Method for improving high-temperature strength of A357 alloy through manganese-antimony combined microalloying

Abstract

The invention discloses a method for improving the high-temperature strength of an A357 alloy through manganese-antimony combined microalloying, which comprises the following steps: (1) adding Mn and Sb in the smelting process of an A357 alloy raw material, and pouring into a casting mold to form a casting or a cast ingot; and (2) the casting / cast ingot obtained in the step (1) is subjected to solution treatment and aging treatment, a large number of nanoscale Al15Mn3Si2 heat-resistant phases are separated out in a matrix, and more beta ''and beta 'strengthening phases are promoted to be separated out by adding the Sb element, so that the high-temperature strength of the alloy is improved. According to the invention, the high-temperature strength of the A357 alloy at 200 DEG C and 250 DEG C can be obviously improved, and the preparation process is simple and does not cause pollution to the environment.

Description

Technical Field

[0001] The present invention relates to a method for improving the high-temperature strength of A357 alloy, and particularly to a method for improving the high-temperature strength of A357 alloy by combined microalloying of manganese and antimony. Background Art

[0002] Aluminum and its alloys are traditional metallic materials, and their production and consumption are second only to steel, and their role in the national economy and national defense construction is becoming increasingly important. Aluminum alloy is an alloy obtained by adding other elements to aluminum, and has the characteristics of low density, high electrical conductivity, high specific strength, good corrosion resistance, high recycling rate, etc. It is widely used in aerospace materials, and the application proportion in the manufacturing of automobile bodies and parts is also gradually increasing, and it is increasingly widely used in parts of the thermal management system in the electronics industry. Therefore, the industry has higher requirements for the performance indicators of aluminum alloys. Many researchers have also been constantly searching for different means to optimize the microstructure of aluminum alloys and improve the mechanical properties of aluminum alloys.

[0003] Al-Si-Mg series alloys are the most widely used casting alloys, and the typical representatives are A356 and A357 aluminum alloys. As a heat-treatable aluminum alloy, the Mg and Si elements in it will precipitate a large number of finely dispersed Mg-Si strengthening phases (β″ and β′ phases) in the matrix after solution aging treatment, and hinder the movement of dislocations, thereby producing a significant precipitation hardening effect, so it is widely used. A357 alloy is often used to manufacture automobile engine cylinder heads, automobile wheels, turbine pump bodies, thermal management system components, etc. However, at high temperatures, the strength of this alloy is relatively low because its main strengthening phases (β″ and β′ phases) will rapidly coarsen above 180°C, thus greatly reducing the strengthening effect, which makes A357 unable to meet people's requirements when used at medium and high temperatures.

[0004] Therefore, it is very important to develop Al-Si-Mg series alloys with more excellent high-temperature strength. Summary of the Invention

[0005] Technical Problem: The purpose of the present invention is to provide a method for improving the high-temperature strength of A357 alloy by combined microalloying of manganese and antimony with a simple process. The present invention can significantly improve the high-temperature strength of A357 alloy at 200°C and 250°C, and the preparation process is simple and will not cause pollution to the environment.

[0006] Technical Solution: A method for improving the high-temperature strength of A357 alloy by combined microalloying of manganese and antimony according to the present invention includes the following steps:

[0007] Step 1. Add Mn and Sb elements during the melting process of A357 alloy raw materials, and pour them into a mold to form a casting or ingot;

[0008] Step 2. Subject the obtained castings or ingots to solution treatment and aging treatment to precipitate nano-scale manganese-rich heat-resistant phases in the matrix, and promote the precipitation of more β″ and β′ strengthening phases by adding Sb element.

[0009] Among them,

[0010] In Step 1, Mn and Sb are co-microalloyed by adding 0.2-0.4% Mn and 0.015-0.025% Sb in the form of Al-Mn and Al-Sb master alloys.

[0011] In Step 2, after the co-microalloying of Mn and Sb, a large number of nano-scale Al 15 Mn3Si2 heat-resistant phases are formed and more β″ and β′ strengthening phases are precipitated through heat treatment.

[0012] In Step 2, the solution treatment temperature is 535±5°C and the time is 8-10 h.

[0013] In Step 2, the aging treatment temperature is 175±5°C and the time is 4-6 h.

[0014] After the co-microalloying of Mn and Sb, nano-scale Al 15 Mn3Si2 heat-resistant phases are dispersed in the matrix, and more β″ and β′ strengthening phases are precipitated in the matrix.

[0015] A method for improving the high-temperature strength of A357 alloy by co-microalloying of manganese and antimony according to the present invention specifically includes the following steps:

[0016] Step 1. Heat the aluminum alloy raw materials to the temperature range of 740-750°C to melt the alloy ingots and then keep them warm to obtain the first alloy melt;

[0017] Step 2. Cool the first alloy melt obtained in Step 1 in the furnace to the temperature range of 700-720°C and keep it warm for degassing and slag removal purification treatment to obtain the second alloy melt;

[0018] Step 3. Cool the second alloy melt obtained in Step 2 in the furnace to 720-730°C and keep it warm continuously, then add Mg and stir slightly; Mn and Sb are co-microalloyed by adding 0.2-0.4% Mn and 0.015-0.025% Sb in the form of Al-Mn and Al-Sb master alloys to obtain the third alloy melt;

[0019] Step 4. Keep the third alloy melt obtained in Step 3 in the furnace continuously to obtain the fourth alloy melt;

[0020] Step 5. Pour the fourth alloy melt obtained in Step 4 into a casting mold or die, and prepare an ingot or casting of the A357 alloy with combined Mn and Sb microalloying after natural cooling.

[0021] Step 6. Perform solution treatment and aging treatment on the ingot or casting obtained in Step 5.

[0022] In Step 1, keep the temperature for 25 - 30 min after melting the alloy ingot.

[0023] In Step 3, keep the temperature for 25 - 30 min continuously.

[0024] In Step 4, keep the temperature for 25 - 30 min continuously.

[0025] Principle of the invention: By adding a small amount of Mn and Sb elements into the A357 alloy and performing solution treatment and aging treatment, a large number of nano-scale, dispersed manganese-rich heat-resistant phases are formed in the matrix, resulting in precipitation strengthening effect; at the same time, compared with adding Mn alone, due to the addition of Sb, the number of β″ and β′ precipitation phases in the alloy also increases significantly, strengthening the age hardening effect; thus improving the strength of the alloy ingot or casting at room temperature and high temperature, and the high temperature strength at 200 °C and 250 °C is significantly improved.

[0026] Beneficial effects: Compared with the prior art, the present invention has achieved the following remarkable effects: (1) By adding only 0.2 - 0.4 wt% Mn and 0.015 - 0.25 wt% Sb elements into the A357 alloy, the strength of the alloy at room temperature and high temperature can be significantly improved. Adding 0.3 wt% Mn and 0.02 wt% Sb elements to the A357 alloy, after solution treatment and aging treatment, the tensile strength of the alloy at room temperature is increased from 309 MPa to 337 MPa, and the yield strength is increased from 287 MPa to 328 MPa; the yield strength at 200 °C is increased from 243 MPa to 258 MPa, and the yield strength at 250 °C is increased from 205 MPa to 226 MPa. (2) Through combined Mn + Sb microalloying, a large number of nano-scale, dispersed manganese-rich heat-resistant phases are formed in the matrix, resulting in precipitation strengthening effect; at the same time, compared with adding Mn alone, due to the addition of Sb, the number of β″ and β′ phase age precipitation phases in the alloy also increases significantly, strengthening the age hardening effect; thus improving its strength at room temperature and high temperature, and the high temperature strength at 200 °C and 250 °C is significantly improved. (3) The transition metal Mn can form excellent heat-resistant phase Al in the Al-Si alloy. 15The Mn3Si2 phase enhances the high-temperature strength of the alloy; Sb can combine a large number of vacancies during solid solution and release them during aging, promoting the formation of β″ and precipitating more age-hardening phases. (4) The preparation method of the material of the present invention is resistance furnace melting, and the heat treatment process is conventional solution + aging treatment, and the preparation process is simple. (5) Compared with the existing production process, the present invention has significantly improved strength at both room temperature and high temperature, and the production process is simple, which is suitable for industrial production applications. Description of the Drawings

[0027] Figure 1 It is a transmission electron microscope photograph of the microstructure of the alloy in Example 1 after solution and aging treatments.

[0028] Figure 2 It is a transmission electron microscope photograph of the precipitated phases of the alloys in Example 1 and Example 2 after solution and aging treatments. Among them, Figure 2 in (a) is the transmission electron microscope photograph of the aging precipitated phases of the alloy in Example 1 after solution and aging treatments, Figure 2 in (b) is the transmission electron microscope photograph of the aging precipitated phases of the alloy in Example 2 after solution and aging treatments. Detailed Embodiments

[0029] The present invention will be further described in detail below.

[0030] Example 1

[0031] 1. Alloy Composition Design and Preparation

[0032] (1) All materials and molds in contact with the melt need to be preheated for more than 30 minutes, and the preheating temperature is 250 °C. Place the A357 aluminum alloy raw materials in a resistance crucible furnace and heat up to 600 °C;

[0033] (2) Heat the raw materials in step (1) to 750 °C for melting. After melting and clearing, keep it warm for 30 min;

[0034] (3) Cool the alloy melt in the furnace in step (2) to 720 °C for degassing and slag removal purification treatment;

[0035] (4) Keep the alloy melt in the furnace at 720 °C for 30 min, and successively add Mg ingots, Al-Mn master alloy and Al-Sb master alloy, and stir gently. The addition amount of Mg takes into account the burning loss of Mg during melting, the addition amount of Mn is 0.3 wt%, and the addition amount of Sb is 0.02 wt%;

[0036] (5) Keep the alloy obtained in step (4) at 720 °C for 30 min continuously;

[0037] (6) Pour the alloy melt obtained in step (5) into a sand mold, and wait for natural cooling to complete the preparation of ingots or castings of A357 alloy with combined microalloying of manganese and antimony;

[0038] (7) Heat-treat the alloy sample obtained in step (6), and the treatment process is: solution treatment at 535 °C for 10 h, and aging treatment at 175 °C for 6 h.

[0039] 2. Characterization of the mechanical properties of the alloy at room temperature and high temperature

[0040] Machine the casting into tensile test samples, and the sample size information is: diameter 10 mm, gauge length 90 mm. Conduct tensile tests at room temperature, 200 °C, and 250 °C on a CMT5105 electronic universal testing machine, with a loading rate of 1 mm / min. At least 3 groups of experiments are carried out for each alloy combination to obtain the tensile properties of the alloy at room temperature, 200 °C, and 250 °C. The performance evaluation index of high-temperature strength is mainly the yield strength. The mechanical properties obtained from the experiments are shown in Table 1.

[0041] Figure 1 It is a transmission electron microscope photo of the microstructure of the alloy in Example 1 after solution treatment and aging treatment. It can be seen that there are many nano-scale and dispersedly distributed manganese-rich heat-resistant phases Al 15 Mn3Si2 in the matrix, and this kind of precipitation phase can play a good second-phase strengthening effect during the tensile process at room temperature / high temperature.

[0042] 3. Experimental results

[0043] Table 1 Tensile properties of sand-cast A357 alloy with combined microalloying of manganese and antimony at different temperatures

[0044]

[0045]

[0046] Example 2

[0047] 1. Alloy composition design and preparation

[0048] (1) All materials and molds in contact with the melt need to be preheated for more than 30 minutes, and the preheating temperature is 250 °C. Place the A357 aluminum alloy raw material in a resistance crucible furnace and heat it up to 600 °C;

[0049] (2) Heat the raw material in step (1) to 750 °C for melting. After melting and clarification, hold for 30 min;

[0050] (3) Cool the alloy melt in the furnace in step (2) to 720 °C, and carry out degassing and slag removal purification treatment;

[0051] (4) Keep the alloy melt in the furnace at 720 °C for 30 min, add Mg ingots and Al-Mn master alloy in sequence, and stir gently. The addition amount of Mg takes into account the loss of Mg during melting, and the addition amount of Mn is 0.3 wt%.

[0052] (5) Keep the alloy obtained in step (4) at 720 °C for 30 min continuously.

[0053] (6) Pour the alloy melt obtained in step (5) into a sand mold, and wait for natural cooling to prepare ingots or castings of manganese microalloyed A357 alloy.

[0054] (7) Heat-treat the alloy samples obtained in step (6), and the treatment process is: solution treatment at 535 °C for 10 h and aging treatment at 175 °C for 6 h.

[0055] 2. Characterization of mechanical properties of the alloy at room temperature and high temperature

[0056] Machine the casting into tensile test samples, and the sample size information is: diameter 10 mm, gauge length 90 mm. Conduct tensile tests at room temperature, 200 °C, and 250 °C on a CMT5105 electronic universal testing machine, and the loading rate is 1 mm / min. At least 3 groups of experiments are carried out for each alloy combination to obtain the tensile properties of the alloy at room temperature, 200 °C, and 250 °C. The main performance evaluation index of high-temperature strength is the yield strength. The mechanical properties obtained from the experiments are shown in Table 2.

[0057] Figure 2 For the transmission electron microscope photos of the precipitated phases after solution treatment and aging treatment of the alloys in Example 1 and Example 2, it can be seen that the β″ and β′ strengthening phases in the alloy of Example 1 are significantly more than those in Example 2.

[0058] 3. Experimental results

[0059] Table 2 Tensile properties of sand-cast manganese microalloyed A357 alloy at different temperatures

[0060] Tensile temperature Tensile strength / MPa Yield strength / MPa Normal temperature 320 303 200℃ 265 256 250℃ 225 216

[0061] Example 3

[0062] 1. Alloy composition design and preparation

[0063] (1) All materials and molds in contact with the melt need to be preheated for more than 30 minutes, and the preheating temperature is 250 °C. Place the A357 aluminum alloy raw materials in a resistance crucible furnace and heat up to 600 °C.

[0064] (2) Heat the raw materials in step (1) to 750 °C for melting. After melting and clarification, keep it for 30 min.

[0065] (3) Cool the alloy melt in the furnace to 720 °C in step (2) and conduct degassing and slag removal purification treatment;

[0066] (4) Keep the alloy melt in the furnace at 720 °C for 30 min in step (3), add Mg ingots, and stir gently. The addition amount of Mg takes into account the burning loss of Mg during melting;

[0067] (5) Keep the alloy obtained in step (4) at 720 °C for 30 min continuously;

[0068] (6) Pour the alloy melt obtained in step (5) into a sand mold, and wait for natural cooling to prepare ingots or castings of A357 alloy;

[0069] (7) Conduct heat treatment on the alloy sample obtained in step (6). The treatment process is: solution treatment at 535 °C for 10 h and aging treatment at 175 °C for 6 h.

[0070] 2. Characterization of the mechanical properties of the alloy at room temperature and high temperature

[0071] Machine the casting into tensile test samples. The sample size information is: diameter 10 mm, gauge length 90 mm. Conduct tensile tests at room temperature, 200 °C, and 250 °C on a CMT5105 electronic universal testing machine, and the loading rate is 1 mm / min. At least 3 groups of experiments are carried out for each group of alloys to obtain the tensile properties of the alloy at room temperature, 200 °C, and 250 °C. The performance evaluation index of high-temperature strength is mainly the yield strength. The mechanical properties obtained from the experiments are shown in Table 2.

[0072] 3. Experimental results

[0073] Table 3 Tensile properties of sand-cast A357 alloy at different temperatures

[0074] Tensile temperature Tensile strength / MPa Yield strength / MPa Normal temperature 309 287 200℃ 251 243 250℃ 207 205

[0075] The method for improving the room-temperature strength and high-temperature strength of A357 alloy provided by the present invention, through the combined microalloying of Mn and Sb, after conventional solution treatment and aging treatment, a large number of nano-scale and dispersedly distributed manganese-rich heat-resistant phases are precipitated in the matrix to produce a precipitation strengthening effect. At the same time, compared with the addition of Mn alone, due to the addition of Sb, the number of β″ and β′ phase aging precipitation phases in the alloy also increases significantly, strengthening the age hardening effect, thereby improving its room-temperature and high-temperature strength. The high-temperature strength at 200 °C and 250 °C is significantly improved, making the tensile strength of the alloy at room temperature increase from 309 MPa to 337 MPa, the yield strength increase from 287 MPa to 328 MPa, the yield strength at 200 °C increase from 243 MPa to 258 MPa, and the yield strength at 250 °C increase from 205 MPa to 226 MPa. The combined microalloying of Mn and Sb has a better strengthening effect than the single microalloying of Mn.

Claims

1. A method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying, characterized in that: The following steps are involved: Step 1. Adding Mn and Sb elements during the smelting process of A357 alloy raw material, pouring into a casting mold to form a casting or ingot; Step 2: subjecting the obtained casting or ingot to a solution treatment and an aging treatment, precipitating a nano-scale manganese-rich heat-resistant phase in the matrix, and promoting the precipitation of more β″ and β′ strengthening phases by adding the Sb element.

2. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 1, characterized in that: In step 1, 0.2-0.4% by mass of Mn and 0.015-0.025% by mass of Sb are added in the form of Al-Mn and Al-Sb master alloys to perform Mn and Sb combined microalloying.

3. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 1, characterized in that: In step 2, the Mn and Sb are combined and micro-alloyed to form a large amount of nano-scale Al 15 Mn3Si2 heat-resistant phase and precipitation of more β″ and β′ strengthening phases.

4. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 1, characterized in that: In step 2, the solution treatment temperature is 535±5°C and the time is 8-10h.

5. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 1, characterized in that: In step 2, the aging treatment temperature is 175±5°C and the time is 4-6h.

6. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 2, characterized in that The Mn and Sb are combined to form nano-scale Al in the matrix structure. 15 The heat-resistant Mn3Si2 phase is dispersed in the matrix, and more β″ and β′ strengthening phases are precipitated in the matrix.

7. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 1, characterized in that: The specific steps include: Step 1. heating the aluminum alloy raw material to a temperature between 740° C. and 750° C. to melt the alloy ingot and then keep the temperature to obtain a first alloy melt; Step 2: Cool the first alloy melt obtained in step 1 to a temperature of 700-720° C. in a furnace, and perform a degassing and slag removal purification process to obtain a second alloy melt; Step 3. The second alloy melt obtained in step 2 is cooled to 720-730° C. in a furnace and kept warm, and then Mg is added and slightly stirred; 0.2-0.4% Mn and 0.015-0.025% Sb are added in the form of Al-Mn and Al-Sb master alloys to perform Mn and Sb combined microalloying to obtain a third alloy melt; Step 4. Keeping the third alloy melt obtained in step 3 in a furnace to obtain a fourth alloy melt; Step 5. pouring the fourth alloy melt obtained in step 4 into a casting mold or a die, and preparing an ingot or casting of a manganese-antimony combined microalloyed A357 alloy after natural cooling; Step 6. The ingot or casting obtained in step 5 is subjected to solution treatment and aging treatment.

8. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 7, characterized in that: After melting the alloy ingot in step 1, keep it warm for 25-30 minutes.

9. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 7, characterized in that: In step 3, keep warm for 25-30 minutes.

10. The method for improving the high temperature strength of A357 alloy by manganese-antimony combined microalloying according to claim 7, characterized in that: In step 4, keep warm for 25-30 minutes.

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