WO2022160457A1

WO2022160457A1 - Heat treatment strengthening process for aluminum and magnesium as-cast alloy and application thereof

Info

Publication number: WO2022160457A1
Application number: PCT/CN2021/084380
Authority: WO
Inventors: 刘洪涛; 齐志峰; 晁延吉; 周吉学; 李涛; 刘运腾; 杨化冰; 吴建华; 王娜娜; 李航; 马百常; 王西涛
Original assignee: 山东省科学院新材料研究所
Priority date: 2021-01-29
Filing date: 2021-03-31
Publication date: 2022-08-04
Also published as: CN112962038A; CN112962038B

Abstract

A heat treatment strengthening process for an aluminum and magnesium as-cast alloy and an application thereof. The aluminum alloy and the magnesium alloy are subjected to multi-process combined treatment such as primary ultralow-temperature treatment, warm isostatic pressing solution treatment, secondary ultralow-temperature treatment, and aging treatment; casting defects such as air holes and shrinkage porosity in an aluminum alloy structure are greatly reduced, residual stress and precipitation strengthening phase distribution is more dispersed, and the aging strengthening effect is more ideal, the strength and elongation of the aluminum and magnesium as-cast alloy are obviously improved. The process steps are simple, the process parameters of warm isostatic pressing and ultralow-temperature treatment can be adjusted according to different as-cast alloy types, the problems of air holes, shrinkage porosity, residual stress and the like in the casting process of the as-cast alloy are effectively solved, and the microstructure and mechanical properties of the aluminum and magnesium as-cast alloy are greatly improved. Moreover, the process steps are simple, the process parameters of warm isostatic pressing and ultralow-temperature treatment can be adjusted according to different as-cast alloy types, the problems of air holes, shrinkage porosity, residual stress and the like in the casting process of the as-cast alloy are effectively solved, and the microstructure and mechanical properties of the aluminum and magnesium as-cast alloy are greatly improved. The heat treatment strengthening process has important significance for expanding the engineering application of the aluminum and magnesium as-cast alloy.

Description

A kind of heat treatment strengthening process of aluminum and magnesium as-cast alloy and its application

technical field

The invention relates to the technical field of heat treatment of non-ferrous metals, in particular to a heat treatment strengthening process of aluminum and magnesium as-cast alloys and its application.

Background technique

The disclosure of information in this Background section is only for enhancement of understanding of the general background of the invention and should not necessarily be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.

Energy shortage and environmental pollution are prominent problems in today's world. Reducing one's own weight has become an effective way to reduce environmental pollution and save energy in the fields of automobiles, aerospace and other fields. According to statistics, the fuel consumption can be reduced by 0.7 liters for every 100 kg reduction in the mass of the car. In aerospace vehicles, the reduction in structural weight reduces fuel costs by a factor of 100 compared to the automotive industry. Aluminum alloys and magnesium alloys are the lightest metal structural materials at present. They have the advantages of low density, high specific strength, and easy forming. They are widely used in aerospace, automotive electronics and other fields. In the automotive field, aluminum alloys and magnesium alloys can be used not only as instrument panel bases, seat frames, steering wheel shafts, gearbox casings, etc., but also in key parts such as engines and car chassis, and have broad application prospects in the automotive field.

In the process of aluminum alloy and magnesium alloy engineering application, alloy casting is an indispensable key link, and the quality of casting has a significant impact on the engineering parts of aluminum alloy and magnesium alloy. Due to the physical and chemical properties of aluminum alloys and magnesium alloys, casting defects are easily generated, resulting in reduced mechanical properties of castings. For example: (1) During the melting and casting process of aluminum alloys and magnesium alloys, entrainment is very likely to occur, and the buoyancy of the involved nitrogen bubbles and hydrogen bubbles is small, which makes it difficult for a large amount of hydrogen and nitrogen to escape. The form remains in the casting, and the pores will become the source of crack propagation during the service of the casting; (2) The aluminum alloy and magnesium alloy will shrink in volume during the casting process. (3) During the casting process of aluminum alloy and magnesium alloy, due to the inconsistent solidification time of different parts, large residual thermal stress will be generated, and even hot cracking will occur. This problem is especially obvious for castings with complex structures;

It can be seen from the above that the physical properties of aluminum alloys and magnesium alloys are quite different from those of metal materials such as steel, which makes the problems of pores, shrinkage porosity and residual stress very prominent during the casting process. Casting performance is reduced. From the perspective of ensuring the integrity of the casting, the rationality of the manufacturing process, and the reliability of the use process, the deformation, fracture, and failure of engineering components caused by pores, shrinkage defects and residual stress have seriously limited aluminum alloys. and engineering application of magnesium alloy castings. Therefore, how to effectively eliminate various casting microstructure defects, effectively enhance the casting quality of aluminum alloys and magnesium alloys, and improve their service performance has become one of the bottleneck technologies that restrict the engineering application of aluminum alloys and magnesium alloys and one of the key technologies to be solved urgently. .

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art, the present invention proposes a heat treatment strengthening process for aluminum and magnesium as-cast alloys and its application. This process is suitable for ageing-strengthened aluminum alloys or magnesium alloys. One ultra-low temperature treatment, followed by warm isostatic pressing at the alloy solution temperature, followed by a second ultra-low temperature treatment, and finally aging strengthening treatment, can greatly improve the mechanical properties of aluminum and magnesium alloy castings.

In order to achieve the above object, a first aspect of the present invention provides a heat treatment strengthening process of aluminum and magnesium as-cast alloys, which specifically includes:

(1) Put the light alloys such as aluminum or magnesium to be treated into a closed cavity, gradually cool the ambient temperature of the cavity to an ultra-low temperature, and perform the first ultra-low temperature treatment;

(2) After the first ultra-low temperature treatment of the aluminum alloy or magnesium alloy is completed, the temperature is slowly returned to room temperature, and then placed in a warm isostatic pressing equipment, and an inert protective gas is introduced at the solid solution temperature of the alloy material for gas pressure heat treatment ; After the warm isostatic pressing process, the aluminum alloy or magnesium alloy will return to room temperature with the furnace, release the inert protective gas, reduce the static pressure of the cavity, and gradually return to normal pressure; after the static gas pressure drops to normal pressure, the aluminum alloy Or the magnesium alloy is quickly transferred and immersed in water until it is completely cooled;

(3) After the temperature isostatic pressing of the aluminum alloy or magnesium alloy is completed, the ambient temperature of the cavity is gradually cooled, and the second ultra-low temperature treatment is performed;

(4) After the secondary ultra-low temperature treatment of aluminum alloy or magnesium alloy is completed, the aluminum alloy or magnesium alloy is put into an aging furnace for aging treatment;

(5) After the aging process is finished, the alloy material is taken out from the aging furnace and air-cooled;

The second aspect of the present invention provides the application of the above-mentioned heat treatment strengthening process of aluminum and magnesium as-cast alloys in the preparation of as-cast alloys.

One or more embodiments of the present invention have at least the following beneficial effects:

(1) The present invention discloses a heat treatment strengthening process for aluminum and magnesium as-cast alloys. The aluminum alloy and magnesium alloy are subjected to multiple processes such as primary ultra-low temperature treatment, warm isostatic pressing solution treatment, secondary ultra-low temperature treatment and aging treatment. The combined treatment greatly reduces the casting defects such as pores and shrinkage porosity in the aluminum alloy structure, the residual stress, and the precipitation strengthening phase distribution is more dispersed, and the aging strengthening effect is more ideal. The strength and elongation of aluminum and magnesium as-cast alloys are obvious. improve.

Among them, the first ultra-low temperature treatment is mainly based on the volume shrinkage effect, which reduces the atomic spacing, shrinks the lattice, reduces the size of hole defects, and even closes some tiny voids directly, laying the foundation for the next warm isostatic pressing treatment;

The warm isostatic pressing treatment causes plastic flow diffusion inside the casting, bonding and bridging of the microstructure holes, and the as-cast structure is more uniform and dense, and the space occupied by defects such as pores and shrinkage porosity is extremely limited on the macroscopic level, so it will not change. The size or shape of the casting.

There are two purposes of the second ultra-low temperature treatment. One is to generate a large internal stress inside the material, which induces a large number of dislocations and sub-crystals. The strength and toughness of the alloy are improved. Second, a large number of supersaturated point defects (vacancies) can be obtained at ultra-low temperature. The interaction between vacancies and solute atoms makes the next aging precipitate more dispersed and the volume fraction increases.

The aging strengthening is carried out on the basis of the second ultra-low temperature treatment. Since there are more dislocations and vacancies in the microstructure, it is more conducive to the diffusion of solute atoms, and the formed strengthening phase is more dispersed, and the aging strengthening effect is more effective. ideal.

(2) The steps of the present invention are simple, and the process parameters of temperature isostatic pressing and ultra-low temperature treatment can be adjusted according to different as-cast alloy types, effectively solving the problems of pores, shrinkage porosity and residual stress during the casting process of the as-cast alloy, greatly improving aluminum, The microstructure and mechanical properties of magnesium as-cast alloys are of great significance for expanding the engineering applications of aluminum and magnesium as-cast alloys.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Figure 1 is a comparison of the tensile properties of the ZL109 as-cast aluminum alloy in Example 1(a) after the treatment of the present invention and the conventional heat treatment in Comparative Example 1(b).

Figure 2 is a comparison of the tensile properties of the AZ91 as-cast magnesium alloy in Example 2(a) after the treatment of the present invention and the conventional heat treatment in Comparative Example 2(b).

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

As described in the background art, in the prior art, problems such as pores, shrinkage porosity and residual stress during the melting and casting of aluminum and magnesium as-cast alloys are very prominent. The present invention proposes a heat treatment strengthening process for aluminum and magnesium as-cast alloys, which specifically includes:

(3) After the temperature isostatic pressing of the aluminum alloy or magnesium alloy is completed, the ambient temperature of the cavity is gradually cooled to the ultra-low temperature required by the alloy, and the second ultra-low temperature treatment is performed;

(5) After the aging process is completed, the alloy material is taken out from the aging furnace and air-cooled.

In one or more embodiments of the present invention, in the step (1), the temperature of the cavity is controlled by pumping liquid nitrogen, the temperature control accuracy is ±1°C, and the cooling rate is controlled at 10-20°C/min, So that the cavity temperature can be adjusted in the range of room temperature to -190 ℃;

In one or more embodiments of the present invention, in the step (1), the temperature range of the first ultra-low temperature treatment is -120 to -180°C, and the ultra-low temperature treatment time is determined according to the type of alloy. , the treatment time is 5-7h, and when aluminum alloy is used, the treatment time is 6-8h.

In one or more embodiments of the present invention, in the step (2), the inert protective gas is argon or nitrogen, and the vacuum degree must be evacuated to below 10 mPa before introducing the inert protective gas;

In one or more embodiments of the present invention, in the step (2), in the process of filling the cavity with the inert protective gas, the static gas pressure is first controlled at about 70 MPa, and the required solid solution temperature of the alloy is equal to After stabilization, adjust the static pressure to 100-200MPa;

In one or more embodiments of the present invention, in the step (2), the time of the warm isostatic pressing is determined according to the type of alloy. When magnesium alloy is used, the processing time is 9-10h, and when aluminum is used When alloying, the treatment time is 4-5h.

In one or more embodiments of the present invention, in step (2), the water temperature does not exceed 65°C, and the transfer time does not exceed 20s;

In one or more embodiments of the present invention, in the step (3), the cooling rate is controlled at 50-60°C/min, the temperature of the second ultra-low temperature treatment is -130--190°C, and the treatment time is based on the alloy. To determine the type, when using magnesium alloy, the treatment time is 15-17h, when using aluminum alloy, the treatment time is 13-15h.

In the step (4), the aging treatment process of the alloy is reasonably determined according to the corresponding national standards of different grades or relevant literature.

In order to enable those skilled in the art to understand the technical solutions of the present invention more clearly, the technical solutions of the present invention will be described in detail below in conjunction with specific embodiments.

Example 1

Utilize the heat treatment method of the present invention to carry out strengthening treatment to ZL109 as-cast aluminum alloy:

(1) Put the ZL109 aluminum alloy into a closed cavity, pass in liquid nitrogen, and gradually cool to -165°C, the cooling rate is 20°C/min, and the treatment time is 7h;

(2) After the ultra-low temperature treatment is completed, the temperature is slowly returned to room temperature, the ZL109 as-cast aluminum alloy is put into the warm isostatic pressing equipment, and nitrogen is introduced to pressurize. 495 ℃, the static gas pressure was adjusted to 150MPa, and the treatment time was 4h; after the warm isostatic pressing process, the ZL109 aluminum alloy was returned to room temperature with the furnace, and the protective gas was released to reduce the static pressure of the cavity. During this process, the temperature remained constant. After the static pressure drops to normal pressure, the ZL109 aluminum alloy is quickly transferred and immersed in water at 65 °C, and the transfer time does not exceed 20s;

(3) After the ZL109 aluminum alloy temperature isostatic pressing treatment is completed, a second ultra-low temperature treatment is performed, and the ambient temperature of the cavity is rapidly cooled to -180 °C at a speed of 50 °C/min, and treated for 10 hours;

(4) After the secondary ultra-low temperature treatment is completed, put the ZL109 aluminum alloy into the aging furnace, the aging treatment temperature is 180°C, and the treatment time is 14h;

After the treatment, the tensile properties of ZL109 aluminum alloy were tested, and the tensile strength reached 305.7MPa. The test results are shown in Figure 1(a).

Example 2

Utilize the heat treatment method of the present invention to carry out strengthening treatment to AZ91 as-cast magnesium alloy:

(1) Put the AZ91 magnesium alloy into a closed cavity, pour liquid nitrogen, and gradually cool it to -145°C, the cooling rate is 15°C/min, and the treatment time is 6h;

(2) After the ultra-low temperature treatment is completed, the temperature is slowly returned to room temperature, the AZ91 magnesium alloy is put into the warm isostatic pressing equipment, and nitrogen is introduced to pressurize. , the static gas pressure was adjusted to 120MPa, and the treatment time was 10h; after the warm isostatic pressing process, the AZ91 magnesium alloy was returned to room temperature with the furnace, the protective gas was released, and the static pressure of the cavity was reduced, and the temperature remained unchanged during this process; After the static pressure dropped to normal pressure, the AZ91 magnesium alloy was quickly transferred and immersed in water at room temperature, and the transfer time did not exceed 20s;

(3) After the warm isostatic pressing of AZ91 magnesium alloy is completed, a second ultra-low temperature treatment is performed, and the ambient temperature of the cavity is rapidly cooled to -170 °C at a speed of 50 °C/min, and treated for 8 hours;

(4) After the secondary ultra-low temperature treatment, put the AZ91 magnesium alloy into the aging furnace, the aging treatment temperature is 220 °C, and the treatment time is 16 h;

After the treatment, the tensile properties of the AZ91 magnesium alloy were tested, and the tensile strength reached 285.9 MPa. The test results are shown in Figure 2(a).

Comparative Example 1

According to the national standard GB/T 25745-2010, conventional heat treatment is used for the ZL109 as-cast aluminum alloys of the same batch and specification, at 495 °C, solution treatment for 4 hours, and then water-cooled at 180 °C for 14 hours of aging treatment time. After the conventional heat treatment, the tensile properties were tested, and the results are shown in Fig. 1(b). The ZL109 as-cast aluminum alloy obtained in Example 1 has a tensile strength of 305.7 MPa, while the ZL109 obtained in Comparative Example 1 has a tensile strength of only 247.6 MPa. Compared with Example 1, the tensile strength is significantly lower. Therefore, compared with the conventional heat treatment method, the tensile properties of the ZL109 as-cast aluminum alloy treated by the process of the present invention are significantly improved.

Comparative Example 2

Referring to relevant literature, conventional heat treatment was used for AZ91 as-cast magnesium alloys of the same batch and specification, at 410 °C, solution treatment for 10 h, and after water cooling at 220 °C, the aging treatment time was 16 h. After conventional heat treatment, the tensile properties were tested, and the results are shown in Fig. 2(b). In Example 2, the tensile strength of AZ91 reached 285.9 MPa, while the tensile strength of AZ91 obtained in Comparative Example 2 was only 234.1 MPa. Compared with Example 1, the tensile strength was significantly lower. Therefore, compared with the conventional heat treatment method, the tensile properties of the AZ91 as-cast magnesium alloy treated by the process of the present invention are significantly improved.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

A heat treatment strengthening process for aluminum and magnesium as-cast alloys, which is characterized in that: it specifically includes:

(1) Put the aluminum or magnesium light alloy to be treated into a closed cavity, gradually cool the ambient temperature of the cavity to an ultra-low temperature, and perform the first ultra-low temperature treatment;

(2) After the first ultra-low temperature treatment of the aluminum alloy or magnesium alloy is completed, the temperature is slowly returned to room temperature, and then placed in a warm isostatic pressing equipment, and an inert protective gas is introduced at the solid solution temperature of the alloy material for gas pressure heat treatment ; After the warm isostatic pressing process, the aluminum alloy or magnesium alloy will return to room temperature with the furnace, release the inert protective gas, reduce the static pressure of the cavity, and gradually return to normal pressure; after the static gas pressure drops to normal pressure, the aluminum alloy Or the magnesium alloy is quickly transferred and immersed in water until it is completely cooled;

(3) After the temperature isostatic pressing of the aluminum alloy or magnesium alloy is completed, the ambient temperature of the cavity is gradually cooled to the ultra-low temperature required by the alloy, and the second ultra-low temperature treatment is performed;

(4) After the secondary ultra-low temperature treatment of aluminum alloy or magnesium alloy is completed, the aluminum alloy or magnesium alloy is put into an aging furnace for aging treatment;

(5) After the aging process is completed, the alloy material is taken out from the aging furnace and air-cooled.
The process of claim 1, wherein: in the step (1), the temperature of the cavity is controlled by pumping liquid nitrogen, the temperature control accuracy is ±1°C, and the cooling rate is controlled at 10-20°C/ min, so that the chamber temperature can be adjusted in the range of room temperature to -190 °C.
The process according to claim 1, wherein: in the step (1), the temperature range of the first ultra-low temperature treatment is -120～-180°C, and the ultra-low temperature treatment time is determined according to the type of alloy. When the alloy is used, the treatment time is 5-7h, and when the aluminum alloy is used, the treatment time is 6-8h.
The process according to claim 1, characterized in that: in the step (2), the inert protective gas is argon or nitrogen, and the vacuum degree must be evacuated to below 10 mPa before the inert protective gas is introduced.
The process according to claim 1, characterized in that: in the step (2), in the process of filling the cavity with the inert protective gas, the static gas pressure is first controlled at 70 MPa, which is equal to the required solid solution temperature of the alloy. After stabilization, the static pressure was adjusted to 100-200MPa.
The process according to claim 1, characterized in that: in the step (2), the time of the warm isostatic pressing is determined according to the type of the alloy, when a magnesium alloy is used, the processing time is 9-10h, when the For aluminum alloys, the treatment time is 4-5h.
The process of claim 1, wherein in the step (2), the water temperature does not exceed 65°C, and the transfer time does not exceed 20s.
The process according to claim 1, characterized in that: in the step (3), the cooling rate is controlled at 50-60°C/min.
The process according to claim 1, characterized in that: in the step (3), the temperature of the second ultra-low temperature treatment is -130 to -190°C, and the treatment time is determined according to the type of alloy. When magnesium alloy is used , the treatment time is 15-17h, and when aluminum alloy is used, the treatment time is 13-15h.
Application of the heat treatment strengthening process of aluminum and magnesium as-cast alloys according to any one of claims 1 to 8 in the preparation of as-cast alloys.