A 700MPa grade large aluminum alloy forging and its preparation method

Abstract

The present invention discloses a 700MPa-grade large aluminum alloy forging and a preparation method thereof. The preparation method is to subject a spray-deposited aluminum alloy ingot to homogenization treatment and then sequentially subject it to hot pressing and densification treatment, forging treatment, solution quenching treatment, cold deformation treatment and two-stage aging treatment. The present invention can eliminate the loose defects in large-size ingots prepared by spray deposition through hot pressing and densification, forging and solid solution aging treatment, and improve the thermal processing performance of the ingot. At the same time, the method can greatly improve the material utilization rate and reduce the preparation cost of forgings. The targeted forging and heat treatment processes can enable the forgings to obtain excellent comprehensive performance.

Description

Technical Field

[0001] The invention relates to a 700MPa-level large-scale aluminum alloy forging and a preparation method thereof, belonging to the technical field of aluminum alloy preparation process. Background Art

[0002] The use of higher strength aluminum alloys to prepare large integral components is an important measure to achieve the requirements of low structural weight and long service life in the fields of aviation, aerospace and weapons. However, the main way to improve the strength of aluminum alloys is to increase the content of strengthening elements in the alloy. Generally speaking, when the strength of the alloy reaches 700MPa, the total amount of the main alloying elements is close to or exceeds 15wt%. At this time, the casting forming performance of the alloy is seriously deteriorated (very easy to crack), and it is difficult to prepare large-sized ingots (the ingot diameter is generally not more than 450mm) by traditional melting and casting processes, so it is impossible to meet the material requirements of large-sized 700MPa-grade aluminum alloy forgings. The use of spray deposition technology can realize the preparation of large-sized ingots of high-alloy content aluminum alloys, but due to the limitations of the characteristics of the spray deposition preparation technology itself, there is a certain amount of looseness in the prepared ingots, which will seriously deteriorate the hot working process performance of the ingots, and it is easy to crack when directly forged. The spray deposition ingots used at this stage are first extruded into bars and then processed in a hot working manner, but there are usually some defects in the organization of the head and tail ends during extrusion, which need to be removed. At the same time, the extruded billet cannot be fully used during extrusion, and there is some "excess pressure", resulting in low utilization rate. The material utilization rate of the extruded material is 70%. The low material utilization rate and limited rod diameter also cannot meet the material requirements of large-size forgings. At present, the spray-deposited alloy deposited billet is subjected to large plastic deformation or high-temperature hot isostatic pressing above 440°C to improve density and reduce metallurgical defects, but the specifications of hot isostatic pressing equipment are limited, the pressure is relatively low (generally the high temperature is below 200MPa) and the cost is high, making it difficult to achieve industrial application of large-size ingots. Summary of the invention

[0003] In view of the defects existing in the aluminum alloy forgings in the prior art, the first purpose of the present invention is to provide a 700MPa-grade large-scale aluminum alloy forging, which has the advantages of high strength, tensile strength up to 700MPa, good corrosion resistance and fracture toughness, long service life, etc., and can meet the use requirements in the fields of aviation, aerospace and weapons.

[0004] The second object of the present invention is to provide a method for preparing large-sized aluminum alloy free forgings. The present invention can eliminate the loose defects in large-sized ingots prepared by spray deposition through hot pressing densification, forging forming, and solid solution aging treatment, improve the hot processing performance of the ingot, and ensure the smoothness of the forging. At the same time, hot pressing densification can greatly improve the material utilization rate and reduce the cost of forging preparation. The targeted forging and heat treatment process can enable the forging to obtain excellent comprehensive performance.

[0005] In order to achieve the above technical objectives, the present invention provides a method for preparing 700MPa grade large aluminum alloy forgings, which comprises subjecting a spray-deposited aluminum alloy ingot to surface treatment and then sequentially subjecting it to hot pressing densification treatment, forging treatment, solution quenching treatment, cold deformation treatment and two-stage aging treatment.

[0006] The present invention can eliminate the loose defects in large-sized ingots prepared by spray deposition by hot pressing densification, forging and solution aging treatment of spray-deposited aluminum alloy ingots, improve the thermal processing performance of the ingots, and ensure the comprehensive performance of large-sized forgings. The present invention first performs a surface treatment method of homogenizing and peeling the aluminum alloy ingots, which can eliminate the heterogeneity in chemical composition and structure, and preliminarily improve the plastic deformation ability of the aluminum alloy ingots, while facilitating subsequent operations. The hot pressing densification treatment is to place the ingot in an extrusion barrel or mold with a blind mold, and use axial hot extrusion or hot forging at high temperature to expand the diameter of the ingot and deform it, thereby welding the looseness in the ingot. The material deformation in the densification process is uniform, and the utilization rate can reach more than 95%, which greatly improves the material utilization rate and reduces the cost of forging preparation. After obtaining a forging billet with good forging performance, a multi-directional, overall large forging ratio forging process is adopted to fully crush the second phase particles and obtain a uniform deformation structure. Combined with the subsequent precision heat treatment process, excessive residual stress caused by higher strength can be avoided, so that the forging can obtain excellent comprehensive performance. Finally, the cold deformation treatment of double-sided cold pressing can completely eliminate the residual stress in the forging and obtain an aluminum alloy forging with high strength and tensile strength.

[0007] As a preferred solution, the density of the aluminum alloy ingot after spray deposition in the present invention is 2.7-3.5 g / cm 3 , porosity <1%.

[0008] As a preferred solution, the hot pressing densification treatment is specifically as follows: the aluminum alloy ingot is first heated to 380-440°C, then kept warm for 10-12 hours and then pressed to make the ingot have good thermoplasticity, thereby facilitating hot deformation treatment. More preferably, the temperature is 400-420°C.

[0009] As a preferred solution, the pressing process is a blind die extrusion process or a die forging process.

[0010] As a preferred solution, the conditions for the blind die extrusion treatment are: die temperature: 350-420°C, sleeve temperature: 380-410°C, and the maximum pressure per unit cross section applied is 300-450 MPa.

[0011] As a preferred solution, the conditions of the die forging treatment are: the die temperature is: 390-440°C, and the maximum pressure per unit cross section is applied according to 350-500MPa. The present invention controls the conditions of hot pressing and densification treatment to eliminate the loose defects in large-sized ingots prepared by spray deposition and improve the hot processing performance of the ingot. Reasonable temperature setting is the key to the ingot having low deformation resistance, good process plasticity, loose welding and avoiding local "overheating". Too high or too low temperature cannot guarantee the low deformation resistance and high plasticity of the ingot.

[0012] As a preferred solution, the deformation amount of the hot pressing and densification treatment is 50-70%. Under the preferred deformation amount of the present invention, the loose defects can be fully eliminated through the flow deformation of the tissue, and at the same time, it will not cause an excessively high deformation temperature rise.

[0013] As a preferred solution, the forging conditions are: heating temperature of 370-430°C, holding time of 6-10h, die temperature of 410-440°C, forging method of at least two reversing forgings (two piers + two draws or two draws + two piers), and the total forging ratio is not less than 8. The forging process used in the present invention can obtain a uniform aluminum alloy deformation structure and ensure the performance of the forging.

[0014] As a preferred solution, taking into account the full dissolution of high-content alloying elements in the alloy and the overburning temperature limit, the conditions for the solution quenching treatment are: the solution temperature is 465-475°C, and the holding time is: when the maximum cross-sectional thickness T does not exceed 20 mm, the holding time is 30-60 min, when the maximum cross-sectional thickness T exceeds 20 mm, the holding time is T×3 min, the quenching water temperature is 35-60°C, and the quenching transfer time does not exceed 25 s; T is the maximum cross-sectional thickness of the aluminum alloy forging, in mm.

[0015] As a preferred solution, considering that the residual stress after quenching increases with the increase of alloy strength, and at the same time, the alloy of the present invention has a strong natural aging response, a large number of tests have verified that the double-sided cold pressing method within 120 minutes after quenching can well eliminate the residual stress in the forging. Therefore, the conditions of the cold deformation treatment are: the double-sided cold pressing deformation method is adopted, the forging deformation amount of each side is 1.0-2.5%, and the time interval between the cold deformation treatment and the quenching is less than 120 minutes.

[0016] As a preferred solution, the primary aging conditions of the two-stage aging treatment are: temperature of 115-125°C, and insulation time of 7-10 hours; the secondary aging conditions of the two-stage aging treatment are: temperature of 145C-165°C, and insulation time of 6-14 hours.

[0017] The present invention also provides a 700MPa-level large aluminum alloy forging. In order to ensure that the strength of the alloy can reach 700MPa, the content range of Zn, Mg, and Cu elements constituting the main strengthening phase is obtained through a large number of experiments and theoretical calculations. In addition, considering the casting formability of the ingot and the subsequent processing technology performance, the upper limit of the alloy element and the type and content of the micro-alloying element are determined, and it is finally determined that the alloy is composed of the following elements in weight percentage: Zn: 11.0-13.0%, Mg: 2.4-3.6%, Cu: 1.5-2.5%, Zr: 0.08-0.20%, Ti: 0.01-0.05%, Mn: 0.05-0.35%, Si≤0.10%, Fe≤0.15%, inevitable impurities≤0.05%, and the balance is Al.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0019] 1. Compared with the method of preparing forgings by extruding rods, the method for preparing large-size 700MPa-grade aluminum alloy forgings provided by the present invention is easy to implement, can shorten the preparation process, does not have partial "overpressure", and does not need to cut off the defective parts at the head and tail ends of the ingot, thereby greatly improving the material utilization rate.

[0020] 2. The large-size 700MPa aluminum alloy forgings provided by the present invention are large in size and excellent in comprehensive performance. The ultra-high-strength aluminum alloy forgings prepared by the method of the present invention can increase the weight of a single forging blank to about 3 tons, which can meet the needs of most large forgings in the fields of aviation and aerospace. At the same time, the prepared forgings have a high strength of 700MPa and have the characteristics of low anisotropy, high fracture toughness and good fatigue resistance. DETAILED DESCRIPTION

[0021] The following examples are only specific descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention. For ordinary technicians in the technical field, any improvements made without departing from the present invention should be deemed to be within the scope of protection of the present invention.

[0022] Embodiment 1:

[0023] In this embodiment, the composition and weight percentage of the 700 MPa grade large aluminum alloy forging are: Zn: 12.8%, Mg: 3.2%, Cu: 1.5%, Zr: 0.11%, Ti: 0.03%, Mn: 0.15%, Si: 0.08%, Fe: 0.12%, and the balance is Al.

[0024] The preparation method of the 700MPa grade large aluminum alloy forging in this embodiment is as follows:

[0025] S1. Hot pressing and densification treatment: a spray-deposited aluminum alloy ingot with a size of Φ830×2100 mm (density of 3.10 g / cm 3 , porosity <1%), after homogenization and peeling, put it into an air circulation furnace for heating, heating to 420℃, holding time 11h, after holding is completed, put the billet vertically into a forging die with a diameter of 1400mm for forging and densification, the die temperature is 410℃, the pressure is 350MPa, forging downward until the die is completely filled, holding pressure for 3 to 5min and then releasing the pressure, the deformation of hot pressing and densification is 65%, take out the densified ingot, and air cool to room temperature;

[0026] S2. Forging treatment: the forging blank is placed in an air circulation furnace for heating at a temperature of 400°C and kept warm for 6 hours. After being taken out of the furnace, it is subjected to radial drawing → roughing → reversing drawing → roughing → reversing drawing → roughing → trimming on a 30,000-ton forging press to form a free forging with a width of 900-1000mm, a thickness of 110mm, and a length of 8.4-10m. The total forging ratio is 8.7, the die temperature during forging is 410°C, and the temperature of the forging after final forging is 398°C.

[0027] S3. Solution quenching treatment: After the forgings are placed at room temperature, they are solution treated in a heating furnace at a solution temperature of 472°C and a holding time of 5.5 hours. They are then quenched out of the furnace at a quenching water temperature of 45°C and a transfer time of 15 seconds. The forgings are shaken up and down until they are completely cooled and then taken out of the water tank.

[0028] S4. Cold deformation treatment: After quenching, the forgings are subjected to forging deformation treatment within 30 minutes, and double-sided cold pressing treatment is adopted. After one side of the forging is completely cold pressed, it is turned 180° and cold pressed on the other side. Each side is 2mm downward along the thickness direction. The single-sided forging deformation is 1.8% and the total deformation is 3.6%.

[0029] S5. Two-stage aging treatment: Place the forgings after cold deformation into an air circulation heating furnace for artificial aging treatment. The first-stage aging temperature is 120°C, the holding time is 8h, the second-stage aging temperature is 150°C, the holding time is 8h, and then air cool to room temperature.

[0030] Embodiment 2:

[0031] In this embodiment, the composition and weight percentage of the 700 MPa grade large aluminum alloy forging are: Zn: 12.6%, Mg: 2.6%, Cu: 1.8%, Zr: 0.12%, Ti: 0.02%, Mn: 0.32%, Si: 0.06%, Fe: 0.10%, and the balance is Al.

[0032] The preparation method of the 700MPa grade large aluminum alloy forging in this embodiment is as follows:

[0033] S1. Hot pressing and densification treatment: a spray-deposited aluminum alloy ingot with a size of Φ650×1800 mm (density of 2.915 g / cm 3 , porosity <1%), after homogenization and peeling, put it into an air circulation furnace for heating, heated to 400℃, and kept warm for 10h. After the insulation is completed, put the billet into an extruder with a diameter of 1000mm for extrusion treatment, the mold temperature is 420℃, the sleeve temperature is 390℃, pressurized to 300MPa, extruded until the mold is completely filled, and released after holding the pressure for 10min. The deformation of hot pressing densification is 58%. The densified ingot is taken out and air-cooled to room temperature;

[0034] S2. Forging treatment: the forging blank is placed in an air circulation furnace for heating at a temperature of 420°C and kept warm for 8 hours. After being taken out of the furnace, the forging blank is subjected to axial roughening → reversing drawing → roughening → reversing drawing → roughening → punching → horse frame ring forging on a 10,000-ton forging press to prepare a ring forging with an inner diameter of 2100 mm, a thickness of 150 mm, and a height of 580 mm. The total forging ratio is 9.0, and the die temperature during forging is 420°C.

[0035] S3. Solution quenching treatment: After the forgings are placed at room temperature, they are solution treated in a heating furnace at a solution temperature of 475°C and a holding time of 7.5 hours. They are then quenched out of the furnace at a quenching water temperature of 40°C and a transfer time of 20 seconds. The forgings are shaken up and down until they are completely cooled and then removed from the water tank.

[0036] S4. Cold deformation treatment: After quenching, the forgings are subjected to double-sided forging deformation treatment within 100 minutes, with the forging deformation amounts of 1.2% and 1.5% on each side respectively;

[0037] S5. Two-stage aging treatment: Place the forgings after cold deformation into an air circulation heating furnace for artificial aging treatment. The first-stage aging temperature is 120°C, the holding time is 10h, the second-stage aging temperature is 153°C, the holding time is 10h, and then air cool to room temperature.

[0038] Embodiment 3:

[0039] The only difference between this embodiment and embodiment 1 is that the heating temperature of the ingot during the hot pressing and densification process is 380°C.

[0040] Embodiment 4:

[0041] The only difference between this embodiment and embodiment 1 is that the holding time of the ingot during the hot pressing and densification process is 12 hours.

[0042] Embodiment 5:

[0043] The only difference between this embodiment and embodiment 1 is that the deformation amount of the hot pressing and densification treatment is 70%.

[0044] Comparative Example 1:

[0045] The difference between this comparative example and Example 1 is that no hot pressing and densification treatment is added, and the other conditions are the same. Comparative Example 2:

[0046] The difference between this comparative example and Example 2 is that no hot pressing and densification treatment is added, and the other conditions are the same.

[0047] The difference between this comparative example and Example 1 is only that the heating temperature of the ingot during the hot pressing and densification process is different, and the heating temperature of the ingot is set to 370° C., and the other conditions are the same.

[0048] S1. Hot pressing and densification treatment: After homogenization and peeling treatment, the spray-deposited aluminum alloy ingot with a size of Φ830×2100mm is placed in an air circulation furnace for heating to 370℃ for 11h. After the insulation is completed, the billet is vertically placed in a forging die with a diameter of 1400mm for forging and densification. The die temperature is 410℃, and the billet is forged downward until the die is completely filled. The pressure is maintained for 3 to 5 minutes and then released. The deformation amount of hot pressing and densification is 65%. The densified ingot is taken out and air-cooled to room temperature.

[0049] Comparative Example 4:

[0050] The difference between this comparative example and Example 1 is that the heating temperature of the ingot during the hot pressing and densification process is different. The heating temperature of the ingot is set to 450° C., and the other conditions are the same.

[0051] S1. Hot pressing and densification treatment: After homogenization and peeling treatment, the spray-deposited aluminum alloy ingot with a size of Φ830×2100mm is placed in an air circulation furnace for heating to 450℃ and kept at temperature for 11 hours. After the insulation is completed, the billet is vertically placed in a forging die with a diameter of 1400mm for forging and densification. The die temperature is 410℃, and the billet is forged downward until the die is completely filled. The pressure is maintained for 3 to 5 minutes and then released. The deformation amount of hot pressing and densification is 65%. The densified billet is taken out and air-cooled to room temperature.

[0052] Comparative Example 5:

[0053] The difference between this comparative example and Example 1 is that the deformation amount of the hot pressing densification treatment is 47%, and the other conditions are the same.

[0054] Comparative Example 6:

[0055] The difference between this comparative example and Example 1 is that the deformation amount of the hot pressing densification treatment is 75%, and the other conditions are the same.

[0056] Comparative Example 7:

[0057] The only difference between this comparative example and Example 1 is that the forging conditions are a temperature of 350° C. and a holding time of 5 h, and the other conditions are the same.

[0058] Comparative Example 8:

[0059] The difference between this comparative example and Example 1 is that the forging conditions are: temperature 450° C., holding time 11 h, and the other conditions are the same.

[0060] The 700 MPa grade large aluminum alloy forgings prepared in the above Examples 1 to 5 and Comparative Examples 1 to 8 were subjected to tensile property tests. The test method was based on standard GB / T 228.1. The results are shown in Table 1.

[0061] The 700 MPa grade large aluminum alloy forgings prepared in the above Examples 1 to 5 and Comparative Examples 1 to 8 were subjected to fracture toughness and corrosion performance tests. The test methods were based on the standards: (GB / T4161, GB / T22639). The results are shown in Table 2.

[0062] Table 1: Test results of tensile properties of 700 MPa grade large aluminum alloy forgings prepared in Examples 1 to 5 and Comparative Examples 1 to 8

[0063]

[0064]

[0065] It can be seen from Table 1 that when the hot pressing and densification treatment is not used, the tensile properties of the aluminum alloy forgings are significantly reduced, especially the tensile properties of ST or radial R are significantly reduced, and cracks will appear during the forging process, and it is impossible to obtain aluminum alloy forgings with excellent performance and meeting industrial application requirements, which shows that the hot pressing and densification treatment used in the present invention can greatly improve the material utilization rate, and the prepared forgings have high tensile properties and low anisotropy. It can be seen from the data of Comparative Example 3, Comparative Example 4 and Example 1 that when the temperature of the hot pressing and densification treatment is too low or too high, the anisotropy of the aluminum alloy forgings will also increase, and the tensile properties in the L direction, LT direction and ST direction will all be reduced, and cracks will appear during forging. At the same time, the control of the deformation amount in the hot pressing and densification treatment and the temperature and time of the forging treatment will affect the performance of the aluminum alloy forgings.

[0066] Table 2: Fracture toughness and corrosion performance test results of 700MPa grade large aluminum alloy forgings prepared in Examples 1 to 5 and Comparative Examples 1 to 8

[0067]

[0068]

[0069] Since the ring-shaped aluminum alloy forgings prepared in Example 2 and Comparative Example 2 are measured in the TR, AT and AR directions, the other examples and comparative examples are block-shaped aluminum alloy forgings, so the LT, TL and SL directions are measured.

[0070] It can be seen from Table 1 that when the hot pressing and densification treatment is not used, the fracture toughness of the aluminum alloy forging is significantly reduced, especially the fracture toughness performance of ST is significantly reduced, indicating that the hot pressing and densification treatment used in the present invention can greatly improve the fracture toughness of the aluminum alloy and has low anisotropy. It can be seen from the data of Comparative Example 3, Comparative Example 4 and Example 1 that when the temperature of the hot pressing and densification treatment is too low or too high, the fracture toughness of the aluminum alloy will be reduced and the anisotropy will be more obvious. At the same time, the control of the deformation amount in the hot pressing and densification treatment and the temperature and time of the forging treatment will affect the fracture toughness performance of the aluminum alloy forging.

Claims

1. A method for preparing a 700MPa grade large aluminum alloy forging, characterized in that: After the spray-deposited aluminum alloy ingot is subjected to surface treatment, hot pressing and densification treatment, forging treatment, solution quenching treatment, cold deformation treatment and double-stage aging treatment are sequentially performed to obtain; The hot pressing and densification treatment is specifically as follows: the aluminum alloy ingot is first heated to 380-440° C., then kept at this temperature for 10-12 hours and then pressed; The deformation amount of the hot pressing and densification treatment is 50-70%; The cold deformation treatment conditions are: adopting a double-sided forging deformation method, the forging deformation amount of each side is 1.0-2.5%, and the time interval between the cold deformation treatment and the quenching is less than 120 minutes; The aluminum alloy forging is composed of the following elements in weight percentage: Zn: 11.0-13.0%, Mg: 2.4-3.6%, Cu: 1.5-2.5%, Zr: 0.08-0.20%, Ti: 0.01-0.05%, Mn: 0.05-0.35%, Si≤0.10%, Fe≤0.15%, unavoidable impurities≤0.05%, and the balance is Al; The forging conditions are as follows: a temperature of 370-430°C, a holding time of 6-10 hours, a die temperature of 410-440°C, a forging method of at least two reversing upsetting and drawing methods, and a total forging ratio of not less than 8, wherein the two reversing upsetting and drawing methods are two upsetting and two drawing methods or two drawing and two upsetting methods.

2. The method for preparing a 700MPa grade large aluminum alloy forging according to claim 1, characterized in that: The pressing process is one of a blind die extrusion process or a die forging process; The blind die extrusion treatment conditions are: die temperature: 350-420°C, sleeve temperature: 380-410°C, and the maximum pressure per unit cross section applied is 300-450MPa; The conditions of the die forging treatment are: the die temperature is 390-440° C., and the maximum pressure per unit cross section applied is 350-500 MPa.

3. The method for preparing a 700MPa grade large aluminum alloy forging according to claim 1, characterized in that: The conditions of the solution quenching treatment are: the solution temperature is 465-475°C, the holding time is: when the maximum cross-sectional thickness T does not exceed 20mm, the holding time is 30-60min, when the maximum cross-sectional thickness T exceeds 20mm, the holding time is T×3min, the quenching water temperature is 35-60°C, and the quenching transfer time does not exceed 25s; The T is the maximum cross-sectional thickness of the aluminum alloy forging, in mm.

4. The method for preparing a 700MPa grade large aluminum alloy forging according to claim 1, characterized in that: The first-stage aging conditions of the two-stage aging treatment are: temperature of 115-125°C, and holding time of 7-10h; The secondary aging conditions of the double-stage aging treatment are: temperature of 145°C to 165°C; and holding time of 6 to 14 hours.

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