Method for reducing mechanical property anisotropy of magnesium alloy forgings and use thereof

Abstract

The application provides a preparation method for reducing mechanical property anisotropy of a magnesium alloy forge piece and application thereof, and belongs to the technical field of magnesium alloys. The magnesium alloy forge piece comprises the following components in percentage by mass: Al: 5.50-9.30%, Zn: 0.31-0.55%, Mn: 0.12-0.38%, and the balance of Mg. The preparation method for reducing mechanical property anisotropy of the magnesium alloy forge piece comprises the following steps: smelting, casting, free forging, homogenizing annealing, isothermal forging and aging treatment. Compared with a deformed casting piece, the difference between the longitudinal and transverse yield strengths of the casting piece after the aging treatment is reduced from 80-90 MPa to 5-10 MPa. The application utilizes the characteristics of the deformation mechanism and the coupling of precipitated phases under the texture condition of the isothermal forging process, and realizes the reduction of the anisotropy of the magnesium alloy forge piece at a low cost, and is suitable for batch industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to magnesium alloy deformation processing technology, and in particular to a preparation method for reducing the mechanical property anisotropy of magnesium alloy forgings and its use. BACKGROUND

[0002] Magnesium alloy has excellent shock absorption performance, heat dissipation performance, impact resistance, dent resistance, electromagnetic shielding performance, etc. With the improvement of process technology, combined with the severity of energy and environmental problems, the application demand of magnesium alloy in important industries such as automobiles, rail transportation, construction, 3C, leisure and health, military and energy has increased dramatically in recent years. Due to the low cost, Mg-Al magnesium alloy is the most widely used magnesium alloy in commercial applications. The crystal structure of magnesium alloy is hexagonal close-packed structure, and the room temperature processing performance is poor. By using high temperature and low rate deformation method, the forming ability of magnesium alloy can be significantly improved. Isothermal forging technology is a common method for preparing large magnesium alloy forgings. Due to the activation of non-basal slip of magnesium alloy at high temperature, a specific texture is formed during the forming process, which leads to a certain degree of mechanical property anisotropy of magnesium alloy during service. The weak direction caused by texture limits the load-carrying capacity of large magnesium alloy forgings in complex service environment, which seriously limits the application and industrialization of large magnesium alloy forgings. For the problem of mechanical property anisotropy of large magnesium alloy forgings, the current method is mainly to design a specific die structure and optimize the process parameters. These methods often have high cost, and the optimization space is small due to the structure limitation of specific components. Therefore, it becomes a technical problem to be solved in the field to provide a low-cost and short-process method for reducing the mechanical property anisotropy of large magnesium alloy forgings with a size of 500mm-1000mm and its organization control. SUMMARY

[0003] The purpose of the present application is to provide a preparation method for reducing the mechanical property anisotropy of large magnesium alloy forgings, which has the advantages of simple process, low cost, and reduced mechanical property anisotropy of large magnesium alloy forgings, which can better meet the service requirements.

[0004] It should be noted that in the present application, unless otherwise specified, the specific meaning of "including" involved in the composition limitation and description includes both open-ended "including", "containing" and the like, and closed-ended "consisting of", "consisting of" and the like.

[0005] To achieve the above purpose, the technical solution adopted by the present application is: a preparation method for reducing the mechanical property anisotropy of large magnesium alloy forgings, comprising the following steps:

[0006] Step (1) Ingot preparation: melt the pure magnesium ingot, after the magnesium ingot is completely melted, inert gas is introduced, and manganese chloride, aluminum, zinc are added, under the condition of inert gas introduction, refining is carried out, after the refining is completed, slagging is carried out, and then the ingot is cast;

[0007] Step (2) Blooming and homogenization: after the ingot is annealed, free forging blooming is carried out, and then the blank is subjected to homogenization annealing treatment;

[0008] Step (3) Isothermal forging: heat the mold and the blank, keep the mold temperature at 360-410℃, keep the blank temperature at 350-400℃, the initial deformation speed is 0.5mm / s-1mm / s, after reaching the maximum load, keep the constant speed 0.005-0.01mm / s to the final forming, the load is 35-50MN, the forged piece is taken out of the mold and quenched in cold water;

[0009] Step (4) Aging treatment: the forged piece is subjected to aging treatment at 160-190℃, and the aging time is 5-20h.

[0010] Further, the composition of the magnesium alloy forged piece is: Al: 5.50-9.30%, Zn: 0.31-0.55%, Mn: 0.12-0.38%, and the balance is Mg. Unless otherwise specified, % in the present application is mass percent.

[0011] Further, the composition of the magnesium alloy forged piece is preferably: Al: 7.50-8.50%, Zn: 0.40-0.50%, Mn: 0.12-0.20%, and the balance is Mg.

[0012] Further, in step (1), the pure magnesium ingot is melted at 680-700℃, after the magnesium ingot is completely melted, inert gas is introduced, and after being heated to 770-785℃, manganese chloride, aluminum, zinc are added in sequence, this adding sequence can ensure the effect of removing impurities and avoid burning loss, under the condition of inert gas introduction, refining is carried out, the refining time is 15-25min, auxiliary process is carried out for melt treatment, after the refining is completed, slagging is carried out, then the alloy liquid is placed and cooled to the pouring temperature before being cast into an ingot; the pouring temperature is 680-695℃.

[0013] Further, the inert gas in step (1) is nitrogen and / or argon, or a mixture of carbon dioxide and carbon tetrachloride, preferably the gas is a mixture of carbon dioxide and carbon tetrachloride with a volume ratio of 6:1.

[0014] Further, the auxiliary process in step (1) is ultrasonic melt vibration, the ultrasonic time is 5-10min, using ultrasonic vibration technology can promote the effect of degassing and element dissolution.

[0015] Further, the homogenizing in step (2) is that the ingot is annealed at 400-420 DEG C for 15-25h, then free forging is carried out, and then the blank is homogenized at 370-390 DEG C for 15-30h.

[0016] Further, the isothermal forging in step (3) is that the mold and the blank are heated, the mold temperature is kept at 375-395 DEG C, the blank temperature is kept at 370-390 DEG C, the initial deformation speed is 0.7-0.9mm / s, after reaching the maximum load, the constant speed is kept at 0.005-0.007mm / s to the final forming, and the load is 40-50MN.

[0017] Further, the forging is quickly taken out from the mold by a hoisting device in step (3), and then quenched in water immediately, and the water temperature is 25-30 DEG C.

[0018] Further, the aging treatment in step (4) is that the forging is aged at 170-180 DEG C for 15-20h.

[0019] The application further discloses the use of the preparation method of the magnesium alloy forging with reduced mechanical property anisotropy in the field of magnesium alloy forgings, and is especially suitable for preparing large-size magnesium alloy forgings.

[0020] The application further discloses a magnesium alloy forging prepared by the method, and the forging has excellent mechanical properties and reduced mechanical property anisotropy.

[0021] Further, compared with the deformed castings, the difference between the longitudinal yield strength and the transverse yield strength of the magnesium alloy castings after aging treatment is reduced from 80-90MPa to 5-10MPa.

[0022] The application further discloses the use of the magnesium alloy forging in the fields of automobiles and spaceflight.

[0023] Compared with the prior art, the application has the following substantial characteristics and obvious progress:

[0024] 1) The invention builds the deformation texture and microstructure of magnesium alloy matched with the precipitation strengthening phase by controlling the forging process. For the magnesium alloy with hexagonal close-packed structure, the deformation amount needs to be large enough to improve the strength, thus the basal texture is formed. The degree of basal texture deflection determines the degree of mechanical property anisotropy of the alloy, and under the condition of isothermal forging, the activation of non-basal slip will inevitably lead to the formation of basal texture with a certain degree of deflection in magnesium alloy, thus the anisotropy is inevitable. Therefore, the basal texture without deflection cannot be achieved by adjusting the traditional processing technology, thus the target of reducing the mechanical property anisotropy cannot be directly achieved. However, the basal texture deflected along a specific direction and the degree of basal texture deflection can be achieved by processing technology. The deformation texture in magnesium alloy is mainly related to the deformation temperature and the deformation speed. The activation of different slip systems will lead to the formation of different textures in magnesium alloy, and the dynamic recrystallization during thermal deformation will also affect the texture of the alloy, thus the control of the texture of magnesium alloy can be achieved by using appropriate forging temperature and forging rate. A large number of experiments have verified that for the target magnesium alloy composition, when the forging temperature is 360-390℃ and the deformation speed is 0.005-0.01mm / s, the obtained magnesium alloy texture is the basal texture deflected about 15°-30° along the longitudinal direction, under the condition of the texture, the basal slip can be fully activated, which is most conducive to the coupling of basal slip and precipitated phase, realizing the strengthening of the weak direction, thereby reducing the mechanical property anisotropy.

[0025] 2) The invention realizes the control of the precipitated phase by alloy composition and aging treatment. Precipitation strengthening is a common strengthening method in magnesium alloy, its strengthening effect depends on the size, quantity, distribution and crystallographic orientation relationship of the precipitated phase and the matrix. The Mg 17 Al 12 phase is a common precipitated phase in Mg-Al magnesium alloy, which is divided into dynamic precipitated phase during thermal deformation and static precipitated phase during aging process, the combination of dynamic precipitated phase and static precipitated phase is beneficial to optimize the hindering effect of precipitated phase on dislocation movement, a large number of experiments have verified that when the Al content is 7.50-8.50%, the Zn content is 0.40-0.50%, the forging temperature is 360-390℃, and the deformation speed is 0.005-0.01mm / s, a large number of intracrystalline spherical dynamic Mg 17 Al 12 precipitated phase can be obtained, the size is about 160-190℃, and a large number of continuous Mg 17 Al 12 flaky precipitated phase can be obtained by subsequent aging treatment, thereby improving the precipitation strengthening effect, realizing the coupling with basal slip under the condition of the texture, thereby strengthening the weak direction, and further reducing the mechanical property anisotropy.

[0026] 3) Compared with the conventional high-temperature annealing treatment, the low-temperature aging treatment can reduce the anisotropy of the magnesium alloy forge piece at low cost without changing the texture, by utilizing the characteristics of the deformation mechanism and the coupled precipitated phase under the texture condition of the forging process. Compared with the deformed cast piece, the difference between the longitudinal and transverse yield strengths of the cast piece after the aging treatment is reduced from 80-90 MPa to 5-10 MPa.

[0027] In summary, the preparation method of the application can reduce the anisotropy of the mechanical properties of the magnesium alloy forge piece, is easy to implement, has low production cost, and can be applied to industrial batch production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The scanning electron microscope images of the forge pieces prepared for the comparative examples and the examples, wherein Fig. (a) is a scanning electron microscope image of the forge piece in the forged state, Figs. (b) and (c) are scanning electron microscope images of the forge pieces after aging at 170℃ for 7h and 16h, respectively;

[0029] Figure 2 The X-ray diffraction patterns of the magnesium alloy forge pieces prepared in the application in the forged state and after aging at 170℃ for 16h;

[0030] Figure 3 The texture image based on EBSD of the forge piece in the forged state;

[0031] Figure 4 The room temperature tensile curves of the forge pieces in the longitudinal and transverse directions in the forged state, after aging at 170℃ for 7h and 16h, wherein (a) is the room temperature tensile curve of the magnesium alloy forge piece of Comparative Example 1 and the magnesium alloy of Example 1 and Example 2, and (b) is the tensile curve of the magnesium alloy forge piece in the forged state and the aged state. DETAILED DESCRIPTION

[0032] Hereinafter, the application will be further described in conjunction with the examples. The description of the technical features described below is based on representative embodiments, specific examples of the application, but the application is not limited to these embodiments, specific examples. It should be noted that:

[0033] Unless otherwise specified, the units used in the specification are international standard units, and the numerical values and numerical value ranges appearing in the application should be understood to include the inevitable systematic errors in industrial production.

[0034] In the specification, the numerical value range represented by "numerical value A ~ numerical value B" refers to a range including the end point numerical values A and B.

[0035] In the specification, the numerical value range represented by "above" or "below" refers to a numerical value range including the number.

[0036] In the present specification, the meaning indicated by "may" includes both the meaning that a certain process is performed and the meaning that a certain process is not performed.

[0037] In the present specification, "optionally" or "optional" indicates that the use or non-use of certain substances, components, execution of steps, application of conditions, and the like is optional.

[0038] In the present specification, "normal temperature" or "room temperature" can be 15-30°C.

[0039] In the present specification, the reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by purchase on the market.

[0040] Comparative Example 1

[0041] Comparative Example 1 discloses a magnesium alloy forging isothermal forging preparation method, the magnesium alloy forging includes the following components by mass percentage: Al: 8.3%, Zn: 0.48%, Mn: 0.19%, the balance is Mg. Specifically, the preparation method includes the following steps:

[0042] (1) Ingot preparation: melt the pure magnesium ingot at 690°C, after the magnesium ingot is completely melted, inert gas is introduced, and after heating to 780°C, manganese chloride, aluminum, zinc is added in turn, refining is carried out under the condition of introducing inert gas, the refining time is 20 min, after refining, slagging is carried out, then the alloy liquid is placed and cooled to pouring temperature 685°C, and then cast into ingot;

[0043] (2) Blooming and homogenization: the ingot is annealed at 400°C for 15h, then free forging blooming is carried out, then the blank is homogenized at 385°C for 20h;

[0044] (3) Isothermal forging: heat the mold and the blank, keep the mold temperature at 385°C and the blank temperature at 380°C, the initial deformation speed is 0.8m / s, after reaching the maximum load, keep the constant speed 0.005mm / s to the final forming, the load is 35-50MN, the forging is quickly taken out from the mold by lifting device and immediately quenched in cold water, the water temperature is 25°C, and the magnesium alloy forging is prepared.

[0045] Comparative Example 2

[0046] Comparative Example 2 discloses a magnesium alloy forging isothermal forging preparation method, the magnesium alloy forging includes the following components by mass percentage: Al: 8.1%, Zn: 0.47%, Mn: 0.17%, the balance is Mg. Including the following steps:

[0047] (1) Ingot preparation: melt the pure magnesium ingot at 690°C, after the magnesium ingot is completely melted, inert gas is introduced, and after being heated to 780°C, manganese chloride, aluminum and zinc are sequentially added, refining is carried out under the condition of introducing inert gas, the refining time is 20 min, after the refining is completed, slagging is carried out, then the alloy liquid is placed and cooled to the pouring temperature 685°C, and then cast into an ingot;

[0048] (2) Blooming and homogenization: anneal the ingot at 400°C for 15h, then carry out free forging blooming, then homogenize the blank at 385°C for 20h;

[0049] (3) Isothermal forging: heat the mold and the blank, keep the mold temperature at 360°C and the blank temperature at 350°C, the initial deformation speed is 1.4m / s, after reaching the maximum load, keep the constant speed 0.005mm / s to the final forming, the load is 35-50MN, the forged piece is quickly taken out of the mold by the lifting device and immediately quenched in cold water, the water temperature is 25°C;

[0050] (4) Aging treatment: age the forged piece at 170°C for 16h, to prepare a magnesium alloy forged piece.

[0051] Example 1

[0052] The example 1 discloses a preparation method for reducing the mechanical property anisotropy of a magnesium alloy forged piece, the magnesium alloy forged piece comprises the following components in mass percentage: Al: 8.3%, Zn: 0.48%, Mn: 0.19%, and the balance is Mg. The preparation method comprises the following steps:

[0053] (1) Ingot preparation: melt the pure magnesium ingot at 690°C, after the magnesium ingot is completely melted, inert gas is introduced, and after being heated to 780°C, manganese chloride, aluminum and zinc are sequentially added, refining is carried out under the condition of introducing inert gas, the refining time is 20 min, after the refining is completed, slagging is carried out, then the alloy liquid is placed and cooled to the pouring temperature 685°C, and then cast into an ingot;

[0054] (2) Blooming and homogenization: anneal the ingot at 400°C for 15h, then carry out free forging blooming, then homogenize the blank at 385°C for 20h;

[0055] (3) Isothermal forging: heat the mold and the blank, keep the mold temperature at 385°C and the blank temperature at 380°C, the initial deformation speed is 0.8m / s, after reaching the maximum load, keep the constant speed 0.005mm / s to the final forming, the load is 35-50MN, the forged piece is quickly taken out of the mold by the lifting device and immediately quenched in cold water, the water temperature is 25°C;

[0056] (4) Aging treatment: The forging is aged at 170℃ for 7 hours to obtain magnesium alloy forging.

[0057] Example 2

[0058] This embodiment 1 discloses a method for preparing magnesium alloy forgings with reduced anisotropy in mechanical properties. The magnesium alloy forgings comprise the following components by mass percentage: Al: 8.3%, Zn: 0.48%, Mn: 0.19%, with the balance being Mg. The method includes the following steps:

[0059] (1) Ingot preparation: Pure magnesium ingots are melted at 690℃. After the magnesium ingots are completely melted, inert gas is introduced. After the temperature is raised to 780℃, manganese chloride, aluminum and zinc are added in sequence. Refining is carried out under the condition of introducing inert gas for 20 minutes. After refining, slag is removed. Then the alloy liquid is allowed to stand and cooled to the pouring temperature of 685℃ before being cast into ingots.

[0060] (2) Billet opening and homogenization: The ingot is annealed at 400℃ for 15h, then free forging is performed to open the billet, and then the billet is homogenized and annealed at 385℃ for 20h.

[0061] (3) Isothermal forging: Heat the mold and billet to keep the mold temperature at 385℃ and the billet temperature at 380℃. The initial deformation speed is 0.8m / s. After reaching the maximum load, maintain a constant speed of 0.005mm / s until the final forming. The load is 35-50MN. The forging is quickly removed from the mold by the lifting device and immediately quenched in cold water at a temperature of 25℃.

[0062] (4) Aging treatment: The forgings are aged at 170℃ for 16 hours to obtain magnesium alloy forgings.

[0063] Based on the comparative examples and embodiments, its mechanical properties and microstructure characterization are as follows: Figures 1-4 As shown:

[0064] Figure 1 Scanning electron microscope (SEM) images of magnesium alloy forgings in the forged state, after aging at 170℃ for 7 h and 16 h. The images show that the magnesium alloy in the forged state contains a small amount of spherical dynamic precipitates within the grains and at the grain boundaries. After aging, a large number of precipitates are precipitated within the grains, and the number of precipitates increases with the increase of aging time.

[0065] Figure 2 The XRD diffraction patterns of magnesium alloy forgings are shown in the forged state and after aging at 170℃ for 16 hours. The figures reveal that the forged state mainly consists of an α-Mg matrix and a small amount of β-Mg17Al12 phase. Figure 1 The spherical dynamic precipitate in the middle is also the β-Mg17Al12 phase after aging treatment.

[0066] Figure 3 The figure shows the {0001} texture of a magnesium alloy forging in the forged state. As can be seen from the figure, the texture of the forging is a base plane texture deflected by about 20° in the transverse direction, which results in a lower yield strength in the transverse direction than in the longitudinal direction. Since the aging process temperature is only 170℃, the alloy basically does not recrystallize, and the texture in the aged state can be considered to be consistent with that in the forged state.

[0067] Figure 4 (a) The room temperature tensile curves of the magnesium alloy forging in Comparative Example 1 and the magnesium alloys in Examples 1 and 2 are shown. As can be seen from the figure, the longitudinal and transverse tensile strengths, yield strengths, and elongations in the forged state are 262 MPa, 128 MPa, and 10.7%; and 343 MPa, 214 MPa, and 8.9%, respectively. The difference between the longitudinal and transverse yield strengths is 86 MPa. After aging at 170℃ for 7 hours, the longitudinal and transverse tensile strengths, yield strengths, and elongations are 307 MPa, 178 MPa, and 8.5%; and 347 MPa, 228 MPa, and 7.8%, respectively. The difference between the longitudinal and transverse yield strengths is 46 MPa. After aging at 170℃ for 16 hours, the longitudinal and transverse tensile strengths, yield strengths, and elongations are 343 MPa, 246 MPa, and 3.6%; and 367 MPa, 251 MPa, and 4.8%, respectively. The difference between the longitudinal and transverse yield strengths is 5 MPa. Therefore, it can be seen that the anisotropy of the mechanical properties of magnesium alloy forgings prepared by the process described in this invention can be reduced by aging treatment. As the aging time is extended, the anisotropy of the longitudinal and transverse mechanical properties is reduced more significantly.

[0068] Figure 4 (b) Tensile curves of the forged and aged magnesium alloy forgings of Comparative Example 2. As shown in the figure, the longitudinal and transverse tensile strengths, yield strengths, and elongations of the magnesium alloy forgings prepared using the forging process described in Comparative Example 2 are 303 MPa, 170 MPa, and 9.5% in the forged state, and 356 MPa, 190 MPa, and 12.6% in the transverse state, with a yield strength difference of 20 MPa between the longitudinal and transverse states. After aging at 170℃ for 16 hours, the longitudinal and transverse tensile strengths, yield strengths, and elongations are 334 MPa, 239 MPa, and 2.8% in the forged state, and 369 MPa, 260 MPa, and 3.2% in the transverse state, with a yield strength difference of 21 MPa between the longitudinal and transverse states. Therefore, it can be concluded that the anisotropy of the mechanical properties of the forgings prepared using the process described in Comparative Example 2 is not weakened.

[0069] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A magnesium alloy wrought product, characterized by, Prepared by the following method: Step (1) Ingot preparation: melt pure magnesium ingot at 680-700℃, after the magnesium ingot is completely melted, inert gas is introduced, and after the temperature is raised to 770-785℃, manganese chloride, aluminum, and zinc are sequentially added, which can ensure the effect of impurity removal and avoid burning loss, refining is carried out under the condition of inert gas introduction, the refining time is 15-25min, auxiliary process is carried out for melt treatment, after refining, slag is removed, then the alloy liquid is placed and cooled to pouring temperature before being cast into ingot; the pouring temperature is 680-695℃; the auxiliary process is ultrasonic melt vibration, the ultrasonic time is 5-10min; Step (2) Blooming and homogenization: the ingot is annealed at 400-420℃ for 15-25h, then free forging blooming is carried out, then the blank is homogenized at 370-390℃ for 15-30h; Step (3) Isothermal forging: heat the mold and blank, keep the mold temperature at 375-395℃ and the blank temperature at 370-390℃, the initial deformation speed is 0.7-0.9mm / s, after reaching the maximum load, keep the constant speed at 0.005-0.007mm / s to the final forming, the load is 40-50MN, the forged piece is taken out of the mold and quenched in cold water; Step (4) Aging treatment: the forged piece is aged at 160-190℃ for 5-20h; The magnesium alloy ingot has the following component quality percentage: Al: 7.50-8.50%, Zn: 0.40-0.50%, Mn: 0.12-0.20%, and the balance is Mg; The difference between the longitudinal and transverse yield strengths of the magnesium alloy casting is 5-10MPa.

2. The magnesium alloy wrought article of claim 1, wherein, Step (3) The forged piece is quickly taken out of the mold by the lifting device and immediately quenched in water, the water temperature is 25-30℃.

3. The magnesium alloy wrought article of claim 1, wherein, Step (4) The aging treatment: the forged piece is aged at 170-180℃ for 15-20h.

4. Use of the magnesium alloy ingot of claim 1 in the fields of automobiles and aerospace.

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