Heat treatment method for simultaneously improving strength and ductility of cast Al-Si-Mg-Cu alloy

Abstract

The invention belongs to the technical field of aluminum alloy heat treatment, and particularly relates to a heat treatment method for simultaneously improving the strength and ductility of a cast Al-Si-Mg-Cu alloy. The preparation method comprises the following steps: burdening according to the alloy components of the Al-Si-Mg-Cu alloy, smelting and casting to obtain a casting; the casting is subjected to solution treatment and quenching treatment, and then is subjected to natural aging treatment, low-temperature pre-aging treatment and high-temperature final aging treatment to obtain the Al-Si-Mg-Cu series alloy. Through combination of natural aging, low-temperature pre-aging and high-temperature final aging, sufficient precipitation of a strengthening phase in the cast alloy is promoted, and the comprehensive mechanical property of the Al-Si-Mg-Cu alloy is improved. After the Al-Si-Mg-Cu alloy is subjected to solid solution quenching, a nucleation point and a GP region are mainly formed in the natural aging stage, a fine dispersed GP region and a beta '' pre-precipitation phase are mainly formed in the low-temperature pre-aging stage, a theta '' phase and a beta '' phase are precipitated in the high-temperature final aging stage, and finally double precipitation phase strengthening of the theta '' phase and the beta '' phase is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy heat treatment, and more specifically relates to a heat treatment method for simultaneously improving the strength and elongation of a cast Al-Si-Mg-Cu alloy. Background Art

[0002] Cast Al-Si alloys are widely used in important industries such as aerospace, weapons and ships, and automobile transportation due to their light weight, good thermal conductivity, high strength, good corrosion resistance, and excellent castability. With the rapid development of aerospace technology and the rapid progress of the national defense industry, higher requirements are placed on the strength, toughness, and corrosion resistance of structural materials such as high-strength aluminum alloys.

[0003] At present, cast Al-Si alloys still have problems such as low tensile strength, difficulty in improving elongation after fracture, and insufficient service life. The comprehensive mechanical properties of the alloy urgently need to be improved. In actual use, a small amount of metal elements such as Cu and Mg are usually added to Al-Si alloys to improve their mechanical properties. However, the addition of Cu element will further reduce the elongation after fracture of the alloy, limiting the practical application of cast Al-Si-Mg-Cu alloys.

[0004] Therefore, it is urgent to optimize the heat treatment process and simultaneously improve and enhance the strength and elongation of the cast Al-Si-Mg-Cu alloy. Summary of the invention

[0005] The object of the present invention is to provide a heat treatment method for simultaneously improving the strength and elongation of a cast Al-Si-Mg-Cu alloy. By combining natural aging-low temperature pre-aging-high temperature final aging, the full precipitation of the strengthening phase of the cast Al-Si-Mg-Cu alloy is promoted to achieve double precipitation strengthening, so as to solve the problems existing in the above-mentioned prior art, and the elongation of the cast Al-Si-Mg-Cu alloy is not reduced while the strength is improved.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a heat treatment method for simultaneously improving the strength and elongation of a cast Al-Si-Mg-Cu alloy, the steps comprising:

[0008] The ingredients are prepared according to the alloy composition of the Al-Si-Mg-Cu alloy, and a casting is obtained through smelting and casting;

[0009] The casting is subjected to solution treatment, quenching treatment, natural aging treatment, low-temperature pre-aging treatment and high-temperature final aging treatment to obtain an Al-Si-Mg-Cu alloy.

[0010] Furthermore, a modifier is added during the smelting process to perform a modification treatment.

[0011] Preferably, the modifier includes Sb or Y, and the addition amount is 0.1 to 0.5 wt.%.

[0012] More preferably, the modifier is Sb, and the addition amount is 0.1 to 0.3 wt.%.

[0013] More preferably, the modifier is Y, and the addition amount is 0.2-0.5 wt.%.

[0014] Furthermore, the temperature of the solution treatment is 540-545° C., and the time is 10-14 hours.

[0015] Preferably, the solution treatment is carried out at a temperature of 545° C. and for a time of 12 h.

[0016] Furthermore, the quenching treatment is water quenching, and the water temperature is 40-60°C.

[0017] Furthermore, the temperature of the natural aging treatment is room temperature, and the time is 10 to 12 hours.

[0018] Furthermore, the temperature of the low-temperature pre-aging treatment is 150-160° C., and the time is 6-10 hours.

[0019] Furthermore, the temperature of the high temperature final aging treatment is 165-170° C., and the time is 5-8 hours.

[0020] The second technical solution of the present invention is to provide an Al-Si-Mg-Cu alloy obtained by the above method.

[0021] The third technical solution of the present invention is to provide an application of the above-mentioned Al-Si-Mg-Cu alloy in aerospace.

[0022] The present invention discloses the following technical effects:

[0023] The main strengthening phases of the cast Al-Si-Mg-Cu alloy are GP zone, βˊˊ phase and θˊˊ phase. The optimal precipitation temperature range of βˊˊ phase and θˊˊ phase is about 165°C, but the precipitation order of βˊˊ phase and θˊˊ phase is inconsistent, and the Cu element will inhibit the precipitation of βˊˊ phase. The present invention promotes the full precipitation of strengthening phases in the cast Al-Si-Mg-Cu alloy through the combination of natural aging-low temperature pre-aging-high temperature final aging, and improves the comprehensive mechanical properties of the cast Al-Si-Mg-Cu alloy.

[0024] In the treatment method of the present invention, after the cast Al-Si-Mg-Cu alloy is solution quenched, nucleation points and GP zones are mainly formed in the natural aging stage, fine dispersed GP zones and βˊˊ pre-precipitation phases are mainly formed in the low-temperature pre-aging stage, and θˊˊ phases and βˊˊ phases are precipitated in the high-temperature final aging stage, and finally dual precipitation phase strengthening of θˊˊ phase and βˊˊ phase is achieved. The room temperature tensile strength of the alloy treated by the heat treatment method of the present invention is not less than 380MPa, and the elongation is not less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 is the heat treatment system curve of the present invention;

[0027] Figure 2 The SEM images of castings without adding Sb modifier and with adding Sb modifier in the conventional method for preparing castings, wherein (a) is without adding Sb modifier, and (b) is with adding Sb modifier;

[0028] Figure 3 TEM images of the cast Al-Si-Mg-Cu alloy after treatment at different stages in Example 1, wherein (a) is a TEM image after solution treatment, (b) is a TEM image after solution + natural aging treatment, (c) is a TEM image after solution + natural aging + low-temperature pre-aging treatment, and (d) is a TEM image after solution + natural aging + low-temperature pre-aging + high-temperature final aging treatment. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] The steps of the conventional method for preparing a casting in a specific embodiment of the present invention are:

[0035] (1) According to Si 6-8wt.%, Mg 0.4-0.8wt.%, Cu 0.5-0.8wt.%, Sb 0.1-0.3wt.%, and the balance Al, prepare alloy raw materials, clean the surface of the raw materials, and preheat them in a drying oven at 250°C for 2h;

[0036] (2) Place the graphite crucible, crucible clamp, metal mold and other tools required for smelting in a drying oven and preheat to 250°C, then take out and apply an appropriate amount of water-soluble zinc oxide coating, and then place it in the drying oven again for drying at a temperature of 200°C for 0.5h;

[0037] (3) Put the prepared raw materials into a smelting furnace, heat and stir them, and after they are completely melted, stir them thoroughly to make them evenly mixed, and continue heating to 800°C and keeping the temperature for 5 minutes;

[0038] (4) Controlling the temperature at about 740°C, starting refining, using a 1:1 mixture of potassium chloride and hexachloroethane as the refining agent, and refining time of 10 to 20 minutes;

[0039] (5) Let the aluminum liquid stand for 10 to 20 minutes. Do not stir the aluminum liquid during the process.

[0040] (6) Finally, the temperature is controlled back to 740°C and the melt is poured. Before pouring, the mold is dried and preheated to 300°C. The pouring is slow and steady. After the casting is completed, the casting used in the specific implementation plan is obtained.

[0041] In step (1) of the conventional casting preparation process, the Sb element is a modifier, and the Sb element is provided by the Al-Sb alloy, wherein Figure 2 The figure without adding a modifier is obtained by reducing the Sb addition in step (1).

[0042] Figure 1 This is the heat treatment system curve of the present invention (solution treatment, natural aging treatment, low temperature pre-aging and high temperature final aging).

[0043] Figure 2 The following are SEM images of castings without and with Sb modifiers in the conventional method of preparing castings, where (a) is without Sb modifiers and (b) is with Sb modifiers. Figure 2 It can be seen that when no modifier is added, the eutectic silicon in the casting after heat treatment is in the shape of needles or plates. When the modifier Sb is added, the eutectic silicon in the casting after heat treatment is obviously spheroidized and granular, which is beneficial to the elongation of the material.

[0044] Example 1

[0045] The heat treatment method steps for simultaneously improving the strength and elongation of the cast Al-Si-Mg-Cu alloy are as follows:

[0046] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0047] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0048] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0049] S4. After quenching, natural aging treatment is performed at room temperature for 10 hours;

[0050] S5. After natural aging treatment, low temperature pre-aging treatment is carried out at 155°C for 8h;

[0051] S6. After low-temperature pre-aging treatment, high-temperature final aging treatment is carried out at 165°C for 6 hours to obtain Al-Si-Mg-Cu alloy.

[0052] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 382 MPa, a yield strength of 336 MPa, and an elongation of 5.4%.

[0053] Figure 3 TEM images of the cast Al-Si-Mg-Cu alloy after treatment at different stages in Example 1, wherein (a) is a TEM image after solution treatment, (b) is a TEM image after solution + natural aging treatment, (c) is a TEM image after solution + natural aging + low-temperature pre-aging treatment, and (d) is a TEM image after solution + natural aging + low-temperature pre-aging + high-temperature final aging treatment. It can be seen from the figure that in the natural aging stage, the nucleation points of the β″ phase and a large number of GP zones are mainly formed, the βˊˊ phase has obvious precipitation in the low-temperature pre-aging stage, and the θˊˊ phase and βˊˊ phase are precipitated in the high-temperature final aging stage, realizing the dual precipitation phase strengthening of the θˊˊ phase and the βˊˊ phase.

[0054] Example 2

[0055] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0056] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0057] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0058] S4. After quenching, natural aging treatment is performed at room temperature for 10 hours;

[0059] S5. After natural aging treatment, low temperature pre-aging treatment is carried out at 155°C for 10h;

[0060] S6. After low-temperature pre-aging treatment, high-temperature final aging treatment is carried out at 165°C for 6 hours to obtain Al-Si-Mg-Cu alloy.

[0061] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 380 MPa, a yield strength of 325 MPa, and an elongation of 5.0%.

[0062] Example 3

[0063] The heat treatment method steps for simultaneously improving the strength and elongation of the cast Al-Si-Mg-Cu alloy are as follows:

[0064] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0065] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0066] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0067] S4. After quenching, natural aging treatment is performed at room temperature for 10 hours;

[0068] S5. After natural aging treatment, low temperature pre-aging treatment is carried out at 155°C for 6h;

[0069] S6. After low-temperature pre-aging treatment, high-temperature final aging treatment is carried out at 165°C for 8 hours to obtain Al-Si-Mg-Cu alloy.

[0070] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 380 MPa, a yield strength of 310 MPa, and an elongation of 5.1%.

[0071] Comparative Example 1

[0072] The castings are processed as follows:

[0073] Artificial single-stage aging of cast Al-Si-Mg-Cu alloy

[0074] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0075] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0076] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0077] S4. After quenching, artificial aging treatment is carried out at 165°C for 8 hours to obtain Al-Si-Mg-Cu alloy.

[0078] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 330 MPa, a yield strength of 247 MPa, and an elongation of 5.0%.

[0079] Comparative Example 2

[0080] The castings are processed as follows:

[0081] Artificial two-stage aging of cast Al-Si-Mg-Cu alloy

[0082] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0083] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0084] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0085] S4. After quenching treatment, double-stage aging is carried out. The temperature of the first stage aging is 155°C and the holding time is 8h; the temperature of the second stage aging is 170°C and the holding time is 4h, and Al-Si-Mg-Cu alloy is obtained.

[0086] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 375 MPa, a yield strength of 340 MPa, and an elongation of 1.7%.

[0087] Comparative Example 3

[0088] The castings are processed as follows:

[0089] Natural aging + artificial single-stage aging of cast Al-Si-Mg-Cu alloy

[0090] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0091] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0092] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0093] S4. After quenching, natural aging treatment is performed at room temperature for 10 hours;

[0094] S5. After natural aging treatment, low-temperature pre-aging treatment is carried out at 165°C for 8h to obtain Al-Si-Mg-Cu alloy.

[0095] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 355 MPa, a yield strength of 290 MPa, and an elongation of 2.6%.

[0096] Comparative Example 4

[0097] The castings are processed as follows:

[0098] The cast Al-Si-Mg-Cu alloy is subjected to natural aging + artificial double-stage aging, but in the artificial double-stage aging, high temperature pre-precipitation is performed first and then low temperature aging is performed.

[0099] S1. Prepare alloy raw materials according to Si 7.0wt.%, Mg 0.7wt.%, Cu 0.6wt.%, Ti 0.15wt.%, and the balance is Al;

[0100] S2, according to the conventional method, the raw materials in S1 are smelted and cast by sand casting to obtain a casting; and a modifier Sb (0.2wt.%) is added during the smelting process;

[0101] S3, the obtained casting is first subjected to solution treatment at a temperature of 545°C and a holding time of 12h, and then subjected to quenching treatment, and the quenching water temperature is controlled at about 50°C;

[0102] S4. After quenching, natural aging treatment is performed at room temperature for 10 hours;

[0103] S5. After natural aging treatment, high temperature pre-precipitation aging treatment is carried out at 165°C for 6 hours;

[0104] S6. After high-temperature pre-precipitation aging treatment, high-temperature final aging treatment is performed at 120°C for 10 hours to obtain Al-Si-Mg-Cu alloy.

[0105] The Al-Si-Mg-Cu alloy obtained after the above treatment has a room temperature tensile strength of 340 MPa, a yield strength of 260 MPa, and an elongation of 5.3%.

[0106] Test example

[0107] Table 1 shows the element proportions of the ingots used in Examples 1 to 3 and Comparative Examples 1 to 4.

[0108] Table 1

[0109]

[0110] Table 2 shows the mechanical properties of the ingots treated by the methods of Examples 1 to 3 and Comparative Examples 1 to 4. The original untreated ingot (the ingot with the addition of a modifier obtained by a conventional casting method) is used as the control group. The test method is as follows:

[0111] The prepared samples were tested for room temperature mechanical properties, including tensile strength, yield strength and elongation, on a universal testing machine (SANS-CMJ5105). The tensile rate was 2 mm / min and the ambient temperature was approximately 23 °C.

[0112] Table 2

[0113] sample Room temperature tensile strength (MPa) Room temperature yield strength (MPa) Elongation(%) Example 1 382 336 5.4 Example 2 380 325 5.0 Example 3 380 310 5.1 Comparative Example 1 330 247 5.0 Comparative Example 2 375 340 1.7 Comparative Example 3 355 290 2.6 Comparative Example 4 340 260 5.3 Control group 159 106 2.9

[0114] From the performance comparison of the above embodiments, comparative examples and control groups, it can be seen that the mechanical properties of the cast Al-Si-Mg-Cu alloy in the cast state are relatively low. After solution aging heat treatment, the properties can be greatly improved. However, only single-stage artificial aging, natural aging + single-stage artificial aging, etc. cannot simultaneously improve the strength and elongation of the alloy. Only natural aging combined with a two-stage artificial aging system of low temperature followed by high temperature can the strengthening phase in the alloy be fully precipitated, with uniform size, increased quantity and type, thereby improving the strength and elongation of the alloy.

[0115] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0116] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat treatment method for simultaneously improving the strength and elongation of a cast Al-Si-Mg-Cu alloy, characterized in that the steps include: The ingredients are prepared according to the alloy composition of the Al-Si-Mg-Cu alloy, and a casting is obtained through smelting and casting; The casting is subjected to solution treatment, quenching treatment, natural aging treatment, low-temperature pre-aging treatment and high-temperature final aging treatment to obtain an Al-Si-Mg-Cu alloy.

2. The method according to claim 1, characterized in that During the smelting process, a modifier is added to perform a modification treatment.

3. The method according to claim 2, characterized in that The modifier includes Sb or Y, and the addition amount is 0.1-0.5wt.%.

4. The method according to claim 1, characterized in that: The temperature of the solution treatment is 540-545° C., and the time is 10-14 hours.

5. The method according to claim 1, characterized in that The quenching treatment is water quenching, and the water temperature is 40-60°C.

6. The method according to claim 1, characterized in that The temperature of the natural aging treatment is room temperature, and the time is 10 to 12 hours.

7. The method according to claim 1, characterized in that The temperature of the low-temperature pre-aging treatment is 150-160° C., and the time is 6-10 hours.

8. The method according to claim 1, characterized in that The temperature of the high temperature final aging treatment is 165-170° C., and the time is 5-8 hours.

9. An Al-Si-Mg-Cu alloy obtained by the method according to any one of claims 1 to 8.

10. Use of the Al-Si-Mg-Cu alloy according to claim 9 in aerospace.

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