A densification heat treatment method for ZL205A alloy castings

Abstract

The present invention provides a kind of ZL205A alloy casting densification heat treatment method, for the problem that ZL205A casting is easy to produce loose when solidifying, propose a kind of new densification heat treatment process, in order to reduce the loose defects of casting, improve the qualified rate of casting once, further improve casting performance.First, casting is placed in a vacuum heat treatment furnace, vacuum heat treatment is carried out on casting, hydrogen dissolved in casting is extracted, then the loose area on the casting surface is sealed with an argon arc welding gun, followed by hot isostatic pressing, and finally casting is subjected to solid solution and aging treatment according to industry standards. This heat treatment process can effectively reduce the hydrogen content in casting, press-fit most of the loose defects of ZL205A casting, and greatly improve the qualified rate of casting once. After casting is heat-treated by the present invention, mechanical properties are effectively improved, and its tensile strength is higher than the ZL205A-T5 standard value specified in GB1173-2013 by nearly 13%, and elongation is higher than the standard value by nearly 50%, while having good fatigue performance.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a densification heat treatment method for a ZL205A alloy casting. Background Art

[0002] ZL205A alloy is one of the strongest cast aluminum alloys currently available. It is widely used in the aviation, aerospace, and military sectors as static load-bearing components and cabin structural parts. ZL205A alloy is a cast Al-Cu alloy with a Cu content of 4.6-5.3%. According to the Al-Cu binary phase diagram, this Al-Cu alloy solidifies in a mushy state, which is prone to porosity defects during solidification, significantly affecting the performance of the casting itself.

[0003] ZL205A alloy solidifies in a paste-like state, with a large temperature difference between its solid and liquid phases (nearly 100°C). This makes it prone to porosity defects during solidification shrinkage, and most of these defects are penetrating porosity. The porosity area has a loose structure and a high hydrogen content, which makes it very easy to generate gas during repair welding, resulting in weld porosity or expansion of the weld area. Because the porosity is a penetrating structure, hot isostatic pressing cannot press the porosity together. If it is not discovered, it is very easy to cause component overload failure and safety hazards. At the same time, when repair welding is performed to remove the looseness of the casting, the loose areas are very likely to generate gas, causing the internal quality of the repair area to exceed the standard, the repair area to expand, and the casting to be scrapped beyond the industry standard requirements. Currently, the method of setting chills and strengthening shrinkage in thick and large parts of the casting is usually adopted to guide the sequential solidification of ZL205A alloy and minimize porosity defects. However, this problem is more difficult to solve for some thick and large parts, complex parts, or parts that are difficult to remove after the runner is installed. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a densification heat treatment process for ZL205A alloy castings, in order to effectively improve the first-time pass rate of ZL205A castings and simultaneously improve the performance of ZL205A alloy. The specific technical solution is as follows:

[0005] A densification heat treatment method for a ZL205A alloy casting comprises the following steps:

[0006] S1. Solid-state vacuum heat treatment of castings: put the castings into the furnace chamber for vacuum treatment, and draw the vacuum degree of the furnace chamber to 2×10 -4 ~2×10 -5 Pa, then raise the furnace temperature to 480-510℃ and keep it warm for 2-3h; keep the vacuum pump on during the insulation process and keep the vacuum degree of the furnace chamber no greater than 2.3×10 -4 Pa;

[0007] S2. Perform 100% fluorescent treatment on the casting surface to detect loose areas;

[0008] S3. Use argon arc welding machine to perform arc sealing treatment on the loose area;

[0009] S4. Perform fluorescence treatment on the sealed loose area. If it fails, repeat step S3 until it passes.

[0010] S5. The casting is subjected to hot isostatic pressing treatment. The pressure medium is high-purity argon gas. The casting is subjected to pressure maintenance treatment at 510-530°C and the pressure is 110-130 MPa. After the pressure maintenance, the furnace is cooled to below 200°C and taken out of the furnace;

[0011] S6. Solution treatment and aging treatment are performed on the casting: the casting is kept at 538°C for 15 hours, water quenched at room temperature, and then kept at 155°C for 10 hours to obtain a high-performance ZL205A casting.

[0012] Preferably, the chemical composition of the ZL205A alloy casting complies with the requirements of GB / T 1173-2013.

[0013] Preferably, the mass percentages of the components of the ZL205A alloy casting are: Cu: 5.1%, Mn: 0.40%, Ti: 0.18%, Cd: 0.20%, V: 0.19%, Zr: 0.22%, B: 0.06%, Fe: 0.10%, other impurities are not more than 0.20%, and the balance is aluminum.

[0014] Preferably, the step S2 is carried out in accordance with the method specified in GB / T 9438-2013.

[0015] Preferably, in step S3, the welding current of the argon arc welding machine is 40-55A, the tungsten electrode diameter is 3-4mm, the nozzle diameter is 5-8mm, and the distance between the nozzle and the loose surface of the casting is controlled at 20-30mm; the sealing treatment time is about 20-35s.

[0016] Preferably, the step S3 is repeated no more than 3 times.

[0017] Preferably, the purity of the high-purity argon gas in step S5 is not less than 99.5%.

[0018] Preferably, the pressure holding time in step S5 is 1 to 1.5 hours.

[0019] Preferably, the processing parameters of step S6 refer to the provisions of ZL205A alloy in GB / T 1173-2013 standard.

[0020] The principle of densifying ZL205A alloy castings of the present invention is:

[0021] The present invention performs vacuum evacuation treatment on ZL205A alloy. Through the H element concentration difference between the casting at high temperature and the vacuum environment, H atoms in the casting are separated from the casting by diffusion, thereby achieving the purpose of reducing the hydrogen content in the casting. It can effectively reduce the generation of bubbles during the casting repair welding process and reduce the repair welding porosity defects.

[0022] Because ZL205A alloy solidifies in a paste-like state, its porosity defects are generally penetrating. Surface fluorescent penetrant treatment can be used to identify the location and approximate area of ​​the porosity. Arc sealing is then performed on the loose areas on both sides of the casting, melting the surface to achieve a surface sealing effect. Hot isostatic pressing (HIP) is then performed on the sealed casting to compact the loose structures and also effectively densify other non-loose structures (such as areas with pinholes).

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention proposes a densification process for ZL205A castings. The castings are first placed in a vacuum heat treatment furnace for vacuum heat treatment to remove dissolved hydrogen. The loose areas on the casting surface are then sealed with an argon arc welding torch. Hot isostatic pressing (HIP) is then performed, and finally, the castings undergo solution and aging heat treatments according to industry standards. This heat treatment process effectively reduces the hydrogen content in the castings, seals most loose defects in ZL205A castings, and significantly improves the first-pass yield of castings.

[0025] 2. The present invention performs vacuum evacuation treatment on ZL205A alloy. By taking advantage of the H element concentration difference between the casting at high temperature and the vacuum environment, the H atoms dissolved in the casting are released, thereby reducing the hydrogen content in the casting. This can effectively reduce gas precipitation during subsequent repair welding of the casting and reduce repair welding porosity defects.

[0026] 3. The present invention performs arc sealing treatment on the loose areas on the front and back surfaces of the casting to achieve a surface sealing effect. When the arc approaches the surface of the casting, the loose areas on the surface undergo a solid-semi-solid (or liquid) transition, effectively sealing the loose surface; the arc does not directly contact the surface, minimizing the impact on the external dimensions and other positions.

[0027] 4. The castings after sealing treatment are subjected to hot isostatic pressing to press the loose structure together, while also having a good densification effect on other non-loose structures.

[0028] 5. After the heat treatment of the present invention, the mechanical properties of the casting are significantly improved. Compared with the ZL205A-T5 standard value specified in GB 1173-2013, its tensile strength is nearly 13% higher than the standard value, and its elongation is nearly 50% higher than the standard value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 This is a comparison of the internal quality of the ZL205A alloy casting before and after surface sealing treatment in comparative example 2. A is an X-ray inspection image of the ZL205A alloy casting before surface sealing, and B is an X-ray inspection image of the ZL205A alloy casting after surface sealing;

[0031] Figure 2 Comparison of the internal quality of the ZL205A alloy casting before and after hot isostatic pressing (HIP) in Comparative Example 3. A is an X-ray inspection image of the ZL205A alloy casting before HIP, and B is an X-ray inspection image of the ZL205A alloy casting after HIP. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0033] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0034] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0035] Example 1

[0036] Densification Heat Treatment of ZL205A Alloy Castings

[0037] The mass percentages of the components of ZL205A alloy are: Cu: 5.1%, Mn: 0.40%, Ti: 0.18%, Cd: 0.20%, V: 0.19%, Zr: 0.22%, B: 0.06%, Fe: 0.10%, other impurities are not more than 0.20%, and the balance is aluminum.

[0038] S1. The obtained ZL205A casting is subjected to solid vacuum degassing treatment: the casting is pushed into the furnace chamber and vacuumed to 2×10 -4 Pa, then the furnace temperature was raised to 500 °C and kept at this temperature for 2 h. During the holding process, the vacuum in the furnace was kept at 2.3 × 10 - 4 Pa;

[0039] S2. Perform 100% fluorescent treatment on the surface of the casting according to the method specified in GB / T 9438-2013 to detect the loose areas;

[0040] S3. Use an argon arc welding machine to perform arc treatment on the surface of the loose area. Control the welding current to 45A, the tungsten electrode diameter to 3mm, the nozzle diameter to 6mm, keep the nozzle 20mm away from the loose surface of the casting, and the arc treatment time to 30s.

[0041] S4. Perform fluorescent treatment on the loose areas after arc sealing treatment, and the surface quality should show no looseness.

[0042] S5. Perform hot isostatic pressing on the castings. The medium is high-purity argon gas with a purity of 99.8%. Maintain pressure on the castings at 510°C and 120 MPa for 1 hour. Cool the furnace to below 200°C and then air cool.

[0043] S6. Solution treatment and aging treatment are performed on the casting: the casting is kept at 538°C for 15 hours, water quenched at room temperature, and then kept at 155°C for 10 hours to obtain a high-performance ZL205A casting.

[0044] Example 2

[0045] Densification Heat Treatment of ZL205A Alloy Castings

[0046] The mass percentages of the components of ZL205A alloy are: Cu: 5.0%, Mn: 0.40%, Ti: 0.18%, Cd: 0.20%, V: 0.19%, Zr: 0.22%, B: 0.06%, Fe: 0.10%, other impurities are not more than 0.20%, and the balance is aluminum.

[0047] S1. The obtained ZL205A casting is subjected to solid vacuum degassing treatment: the casting is pushed into the furnace chamber and vacuumed to 2×10 -4 Pa, then the furnace temperature was raised to 500 °C and kept at this temperature for 2 h. During the holding process, the vacuum in the furnace was kept at 2.3 × 10 - 4 Pa;

[0048] S2. Perform 100% fluorescent treatment on the surface of the casting according to the method specified in GB / T 9438-2013 to detect the loose areas;

[0049] S3. Use an argon arc welding machine to perform arc treatment on the surface of the loose area. Control the welding current to 45A, the tungsten electrode diameter to 3mm, the nozzle diameter to 6mm, keep the nozzle 20mm away from the loose surface of the casting, and the arc treatment time to 30s.

[0050] S4. Perform fluorescent treatment on the loose areas after arc sealing treatment, and the surface quality should show no looseness.

[0051] S5. Perform hot isostatic pressing on the castings. The medium is high-purity argon gas with a purity of 99.8%. Maintain pressure on the castings at 510°C and 120 MPa for 1 hour. Cool the furnace to below 200°C and then air cool.

[0052] S6. Solution treatment and aging treatment are performed on the casting: the casting is kept at 538°C for 15 hours, water quenched at room temperature, and then kept at 155°C for 10 hours to obtain a high-performance ZL205A casting.

[0053] Experimental Example 1

[0054] Investigating the properties of the ZL205A alloy castings of the present invention

[0055] The tensile strength, yield strength and elongation of the ZL205A alloy subjected to densification heat treatment in Example 1-2 were tested according to GB / T 228.1-2010.

[0056] The axial fatigue properties of the ZL205A alloy subjected to densification heat treatment in Example 1-2 were tested according to GB / T 3075-2008.

[0057] Table 1 Performance comparison of ZL205A alloy treated in Example 1-2 and GB / T 1173-2013 standard

[0058]

[0059] The results are shown in Table 1. The castings were dissected and the tensile strength of the alloy reached 498-510 MPa, significantly exceeding the ZL205A-T5 standard value specified in GB 1173-2013 and nearly 13% higher than the conventionally treated ZL205A alloy. The yield strength was 390-411 MPa, and the elongation reached 12.3-12.6%, nearly 50% higher than the standard value.

[0060] The castings have been tested for axial fatigue and the fatigue life is more than 10 7 Second-rate.

[0061] The above results show that the mechanical properties of the castings are significantly improved after the heat treatment according to the present invention.

[0062] Experimental Example 1

[0063] Investigating the effect of vacuum pumping on hydrogen content in ZL205A alloy castings

[0064] The hydrogen content in ZL205A alloy castings before and after vacuum pumping was tested according to GB / T 20975.30-2019 test standard.

[0065] The results show that after vacuum pumping treatment, the hydrogen content in the casting dropped from 0.14 mg / 100 g to 0.08 mg / 100 g. The effect of reducing the hydrogen content in the casting can effectively reduce gas precipitation in the subsequent repair welding of the casting and reduce the porosity defects in the repair welding.

[0066] Comparative Example 1

[0067] Comparison of conventional ZL205A castings and ZL205A castings of the present invention

[0068] The mass percentages of the components of ZL205A alloy are: Cu: 5.1%, Mn: 0.40%, Ti: 0.18%, Cd: 0.20%, V: 0.19%, Zr: 0.22%, B: 0.06%, Fe: 0.10%, other impurities are not more than 0.20%, and the balance is aluminum.

[0069] The ZL205A alloy casting was directly subjected to solution treatment and aging treatment: the casting was kept at 538°C for 15 hours, water quenched at room temperature, and then kept at 155°C for 10 hours to obtain a conventional ZL205A casting. The mechanical properties of the conventional casting and the casting of the present invention were tested according to the same testing standards.

[0070] The results are shown in Table 1. The tensile strength, yield strength, elongation and fatigue life of conventional castings without surface sealing and hot isostatic pressing are significantly lower than those of the castings of the present invention, indicating that the densification heat treatment method of the present invention significantly improves the mechanical properties of the castings.

[0071] Comparative Example 2

[0072] Investigating the effect of surface sealing on the properties of ZL205A alloy castings

[0073] No surface arc treatment was performed on the porosity area. The remaining steps were the same as in Example 1. Hot isostatic pressing was performed directly after the porosity area was detected. Internal quality inspection was performed on the ZL205A alloy castings with the two treatments according to the requirements of GB / T 9438-2013. The X-ray films met the requirements of the level 1 porosity defect standard film.

[0074] The results are as follows Figure 1 As shown in the figure, without surface sealing treatment, the casting is directly subjected to hot isostatic pressing treatment, and the looseness still exists, indicating that the surface sealing treatment has a significant impact on the performance of the casting.

[0075] Comparative Example 3

[0076] Investigating the effect of hot isostatic pressing on the properties of ZL205A alloy castings

[0077] The casting was not subjected to hot isostatic pressing. The remaining processing steps were the same as in Example 1, except that solution treatment and aging treatment were performed directly after the surface sealing treatment. The ZL205A alloy castings subjected to the two treatments were internally quality inspected according to the requirements of GB / T 9438-2013, and the X-ray films met the requirements of the Class 1 porosity defect standard film.

[0078] The results are as follows Figure 2 As shown, after the full set of heat treatment processes of the present invention, the hot isostatic pressing closes the loose structure and the loose defects disappear. In addition, the hot isostatic pressing not only presses the loose structure, but also has a good densification effect on other non-loose structures.

Claims

1. A densification heat treatment method for ZL205A alloy castings, characterized in that: The following steps are involved: S1. Solid-state vacuum heat treatment of castings: put the castings into the furnace chamber for vacuum treatment, and draw the vacuum degree of the furnace chamber to 2×10 -4 ~2×10 -5 Pa, then raise the furnace temperature to 480~510℃ and keep it warm for 2~3h; Keep the vacuum pump on during the insulation process and keep the vacuum degree of the furnace chamber no greater than 2.3×10 -4 Pa; S2. Perform 100% fluorescent treatment on the casting surface to detect loose areas; S3. Use an argon arc welder to perform arc sealing treatment on the loose area; the welding current of the argon arc welder is 40-55A, the tungsten electrode diameter is 3-4mm, the nozzle diameter is 5-8mm, and the distance between the nozzle and the loose surface of the casting is controlled at 20-30mm; the sealing treatment time is 20-35s; S4. Perform fluorescence treatment on the sealed loose area. If it fails, repeat step S3 until it passes. S5. The casting is subjected to hot isostatic pressing treatment. The pressure medium is high-purity argon gas with a purity of not less than 99.5%. The casting is subjected to pressure holding treatment at 510-530°C, a pressure of 110-130 MPa, and a pressure holding time of 1-1.5 hours. After the pressure holding, the furnace is cooled to below 200°C and the casting is taken out of the furnace. S6. Performing solution treatment and aging treatment on the casting: keeping the casting at 538° C. for 15 h, water quenching at room temperature, and then keeping it at 155° C. for 10 h to obtain a ZL205A alloy casting.

2. The densification heat treatment method of a ZL205A alloy casting according to claim 1, characterized in that: The chemical composition of ZL205A complies with the requirements of GB / T 1173-2013.

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