Al-zn-mg-cu alloy chemical composition design method and application

Abstract

The application discloses a kind of Al-Zn-Mg-Cu alloy chemical composition design method and application, the application is by studying the mechanism of action of the effect of main alloying element in alloy on alloy organization performance, simultaneously combining phase diagram thermodynamic calculation research mechanism of action of main alloying element in alloy, provide a kind of super high strength high toughness Al-Zn-Mg-Cu alloy composition design criterion, in the Al-Zn-Mg-Cu alloy, η Phase precipitated quantity and (Zn+Mg) total amount, Zn / Mg ratio need satisfy the functional relationship of formula 1, the Al-Zn-Mg-Cu alloy chemical composition designed by the Al-Zn-Mg-Cu alloy chemical composition design method provided by the application, the tensile strength of Al-Zn-Mg-Cu alloy finally prepared is higher than 650MPa, plane strain fracture toughness value is higher than 40MPa·m 1 / 2 , with excellent comprehensive performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy, and particularly relates to a chemical composition design method and application of an Al-Zn-Mg-Cu alloy. BACKGROUND

[0002] The Al-Zn-Mg-Cu alloy has high specific strength, good fracture toughness, good corrosion resistance, good processing forming property and excellent welding performance. The Al-Zn-Mg-Cu alloy can be processed by pressure processing, such as extrusion and rolling, to produce extruded materials, plates and forgings of various specifications. As a light structure material, the Al-Zn-Mg-Cu alloy has been widely applied to important fields such as rail transportation and automobiles. With the development of rail transportation, the Al-Zn-Mg-Cu alloy with strength, toughness, corrosion resistance and fatigue resistance has been widely applied as an important light structure material. However, in the actual production process, the improvement of many properties is often accompanied by the decline of other properties. Therefore, it is of great practical significance to develop a design method that balances various properties and significantly improves the comprehensive performance of the Al-Zn-Mg-Cu alloy. SUMMARY

[0003] In view of the deficiencies of the prior art, a first object of the application is to provide an Al-Zn-Mg-Cu alloy chemical composition design method with ultra-high strength and high toughness.

[0004] A second object of the application is to provide an application of the Al-Zn-Mg-Cu alloy chemical composition design method. The Al-Zn-Mg-Cu alloy chemical composition designed by the Al-Zn-Mg-Cu alloy chemical composition design method has a tensile strength higher than 650 MPa, a plane strain fracture toughness value higher than 40 MPa·m 1 / 2 , and excellent comprehensive performance.

[0005] In order to achieve the above objects, the application provides the following technical solutions.

[0006] The Al-Zn-Mg-Cu alloy design method provided by the application has the following advantages.

[0007]

[0008] wherein,

[0009] x=c Zn +c Mg

[0010] y=cZn / c Mg

[0011] In formula 1, M η is the η phase precipitation amount, which ranges from 6.30% to 10.20%; C Zn , C Mg are the mass contents of Zn and Mg in the Al-Zn-Mg-Cu alloy, respectively.

[0012] In the above formula 1, M η is the η phase precipitation amount when the alloy is composed of Al, Zn and Mg, and is the mass percentage content.

[0013] In the present application, the η phase precipitation amount is precipitated from the Al-Zn-Mg-Cu alloy under the T6 system.

[0014] In the Al-Zn-Mg-Cu alloy, the main secondary phase at room temperature includes Mg(Zn, Cu, Al)2, Al7Cu2Fe, etc. Among them, the MgZn2 phase is the most important strengthening phase in the alloy, which is in the form of near-spherical and fine rod-like morphology, and is uniformly distributed on the substrate. The composition ratio of Zn and Mg main elements is the key to determine the mechanical properties of the Al-Zn-Mg-Cu alloy. Therefore, the microstructure characteristics of the MgZn2 precipitated phase in the Al-Zn-Mg-Cu alloy and its influence on the performance under the joint action of Zn and Mg contents and Zn / Mg ratio are very important, and need to be considered in the alloy design process. Another type of Cu-containing phase presents blocky and long strip shape, and the interaction with the fatigue crack improves the fatigue crack propagation resistance. In the alloy design process, the Zn / Mg element ratio needs to be controlled to precipitate more MgZn2 phase to improve the performance. With the decrease of Zn content and the increase of Mg content, the number of coarse secondary phases in the Al-Zn-Mg-Cu alloy substrate gradually decreases. The inventors calculated the η phase (MgZn2 phase) precipitation amount and performance data in the Al-Zn-Mg-Cu system under each Zn and Mg content by using the phase diagram contour method in a large number of experiments, and then drew the equal precipitation curve (η phase) with the change of Zn and Mg (formula 1). Through analysis of the equal precipitation curve, it can be more clearly seen from the figure that the influence law of Zn and Mg elements on the η phase precipitation amount. The function relationship of the η phase precipitation amount with the total amount of (Zn+Mg) and the Zn / Mg ratio obtained by fitting is shown in formula 1. The composition conforming to the function relationship has the optimal comprehensive performance of the final alloy. Figure 1

[0015] However, the inventors found through a large number of experiments that the more the η phase precipitation amount, the more optimal the hardness and room temperature tensile strength of the final material. Figure 1 ​It can also be seen that the amount of η phase precipitated in the Al-Zn-Mg-Cu alloy increases with the increase of the total amount of (Zn+Mg). Specifically, the total amount of Zn and Mg is related to the total amount of η phase, and the greater the total amount of Zn and Mg, the more the total amount of η phase. The Zn / Mg ratio is related to the minimum total amount of Zn and Mg when the amount of η phase is equal. At the same time, it can be concluded that when the total amount of Zn and Mg is constant and the Zn / Mg ratio is less than 4.9, the amount of η phase increases with the increase of the Zn / Mg ratio. When the Zn / Mg ratio is greater than 4.9, the amount of η phase decreases with the increase of the Zn / Mg ratio. When the Zn / Mg ratio is equal to 4.9, the alloy requires the least amount of Zn and Mg under the condition of equal amount of η phase precipitation. The more the amount of η phase, the higher the strength of the Al-Zn-Mg-Cu alloy. The addition of Cu element increases the amount of η phase, but the amount of η phase in the matrix does not increase with the increase of Cu content. With the increase of Cu content, the amount of AlCu phase increases, and the fracture toughness value increases.

[0016] Preferably, in the Al-Zn-Mg-Cu alloy, the mass percentage of (Zn+Mg) is 7.0wt%-12.0wt%. The mass percentage of (Zn+Mg) refers to the sum of the mass percentages of Zn and Mg.

[0017] Further preferably, in the Al-Zn-Mg-Cu alloy, the mass percentage of (Zn+Mg) is 9.0wt%-11.0wt%.

[0018] Preferably, in the Al-Zn-Mg-Cu alloy, the mass ratio of Zn:Mg is 3-5.

[0019] Further preferably, in the Al-Zn-Mg-Cu alloy, the mass ratio of Zn:Mg is 4.9.

[0020] Preferably, in the Al-Zn-Mg-Cu alloy, the mass percentage of Cu is 1wt%-3wt%.

[0021] Further preferably, in the Al-Zn-Mg-Cu alloy, the mass percentage of Cu is 1.7wt%-2.5wt%.

[0022] Preferably, in the Al-Zn-Mg-Cu alloy, the mass percentage of trace elements is ≤0.67%.

[0023] Further preferably, the trace elements are selected from at least one of Si, Fe, Mn, Cr, Zr, and Ti.

[0024] In the present application, the trace elements refer to elements other than Al, Zn, Mg and Cu in the Al-Zn-Mg-Cu alloy.

[0025] The application of the Al-Zn-Mg-Cu alloy chemical component design method is to obtain an Al-Zn-Mg-Cu alloy.

[0026] In a preferred embodiment, the Al-Zn-Mg-Cu alloy is obtained by first designing the alloy components by the Al-Zn-Mg-Cu alloy chemical component design method, then obtaining an ingot by smelting alloy raw materials in the designed component proportions, and then performing post-processing to obtain the alloy.

[0027] The Al-Zn-Mg-Cu alloy components designed according to the present application can be obtained by using existing conventional production processes, such as smelting, ingot casting, homogenization treatment, hot extrusion, quenching, and aging treatment, and the specific production process conditions can be determined according to the alloy element components and contents and the actual production process.

[0028] In a preferred embodiment, the alloy raw materials are smelted at 730-750°C, cooled to 715-725°C and then cast at 680-700°C to obtain an ingot.

[0029] In a preferred embodiment, the post-processing process is homogenization treatment, extrusion treatment, quenching, and aging treatment.

[0030] Further preferably, the homogenization treatment process is to first heat the ingot at 500-540°C for 8-20h, then slowly cool it to 400-440°C at a rate of 2-10°C / min, and then rapidly cool it to 180-220°C at a rate of 20-60°C / min.

[0031] Further preferably, the extrusion treatment process is to preheat the homogenization-treated blank to 460-490°C, set the extrusion cylinder temperature to 410-450°C, and then extrude it at a speed of 0.5-2m / min. Further preferably, the quenching is online water quenching.

[0032] Further preferably, the aging treatment process is to first age it at 110-140°C for 8-30h, then heat it at 155-185°C for 60-180min, and then heat it at 110-140°C for 8-30h.

[0033] In summary, the application provides a component design criterion of Al-Zn-Mg-Cu alloy with high comprehensive performance by studying the mechanism of the main alloying elements in the alloy affecting the structure and performance of the alloy, and studying the interaction mechanism of the main alloying elements and the corresponding second phase in the alloy through phase diagram thermodynamic calculation, and coordinating the surface quality, strength, toughness and other properties of the alloy. Through the design criterion, an Al-Zn-Mg-Cu alloy with ultra-high strength and high toughness can be designed. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The contour map of the η phase precipitation amount in the Al-Zn-Mg-Cu system with the change of Zn and Mg content.

[0035] Figure 2 The TEM diagram of intragranular precipitated phase of the Al-Zn-Mg-Cu alloy in Example 1. As can be seen from the figure, the η phase size of the Al-Zn-Mg-Cu alloy prepared according to the component design criterion of the application is small, the precipitation free zone is not obviously coarsened, and the η phase precipitation amount is 12.56%. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0037] In order to verify the advantages of the Al-Zn-Mg-Cu alloy extruded material described in the application, the detection method adopted is as follows:

[0038] Tensile properties of extruded material: detection and analysis are carried out according to GBT228.1-2010 Metal Materials Tensile Test Part 1 Room Temperature Test Method;

[0039] Fracture toughness: according to ISO12737-2010 Metal Materials Plane Deformation Fracture Toughness Measurement;

[0040] Comparative Example 1

[0041] The alloy component is designed according to the component design criterion described in the application, and the alloy component is prepared according to the mass percentage: Zn: 9.7%, Mg: 2.6%, Cu: 2.5%, Fe: 0.15%, Zr: 0.13%, the total amount of other trace elements ≤0.3%, and the balance is Al, wherein the Zn / Mg ratio is 3.73, and the η phase precipitation amount is 10.75%. The (Zn+Mg) element content of the alloy does not meet the design criterion shown in formula 1.

[0042] The alloy is prepared according to the component design criteria, and the alloy components are prepared according to the mass percentage: Zn: 9.5%, Mg: 2.0%, Cu: 3.5%, Fe: 0.15%, Zr: 0.1%, and the total amount of other trace elements is ≤0.3%, and the balance is Al, wherein the Zn / Mg ratio is 4.75, and the η phase precipitation amount is 10.78%. The Cu element content of the alloy is not within the range of the present application.

[0043] Comparative Example 2

[0044] The alloy is prepared according to the component design criteria, and the alloy components are prepared according to the mass percentage: Zn: 9.5%, Mg: 2.0%, Cu: 3.5%, Fe: 0.15%, Zr: 0.1%, and the total amount of other trace elements is ≤0.3%, and the balance is Al, wherein the Zn / Mg ratio is 4.75, and the η phase precipitation amount is 10.78%. The Cu element content of the alloy is not within the range of the present application.

[0045] The alloy is prepared according to the component design criteria, and the alloy components are prepared according to the mass percentage: Zn: 9.5%, Mg: 2.0%, Cu: 3.5%, Fe: 0.15%, Zr: 0.1%, and the total amount of other trace elements is ≤0.3%, and the balance is Al, wherein the Zn / Mg ratio is 4.75, and the η phase precipitation amount is 10.78%. The Cu element content of the alloy is not within the range of the present application.

[0046] Comparative Example 3

[0047] The alloy is prepared according to the component design criteria, and the alloy components are prepared according to the mass percentage: Zn: 9.5%, Mg: 2.0%, Cu: 3.5%, Fe: 0.15%, Zr: 0.1%, and the total amount of other trace elements is ≤0.3%, and the balance is Al, wherein the Zn / Mg ratio is 4.75, and the η phase precipitation amount is 10.78%. The Cu element content of the alloy is not within the range of the present application.

[0048] The materials were batched according to the set ratio, melted at 740℃, and held at 720℃. The ingots for extrusion were cast at 690℃ using a semi-continuous casting method. The homogenization process was as follows: the ingots were held at 520℃ for 10 hours, then slowly cooled to 420℃ at a rate of 5℃ / min, and then rapidly cooled to 200℃ at a rate of 40℃ / min before being cooled in the air after exiting the furnace. The extrusion process was as follows: the extrusion ingots were preheated to 480℃, the extrusion barrel temperature was set to 430℃, and then extruded at an extrusion speed of 1m / min. The extrusion was carried out using online water cooling quenching, followed by aging at 120℃ for 24 hours, aging at 175℃ for 135 minutes, and then aging at 120℃ for 24 hours to obtain the Al-Zn-Mg-Cu extruded profiles. The properties of the obtained extruded materials are shown in Table 1.

[0049] Example 1

[0050] According to the composition design criteria described in this invention, the alloy composition is designed firstly by taking M according to Equation 1. η The Zn / Mg ratio is 4.9, and according to Equation 1, the maximum value of Zn is 9.7%, thus determining Mg to be 1.98%. Based on the Cu element mass percentage of 1.7wt% to 2.5wt%, Cu is taken as 2.5%. Finally, based on the trace element mass percentage ≤ 0.67%, the specific composition of the example is: Zn: 9.7%, Mg: 1.98%, Cu: 2.5%, Fe: 0.15%, Zr: 0.15%, Si: 0.12%, Fe: 0.15%, with the balance being Al, wherein the Zn / Mg ratio is 4.9.

[0051] The materials were batched according to a set ratio, melted at 740℃, and held at 720℃. The ingots for extrusion were cast at 690℃ using a semi-continuous casting method. The homogenization process was as follows: the ingots were held at 520℃ for 10 hours, then slowly cooled to 420℃ at a rate of 5℃ / min, and then rapidly cooled to 200℃ at a rate of 40℃ / min before being cooled in the furnace air. The extrusion process was as follows: the extruded ingots were preheated to 480℃, the extrusion barrel temperature was set to 430℃, and then extruded at an extrusion speed of 1m / min. The extrusion was carried out using online water quenching, followed by aging at 120℃ for 24 hours, aging at 175℃ for 135 minutes, and then aging at 120℃ for 24 hours to obtain the Al-Zn-Mg-Cu extruded profiles. The η phase precipitation of the Al-Zn-Mg-Cu extruded profiles was 12.56%. The properties of the obtained extruded materials are shown in Table 1.

[0052] Example 2

[0053] The alloy component is designed according to the component design criterion of the application, and the alloy component is prepared in mass percentage as follows: Zn: 9.5%, Mg: 1.9%, Cu: 2.5%, Fe: 0.12%, Zr: 0.1%, Mn: 0.05%, Cr: 0.05%, and the balance of Al, wherein the Zn / Mg ratio is 5.

[0054] The ingredients are prepared according to the set proportion, smelted at 740 ℃, and the standing temperature is 720 ℃. The ingot for extrusion is cast by a semi-continuous casting method at 690 ℃. The homogenization treatment process is as follows: 520 ℃ for 10 h, then slowly cooled to 420 ℃ at a speed of 5 ℃ / min, and then rapidly cooled to 200 ℃ in air. The extrusion system is as follows: the extrusion ingot is preheated to 480 ℃, the extrusion cylinder temperature is set to 430 ℃, then extruded at a speed of 1 m / min, and then online water quenching is adopted. Aging is carried out at 120 ℃ for 24 h, at 175 ℃ for 135 min, and then at 120 ℃ for 24 h, to obtain the Al-Zn-Mg-Cu series extruded profile, and the precipitation amount of η phase is 12.07%. The performance of the obtained extruded profile is shown in Table 1.

[0055] Example 3

[0056] The alloy component is designed according to the component design criterion of the application, and the alloy component is prepared in mass percentage as follows: Zn: 9.5%, Mg: 1.9%, Cu: 2.5%, Fe: 0.12%, Zr: 0.1%, Mn: 0.05%, Cr: 0.05%, and the balance of Al, wherein the Zn / Mg ratio is 5.

[0057] The ingredients are prepared according to the set proportion, smelted at 740 ℃, and the standing temperature is 720 ℃. The ingot for extrusion is cast by a semi-continuous casting method at 690 ℃. The homogenization treatment process is as follows: 520 ℃ for 10 h, then slowly cooled to 420 ℃ at a speed of 5 ℃ / min, and then rapidly cooled to 200 ℃ in air. The extrusion system is as follows: the extrusion ingot is preheated to 480 ℃, the extrusion cylinder temperature is set to 430 ℃, then extruded at a speed of 1 m / min, and then online water quenching is adopted. Aging is carried out at 120 ℃ for 24 h, at 175 ℃ for 135 min, and then at 120 ℃ for 24 h, to obtain the Al-Zn-Mg-Cu series extruded profile, and the precipitation amount of η phase is 12.07%. The performance of the obtained extruded profile is shown in Table 1.

[0058] The results are shown in Table 1.

[0059] Table 1 Performance of the extruded profiles obtained in Comparative Examples 1-3 and Examples 1-3

[0060] Sample Tensile strength / MPa Fracture toughness / MPa-m 1 / 2 ]]> Comparative Example 1 640 39.01 Comparative Example 2 648 30.11 Comparative Example 3 635 35.25 Example 1 666 46.47 Example 2 657 39.68 Example 3 655 40.04

[0061] From Figure 1 It can be seen from the above that with the aging time prolonging, the intragranular and grain boundary precipitated phases are gradually grown and coarsened, the grain boundary is widened, and the obvious non-precipitated zone appears. After the alloy is treated at 120 DEG C for 24 hours, the intragranular and grain boundary precipitated phases are grown to a certain extent. The strength of the alloy treated at 120 DEG C for 24 hours is the highest, and the plasticity is also better, and the fracture toughness value of the material is also higher.

[0062] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-described embodiments. The improvements and changes obtained by those skilled in the art without departing from the technical concept of the present application should also be considered as the protection scope of the present application.

Claims

1. A method of designing an Al-Zn-Mg-Cu alloy, characterised by: The function relation of the η phase precipitation amount and the total amount of (Zn+Mg) and the Zn / Mg ratio in the Al-Zn-Mg-Cu alloy is shown in formula 1: wherein, x = c Zn + c Mg y = c Zn / c Mg In formula 1, M η is the η phase precipitation amount, which ranges from 6.30% to 10.20%; C Zn , C Mg are the mass contents of Zn and Mg in the Al-Zn-Mg-Cu alloy, respectively.

2. The Al-Zn-Mg-Cu alloy design method according to claim 1, characterized in that: The mass percentage of (Zn+Mg) in the Al-Zn-Mg-Cu alloy is 7.0wt%-12.0wt%. The mass ratio of Zn:Mg in the Al-Zn-Mg-Cu alloy is 3-5.

3. The Al-Zn-Mg-Cu alloy design method according to claim 2, characterized in that: The mass percentage of (Zn+Mg) in the Al-Zn-Mg-Cu alloy is 9.0wt%-11.0wt%. The mass ratio of Zn:Mg in the Al-Zn-Mg-Cu alloy is 4.

9.

4. The Al-Zn-Mg-Cu alloy design method according to claim 1, characterized in that: The mass percentage of Cu in the Al-Zn-Mg-Cu alloy is 1wt%-3wt%.

5. The Al-Zn-Mg-Cu alloy design method according to claim 4, characterized in that: The mass percentage of Cu in the Al-Zn-Mg-Cu alloy is 1.7wt%-2.5wt%.

6. The Al-Zn-Mg-Cu alloy design method according to claim 1, characterized in that: The mass percentage of trace elements in the Al-Zn-Mg-Cu alloy is ≤0.67%; The trace elements are selected from at least one of Si, Fe, Mn, Cr, Zr and Ti.

7. Use of a method of designing an Al-Zn-Mg-Cu alloy according to any one of claims 1 to 6, characterized in that: The Al-Zn-Mg-Cu alloy chemical composition design method is applied to obtain an Al-Zn-Mg-Cu alloy.

8. Use of a method of designing an Al-Zn-Mg-Cu alloy according to claim 7, characterized in that: The Al-Zn-Mg-Cu alloy is obtained by first designing the alloy composition by the Al-Zn-Mg-Cu alloy chemical composition design method, then obtaining an ingot by melting alloy raw materials in a designed proportion, and then performing post-processing on the ingot.

9. Use of a method of designing an Al-Zn-Mg-Cu alloy according to claim 6, characterized in that: The alloy raw materials are melted at 730-750℃, cooled to 715-725℃ and then cast at 680-700℃ to obtain an ingot. The post-processing process is in sequence: homogenization treatment, extrusion treatment, quenching, and aging treatment.

10. The application of the Al-Zn-Mg-Cu alloy design method according to claim 9, characterized in that: The homogenization treatment process is to first heat the ingot at 500-540℃ for 8-20h, then slowly cool it to 400-440℃ at a speed of 2-10℃ / min, and then rapidly cool it to 180-220℃ at a speed of 20-60℃ / min to cool in the air; The extrusion treatment process is to preheat the homogenization-treated blank to 460-490℃, set the extrusion cylinder temperature to 410-450℃, and then extrude at an extrusion speed of 0.5-2m / min. The aging process is aging at 110-140℃ for 8-30h, then holding at 155-185℃ for 60-180min, and then aging at 110-140℃ for 8-30h. The aging process is aging at 110-140℃ for 8-30h, then holding at 155-185℃ for 60-180min, and then aging at 110-140℃ for 8-30h.

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