Method for improving fatigue crack propagation resistance of al-zn-mg alloy extrusions

Abstract

The present application relates to Al-Zn-Mg alloy extruded profiles, and particularly relates to a method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy extruded profiles. The method comprises: subjecting an Al-Zn-Mg alloy ingot to multi-stage homogenization annealing treatment, and then subjecting the homogenization annealed ingot to hot extrusion to obtain an Al-Zn-Mg alloy hot extruded profile; and then subjecting the Al-Zn-Mg alloy hot extruded profile to solid solution treatment and artificial aging treatment in sequence; the content of V in the Al-Zn-Mg alloy is 0.05-0.1% by mass percentage. The method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy extruded profiles by adding V further improves the service life of Al-Zn-Mg alloy extruded profiles through component design and process optimization.

Description

TECHNICAL FIELD

[0001] The present application relates to Al-Zn-Mg alloy extruded profiles, in particular to a method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy extruded profiles by adding V. BACKGROUND

[0002] Al-Zn-Mg alloy has high specific strength, good fracture toughness, good corrosion resistance, good processing performance and excellent welding performance. Various specifications of extruded profiles, plates and forgings can be produced by pressure processing such as extrusion, rolling and the like. As a lightweight structural material, Al-Zn-Mg alloy extruded profiles have been widely used in important fields such as rail transportation and automobiles. With the development of rail transportation industry, Al-Zn-Mg alloy extruded profiles with strength, toughness, corrosion resistance and fatigue resistance have been widely used as important lightweight structural materials. Further improving the service life of Al-Zn-Mg alloy extruded profiles is of great significance to ensure the safety and reliability of rail transportation. SUMMARY

[0003] The present application provides a method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy extruded profiles, which further improves the service life of Al-Zn-Mg alloy extruded profiles through composition design and process optimization.

[0004] A method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy, comprising: performing multi-stage homogenization annealing treatment on Al-Zn-Mg alloy ingot, then performing high extrusion ratio hot extrusion on the homogenization annealing treated ingot to obtain Al-Zn-Mg alloy hot extruded profile; and then sequentially performing solid solution treatment and artificial aging treatment on the Al-Zn-Mg alloy hot extruded profile.

[0005] According to the embodiment of the present application, the content of V (vanadium element) in the Al-Zn-Mg alloy is 0.05-0.1% in terms of mass percentage, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%. Research shows that if the content of V is less than 0.05%, the amount of dispersed phase precipitates is less, the effect on preventing recrystallization and refining grains is limited, and the improvement of the tensile properties of the alloy is also limited. Compared with the alloy without V, the improvement of the median fatigue strength of the alloy with V content less than 0.05% is also limited, and the improvement of the fatigue property by adding V content less than 0.05% is limited, and the anti-fatigue crack propagation performance is not obviously improved. If the content of V is higher than 0.1%, the amount of dispersed phase precipitates increases, the existence of a large amount of dispersed phase delays the recrystallization process and increases the recrystallization temperature, showing high recrystallization resistance, and refining the grains; compared with the alloy without V, the tensile strength is obviously improved, and at the same time, with the excessive addition of V, the improvement of the tensile strength of the alloy is limited. At the same time, the median fatigue strength of the alloy is improved, but the microsecond phase distribution in the alloy is poor, although the alloy has high anti-recrystallization ability, but the number of micro-coarse particles which are easy to form fatigue crack sources increases, and the anti-fatigue crack propagation performance of the alloy will decrease.

[0006] The inventor found that by adding V element appropriately, the fine dispersed V-containing phase formed in the aluminum matrix during high extrusion ratio hot extrusion hinders the migration of recrystallized grain boundaries, inhibits recrystallization, forms a grain structure mainly with {111} Al deformation texture, and the fine dispersed V-containing phase and the deformation texture jointly hinder crack propagation.

[0007] According to the embodiment of the present application, the composition of the Al-Zn-Mg alloy ingot is as follows in terms of mass percentage: Zn: 4.05-5.05%, Mg: 0.75-1.5%, Cu: 0.1-0.2%, Mn: 0.25-0.35%, Zr: 0.1-0.2%, Cr: 0.2-0.3%, Ti: 0.05-0.1%, V: 0.05-0.1%, Si: 0.05-0.15%, Fe: 0.05-0.2%, and the balance is Al.

[0008] According to the embodiment of the present application, the multi-stage homogenization annealing treatment includes: sequentially homogenizing at 350-410℃ for 5-10h, homogenizing at 410-450℃ for 1-6h, and homogenizing at 460-490℃ for 10-24h. Research shows that the multi-stage homogenization annealing treatment under the above conditions can eliminate the internal stress of the ingot in the production process, make the microstructure uniform, eliminate the dendrites, improve the distribution of the second phase, and make the dispersed phase in the alloy more uniform, thereby improving the anti-fatigue crack propagation performance of the Al-Zn-Mg alloy.

[0009] Specifically, the multi-stage homogenization annealing treatment comprises homogenization at 380 DEG C for 8h, homogenization at 430 DEG C for 4h, and homogenization at 475 DEG C for 16h.

[0010] According to the embodiment of the present application, the hot extrusion comprises heating the multi-stage homogenization annealing treated ingot to 420-490 DEG C, the extrusion cylinder temperature is 420-490 DEG C, the extrusion speed of the extrusion material is 4-20 m / min, and the extrusion ratio is greater than or equal to 10. Research shows that the high extrusion ratio hot extrusion treatment under the above conditions can improve the distribution of the second phase, make the dispersion phase in the alloy more uniform, dense and small, the pinning effect of dislocations more significant, and the grain uniformity improved, thereby further improving the fatigue crack propagation resistance of the Al-Zn-Mg alloy extrusion material.

[0011] According to the embodiment of the present application, the extrusion speed of the extrusion material during the hot extrusion is 5-18 m / min.

[0012] According to the embodiment of the present application, the extrusion ratio of the hot extrusion is 10, 11 or 12.

[0013] Specifically, the hot extrusion comprises heating the multi-stage homogenization annealing treated ingot to 450-470 DEG C, the extrusion cylinder temperature is 450-470 DEG C, the extrusion speed of the extrusion material is 5-15 m / min, and the extrusion ratio is 12.

[0014] According to the embodiment of the present application, the temperature of the solid solution treatment is 450-490 DEG C, and the time of the solid solution treatment is 1-3h. Specifically, the temperature of the solid solution treatment is 475 DEG C, and the time of the solid solution treatment is 1h. After the solid solution treatment, water cooling is performed to room temperature.

[0015] According to the embodiment of the present application, the artificial aging treatment is aging at 90-130 DEG C for 10-20h. For example, aging at 120 DEG C for 15h.

[0016] The present application also comprises the Al-Zn-Mg alloy extrusion profile prepared by the above method.

[0017] The present application provides a method for improving the fatigue crack propagation resistance of Al-Zn-Mg alloy extrusion material. The Al-Zn-Mg alloy ingot is subjected to multi-stage homogenization annealing treatment, then the ingot after the homogenization annealing treatment is subjected to high extrusion ratio hot extrusion to obtain Al-Zn-Mg alloy profile, and finally the Al-Zn-Mg alloy hot extrusion profile is subjected to solid solution treatment and artificial aging treatment in sequence. Through optimization of the homogenization process, high extrusion ratio hot extrusion, solid solution and aging heat treatment, a microstructure with small size, dispersed V-containing second phase and {111} Al deformation texture is obtained, thereby effectively improving the fatigue crack propagation resistance of the Al-Zn-Mg alloy extrusion material. DETAILED DESCRIPTION

[0018] The following examples are used to illustrate the present application, but are not intended to limit the scope of the present application.

[0019] The following method is used to prepare the Al-Zn-Mg alloy ingot: the raw materials are taken according to the designed components, and the Al-Zn-Mg ingot is obtained by melting and casting.

[0020] Example 1

[0021] The present example provides a method for improving the fatigue crack propagation resistance of an Al-Zn-Mg alloy extruded product, which comprises:

[0022] ① Multi-stage homogenization annealing: after machining the outer surface of the Al-Zn-Mg ingot, homogenization treatment is performed in a heat treatment furnace, and the homogenization treatment process is 8h at 380℃, 4h at 430℃, and 16h at 475℃.

[0023] ② Hot extrusion: the ingot after multi-stage homogenization annealing is heated to 450℃, the extrusion cylinder temperature is 470℃, the extrusion speed of the extruded product is 10m / min, and the extrusion ratio is 12.

[0024] ③ Solution treatment: the solution treatment temperature is 475℃, the solution treatment time is 1h, and after the solution treatment is completed, water cooling is performed to room temperature.

[0025] ④ Artificial aging: aging is performed at 120℃ for 15h.

[0026] The component composition of the Al-Zn-Mg alloy ingot of the present example is as follows: Zn: 4.50%, Mg: 1.21%, Cu: 0.13%, Mn: 0.30%, Zr: 0.15%, Cr: 0.22%, Ti: 0.06%, V: 0.1%, Si: 0.07%, Fe: 0.06%, and the balance is Al.

[0027] Example 2

[0028] The present example provides a method for improving the fatigue crack propagation resistance of an Al-Zn-Mg alloy extruded product, which differs from Example 1 only in that the content of V in the Al-Zn-Mg alloy ingot is 0.05%.

[0029] Example 3

[0030] The present example provides a method for improving the fatigue crack propagation resistance of an Al-Zn-Mg alloy extruded product, which differs from Example 1 only in that the content of V in the Al-Zn-Mg alloy ingot is 0.09%.

[0031] Comparative Example 1

[0032] The difference between this comparative example and Example 1 is only in the homogenization annealing, which is as follows: 1) Homogenization annealing: the Al-Zn-Mg ingot was machined on the outer surface and then homogenized in a heat treatment furnace at 475°C for 16h.

[0033] Comparative Example 2

[0034] The difference between this comparative example and Example 1 is only in the homogenization annealing and hot extrusion, which is as follows:

[0035] 1) Homogenization annealing: the ingot was machined on the outer surface and then homogenized in a heat treatment furnace at 475°C for 16h.

[0036] 4) Hot extrusion: the homogenized ingot was heated to 450°C, the extrusion cylinder temperature was 470°C, the extrusion speed of the extrusion material was 10m / min, and the extrusion ratio was 6.

[0037] Comparative Example 3

[0038] The difference between this comparative example and Example 1 is only in the hot extrusion, which is as follows:

[0039] 4) Hot extrusion: the homogenized ingot was heated to 450°C, the extrusion cylinder temperature was 470°C, the extrusion speed of the extrusion material was 25m / min, and the extrusion ratio was 8.

[0040] Comparative Example 4

[0041] The difference between this comparative example and Example 1 is only in that the content of V in the Al-Zn-Mg ingot is 0.03%.

[0042] Comparative Example 5

[0043] The difference between this comparative example and Example 1 is only in that the content of V in the Al-Zn-Mg ingot is 0.15%.

[0044] Experimental Example

[0045] Table 1 is the fatigue crack growth rate of the Al-Zn-Mg alloy profiles prepared in Examples 1-3 and Comparative Examples 1-5. The detection method is ASTM E647 Standard test method for measurement of fatigue crack growth rates.

[0046] Table 1

[0047]

[0048] As can be seen, the comparative examples have a high fatigue crack growth rate, the crack growth rate of the examples is lower relative to the comparative examples, and Example 1 has a lower fatigue crack growth rate. This indicates that the fatigue crack growth resistance of the examples is better.

[0049] While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. It is therefore intended that such changes and modifications be included within the scope of the application as defined by the appended claims.

Claims

1. A method of improving the fatigue crack growth resistance of an Al-Zn-Mg alloy characterised in that, The application relates to an Al-Zn-Mg alloy and a preparation method thereof. The Al-Zn-Mg alloy ingot is subjected to multistage homogenization annealing treatment, and then the ingot after the homogenization annealing treatment is subjected to hot extrusion to obtain an Al-Zn-Mg alloy hot extrusion profile; The Al-Zn-Mg alloy hot extrusion profile is sequentially subjected to solid solution treatment and artificial aging treatment; The multistage homogenization annealing treatment comprises the following steps: homogenization at 350-410 DEG C for 5-10 h, homogenization at 410-450 DEG C for 1-6 h, and homogenization at 460-490 DEG C for 10-24 h; The hot extrusion comprises the following steps: heating the ingot after the multistage homogenization annealing treatment to 420-490 DEG C, setting the extrusion cylinder temperature to 420-490 DEG C, setting the extrusion speed of the extrusion material to 4-20 m / min, and setting the extrusion ratio to 10, 11 or 12; The Al-Zn-Mg alloy ingot comprises the following components in percentage by mass: Zn: 4.05-5.05%, Mg: 0.75-1.5%, Cu: 0.1-0.2%, Mn: 0.25-0.35%, Zr: 0.1-0.2%, Cr: 0.2-0.3%, Ti: 0.05-0.1%, V: 0.05-0.1%, Si: 0.05-0.15%, Fe: 0.05-0.2%, and the balance of Al.

2. The method of claim 1, wherein the Al-Zn-Mg alloy is a wrought alloy. The multistage homogenization annealing treatment comprises the following steps: homogenization at 380 DEG C for 8 h, homogenization at 430 DEG C for 4 h, and homogenization at 475 DEG C for 16 h.

3. The method of improving the fatigue crack growth resistance of an Al-Zn-Mg alloy according to claim 1 or 2, characterized in that The hot extrusion comprises the following steps: heating the ingot after the multistage homogenization annealing treatment to 450-470 DEG C, setting the extrusion cylinder temperature to 450-470 DEG C, setting the extrusion speed of the extrusion material to 5-15 m / min, and setting the extrusion ratio to 12.

4. The method of claim 1, wherein the Al-Zn-Mg alloy is a 7XXX-series aluminum alloy. The solid solution treatment is performed at a temperature of 450-490 DEG C for 1-3 h.

5. The method of claim 1, wherein the Al-Zn-Mg alloy is a 7XXX-series aluminum alloy. The artificial aging treatment is aging at 90-130 DEG C for 10-20 h.

6. An Al-Zn-Mg alloy extruded profile, characterized in that The Al-Zn-Mg alloy is prepared by the method in any one of claims 1-5.

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