CN110885942B

CN110885942B - Medium-strength 7xxx series aluminum alloy plate suitable for hot stamping forming-quenching integrated process

Info

Publication number: CN110885942B
Application number: CN201911301001.9A
Authority: CN
Inventors: 吴浩; 刘成; 黄鸣东; 郑志凯; 周泽宇
Original assignee: China Aluminum Material Application Institute Co ltd
Current assignee: Chinalco Institute Of Science And Technology Co ltd; Chinalco Materials Application Research Institute Co Ltd
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2021-05-07
Anticipated expiration: 2039-12-17
Also published as: EP4063530A4; EP4063530A1; CN114929913A; WO2021121343A1; CN110885942A

Abstract

The invention discloses a special medium-strength 7xxx series aluminum alloy plate suitable for a hot forming-quenching integrated process, which comprises the following chemical components, by weight, 5.1-6.7% of Zn, 1.9-2.9% of Mg, 1.2-2.6% of Cu, 0-0.5% of Fe, 0-0.4% of Si, 0-0.1% of Cr, 0-0.08% of Zr and 0-0.25% of Mn, wherein the total content of other trace elements for controlling the grain size, such as Cr, Mn, Zr and the like, is less than or equal to 0.25%, and the balance of Al. Based on the characteristics of the hot forming-quenching integrated process, the alloy plate has the characteristics of short-time solid solubility, low quenching sensitivity, excellent age hardening and the like. The alloy plate can quickly complete the solution treatment in a short time, and after the alloy plate is subjected to water cooling or die cooling or air cooling and then is subjected to artificial peak aging or baking finish treatment, the final plate has the yield strength of more than 400MPa, the tensile strength of more than 450MPa and the elongation of more than 6.5 percent. The 7xxx aluminum alloy plate is specially used for preparing a 450 MPa-grade medium-strength 7xxx series aluminum structural member of a quenching process in a hot stamping die.

Description

Medium-strength 7xxx series aluminum alloy plate suitable for hot stamping forming-quenching integrated process

Technical Field

The invention particularly relates to a 7xxx aluminum alloy plate, in particular to a medium-strength 7xxx aluminum alloy plate suitable for a hot forming-quenching integrated process, and belongs to the field of non-ferrous metal aluminum alloy materials.

Background

In recent years, the automobile industry is rapidly developed, and the lightweight requirement of automobiles is also very urgent due to the influence of energy environment and the like. The weight of the automobile body accounts for about 40% of the total weight of the automobile, the light weight of the automobile body plays a decisive role in the light weight of the whole automobile, and the light weight of the automobile body becomes the leading edge and the hot spot of the current automobile manufacturing technology. Currently, aluminum alloy automotive panels commonly used for vehicle bodies are mainly 5xxx and 6xxx series aluminum alloys, but their strength is low. While the room temperature formability of high strength 2xxx and 7xxx series aluminum alloys is low, limiting their wide application in vehicle bodies. However, in a higher temperature range (between 200 ℃ and 500 ℃), the increase of the temperature improves the formability of the high-strength aluminum alloy plate, which is beneficial to the forming of parts.

In order to ensure the formability and the strength of parts of the plate, the traditional hot forming process is to heat a plate blank to a required temperature, transfer the plate blank into a die for hot forming, and then carry out conventional solid solution aging strengthening treatment on the formed part to obtain the part with final performance. The latest hot forming-quenching integrated process is a composite process technology combining heat treatment and hot forming of aluminum alloy, combines the forming process and the heat treatment process, and realizes forming and control by the same set of die. The process improves the plasticity of the material in the forming process while ensuring the strength of the material. And (3) rapidly transferring the aluminum alloy plate after complete solid solution to a water-cooled mold, rapidly closing the mold for forming, keeping closing the mold after forming to finish quenching in the part mold, and finally performing aging treatment to improve the strength of the part mold. The process is a novel process with the greatest prospect in the hot forming of the high-strength aluminum alloy plate, and can solve the problems of poor forming plasticity, large resilience and shape distortion during heat treatment of the aluminum alloy plate.

However, although hot forming-quenching integrated process technology is commercially applied so far, the current main application reports mainly focus on high-strength steel, 5xxx and 6xxx series aluminum alloys, such as AA5754, AA6016, AA6111, and the like, and the formability of the original plate is improved through an aluminum alloy hot stamping process to produce parts with more complex shapes, but the strength of 5xxx and 6xxx aluminum alloy parts commonly used for automobile bodies at present is less than 300MPa, and the 5xxx and 6xxx aluminum alloy parts cannot meet the performance requirement of high strength of automobile body structural parts. For 2xxx and 7xxx series high-strength aluminum alloys with better mechanical properties, the hot stamping research application of the high-strength aluminum alloy belongs to the starting stage because the high-strength aluminum alloy is mainly applied to the aerospace field and is less used in a vehicle body, and the process flow has high requirements on the material properties of the 2xxx and 7xxx series high-strength aluminum alloys and requires that the alloy plate has the characteristics of short-time solid solubility, low quenching sensitivity, good hot forming, age hardening and the like. At present, 2xxx and 7xxx series high-strength aluminum alloy materials suitable for hot forming-quenching integrated process attributes are blank at home and abroad.

Disclosure of Invention

In order to solve the problems in the prior art, the invention develops a medium-strength 7xxx series aluminum alloy plate with the strength of more than 450MPa, which is suitable for a hot forming-quenching integrated process.

The invention provides a medium-strength 7xxx series aluminum alloy plate suitable for a hot forming-quenching integrated process, which comprises the following alloy components in percentage by weight: 5.1 to 6.7 percent of Zn, 1.9 to 2.9 percent of Mg, 1.2 to 2.6 percent of Cu, 0 to 0.5 percent of Fe, 0 to 0.4 percent of Si, 0 to 0.1 percent of Cr, 0 to 0.08 percent of Zr or 0 to 0.25 percent of Mn, and other trace elements for controlling the grain size, such as Cr, Mn, Zr and the like, can exist singly or in combination of two or more, but the total content is less than or equal to 0.25 percent, and the balance is Al.

Based on the requirements of the hot forming-quenching integrated process on solid solubility and quenching sensitivity of an aluminum alloy material, the medium-strength aluminum alloy provided by the invention comprises the following optimal components in percentage by weight: 5.4 to 6.5 percent of Zn, 2.0 to 2.7 percent of Mg, 1.6 to 2.3 percent of Cu, 0 to 0.4 percent of Fe, 0 to 0.3 percent of Si, 0 to 0.05 percent of Cr, 0 to 0.05 percent of Zr or 0 to 0.15 percent of Mn, and other trace elements for controlling the grain size, such as Cr, Mn, Zr and the like, can exist singly or in combination of two or more, but the total content is less than or equal to 0.15 percent, and the balance is Al.

Based on the property requirements of the hot forming-quenching integrated process on the aluminum alloy material, the invention strictly controls the contents of main alloy elements Zn, Mg and Cu, and reduces the high-temperature residual phase Al₂The CuMg phase ensures that the second phase remained in the alloy plate can be quickly dissolved back into the matrix in the heating and short-time heat preservation stages of the thermoforming-quenching integrated process, and ensures the thermoforming property and subsequent mechanical property of the alloy.

The design of the content of impurity elements Fe and Si in the alloy components provided by the invention aims to reduce the preparation and subsequent use cost of the whole alloy raw materials and has a certain effect of refining the grain structure.

The invention strictly controls the contents of trace elements Cr, Zr and Mn, ensures that the alloy plate has lower quenching sensitivity, controls the grain size of the plate, ensures that a matrix can obtain larger supersaturation degree after the plate is subjected to high-temperature solid solution mold cold quenching, has better grain structure, and finally has the yield strength of more than 400MPa, the tensile strength of more than 450MPa and the elongation of more than 6.5 percent after the subsequent artificial peak aging or baking finish treatment.

The aluminum alloy plate can be quickly subjected to solid solution after being subjected to heat preservation at 450-510 ℃ for 5-20 min, then is subjected to air cooling or mold cooling or water cooling, and then is subjected to artificial peak aging or baking finish treatment, so that the yield strength of the medium-strength 7xxx aluminum alloy plate is more than 400MPa, the tensile strength of the medium-strength 7xxx aluminum alloy plate is more than 450MPa, and the elongation of the medium-strength 7xxx aluminum alloy plate is more than 6.5%. The medium-strength 7xxx series aluminum alloy plate has the characteristics of quick solid solubility, low quenching sensitivity, age hardening and the like.

The invention relates to a cold rolled or O-state or T4-state plate with a thickness of 1.0-4.0 mm for a medium-strength 7xxx series aluminum alloy suitable for a hot forming-quenching integrated process.

The implementation of the invention has the following advantages:

based on the property requirements of the hot forming-quenching integrated process on the aluminum alloy material, compared with the existing 7xxx aluminum alloy plates of the same type, the alloy plate provided by the invention has better short-time solid solubility, quenching sensitivity and age hardening or paint baking hardenability, and is a medium-strength 7xxx aluminum alloy suitable for the hot forming-quenching integrated manufacturing process of an aluminum alloy structural member.

Drawings

FIG. 1 shows the grain structure of a low-Fe, Si, trace-element-free A1 alloy plate after heat treatment;

FIG. 2 shows the grain structure of the heat-treated high Fe, Si trace element-free A3 alloy plate;

FIG. 3 shows the grain structure of a high Fe, Si and low Cr A5 alloy plate after heat treatment;

FIG. 4 shows the grain structure of a C3 alloy plate with low Fe and Si contents and high Cr contents after heat treatment;

FIG. 5 shows the grain structure of a high Fe, Si and low Zr containing A4 alloy plate after heat treatment;

FIG. 6 shows the grain structure of a C1 alloy plate with low Fe and Si contents and high Zr content after heat treatment;

FIG. 7 shows the grain structure of a high Fe, Si and Mn element A6 alloy plate after heat treatment;

FIG. 8 shows the grain structure of the C5 alloy plate after heat treatment, which is prepared by using high-purity aluminum as a raw material.

Detailed Description

The present invention will be further described with reference to the following drawings and detailed description, but the present invention is not limited to the following examples.

The preparation process of the 7xxx aluminum alloy cooling plate comprises the following steps: the alloy ingot is prepared by adopting an industrial semi-continuous process, the components of the alloy ingot are shown in table 1, the ingot is respectively homogenized according to the characteristics of trace elements contained in each ingot, the homogenization process is that the alloy ingot is subjected to heat preservation for 5-10 h at 400-450 ℃, then is subjected to heat preservation for 10-36 h at 470-490 ℃, the heating rate is 25-75 ℃/h, and then is subjected to air cooling or air cooling to room temperature; preserving the heat of the homogenized blank at 380-450 ℃ for 3-20 h, performing hot rough rolling and hot finish rolling to 4-8 mm, wherein the finish rolling temperature is 250-350 ℃, then curling, and air cooling the alloy hot-rolled coil to room temperature; and finally, performing cold rolling (cold rolling, intermediate annealing and cold rolling processes can be selected according to conditions, namely, cold rolling of an intermediate annealed and CAC cold-rolled sheet) on the alloy hot-rolled coil with the thickness of 4-8 mm, and curling to finally obtain the alloy cold-rolled sheet with the thickness of 1-4 mm. The cold rolled coil can also be selectively annealed in a box or continuous mode to obtain O-state or T4-state plates. The alloy compositions and the plate states of the examples and comparative examples are shown in Table 1.

TABLE 1 average composition (in weight percent) of alloy sheets for examples and comparative examples

Alloy element	Zn	Mg	Cu	Fe	Si	Cr	Zr	Mn	Al	Status of state
											A1 (example 1)	5.63	2.73	1.59	0.10	0.02	0.0021	0.0003	0.005	Balance of	2mm cold rolled state
A2 (example 2)	6.11	2.40	2.19	0.09	0.02	0.0027	0.0002	0.004	Balance of	2mm cold rolled state
											A3 (example 3)	5.52	2.59	1.72	0.30	0.20	0.0015	0.0003	0.004	Balance of	2mm cold rolled state
A4 (example 4)	5.52	2.53	1.70	0.21	0.12	0.0015	0.0452	0.004	Balance of	2mm cold rolled state
											A5 (example 5)	5.69	2.66	1.69	0.23	0.13	0.0442	0.0002	0.005	Balance of	2mm cold rolled state
A6 (example 6)	5.73	2.72	1.82	0.25	0.12	0.0024	0.0003	0.122	Balance of	2mm cold rolled state
											A7 (example 7)	5.71	2.68	1.79	0.24	0.11	0.0481	0.0001	0.004	Balance of	1mm cold rolled state
A8 (example 8)	5.65	2.70	1.73	0.21	0.14	0.0425	0.0003	0.003	Balance of	Cold rolled state of 4mm
											A9 (example 9)	5.70	2.68	1.64	0.24	0.11	0.0441	0.0002	0.005	Balance of	2mm CAC State
A10 (example 10)	5.69	2.63	1.67	0.23	0.13	0.0472	0.0003	0.004	Balance of	2mm O state
											A11 (example 11)	5.59	2.71	1.70	0.26	0.14	0.0435	0.0001	0.003	Balance of	2mm T4 state
C1 (comparison example 1)	5.60	2.60	1.60	0.10	0.03	0.0032	0.0791	0.004	Balance of	2mm cold rolled state
											C2 (comparison example 2)	5.75	2.65	1.72	0.24	0.12	0.1241	0.0006	0.004	Balance of	2mm cold rolled state
C3 (comparison example 3)	5.71	2.56	1.6	0.1	0.03	0.1811	0.0002	0.004	Balance of	2mm cold rolled state
											C4 (comparison example 4)	5.71	2.73	1.79	0.21	0.13	0.0019	0.0003	0.263	Balance of	2mm cold rolled state
C5 (comparison example 5)	5.67	2.54	1.52	0.02	0.01	0.0054	0.0001	0.003	Balance of	2mm cold rolled state
											C6 (comparison example 6)	5.49	1.42	0.28	0.25	0.12	0.0011	0.0002	0.003	Balance of	2mm cold rolled state

Based on the characteristics of the hot forming-quenching integrated process, after the alloy cold-rolled plates in the examples and the comparative examples are subjected to rapid solution treatment at 450-510 ℃ for 5-20 min (the process production can be subjected to on-line continuous solution treatment), a water cooling (WQ) or air cooling (AQ) two-pole end cooling mode is carried out, then T6 Peak Aging (PA) at 120 ℃/24h or baking finish treatment (BH) at 180 ℃/30min or 185 ℃/25min is carried out, the plates treated by different processes are subjected to mechanical property tests, and the test results are shown in Table 2.

Table 2 partial process treatment test results for alloy sheets of examples and comparative examples

As can be seen from Table 2, the final mechanical properties of the medium-strength 7xxx aluminum alloy plates A1-A9 in the examples 1-9 of the application are obviously higher than those of the C1-C6 alloy plates in the comparative examples 1-6, the yield strengths of the alloy plates A1-A9 in the examples are all more than 400MPa, the tensile strengths of the alloy plates A1-A9 are all more than 450MPa, and the elongations of the alloy plates A1-A9 are all more than 6.5%.

The embodiment 1 and the embodiment 2 are low-Fe and low-Si alloy without trace elements, the quenching sensitivity of the alloy plate is lower, the average grain size is 64 mu m (as shown in figure 1), and the mechanical property of the plate after the process treatment is better.

The embodiment 3 is the alloy with high Fe and Si and no trace elements, the quenching sensitivity of the alloy plate is lower, the average grain size is reduced by 61 mu m (as shown in figure 2) compared with the alloy of the embodiment 1, and the mechanical property of the plate after the process treatment is better.

Compared with the alloy of the comparative example 5 prepared by taking high-purity aluminum as a raw material, the alloy of the comparative example 5 has low Fe and Si elements, but after the alloy plate is subjected to solution treatment, the average grain size is larger than 100 micrometers (as shown in figure 8), the grain size distribution is uneven, and the mechanical property after each process treatment is obviously lower than that of the alloy of the examples 1 and 3, so that proper amounts of Fe and Si are beneficial to inhibiting the grain growth of the plate under high-temperature treatment and regulating the grain structure, as shown in figures 1, 2 and 8.

Example 4 is an alloy with high Fe and Si and low trace element Zr, as shown in fig. 5, the average grain size of the alloy plate is 37 μm, which is significantly reduced compared to the alloy without Zr in example 3, but the quenching sensitivity of the alloy is increased compared to the alloy without Zr, and the mechanical properties of the plate are weakened by AQ + BH process treatment.

However, when the content of trace element Zr in the alloy is further increased, like the high Zr alloy in the comparative example 1, although the average grain size can be further reduced to about 25 μm (as shown in FIG. 6), the quenching sensitivity is obviously increased and the mechanical property is obviously reduced compared with the low Zr alloy in the example 4. Therefore, the grain size of the alloy plate can be obviously reduced and the alloy grain structure can be effectively regulated and controlled while the quenching sensitivity can not be greatly increased by a proper amount of trace element Zr.

In example 5, the alloy cold rolled sheet with high Fe and Si and low trace element Cr had a significantly reduced average grain size (see fig. 2 and 3) but improved quench sensitivity and reduced mechanical properties at final alloy state compared to the Cr-free high Fe and Si alloy of example 3. But compared with comparative examples 2 and 3 of the Cr alloy, the alloy quenching sensitivity is obviously reduced, the mechanical property of the plate is superior to that of the alloy plates of the comparative examples 2 and 3 after the treatment of each process, the influence of the Cr element on the alloy quenching sensitivity is obviously larger, and the final mechanical property of the plate is continuously reduced along with the increase of the Cr content.

The alloy plate of example 6, which is high in Fe and Si and contains Mn as a trace element, has a significantly reduced average grain size of about 24 μm (as shown in fig. 7) compared to the alloy plate of example 3, but has an improved quenching sensitivity, and the mechanical properties of the alloy plate after each process are reduced. But compared with the alloy plate which is high in Fe and Si in the proportion of 4 and contains trace element Mn, the quenching sensitivity is obviously reduced, and the mechanical property is obviously improved.

Therefore, the dispersion phase formed by adding trace elements such as Cr, Mn, Zr and the like has a strong regulation and control effect on the grain structure, although the average grain size of the alloy can be effectively reduced, the influence on the quenching sensitivity of the plate is large, the mechanical property of the alloy is not facilitated, and the grain structure needs to be properly added according to the actual demand of the grain structure for regulation and control.

Compared with example 5, in example 7 and example 8, the alloy components are basically similar, but the thickness of the prepared final plate is different, the quenching sensitivity of the alloy is not obviously changed, and the mechanical properties are basically similar.

In examples 9 to 11, compared with example 5, the alloy components are basically similar, but the states of preparing the final plate are different, example 5 is a cold-rolled plate obtained by directly cold-rolling a hot-rolled plate to a thickness of 2mm, example 9 is a cold-rolled plate (CAC state cold-rolled plate) obtained by a cold-rolled plate cold-intermediate annealing-cold-rolling process flow, example 10 is an O state plate, and example 11 is a T4 state plate, although the states of the prepared final state plates are different, the quenching sensitivity is basically not greatly different, and the mechanical properties are basically similar.

Compared with the alloys of examples 1-9, the alloy of comparative example 6 has lower Cu element content, has poorer stability of strengthening phase formed by aging in the alloy, is easy to grow and coarsen, and causes larger loss of mechanical property of the plate.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and optimization can be made without departing from the principle of the present invention, and these modifications and optimization should also be regarded as the protection scope of the present invention.

Claims

1. A medium-strength 7xxx series aluminum alloy plate suitable for a hot forming-quenching integrated process is characterized in that: the chemical components of the alloy comprise, by weight, 5.1-6.7% of Zn, 1.9-2.9% of Mg1.2-2.6% of Cu, 0-0.5% of Fe, 0-0.4% of Si, 0< Cr < 0 > or less than 0.1%, 0< Zr < 0.08%, and 0< Mn < 0.25%; wherein the total weight percentage content of Cr, Mn and Zr is less than or equal to 0.25 percent, and the balance is Al.

2. The medium strength 7xxx series aluminum alloy sheet suitable for use in a hot forming-quenching integrated process of claim 1, wherein: the chemical components of the alloy comprise, by weight, 5.4-6.5% of Zn, 2.0-2.7% of Mg, 1.6-2.3% of Cu, 0-0.4% of Fe, 0-0.3% of Si, 0< Cr < 0 > or less than 0.05%, 0< Zr < 0.05%, and 0< Mn < 0.15%; wherein the total weight percentage content of Cr, Mn and Zr is less than or equal to 0.15 percent, and the balance is Al.

3. A method of treating a medium strength 7 xxx-series aluminum alloy sheet suitable for use in a hot forming-quenching integrated process as claimed in claim 1 or 2, wherein: the 7xxx series aluminum alloy plate can be quickly subjected to solid solution treatment after being kept at 450-510 ℃ for 5-20 min, then is subjected to air cooling or mold cooling or water cooling, and then is subjected to artificial peak aging or baking finish treatment, so that the yield strength of the 7xxx series aluminum alloy plate is more than 400MPa, the tensile strength of the 7xxx series aluminum alloy plate is more than 450MPa, and the elongation of the 7xxx series aluminum alloy plate is more than 6.5%.

4. The method for treating the medium-strength 7xxx series aluminum alloy plate suitable for the hot forming-quenching integrated process as claimed in claim 3, is characterized in that: the 7xxx aluminum alloy plate has fast solid solubility and low quenching sensitivity, and has the integrated hot forming-quenching process attribute.

5. The method for treating the medium-strength 7xxx series aluminum alloy plate suitable for the hot forming-quenching integrated process as claimed in claim 3, is characterized in that: the 7xxx aluminum alloy plate is a cold rolled plate with the thickness of 1.0-4.0 mm, an O-state plate or a T4-state plate.