CN111957892B - Heat treatment method of aluminum/magnesium bimetal for lost foam casting and product - Google Patents
Heat treatment method of aluminum/magnesium bimetal for lost foam casting and product Download PDFInfo
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- CN111957892B CN111957892B CN202010900904.5A CN202010900904A CN111957892B CN 111957892 B CN111957892 B CN 111957892B CN 202010900904 A CN202010900904 A CN 202010900904A CN 111957892 B CN111957892 B CN 111957892B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D19/00—Casting in, on, or around objects which form part of the product
- B22D19/16—Casting in, on, or around objects which form part of the product for making compound objects cast of two or more different metals, e.g. for making rolls for rolling mills
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
Abstract
The invention belongs to the technical field related to heat treatment, and discloses a heat treatment method and a product of aluminum/magnesium bimetal for lost foam casting. The method comprises the following steps: s1 forming an aluminum/magnesium bimetal casting; s2, heating to a first preset temperature, and preserving heat to realize the transformation of the aluminum/magnesium bimetal casting from a low-melting-point phase to a high-melting-point phase; s3, raising the temperature to a second preset temperature again after S2, wherein the second preset temperature is higher than the first preset temperature, preserving the heat and cooling; s4, raising the temperature to a third preset temperature again, wherein the third preset temperature is lower than the first preset temperature, and cooling along with the furnace after heat preservation, so as to realize the heat treatment of the aluminum/magnesium bimetal casting. The invention reduces the stress concentration of the interface metallurgical layer, prevents the generation of crack defects, enhances the connection strength of the metallurgical layer and the aluminum matrix, improves the performance of aluminum/magnesium bimetal and reduces the heat treatment cost.
Description
Technical Field
The invention belongs to the technical field related to heat treatment, and particularly relates to a heat treatment method and a product of aluminum/magnesium bimetal for lost foam casting.
Background
The aluminum/magnesium bimetal part has the advantages of aluminum and magnesium, and has wide application prospect in the fields of automobiles, electronic 3C, aerospace and the like. The lost foam casting solid-liquid composite technology is a new method for preparing the aluminum/magnesium bimetal part, and has a plurality of advantages, such as suitability for preparing complex parts, no need of additional fixation of an inlay, contribution to metallurgical bonding and the like. Typically, the as-cast part requires heat treatment to further improve the properties of the as-cast part. Therefore, the aluminum/magnesium bimetal casting prepared by the lost foam casting solid-liquid composite technology also needs to be further improved in performance through heat treatment.
The aluminum/magnesium bimetal prepared by the lost foam casting solid-liquid composite technology has the particularity, is obviously different from a single-component metal material, and consists of three parts with different components, namely an aluminum matrix, a magnesium matrix and an interface metallurgical reaction layer. The width of the interface metallurgical reaction layer can reach 1500 mu m, and the interface metallurgical reaction layer consists of three different reaction layers: al near the magnesium matrix side12Mg17+ delta-Mg eutectic structure, Al near the aluminum matrix side3Mg2+Mg2Si and Al between two reaction layers12Mg17+Mg2And (3) Si. The components of the reaction layer are distributed unevenly, and the hardness of the reaction layer is obviously higher than that of the aluminum matrix and magnesium matrix metals, so that the stress concentration at the interface is caused, the fracture is easy to occur at the interface, and the performance of the aluminum/magnesium bimetal is reduced; at present, the heat treatment method for the aluminum/magnesium bimetal is mainly used in the fields of welding, rolling and the like, and the purpose is mainly to convert the aluminum/magnesium bimetal from mechanical bonding without metallurgy into metallurgical bonding, so that the performance of the aluminum/magnesium bimetal is improved. But the lost foam casting solid-liquid composite aluminum/magnesium bimetal has a wider metallurgical interface layer and is a metallurgical bonding. Therefore, prior heat treatment processes suitable for use in the welding and rolling arts would no longer be suitable for the bimetallic of this patent.
In general, the heat treatment methods commonly used for aluminum alloys and magnesium alloys include solution treatment, aging treatment and homogenization treatment. The solution treatment is to heat the casting to a certain higher temperature below the solidus line, so that some solid solutions which do not reach the saturated state reach the supersaturated solid solution state under the conditions of higher temperature and long-time heat preservation, and then quickly cool the casting so that second phases are not precipitated in time, thereby realizing the purpose of solution strengthening. The solution treatment needs to rapidly cool the part by quenching, and because the expansion coefficients of the interface layer intermetallic compound and the matrix are greatly different, the aluminum/magnesium bimetal generates crack defects between an interface metallurgical reaction layer and an aluminum matrix in the rapid cooling process. The aging treatment is to re-precipitate the second phase in the supersaturated solid solution to achieve the purpose of aging strengthening, but the single aging treatment has little influence on the structure and the performance of the bimetal because the temperature is lower and the solid solution process is not carried out. The homogenization treatment is to heat the casting to a certain higher temperature below the solidus line, keep the temperature for a long time and then slowly cool the casting down, and the cooling mode of the homogenization annealing is generally air cooling or furnace cooling, so the cooling speed is slow. Therefore, the crack defect occurring at the interface can be eliminated using the homogenization treatment. However, the separate homogenization treatment may cause an overburning phenomenon due to a long treatment time, and also increases the cost. Therefore, it is necessary to develop a new heat treatment method suitable for lost foam casting of solid-liquid composite aluminum/magnesium bimetal, so as to improve the aluminum/magnesium bimetal structure and improve the bimetal performance.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a heat treatment method and a product of aluminum/magnesium bimetal for lost foam casting, which can strengthen the performance of the aluminum/magnesium bimetal by means of multi-stage homogenization treatment and aging treatment.
To achieve the above object, according to one aspect of the present invention, there is provided the method comprising the steps of:
preparation of S1 aluminum/magnesium bimetal casting
Forming an aluminum/magnesium bimetal casting by using an aluminum alloy as a solid inlay and a lost foam casting method of a magnesium alloy pouring foam model;
s2 multistage homogenization treatment
S21 first-stage heating treatment
Putting the aluminum/magnesium bimetal casting prepared in the step S1 into a heat treatment furnace, heating to a first preset temperature, and preserving heat to realize the transformation of the aluminum/magnesium bimetal casting from a low-melting-point phase to a high-melting-point phase;
s22 Secondary Heat treatment
Raising the temperature of the aluminum/magnesium bimetal casting subjected to the step S21 to a second preset temperature, wherein the second preset temperature is higher than the first preset temperature, preserving the heat, cooling, and carrying out heat preservation and cooling on the aluminum/magnesium bimetal castingDuring the stage heating treatment, an Al-based solid solution + Mg is generated between the Al matrix and the aluminum/magnesium interface layer2A new diffusion layer composed of Si, which enhances the connection of the interface structure and the aluminum matrix;
s3 aging treatment
And (4) raising the temperature of the aluminum/magnesium bimetal casting cooled in the step (S2) to a third preset temperature, wherein the third preset temperature is lower than the first preset temperature, and cooling the aluminum/magnesium bimetal casting along with the furnace after heat preservation, so as to realize the heat treatment of the aluminum/magnesium bimetal casting.
Further preferably, in step S21, the first preset temperature in the primary heating treatment is 370 to 390 ℃, the temperature rise rate is 4 to 6 ℃/min, and the heat preservation time is 4 to 8 hours.
Further preferably, in step S22, the second preset temperature in the secondary heating treatment is 410 to 430 ℃, the heating rate is 4 to 6 ℃/min, and the heat preservation time is 6 to 12 hours.
Further preferably, in step S3, the third preset temperature in the aging treatment is 170 to 200 ℃, the temperature rise rate is 4 to 6 ℃/min, and the heat preservation time is 14 to 20 hours.
Further preferably, in steps S22 and S3, the cooling manner is furnace cooling.
Further preferably, in step S1, the method of lost foam casting is performed according to the following steps:
s11, obtaining an aluminum alloy solid inlay, and embedding the aluminum inlay into a foam model after polishing and cleaning to prepare a composite model;
s12, coating paint on the composite model, after the paint is dried, putting the composite model into a sand box, burying sand for molding, and vibrating and compacting;
s13, covering a layer of plastic film on the top of the sand box, and vacuumizing;
s14, pouring the magnesium alloy liquid into the foam model, taking out the casting after the casting is cooled and solidified, and cutting off the pouring system to obtain the aluminum/magnesium bimetal casting.
According to another aspect of the invention, there is provided an aluminum/magnesium bi-metal obtained by the heat treatment method.
Generally, compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. according to the invention, the interface structure of the aluminum/magnesium bimetal can be homogenized by using the heat treatment method of multi-stage homogenization treatment and aging treatment, the hardness of the interface structure is reduced, the stress concentration is reduced, and simultaneously the matrix structure is improved, so that the overall performance of the aluminum/magnesium bimetal is improved, wherein the multi-stage homogenization treatment is used for replacing single-stage homogenization treatment, the heat treatment time can be reduced, the overburning is prevented, and the heat treatment cost is reduced;
2. the multistage homogenization treatment adopts lower heating rate and cooling rate, can regulate and control the expansion and contraction processes of the intermetallic compound of the aluminum/magnesium bimetal interface layer and the matrix, and prevents the generation of crack defects of the interface region in the heat treatment process;
3. after the multi-stage homogenization treatment in the invention, a new Al (Mg) solid solution + Mg is generated between the interface metallurgy reaction layer and the aluminum matrix2The reaction layer composed of Si enhances the connection strength of the interface metallurgy reaction layer and the aluminum matrix.
Drawings
FIG. 1 is a flow chart of a heat treatment constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is a graph of temperature versus time during a heat treatment process constructed in accordance with a preferred embodiment of the present invention;
FIG. 3 is a microstructure of a lost foam cast solid-liquid composite aluminum/magnesium bi-metal constructed in accordance with a preferred embodiment of the present invention, wherein (a) is the interface region microstructure; (b) the microstructure corresponding to region a in panel (a); (c) the microstructure corresponding to region B in panel (a); (d) the microstructure corresponding to region C in panel (a);
FIG. 4 is a multi-stage homogenized + aged aluminum/magnesium bimetallic microstructure constructed in accordance with a preferred embodiment of the present invention, wherein (a) the interface region microstructure; (b) the microstructure corresponding to region a in panel (a); (c) the microstructure corresponding to region B in panel (a); (d) the microstructure corresponding to region C in panel (a);
FIG. 5 is an aluminum/magnesium bimetallic microstructure after a single stage homogenization treatment with air cooling constructed in accordance with a preferred embodiment of the present invention wherein (a) solution treatment; (b) the cooling mode is single-stage homogenization treatment of air cooling.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
A heat treatment method for aluminum/magnesium bimetal cast by a lost foam and a product thereof, wherein the method comprises the following steps:
(a) preparation of aluminum/magnesium bimetal by using lost foam casting solid-liquid composite technology
Preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology and optimized process parameters; the method comprises the following specific steps:
firstly, cutting out a cylindrical A356 aluminum alloy solid inlay by linear cutting, grinding and cleaning the aluminum inlay, and embedding the aluminum inlay into a foam model to prepare a composite model, wherein the liquid-solid volume ratio of the designed composite model is 9.8-23.4; then, coating paint on the composite model, after the paint is dried, putting the composite model into a sand box, burying sand for molding, and vibrating and compacting; then, covering a layer of plastic film on the top of the sand box, vacuumizing to enable the vacuum degree to reach 0.02-0.04 MPa, and preparing to pour AZ91D magnesium alloy; putting the magnesium alloy into a crucible for smelting, and introducing CO in the smelting process2+SF6Protecting gas, and pouring magnesium alloy liquid into the foam model when the temperature of the magnesium alloy liquid reaches 710-750 ℃; and finally, after the casting is cooled and solidified, taking out the casting, and cutting off the gating system to obtain the aluminum/magnesium bimetal casting.
(b) First stage heat treatment
Putting the prepared aluminum/magnesium bimetal into a heat treatment furnace, heating the bimetal from room temperature to a preset temperature at a certain heating rate, and then preserving the heat for a period of time;
(c) secondary heat treatment
After the first-stage heating treatment is finished, heating to a certain preset temperature at a certain heating rate, preserving heat for a period of time, and then cooling.
(d) Aging treatment
And reheating the aluminum/magnesium bimetallic material cooled to room temperature to a lower temperature at a certain heating rate, and cooling after keeping the temperature for a period of time.
Further preferably, in the step (b), the temperature rising rate of the first-stage heating treatment is 4-6 ℃/min, the temperature rises to 370-390 ℃, and the heat preservation time is 4-8 h. In the first stage of the heat treatment, the heating temperature should be selected to be in the range of 370 ℃ to 390 ℃ below the non-equilibrium solidus temperature. At this stage, the eutectic structure is slightly re-dissolved to the matrix, preventing the over-burning phenomenon at the high temperature stage. On the other hand, the lower temperature can make the grain growth slower, and prevent the grain size difference of different parts of the bimetal from being larger, because the larger grain size difference is easy to become a crack source.
Further preferably, in the step (c), the temperature rise rate of the secondary heating treatment is 4-6 ℃/min, the temperature is 410-. Temperature is a main factor influencing the diffusion speed of atoms, the higher the temperature is, the more easily atoms migrate, the larger the diffusion coefficient and diffusion speed are, and the shorter the time required for achieving homogenization is, therefore, in order to shorten the time required for homogenization, we further increase the heating temperature after the first-stage heating. The homogenization treatment cooling mode mainly comprises air cooling and furnace cooling, and earlier researches show that the air cooling mode can cause crack defects in a bimetal interface region, while the furnace cooling mode can not be adopted, so the furnace cooling mode is selected. After the multi-stage homogenization treatment, Al and Al are added to the Al matrix3Mg2+Mg2A solid solution of Al (Mg) and Mg is generated between Si reaction layers2A new diffusion layer consisting of Si, the existence of the diffusion layer strengthens the connection of the interface structure and the aluminum matrix; al in magnesium alloy12Mg17Separated out in a fine lamellar tissue; the structure and the components of the interface and the matrix are more uniform, which is beneficial to improving the performance of the bimetal.
Further preferably, in the step (d), the temperature of the aging treatment is 170-. After artificial aging, Al in the magnesium alloy12Mg17The number of the bimetal is further increased, the size is smaller, the distribution is more dense, and the bimetal performance is further improved.
The present invention will be further illustrated with reference to specific examples.
Example 1
Referring to the temperature profile with time during the heat treatment process of fig. 2, a heat treatment method for lost foam casting solid-liquid composite aluminum/magnesium bimetal according to a preferred embodiment of the present invention comprises the following steps:
firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate is A356, the magnesium substrate is AZ91D, the pouring temperature is 730 ℃, the liquid-solid volume ratio is 14.6, and the vacuum degree is 0.03 MPa. The microstructure of the aluminum/magnesium bimetal is shown in FIGS. 3 (a) to (d), in which the A356 aluminum alloy and the AZ91D magnesium alloy are connected by a metallurgically reactive layer having a width of about 1500 μm, which is formed by Al on the side close to the magnesium matrix12Mg17+ delta-Mg eutectic structure, Al near the aluminum matrix side3Mg2+Mg2Si and Al between two reaction layers12Mg17+Mg2Si composition, this region has no crack defects, but the interface structure is not uniform.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the prepared aluminum/magnesium bimetal into a heat treatment furnace, closing a furnace door, and introducing argon to prevent the aluminum/magnesium bimetal from being oxidized in the heat treatment process;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 5 ℃/min, the temperature rises to 380 ℃, and the heat preservation time is 6 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent heating procedure without taking out the aluminum/magnesium bimetal, wherein the heating rate is 5 ℃/min, the temperature is raised to 420 ℃, and the heat preservation time is 8 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) and resetting the temperature rise program of the heat treatment furnace without taking out the aluminum/magnesium bimetal cooled to room temperature, wherein the temperature rise rate is 5 ℃/min, the temperature is raised to 180 ℃, and the temperature is kept for 16 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
The microstructure of the aluminum/magnesium bimetal after the multi-stage homogenization treatment and the aging treatment is shown in figure 4. As can be seen from FIG. 4, after heat treatment using the method of this example, a solid solution of Al (Mg) and Mg + Mg was formed between the interface metallurgical reaction layer and the A356 substrate2A new reaction layer (shown in fig. 4 (b)) composed of Si, and the presence of this new reaction layer enhances the bonding strength of the interface metallurgical reaction layer and the a356 matrix. The aluminum/magnesium bimetal interface structure is more uniform after heat treatment, and Al12Mg17The δ -Mg crystal grain size in the + δ -Mg eutectic structure becomes large and the number thereof increases (fig. 4 (c) and (d)), which is advantageous for reducing the brittleness of the interface. The heat treatment also had a large effect on the AZ91D magnesium matrix, with Al in the Mg matrix when not heat treated12Mg17Mainly in the form of coarse network distributed near the grain boundary (shown in (d) of FIG. 3), Al in AZ91D matrix after multi-stage homogenization treatment and aging treatment12Mg17A fine lamellar distribution (shown in fig. 4 (d)) is present, which will significantly enhance the performance of the AZ91D substrate. Meanwhile, the heat treatment method of the present patent does not cause crack defects, as compared to solution treatment (shown in fig. 5 (a)) and single-stage homogenization treatment (shown in fig. 5 (b)) in which the cooling method is air cooling. Thus, the overall performance of the aluminum/magnesium bimetal is significantly improved.
Example 2
Firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate mark A356, the magnesium substrate mark AZ91D, the pouring temperature of 710 ℃, the liquid-solid volume ratio of 14.6 and the vacuum degree of 0.03MPa are adopted.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the bimetal into a heat treatment furnace, closing a furnace door, and introducing argon;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 4 ℃/min, the temperature rises to 390 ℃, and the heat preservation time is 4 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent temperature rise procedure without taking out the bimetal, wherein the temperature rise rate is 4 ℃/min, the temperature rises to 410 ℃, and the heat preservation time is 12 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) and resetting the temperature rise program of the heat treatment furnace without taking out the aluminum/magnesium bimetal cooled to room temperature, wherein the temperature rise rate is 4 ℃/min, the temperature rises to 200 ℃, and the temperature is kept for 14 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
Example 3
Firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate mark A356, the magnesium substrate mark AZ91D, the pouring temperature of 710 ℃, the liquid-solid volume ratio of 23.4 and the vacuum degree of 0.04MPa are adopted.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the bimetal into a heat treatment furnace, closing a furnace door, and introducing argon;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 5 ℃/min, the temperature is raised to 370 ℃, and the heat preservation time is 8 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent temperature rise procedure without taking out the bimetal, wherein the temperature rise rate is 5 ℃/min, the temperature rises to 430 ℃, and the heat preservation time is 6 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) and resetting the temperature rise program of the heat treatment furnace without taking out the aluminum/magnesium bimetal cooled to the room temperature, wherein the temperature rise rate is 5 ℃/min, the temperature rises to 170 ℃, and the temperature is kept for 20 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
Example 4
Firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate mark A356, the magnesium substrate mark AZ91D, the pouring temperature is 750 ℃, the liquid-solid volume ratio is 9.8, and the vacuum degree is 0.02 MPa.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the bimetal into a heat treatment furnace, closing a furnace door, and introducing argon;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 6 ℃/min, the temperature is raised to 390 ℃, and the heat preservation time is 4 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent temperature rise procedure without taking out the bimetal, wherein the temperature rise rate is 6 ℃/min, the temperature rises to 410 ℃, and the heat preservation time is 12 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) the aluminum/magnesium bimetal cooled to room temperature is not taken out, the temperature rising program of the heat treatment furnace is reset, the temperature rising rate is 6 ℃/min, the temperature is raised to 180 ℃, and the temperature is preserved for 18 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
Example 5
Firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate mark A356, the magnesium substrate mark AZ91D, the pouring temperature 730 ℃, the liquid-solid volume ratio 9.8 and the vacuum degree 0.02 MPa.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the bimetal into a heat treatment furnace, closing a furnace door, and introducing argon;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 5 ℃/min, the temperature is raised to 390 ℃, and the heat preservation time is 5 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent heating program without taking out the bimetal, wherein the heating rate is 5 ℃/min, the temperature is increased to 425 ℃, and the heat preservation time is 9 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) and resetting the temperature rise program of the heat treatment furnace without taking out the aluminum/magnesium bimetal cooled to room temperature, wherein the temperature rise rate is 5 ℃/min, the temperature rises to 190 ℃, and the temperature is kept for 16 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
Example 6
Firstly, preparing aluminum/magnesium bimetal by using a lost foam casting solid-liquid composite technology, wherein the aluminum substrate mark A356, the magnesium substrate mark AZ91D, the pouring temperature of 720 ℃, the liquid-solid volume ratio of 14.6 and the vacuum degree of 0.02 MPa.
And the second step, primary heating treatment. The method comprises the following specific steps:
(1) putting the bimetal into a heat treatment furnace, closing a furnace door, and introducing argon;
(2) setting a temperature rise program of the heat treatment furnace, wherein the initial temperature is 25 ℃, the temperature rise rate is 5 ℃/min, the temperature rises to 385 ℃, and the heat preservation time is 6 h;
and step three, secondary heating treatment. The method comprises the following specific steps:
(1) continuing the subsequent heating program without taking out the bimetal, wherein the heating rate is 5 ℃/min, the temperature is raised to 428 ℃, and the heat preservation time is 10 h;
(2) and cooling to room temperature. The cooling mode is furnace cooling.
And fourthly, aging treatment. The method comprises the following specific steps:
(1) and resetting the temperature rise program of the heat treatment furnace without taking out the aluminum/magnesium bimetal cooled to the room temperature, wherein the temperature rise rate is 4 ℃/min, the temperature rises to 170 ℃, and the temperature is kept for 17 h.
(2) And cooling to room temperature. The cooling mode is furnace cooling.
In the invention, for a single aluminum alloy or magnesium alloy, common heat treatment methods comprise solution treatment, solution treatment plus aging treatment and homogenization treatment, and the influence effects on the structure and the performance of the alloy are different due to different technological methods and parameters of various heat treatments. The aluminum/magnesium bimetal casting not only comprises aluminum alloy and magnesium alloy parts, but also has an aluminum-magnesium interface structure, namely, the aluminum/magnesium bimetal can be regarded as an assembly consisting of three parts with large property difference. Different parts of the combination have different melting points, different components, different structures and different physicochemical properties, so that a heat treatment process and parameters which can simultaneously meet the three parts need to be selected.
The solidus temperature of AZ91D is 470 ℃ and the solidus temperature of a356 is 557.2 ℃, and the temperature of the heat treatment should also be lower than the temperature of the intermetallic compound at the interface to prevent the intermetallic compound from melting during the heat treatment. According to the report of the literature, Al12Mg17Has a melting point of 460 ℃ and Al3Mg2Has a melting point of 450 ℃ and Mg2The melting point of Si was 1087 ℃. While according to the Al-Mg binary phase diagram, Al12Mg17The temperature of the + delta-Mg eutectic reaction was 440 ℃. Therefore, the heat treatment temperature should be 440 ℃ or lower. Generally, the solution temperature should be selected as high as possible below the solidus of the alloy, and when the solution temperature is 430 ℃ and 435 ℃, micro-melting and over-burning phenomena occur in the interface region, and therefore, the heat treatment temperature should be lower than 430 ℃. The solid solution treatment is continuously tried at the solid solution temperature of 400 ℃, 410 ℃ and 420 ℃, and the crack defects are found to be generated in the interface region of the bimetal casting subjected to the solid solution treatment by adopting water quenching at the temperature of 80 ℃. Therefore, solution treatment and solution + aging treatment are not suitable for aluminum/magnesium bi-metals. Homogenizing annealing refers to heating the casting to a higher temperature below the solidus temperature of the alloy, keeping the temperature for a long time, and then slowly cooling down. Aims to make the elements in the alloy generate solid phase transformation, reduce the non-uniformity of the structure and the segregation of chemical compositions,an aluminum/magnesium bi-metal of various composition and structure may be a suitable heat treatment protocol for this patent.
The temperature of the homogenizing annealing is generally 0.9-0.95TFusion furnace，TFusion furnaceTo begin melting the actual ingot, it is below the solidus on the state diagram. For the aluminum/magnesium bi-metal of this patent, this temperature range is 405-427.5 ℃. However, the temperature may be lower than the non-equilibrium solidus temperature (0.9 to 0.95T)Fusion furnace) The homogenization of the structure cannot be achieved by the homogenization annealing, and even if the homogenization is achieved, the extremely long heat preservation time is often needed, so that the production cost is increased. To solve this problem, the homogenization process can be completed by first heating at a low temperature for a period of time to convert the low-melting phase to the high-melting phase and then raising the temperature. The method can prevent the over-burning of the casting and shorten the heat treatment time. Therefore, the present invention is divided into two heating stages in the homogenization treatment stage.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A method for heat-treating an aluminium/magnesium bi-metal for lost foam casting, comprising the steps of:
preparation of S1 aluminum/magnesium bimetal casting
Forming an aluminum/magnesium bimetal casting by using an aluminum alloy as a solid inlay and a lost foam casting method of a magnesium alloy pouring foam model;
s2 multistage homogenization treatment
S21 first-stage heating treatment
Putting the aluminum/magnesium bimetal casting prepared in the step S1 into a heat treatment furnace, heating to a first preset temperature, and preserving heat to realize the transformation of the aluminum/magnesium bimetal casting from a low-melting-point phase to a high-melting-point phase;
s22 Secondary Heat treatment
Raising the temperature of the aluminum/magnesium bimetal casting subjected to the step S21 to a second preset temperature, wherein the second preset temperature is higher than the first preset temperature, preserving the temperature, cooling, and generating an Al-based solid solution + Mg between the Al matrix and the aluminum/magnesium interface layer in the secondary heating treatment process2A new diffusion layer composed of Si, which enhances the connection of the interface structure and the aluminum matrix;
s3 aging treatment
And (4) raising the temperature of the aluminum/magnesium bimetal casting cooled in the step (S2) to a third preset temperature, wherein the third preset temperature is lower than the first preset temperature, and cooling the aluminum/magnesium bimetal casting along with the furnace after heat preservation, so as to realize the heat treatment of the aluminum/magnesium bimetal casting.
2. The method for heat-treating an aluminum/magnesium bimetal for lost foam casting as claimed in claim 1, wherein the first predetermined temperature in the primary heating process is 370 ℃ to 390 ℃, the heating rate is 4 ℃/min to 6 ℃/min, and the holding time is 4h to 8h in step S21.
3. The method for heat-treating an aluminum/magnesium bimetal for lost foam casting as claimed in claim 1, wherein the second predetermined temperature in the secondary heating is 410-430 ℃, the heating rate is 4-6 ℃/min, and the holding time is 6-12h in step S22.
4. The method for heat-treating an aluminum/magnesium bimetal for lost foam casting according to claim 1, wherein in step S3, the third predetermined temperature in the aging treatment is 170 ℃ to 200 ℃, the heating rate is 4 ℃/min to 6 ℃/min, and the holding time is 14h to 20 h.
5. The method for heat-treating an aluminum/magnesium bimetal by lost foam casting as claimed in claim 1, wherein said cooling is furnace cooling in steps S22 and S3.
6. The heat treatment method of an aluminum/magnesium bimetal for lost foam casting as set forth in claim 1, wherein said lost foam casting method is performed in accordance with the following steps at step S1:
s11, obtaining an aluminum alloy solid inlay, and embedding the aluminum inlay into a foam model after polishing and cleaning to prepare a composite model;
s12, coating paint on the composite model, after the paint is dried, putting the composite model into a sand box, burying sand for molding, and vibrating and compacting;
s13, covering a layer of plastic film on the top of the sand box, and vacuumizing;
s14, pouring the magnesium alloy liquid into the foam model, taking out the casting after the casting is cooled and solidified, and cutting off the pouring system to obtain the aluminum/magnesium bimetal casting.
7. An aluminum/magnesium bi-metal obtained by the heat treatment method according to any one of claims 1 to 6.
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| CN103691909B (en) * | 2014-01-07 | 2016-05-11 | 北京科技大学 | A kind of aluminium/magnesium solid-liquid composite casting forming method |
| CN104057067B (en) * | 2014-07-01 | 2016-08-17 | 合肥工业大学 | A kind of method suppressing magnesium/Al bimetal liquid-solid composite interfacial brittle compound |
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