse emitter composed of 15 parallel supercapacitors. The pulse width is 100 ms, and the voltage and frequency are 80 V and 50 Hz respectively;

[0011] S4: After the pressure holding ends, stop applying the electric pulse, send the formed product into an electric treatment furnace and an oven for pre-aging + simulated baking, and finally cool it to room temperature to obtain a high-strength and corrosion-resistant aluminum alloy product with a strength-ductility product of 10301 - 10614 MPa·%.

[0012] S5: The pre-aging + simulated baking in step S4 can also be a peak aging process.

[0013] In the above technical solution, in step S1, the solution treatment process is 480 °C × 1 h.

[0014] In the above technical solution, in step S4, the pre-aging + simulated baking process is 120 °C / 5 min + air cooling + 180 °C / 30 min.

[0015] In the above technical solution, in step S5, the peak aging process is 120 °C / 24 h.

[0016] An Al-Zn-Mg-Cu series high-strength aluminum alloy and a forming method thereof according to the present invention, compared with the prior art, have the beneficial effects as follows:

[0017] By applying an electric pulse during the forming stage and adopting pre-aging (120 °C / 5 min) + air cooling + simulated baking (180 °C / 30 min) or peak aging process (120 °C / 24 h) during the heat treatment strengthening stage, while ensuring a certain amount of fine and dispersed strengthening phases, the corrosion rate of the alloy is reduced, thereby solving the problems of poor strength-ductility matching, low corrosion resistance, and low production efficiency of the formed products of high-strength aluminum alloys. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the forming method of the Al-Zn-Mg-Cu series high-strength aluminum alloy of the present invention;

[0019] Figure 2 It is a schematic diagram of the temperature change of the present invention;

[0020] Figure 3 It is a schematic diagram of the tensile specimen of the present invention;

[0021] Figure 4 It is a transmission electron microscope (TEM) image of the aluminum alloy of the present invention, where Figure 4 (a) is the TEM image of the precipitated phase in Example 2, Figure 4 (b) is the TEM image of the precipitated phase in Example 3;

[0022] Figure 5 It is a mechanical property diagram of the experimental aluminum alloy of the present invention, where the left side is the mechanical property diagram of the aluminum alloy in Example 2 and the right side is the mechanical property diagram of the aluminum alloy in Example 3;

[0023] Figure 6 This is the aluminum alloy corrosion rate diagram of the present invention. The aluminum alloy corrosion rate diagram of Example 4 is on the left, and the aluminum alloy corrosion rate diagram of Example 5 is on the right. Detailed implementation manners

[0024] The following further illustrates the present invention in conjunction with specific implementation cases and attached Figures 1-6 drawings, but the present invention is not limited to these embodiments.

[0025] Example 1:

[0026] A high-strength Al-Zn-Mg-Cu series aluminum alloy consists of the following components and mass percentages: 0.38% Si, 0.47% Fe, 1.8% Cu, 0.26% Mn, 2.2% Mg, 5.5% Zn, 0.20% Ti, and the balance is Al.

[0027] A forming method of a high-strength Al-Zn-Mg-Cu series aluminum alloy includes the following steps:

[0028] S1: Cut the aluminum alloy sheet and place it in a heat treatment furnace for solution treatment;

[0029] S2: After solution treatment, quickly transfer the sheet to a servo press for hot stamping. The transfer time is 10 s, the target shape is U-shaped, forming and quenching are carried out simultaneously, the stamping speed is 800 mm / s, and the pressure holding time is 15 s;

[0030] S3: Apply an electric pulse synchronously during forming. The electric pulse device uses an electric pulse emitter composed of 15 parallel supercapacitors. The pulse width is 100 ms, and the voltage and frequency are 80 V and 50 Hz respectively;

[0031] S4: After the pressure holding ends, stop applying the electric pulse, send the formed product into an electric treatment furnace and an oven for pre-aging + simulated baking, and finally cool it to room temperature to obtain a high-strength corrosion-resistant aluminum alloy product with a strength-ductility product of 10301 - 10614 MPa·%.

[0032] S5: The pre-aging + simulated baking in step S4 can also be a peak aging process.

[0033] In the embodiment of the present invention, in step S1, the solution process is 480 °C × 1 h.

[0034] In the embodiment of the present invention, in step S4, the pre-aging + simulated baking process is 120 °C / 5 min + air cooling + 180 °C / 30 min.

[0035] In the embodiment of the present invention, in step S5, the peak aging process is 120 °C / 24 h.

[0036] With the above technical solution, by applying an electric pulse during the forming stage and adopting pre-aging (120°C / 5 min) + air cooling + simulated baking (180°C / 30 min) or peak aging process (120°C / 24 h) during the heat treatment strengthening stage. By utilizing the "electroplastic effect" generated by the electric pulse, the plasticity of the alloy can be enhanced, recrystallization can be promoted, and the grain size can be refined; pre-aging can increase the nucleation of GP zones, and simulated baking can precipitate a certain amount of η' strengthening phase in a short time; the peak aging process can also precipitate a high-density η' strengthening phase. This process can reduce the alloy corrosion rate while ensuring a certain amount of fine and dispersed strengthening phases, and solve the problems of poor strength-plasticity matching, low corrosion resistance, and low production efficiency of high-strength aluminum alloy formed products.

[0037] Specifically, the function of the solution treatment of the present invention is to melt refractory elements such as the second phase into the Al matrix to obtain a supersaturated solid solution. The electric pulse-assisted forming technology can fully soften the alloy and make it easy to form. At the same time, it can refine the grains and form a large number of GP zones. The purpose of the aging treatment is to precipitate the strengthening phase from the matrix to obtain a certain amount of finely distributed η' strengthening phase. The precipitation sequence of the precipitated phase is: supersaturated solid solution → GP zone → non-equilibrium phase (η') → equilibrium phase (η).

[0038] Specifically, for the high-strength aluminum alloy formed product made by adopting the technical solution of the present invention, the yield strength and tensile strength are 480 - 492 MPa and 566 - 580 MPa respectively, the elongation is 18 - 19%, and the corrosion rate is 0.70 - 0.80 mg / cm 2 / h.

[0039] Example 2:

[0040] S1: Laser cut a 1.5-mm-thick 7075-T6 aluminum alloy plate produced by Nanan Aluminum Industry to 260 mm × 150 mm;

[0041] S2: Conduct a hot forming quenching test on the specimen through the hot forming quenching + pre-aging + simulated baking process and temperature changes as Figure 1 and 2 shown, and place it in a heat treatment furnace for solution treatment at 480°C for 1 h;

[0042] S3: After solution treatment, quickly transfer the plate to a press by a manipulator for hot stamping forming of a U-shaped part. The transfer time is 10 s, the stamping speed is 800 mm / s, and the pressure holding time is 15 s;

[0043] S4: Apply electric pulses synchronously during forming. The electric pulse device uses an electric pulse emitter composed of 15 parallel supercapacitors. The pulse width is 100 ms, and the voltage and frequency are 80 V and 50 Hz respectively. Stop applying electric pulses after the pressure holding ends. After the pressure holding ends, send the formed product into a heat treatment furnace and an oven for pre-aging (120 °C / 5 min) + air cooling after taking out of the furnace + simulated baking (180 °C / 30 min).

[0044] Among them, the TEM microstructure is as shown in Figure 4 (a), and the mechanical properties are as shown in Figure 5 . Cut the sample into a tensile specimen as shown in Figure 3 . The yield strength and tensile strength are 480 MPa and 566 MPa, and the elongation is 18.2%. The production efficiency is high, and its strength and plasticity meet the service requirements.

[0045] Example 3:

[0046] S1: Laser cut a 7075-T6 aluminum alloy sheet produced by Nanan Aluminum Industry with a thickness of 1.5 mm into 260 mm × 150 mm;

[0047] S2: The process and temperature change of hot forming quenching + peak aging are as shown in Figure 1 and 2 . Conduct a hot forming quenching test on the specimen, and place it in a heat treatment furnace for solution treatment at 480 °C for 1 h;

[0048] S3: After solution treatment, quickly transfer the sheet to a press by a manipulator for hot stamping forming of a U-shaped part. The transfer time is 10 s, the stamping speed is 800 mm / s, and the pressure holding time is 15 s;

[0049] S4: Apply electric pulses synchronously during forming. The electric pulse device uses an electric pulse emitter composed of 15 parallel supercapacitors. The pulse width is 100 ms, and the voltage and frequency are 80 V and 50 Hz respectively;

[0050] S5: Stop applying electric pulses after the pressure holding ends. After the pressure holding ends, send the formed product into a heat treatment furnace for peak aging (120 °C / 24 h).

[0051] Among them, the TEM microstructure is as shown in Figure 4 (b), and the mechanical properties are as shown in Figure 5 . Cut the sample into a tensile specimen as shown in Figure 3 . The yield strength and tensile strength are 492 MPa and 580 MPa, and the elongation is 18.3%. The strength and plasticity meet the service requirements.

[0052] Example 4:

[0053] S1: Cut the hot - formed product in Example 1 into 5mm×5mm×1.5mm specimens;

[0054] S2: Conduct an intergranular corrosion immersion experiment on the sample at 35 ± 2 °C, and the corrosion rate is 0.72 ± 0.02 mg / cm 2 / h, as Figure 6 shown.

[0055] Example 5:

[0056] S1: Cut the hot - formed product in Example 2 into 5mm×5mm×1.5mm specimens;

[0057] S2: Conduct an intergranular corrosion immersion experiment on the sample at 35 ± 2 °C, and the corrosion rate is 0.79 ± 0.02 mg / cm 2 / h, as Figure 6 shown.

[0058] In Examples 1 - 5 of the present invention, the hot - forming equipment used is a 2000kN servo - press, the electro - pulse equipment is a high - frequency pulse power supply, the room - temperature unidirectional tensile equipment is a SANS CMT5000 universal testing machine; the equipment for observing the microstructure is a JEM 2100 - TEM transmission electron microscope.

[0059] In Examples 2 - 3 of the present invention, the hot - formed samples are processed into tensile specimens as Figure 3 shown, where the dimensions of the tensile specimen are that the fixed ends on both sides are 25mm long, 20mm wide, the hole diameter is 6mm, the middle tensile area is 35mm long and 5mm wide, the chamfer between the fixed end and the tensile area is 25mm, and the tensile rate is 2mm / min until fracture.

[0060] In Examples 2 - 3 of the present invention, TEM specimens are prepared by electro - polishing with a 70% methanol and 30% nitric acid solution at - 30 °C and 12V.

[0061] In Examples 4 - 5 of the present invention, a corrosion immersion experiment is conducted at 35 ± 2 °C, the liquid ratio is 10ml H2O2 + 57g NaCl + 1000ml, and the time is 6h. After the test, in order to remove the corrosion products, soak in concentrated nitric acid for 5min, then rinse with a large amount of clear water, spray alcohol, and finally dry in an oven.

[0062] In the description of the present invention, the term "a plurality of" refers to two or more, unless otherwise clearly defined. The orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention; terms such as "connection", "installation", "fixation", etc. should all be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0063] In the description of the present invention, the descriptions of terms such as "one embodiment", "some embodiments", "specific embodiments", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In the present invention, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0064] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A forming method of Al-Zn-Mg-Cu series high-strength aluminum alloy, characterized in that: The steps include: S1: Cut aluminum alloy plates and place them in a heat treatment furnace for solution treatment; S2: After solution treatment, the sheet is quickly transferred to the servo press for hot stamping, where the transfer time is 10 s, the target shape is U-shaped, forming and quenching are carried out simultaneously, the stamping speed is 800 mm / s, and the holding time is 15 s; S3: Electric pulses are applied synchronously during forming. The electric pulse device uses an electric pulse transmitter composed of 15 parallel supercapacitors. The pulse width is 100ms, and the voltage and frequency are 80V and 50Hz respectively; S4: After the pressure holding is completed, the electric pulse is stopped, and the formed product is sent to the electric treatment furnace and the baking oven for pre-aging + simulated baking, and finally cooled to room temperature to obtain a high-strength and corrosion-resistant aluminum alloy product with a strength-plasticity product of 10301-10614 MPa•%; In the step S1, the solution treatment process is 480°C×1 h; In step S4, the pre-aging + simulated baking process is 120°C / 5 min+air cooling+180°C / 30 min; The high-strength aluminum alloy formed products have a yield strength and tensile strength of 480-492 MPa and 566-580 MPa, an elongation of 18-19%, and a corrosion rate of 0.70-0.80 mg / cm 2 / h.

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