Gypsum mold precision casting ZL114A aluminum alloy heat treatment process

Abstract

The application relates to a gypsum mold precision casting ZL114A aluminum alloy heat treatment process in the technical field of heat treatment, which comprises three steps of solid solution treatment, natural pre-aging treatment and artificial aging treatment. Firstly, ZL114A aluminum alloy is placed into a heat treatment furnace under the condition of a temperature of <=300 DEG C, is heated to 540-545 DEG C at a heating rate of <=100 DEG C / h, is quenched after being kept for 3-4 h, the quenching transfer time is <=15 s, then the quenched ZL114A aluminum alloy is placed at room temperature for 12-24 h; then the heat treatment furnace is heated to 165-175 DEG C, and the ZL114A aluminum alloy is aged for 2.5-3.0 h and then is air cooled. The application achieves the target of shortening the heat treatment period and reducing energy consumption, can control the tensile strength of the ZL114A aluminum alloy to be above 300 MPa, the elongation after fracture to be above 4%, and the Brinell hardness to be above 80 HB.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically relating to a heat treatment process for ZL114A aluminum alloy precision casting using a gypsum-type investment casting method. Background Technology

[0002] ZL114A aluminum alloy belongs to the Al-Si hypoeutectic alloy system. It is an Al-Si-Mg series high-strength cast aluminum alloy developed by increasing the magnesium content on the basis of ZL101A alloy. It has the characteristics of high strength, high toughness, good fluidity, air tightness and hot crack resistance. The current standards for the T6 heat treatment process of ZL114A aluminum alloy used in gypsum-type investment casting are GB / T1173-2013 and HB 962-2001. GB / T 1173-2013 specifies a solution treatment temperature of 535±5℃, holding time of 10-14h, cooling medium of water at 60-100℃, aging temperature of 160±5℃, holding time of 4-8h, and air as the cooling medium. HB 962-2001 specifies a solution treatment temperature of 535-545℃, holding time of 8-20h, and aging temperature of 150-170℃, holding time of 6-10h.

[0003] As can be seen from the above, the current process has relatively long solution treatment holding time and artificial aging holding time. At the same time, for castings after solution treatment and water quenching, it is inevitable to stay at room temperature for a certain period of time. This stage is called natural aging. The metastable ZL114A alloy structure will undergo slow desolvation during this stage. Therefore, the influence of natural aging on subsequent artificial aging must be considered. This results in the current heat treatment process having problems such as high energy consumption, low work efficiency, and the need to improve the matching of strength and plasticity. It is not conducive to improving the production efficiency and production quality of plaster mold investment casting.

[0004] Therefore, improvements are urgently needed. Summary of the Invention

[0005] The purpose of this invention is to overcome the existing technical problems and propose a heat treatment process for ZL114A aluminum alloy by gypsum type investment casting.

[0006] This invention is implemented according to the following technical solution:

[0007] A heat treatment process for ZL114A aluminum alloy precision casting using a gypsum-type investment casting method includes the following steps:

[0008] S1. Solution treatment: Under the temperature conditions of ≤300℃, ZL114A aluminum alloy is placed in a heat treatment furnace and heated to 540~545℃ at a heating rate of ≤100℃ / h. After solution treatment and holding for 3~4h, quenching treatment is performed. The quenching transfer time is ≤15s and the quenching medium is water.

[0009] S2. Natural pre-aging treatment: Place the quenched ZL114A aluminum alloy at room temperature for 12-24 hours.

[0010] S3. Artificial aging treatment: After natural pre-aging treatment, ZL114A aluminum alloy is heated to 165-175℃ in a heat treatment furnace, held for aging for 2.5-3.0 hours, and then air-cooled.

[0011] Preferably, in step S1, the quenching water temperature is 80℃ and the quenching time is 5 minutes. Since the effect of water temperature is essentially the effect of cooling rate, a higher cooling rate leads to uneven shrinkage of the casting and makes it prone to deformation. For gypsum-type investment castings, the resulting castings have complex structures and thin walls; therefore, the quenching water temperature needs to be appropriately increased. Especially at a quenching water temperature of 80℃ and a quenching time of 5 minutes, both the quenching efficiency and the quenching quality of the gypsum-type investment castings can be guaranteed.

[0012] Preferably, in step S1, during the solution treatment, the ZL114A aluminum alloy is placed in a heat treatment furnace at a temperature of 300°C.

[0013] Preferably, in step S1, during the solution treatment, the temperature is raised to 540°C at a heating rate of 100°C / h, and after solution treatment and holding at that temperature for 3 hours, quenching is performed.

[0014] Preferably, in step S2, during the natural pre-aging treatment, the quenched ZL114A aluminum alloy is placed at room temperature for 24 hours.

[0015] Preferably, in step S3, during artificial aging treatment: the ZL114A aluminum alloy after natural pre-aging treatment is heated to 170°C in a heat treatment furnace and aged for 2.5 hours.

[0016] Preferably, in step S3, the air is cooled to room temperature.

[0017] The working principle of this invention is as follows: During solution treatment, due to the complex structure and thin walls of gypsum-type investment castings, controlling the heating rate slowly can prevent local overheating of the casting, which could lead to abnormally coarse grains or even remelting structures, thus reducing the mechanical properties of the casting. The solution treatment holding time is selected as 3-4 hours. Its purpose is twofold: firstly, compared to longer solution treatment times, the solubility of Mg and Si in the aluminum matrix is ​​similar, resulting in similar driving forces for subsequent aging and desolvation; secondly, as the solution treatment time increases, the eutectic silicon becomes increasingly rounded and coarsened, leading to a decrease in the strength of ZL114A aluminum alloy and an increase in elongation after fracture. Therefore, a solution treatment holding time of 3-4 hours can effectively balance strength and plasticity.

[0018] The quenching transfer time is controlled within 15 seconds because the quenching transfer process is an air cooling process with a slow cooling rate, which leads to a decrease in the solubility of Mg and Si atoms in the Al matrix and a reduction in the vacancy concentration. This will reduce the number of precipitation strengthening phases after aging treatment, and thus affect the mechanical properties of the casting after heat treatment. Therefore, the quenching transfer time should be shortened as much as possible.

[0019] Natural pre-aging at room temperature for 12–24 hours can affect the density and distribution of the precipitated phase after artificial aging by forming Mg and Si atomic clusters (GP zones). Its functions are: (1) At lower artificial aging temperatures, natural pre-aging before artificial aging can delay or even inhibit the peak age hardness, while increasing the aging temperature can turn this effect into a positive one. The Mg and Si atomic clusters (GP zones) precipitated during the natural pre-aging stage mainly prepare the chemical composition and structure for precipitation strengthening β″ phase. (2) Long-term natural aging treatment can refine the rounded eutectic silicon to a certain extent (the average area and aspect ratio of eutectic silicon are reduced), which can ensure the elongation after fracture of the alloy.

[0020] The artificial aging stage provides a driving force for the removal of solvents from the alloy after natural pre-aging, promoting further transformation of the removal sequence and further improving strength. During artificial aging, the clusters formed by natural pre-aging undergo both nucleation and dissolution simultaneously. At high artificial aging temperatures, the nucleation barrier of the precipitate phase decreases, thus its nucleation rate is greater than its dissolution rate. Simultaneously, vacancies generated by the dissolution of clusters with significantly different compositions and structures from the β″ precipitate phase accelerate the diffusion of solute atoms. These two factors work together to accelerate the precipitation of the precipitate phase. Therefore, the artificial aging time of this invention is much shorter than the T6 heat treatment in the prior art. Typically, T6 heat treatment achieves high solubility of Mg and Si atoms in the Al matrix through prolonged solution treatment, allowing subsequent artificial aging to precipitate a higher density of precipitate phases, resulting in high strength for the alloy. At the same time, prolonged solution treatment coarsens and rounds the eutectic silicon, reducing the alloy's strength but increasing its plasticity. The strength reduction caused by the coarsened eutectic silicon during the solution treatment stage can be compensated for and further improved during the aging stage.

[0021] In the initial stage of solution treatment, the aspect ratio of eutectic silicon continuously decreases. Subsequently, as the solution treatment time is extended, the aspect ratio change tends to level off. After 3-4 hours of solution treatment and heat preservation, the eutectic silicon can achieve both a low average area and aspect ratio, thus achieving a good match between the strength and plasticity of ZL114A aluminum alloy. After natural pre-aging and artificial aging treatments, the average area and aspect ratio of eutectic silicon can be further reduced. At the same time, the precipitation phases during the aging process strengthen the alloy. These combined effects enable the ZL114A aluminum alloy to achieve a good match between strength and plasticity.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention takes into account the influence of natural aging on subsequent artificial aging. By controlling the solution treatment time, natural pre-aging time, and artificial aging temperature and time, it achieves the goal of shortening the heat treatment cycle and reducing energy consumption. Through a determined short-time heat treatment process, the tensile strength of ZL114A aluminum alloy is controlled to reach above 300MPa, the elongation after fracture is above 4%, and the Brinell hardness is above 80HB, which meets the requirements of the T6 heat treatment process for ZL114A aluminum alloy in the HB 962-2001 standard. Attached Figure Description

[0024] Figure 1 These are process curves of the present invention in Examples 1 and 2;

[0025] Figure 2 The image shows the metallographic structure of the product in Example 1.

[0026] Figure 3 The image shows the metallographic structure of the product in Example 2;

[0027] Figure 4 The metallographic structure diagram of the product in Comparative Example 1;

[0028] Figure 5 The metallographic structure of the product in Comparative Example 2 is shown.

[0029] Figure 6 The image shows the metallographic structure of the product in Comparative Example 3. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0031] Example 1

[0032] like Figure 1 As shown in this embodiment, a heat treatment process for ZL114A aluminum alloy using plaster casting includes the following steps:

[0033] S1. Solution treatment: Under the condition of 300℃, ZL114A aluminum alloy is placed in a heat treatment furnace and heated to 540℃ at a heating rate of 100℃ / h. After solution treatment and holding for 3h, quenching treatment is performed. The quenching transfer time is ≤15s. The quenching medium is water, the quenching water temperature is 80℃, and the quenching time is 5min.

[0034] S2. Natural pre-aging treatment: Place the quenched ZL114A aluminum alloy at room temperature for 24 hours.

[0035] S3. Artificial aging treatment: The ZL114A aluminum alloy after natural pre-aging treatment is heated to 170℃ in a heat treatment furnace, aged and held for 2.5 hours, and then air-cooled to room temperature.

[0036] The working principle of this invention is as follows: During solution treatment, due to the complex structure and thin walls of gypsum-type investment castings, controlling the heating rate slowly can prevent local overheating of the casting, which could lead to abnormally coarse grains or even remelting structures, thus reducing the mechanical properties of the casting. A solution treatment holding time of 3 hours is chosen for two reasons: Firstly, compared to longer solution treatment times, the solubility of Mg and Si in the aluminum matrix is ​​similar, resulting in similar driving forces for subsequent aging and solvent removal. Secondly, as the solution treatment time increases, the eutectic silicon becomes rounded and coarsened, leading to a decrease in the strength of ZL114A aluminum alloy and an increase in elongation after fracture. Therefore, a solution treatment holding time of 3 hours provides a good balance between strength and plasticity.

[0037] The quenching transfer time is controlled within 15 seconds because the quenching transfer process is an air cooling process with a slow cooling rate, which leads to a decrease in the solubility of Mg and Si atoms in the Al matrix and a reduction in the vacancy concentration. This will reduce the number of precipitation strengthening phases after aging treatment, and thus affect the mechanical properties of the casting after heat treatment. Therefore, the quenching transfer time should be shortened as much as possible.

[0038] Natural pre-aging at room temperature for 24 hours can affect the density and distribution of the precipitated phase after artificial aging by forming Mg and Si atomic clusters (GP zones). Its functions are: (1) At lower artificial aging temperatures, natural pre-aging before artificial aging will delay or even inhibit the peak age hardness, while increasing the aging temperature can turn this effect into a positive influence. The Mg and Si atomic clusters (GP zones) precipitated during the natural pre-aging stage mainly prepare the chemical composition and structure for the precipitation strengthening β″ phase. (2) Long-term natural aging treatment can refine the rounded eutectic silicon to a certain extent (the average area and aspect ratio of the eutectic silicon are reduced), which can ensure the elongation after fracture of the alloy.

[0039] The artificial aging stage provides a driving force for the removal of solvents from the alloy after natural pre-aging, promoting further transformation of the removal sequence and further improving strength. During artificial aging, the clusters formed by natural pre-aging undergo both nucleation and dissolution simultaneously. At high artificial aging temperatures, the nucleation barrier of the precipitate phase decreases, thus its nucleation rate is greater than its dissolution rate. Simultaneously, vacancies generated by the dissolution of clusters with significantly different compositions and structures from the β″ precipitate phase accelerate the diffusion of solute atoms. These two factors work together to accelerate the precipitation of the precipitate phase. Therefore, the artificial aging time of this invention is much shorter than the T6 heat treatment in the prior art. Typically, T6 heat treatment achieves high solubility of Mg and Si atoms in the Al matrix through prolonged solution treatment, allowing subsequent artificial aging to precipitate a higher density of precipitate phases, resulting in high strength for the alloy. At the same time, prolonged solution treatment coarsens and rounds the eutectic silicon, reducing the alloy's strength but increasing its plasticity. The strength reduction caused by the coarsened eutectic silicon during the solution treatment stage can be compensated for and further improved during the aging stage.

[0040] In the initial stage of solution treatment, the aspect ratio of eutectic silicon continuously decreases. Subsequently, as the solution treatment time is extended, the aspect ratio change tends to level off. After 3 hours of solution treatment and heat preservation, the eutectic silicon can balance low average area and aspect ratio, thus achieving a good match between the strength and plasticity of ZL114A aluminum alloy. After natural pre-aging and artificial aging treatments, the average area and aspect ratio of eutectic silicon can be further reduced. At the same time, the precipitation phases during the aging process strengthen the alloy. These combined effects enable the ZL114A aluminum alloy to achieve a good match between strength and plasticity.

[0041] Example 2

[0042] The only difference from Example 1 is that in step S2, during the natural pre-aging treatment, the quenched ZL114A aluminum alloy is placed at room temperature for 12 hours.

[0043] Comparative Example 1

[0044] The comparative example uses the existing T6 heat treatment process, with a solution treatment temperature of 540℃, a heating rate of 100℃ / h, a solution holding time of 12h, and an artificial aging temperature of 160℃ after quenching, followed by a holding time of 8h.

[0045] Comparative Example 2

[0046] The only difference from Example 1 is that step S2 has been omitted.

[0047] Comparative Example 3

[0048] The only difference from Example 1 is that in step S2, during the natural pre-aging treatment, the quenched ZL114A aluminum alloy is placed at room temperature for 6 hours.

[0049] Based on the above embodiments and comparative examples, the process parameters for heat treatment are summarized in Table 1 as follows.

[0050] Table 1 Comparison of Process Parameters for Heat Treatment

[0051] Solution treatment Natural Time Effects Artificial aging Example 1 Heating rate 100℃ / h, hold at 540℃ for 3h Room temperature 24h Keep warm at 170℃ for 2.5 hours Example 2 Heating rate 100℃ / h, hold at 540℃ for 3h 12 hours at room temperature Keep warm at 170℃ for 2.5 hours Comparative Example 1 Heating rate 100℃ / h, hold at 540℃ for 12h Room temperature 0h Keep warm at 160℃ for 8 hours Comparative Example 2 Heating rate 100℃ / h, hold at 540℃ for 3h Room temperature 0h Keep warm at 170℃ for 2.5 hours Comparative Example 3 Heating rate 100℃ / h, hold at 540℃ for 3h Room temperature for 6 hours Keep warm at 170℃ for 2.5 hours

[0052] The performance test results of the heat-treated products of the above embodiments and comparative examples are shown in Table 2.

[0053] Table 2 Comparison of Performance Test Results of Products After Heat Treatment

[0054] Tensile strength / MPa Elongation after fracture / % Brinell hardness / HB Example 1 327 6.58 102 Example 2 324 5.20 97 Comparative Example 1 330 5.85 111 Comparative Example 2 293 4.54 90 Comparative Example 3 303 5.02 93

[0055] Based on the above embodiments and comparative examples, Figure 2 The image shows the metallographic structure of the heat-treated product in Example 1 (a and b are metallographic images at different magnifications). Figure 3 The image shows the metallographic structure of the heat-treated product in Example 2 (c and d are metallographic images at different magnifications). Figure 4 The image shows the metallographic structure of the heat-treated product in Comparative Example 1 (e and f are metallographic images at different magnifications). Figure 5 The image shows the metallographic structure of the heat-treated product in Comparative Example 2 (g and h are metallographic images at different magnifications). Figure 6 Table 3 shows the metallographic structure of the heat-treated product in Comparative Example 3 (i and j are metallographic images at different magnifications). The statistical results of the average eutectic silicon area and aspect ratio of the heat-treated products in each embodiment and comparative example are shown in Table 3.

[0056] Table 3 Comparison of Statistical Results of Average Eutectic Silicon Area and Aspect Ratio of Products After Heat Treatment

[0057] <![CDATA[Average area of eutectic silicon / μm 2 > Aspect Ratio of Eutectic Silicon Example 1 4.004 1.641 Example 2 4.095 1.660 Comparative Example 1 5.002 1.653 Comparative Example 2 4.671 1.747 Comparative Example 3 4.313 1.674

[0058] In summary, this invention takes into account the influence of natural aging on subsequent artificial aging. By controlling the solution treatment time, natural pre-aging time, and artificial aging temperature and time, it achieves the goal of shortening the heat treatment cycle and reducing energy consumption. Through a determined short-time heat treatment process, the tensile strength of ZL114A aluminum alloy reaches 300MPa, the elongation after fracture reaches 4%, and the Brinell hardness reaches 80HB, which meets the requirements of the T6 heat treatment process for ZL114A aluminum alloy in the HB962-2001 standard.

[0059] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A heat treatment process for ZL114A aluminum alloy precision casting using a plaster casting method, comprising the following steps: S1. Solution treatment: Under the condition of ≤300℃, ZL114A aluminum alloy is placed in a heat treatment furnace and heated to 540~545℃ at a heating rate of ≤100℃ / h. After solution treatment and holding for 3~4h, quenching treatment is performed. The quenching transfer time is ≤15s. The quenching medium is water and the quenching water temperature is 80℃. S2. Natural pre-aging treatment: Place the quenched ZL114A aluminum alloy at room temperature for 12~24h. S3. Artificial aging treatment: The ZL114A aluminum alloy after natural pre-aging treatment is heated to 165~175℃ in a heat treatment furnace, aged and held for 2.5~3.0h, and then air-cooled to room temperature.

2. The heat treatment process for ZL114A aluminum alloy precision casting using plaster casting as described in claim 1, characterized in that: In step S1, the quenching time is 5 minutes.

3. The heat treatment process for ZL114A aluminum alloy precision casting using plaster casting as described in claim 1, characterized in that: In step S1, during the solution treatment, the ZL114A aluminum alloy is placed in a heat treatment furnace at a temperature of 300°C.

4. The heat treatment process for ZL114A aluminum alloy precision casting using plaster casting as described in claim 1, characterized in that: In step S1, during the solution treatment, the temperature is raised to 540℃ at a rate of 100℃ / h, and after solution treatment and holding at that temperature for 3 hours, quenching is performed.

5. The heat treatment process for ZL114A aluminum alloy precision casting using plaster casting as described in claim 1, characterized in that: In step S2, during the natural pre-aging treatment, the quenched ZL114A aluminum alloy is placed at room temperature for 24 hours.

6. The heat treatment process for ZL114A aluminum alloy precision casting using a gypsum board mold according to claim 1, characterized in that: In step S3, during artificial aging treatment: the ZL114A aluminum alloy after natural pre-aging treatment is heated to 170℃ in a heat treatment furnace and aged for 2.5 hours.

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