Al-cu-mg-ag heat-resistant alloy forging toughening and strengthening heat treatment method

Abstract

The application discloses a kind of Al-Cu-Mg-Ag heat-resistant alloy forge piece toughening heat treatment methods, comprising the following steps: (1) alloy ingot is carried out multistage homogenization heat treatment;(2) after the ingot that is carried out multistage homogenization heat treatment is hot deformed breakdown and machining, it is carried out die forging forming;(3) the alloy forge piece of die forging forming is carried out solid solution heat treatment;(4) after the alloy forge piece of solid solution heat treatment is carried out grading control cooling water quenching treatment, cools to room temperature;(5) after the alloy forge piece of cooling is carried out cold pressure deformation treatment;(6) after the alloy forge piece of cold pressure is carried out room temperature parking, and carry out aging heat treatment.The application carries out homogenization-deformation breakdown-die forging-solid solution heat preservation-control cooling quenching-cold deformation-room temperature parking-artificial aging treatment to Al-Cu-Mg-Ag heat-resistant alloy, under the premise of ensuring that organization is uniform, performance is controllable, so that alloy forge piece obtains ideal toughening matching relationship.

Description

Technical Field

[0001] This invention relates to a heat treatment method for strengthening and toughening Al-Cu-Mg-Ag heat-resistant alloy forgings, belonging to the field of aluminum alloy forming and hot working technology. Background Technology

[0002] Due to their high specific stiffness, high specific strength, excellent corrosion resistance, low density, ease of processing, and good fatigue resistance, aluminum alloys have gradually become one of the most widely used structural materials in aerospace, rail transportation, automobiles, ships, and construction. Especially in the civil aviation sector, high-strength, high-toughness, and damage-resistant aluminum alloys, as a key structural material, account for 20% to 35% of the fuselage structure weight. In recent years, with the increasing cruising speed of aircraft, the intense friction between the fuselage surface and the air has led to a significant increase in the temperature of the fuselage skin. Traditionally used 2xxx series heat-resistant aluminum alloys, such as 2219, 2618, and 2D70, exhibit good heat resistance, but the long-term stable operating temperature of these alloys is limited (≤150°C). Therefore, to ensure the safety of aircraft operation and meet the requirements of hypersonic flight, the development of new heat-resistant aluminum alloys capable of stable operation at higher temperatures is particularly urgent. Studies dating back to the 1960s have reported that adding Ag to Al-Cu-Mg alloys affects their aging precipitation behavior, causing the alloy to precipitate not only the Al₂Cu phase but also the Ω phase. The Ω phase is a novel hexagonal disk-shaped phase precipitated along the {111}α matrix, and studies have shown that the Ω phase exhibits superior thermal stability compared to the θ′ phase. Furthermore, Al-Cu-Mg-Ag alloys demonstrate excellent room-temperature properties, damage resistance, and high-temperature performance, making them ideal materials for manufacturing critical components such as aircraft skins and wheel hubs.

[0003] To meet the increasingly stringent requirements for material performance in aerospace vehicles, research institutions and manufacturers have conducted extensive research on optimizing the composition of Al-Cu-Mg-Ag alloys, composite microalloying, and plastic forming processes. For example, patent document CN 101245430 A discloses a high-heat-resistant Al-Cu-Mg-Ag alloy, which increases the nucleation sites of the Ω phase by increasing the Ag / Mg atomic ratio, thereby improving the density of the Ω phase in the alloy matrix and enhancing its performance. Patent document CN 115821130 A discloses a high-temperature resistant Al-Cu-Mg-Ag-Sc alloy and its preparation method; patent document CN 116162833 A discloses a high-plasticity high-temperature resistant Al-Cu-Mg-Ag-Er alloy and its preparation method; patent document CN 115558828 A discloses a heat-resistant low-vanadium Al-Cu-Mg-Ag alloy and its application; and patent document CN104294795 A discloses a method for improving the room-temperature tensile properties and high-temperature creep resistance of Al-Cu-Mg-Ag alloy. The above patent documents respectively disclose that by adding microalloying elements such as Sc, Er, V, and Yb to the alloy, the mechanical properties of the alloy are improved in terms of refining the grain size of the cast alloy, inhibiting the recrystallization degree of the deformed alloy, and delaying the coarsening of the Ω phase. Patent document CN 115537617 B discloses a high-strength, heat-resistant aluminum alloy and its applications. The addition of trace element Sn to an Al-Cu-Mg-Ag alloy captures numerous intergranular vacancies, forming solute atom-vacancy pairs and hindering the formation of the subsequent S phase. Simultaneously, it suppresses Ω phase coarsening, thereby improving the alloy's heat resistance. Patent document CN 101876041 A discloses an Al-Cu-Mg-Ag alloy. An ultrafine-grained Al-Cu-Mg-Ag alloy is obtained through equal-diameter angular extrusion. The improved alloy properties rely on grain refinement after intense plastic deformation and increased precipitation density of the heat-resistant strengthening phase.

[0004] The above survey and analysis show that although a great deal of research has been conducted on Al-Cu-Mg-Ag alloys, it has mainly focused on composition design, element ratio optimization, and strong plastic deformation. However, Al-Cu-Mg-Ag alloy ingots manufactured by semi-continuous casting processes under industrial conditions naturally exhibit specific inhomogeneities in structure and chemical composition distribution. Therefore, suitable homogenization heat treatment, sufficient deformation blanking, optimized solution aging heat treatment processes, and their systematic combination are crucial to ensuring that Al-Cu-Mg-Ag alloy forgings simultaneously possess ideal room temperature and high temperature strength, fracture toughness, regular shape, and low residual stress. This is a pressing problem to be solved in the development of novel strengthening and toughening heat treatment processes for Al-Cu-Mg-Ag alloy forgings. Summary of the Invention

[0005] The purpose of this invention is to provide a novel heat treatment method for strengthening and toughening Al-Cu-Mg-Ag alloy forgings. By controlling the ingot stress-relief annealing process, homogenization heat treatment regime, deformation billet process, die forging process, solution heat treatment regime, graded quenching process, cold pressing deformation amount, room temperature resting time, and artificial aging regime, it is possible to make them not only have ideal strength and toughness, but also have regular shape and low residual stress.

[0006] To achieve the above objectives, the present invention mainly adopts the following technical solutions:

[0007] A method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings, the method comprising the following steps:

[0008] (1) According to the composition of the alloy material, the ingot is obtained by feeding, melting and casting. Then the obtained ingot is subjected to stress relief annealing treatment. The stress relief annealing temperature is 350℃~400℃ and the holding time is 2h~8h.

[0009] (2) The stress-relief annealed ingot is subjected to multi-stage homogenization heat treatment, wherein the homogenization heat treatment temperature range is 440℃~520℃ and the homogenization heat treatment time is 10h~48h.

[0010] (3) The ingot after homogenization heat treatment is deformed and opened by extrusion, forging or a combination of both. Before opening, the ingot temperature is preheated to 400℃~480℃ and kept at this temperature for 3h~12h to ensure that the overall temperature of the ingot is uniform and stable.

[0011] (4) After the alloy blank is deformed and opened, it is machined to remove the surface oxide scale and impurities, and then preheated to 400℃~480℃ and held at this temperature for 3h~12h for a long time before die forging. Before forging, the anvil or die is preheated to 350℃~450℃. During the forging process, lubricant is evenly applied to the surface of the anvil or die to improve the interface contact conditions, reduce friction resistance, and achieve uniform and full deformation of the blank.

[0012] (5) The forgings after deformation are subjected to solution heat treatment. The heating rate is 10℃ / min≤V0≤15℃ / min and the solution temperature is 480℃~520℃. After the heat treatment is completed, the alloy is immediately subjected to graded controlled cooling water quenching treatment. The alloy is cooled from the solution temperature point to T1 at an average cooling rate V1, where V1=60℃ / s~80℃ / s and T1=160℃~200℃. Then, the alloy is cooled from the T1 temperature point to room temperature at a cooling rate V2, where V2=3℃ / s~12℃ / s.

[0013] (6) Perform 1% to 5% cold pressing deformation treatment on the quenched forgings at room temperature;

[0014] (7) The forgings after cold pressing deformation are left to stand at room temperature for 24h~96h;

[0015] (8) Artificial aging treatment is performed on the forgings after they have been left to stand at room temperature. The aging temperature is 145℃~190℃ and the treatment time is 8h~72h. Then the forgings are taken out of the furnace and air-cooled to room temperature.

[0016] Preferably, in step (1), the stress-relief annealing temperature of the ingot is 360℃~380℃, and the holding time is 3h~8h. More preferably, the stress-relief annealing temperature is 365℃~375℃, and the holding time is 4h~5h. More precise temperature and time control avoids grain coarsening caused by excessive temperature, while helping to fully eliminate residual stress in the ingot, reducing energy consumption, and providing a more uniform initial structure for subsequent homogenization treatment.

[0017] Preferably, the homogenization heat treatment process in step (2) employs a multi-stage homogenization regime. First, the ingot is heated to 440℃~460℃ within 9h~13h and held for 4h~6h. Subsequently, the ingot is further heated to 470℃~480℃ within 2h~4h and held for 4h~6h. Finally, the ingot is further heated to 505℃~520℃ within 1h~2h and held for 12h~24h. More preferably, the ingot is heated to 450℃~460℃ within 10h~12h and held for 4h~5h. Subsequently, the ingot is further heated to 470℃~480℃ within 2h~3h and held for 4h~5h. Finally, the ingot is further heated to 505℃~515℃ within 1h~2h and held for 18h~24h. Multi-stage temperature and time-controlled homogenization heat treatment helps to fully dissolve the low-melting-point eutectic phase inside the ingot and reduce the degree of dendrite segregation in the ingot.

[0018] Preferably, after the homogenization heat treatment of the ingot is completed in step (2), the ingot is air-cooled to room temperature and then the surface of the ingot is machined to a depth of 10mm~15mm. After the surface of the ingot is machined, the looseness and oxide scale on the surface can be effectively removed.

[0019] Preferably, in step (3), the ingot is preheated to 410℃~480℃ and held for 3h~12h before deformation and blanking. More preferably, the ingot is preheated to 440℃~460℃ and held for 8h~10h before deformation and blanking.

[0020] Preferably, the ingot deformation and blanking method in step (3) can be cross forging or multi-directional forging. More preferably, multi-directional forging is selected as the ingot deformation and blanking method. Multi-directional forging can make the metal deformation more uniform, refine the grains, and improve anisotropy.

[0021] Preferably, in step (3), during the ingot deformation and billet opening process, the preheating temperature of the extrusion cylinder, extrusion die, gasket, or forging anvil is 380℃~450℃. More preferably, the preheating temperature of the extrusion cylinder, extrusion die, gasket, or forging anvil is 400℃~450℃.

[0022] Preferably, in step (4), the blank after blanking is reheated to 410℃~480℃ and held for 6h~12h before die forging. More preferably, the ingot is reheated to 440℃~460℃ and held for 8h~10h before die forging. Matching the preheating temperature and holding time can reduce the deformation resistance of the alloy and reduce the risk of blank cracking during deformation.

[0023] Preferably, the contact surface of the forging anvil or die used in the blank die forging process in step (4) should be nitrided, and the thickness of the nitrided layer is about 50μm to 150μm. More preferably, the thickness of the nitrided layer is 100 to 150μm. Nitriding treatment of the die improves hardness and wear resistance.

[0024] Preferably, in step (4), during the blank die forging process, the forging anvil or die is preheated to 380℃~450℃ and its surface is uniformly coated with a graphite-oil mixture, molybdenum disulfide, or boron nitride lubricant. The application of lubricant can reduce the interfacial friction coefficient between the alloy and the die surface, promote the full filling of the die cavity by the blank, and ensure the regular shape of the forging.

[0025] Preferably, in step (5), the forging is subjected to graded controlled cooling water quenching immediately after the solution treatment and heat preservation treatment is completed, and the quenching transfer time is ≤3s. The quenching method can be spray quenching or immersion quenching. More preferably, the quenching transfer time is ≤2s.

[0026] Preferably, in step (5), the solution heat treatment temperature of the forging is 500℃~515℃, the furnace heating rate is 11℃ / min≤V0≤13℃ / min, and the holding time is 3h. More preferably, the solution heat treatment temperature is 505℃~515℃. Precise control of the solution temperature and solution time can ensure that the low-melting-point precipitated phases are fully dissolved back into the matrix.

[0027] Preferably, in step (5), after the forging has completed solution treatment and heat preservation, it is immediately subjected to staged controlled cooling water quenching. The forging is cooled from the solution temperature point to temperature point T1 at an average rate V1, and then from temperature point T1 to room temperature at an average cooling rate V2. Wherein, V1 = 70℃ / s~80℃ / s, T1 = 180℃~200℃, and V2 = 3℃ / s~6℃ / s. Staged controlled cooling quenching can balance the cooling rate, avoid the precipitation of the second phase, and control the risk of deformation or cracking caused by thermal stress.

[0028] Preferably, the time interval between the completion of quenching of the forging and the start of the cold pressing deformation process in step (6) is 1h≤t1≤4h; the cold pressing deformation amount is 1.5%~4.0%. More preferably, the time interval is 1h≤t1≤2h; the cold pressing deformation amount is 2.0%~3.5%.

[0029] Preferably, the room temperature storage time of the forging in step (7) is 48h~72h.

[0030] Preferably, in step (8), the artificial aging temperature of the forging is 160℃~170℃, and the treatment time is 12h~32h.

[0031] Preferably, the temperature error in the above-mentioned heat treatment steps is ±3°C. More preferably, the temperature error is ±1.5°C.

[0032] Preferably, the Al-Cu-Mg-Ag heat-resistant alloy forgings applicable to this invention have the following composition: Cu: 0.6~5.2wt%, Mg: 0.3~1.0wt%, Ag: 0.3~0.6wt%, Mn: 0.3~0.8wt%, Fe: 0.06~0.35wt%, Ti: 0.04~0.12wt%, Cr: 0.1~0.2wt%, Zn: 0.2~0.4wt%, Si: 0.05~1.1wt%, with a total impurity content of <0.15wt%, and the remainder being Al.

[0033] Compared with the prior art, the heat treatment method for strengthening and toughening Al-Cu-Mg-Ag alloy forgings of the present invention has the following advantages and beneficial effects:

[0034] (1) By optimizing the heat treatment process parameters, Al-Cu-Mg-Ag alloy forgings can achieve high strength and good toughness at the same time, which solves the problem that it is difficult to balance strength and toughness in traditional heat treatment methods.

[0035] (2) The method of the present invention is accurate, reliable, easy to operate, highly operable and economical; it fully considers the characteristics of Al-Cu-Mg-Ag alloy forgings, which helps to improve the yield of Al-Cu-Mg-Ag alloy forgings and is conducive to large-scale industrial application. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0037] Figure 2 This is a photograph of the microstructure of the alloy ingot in Comparative Example 1 after homogenization heat treatment.

[0038] Figure 3 This is a photograph of the microstructure of the alloy ingot after homogenization heat treatment in Example 3.

[0039] Figure 4 This is a photograph of the aged microstructure of the alloy forging in Comparative Example 1.

[0040] Figure 5 This is a photograph of the aged microstructure of the alloy forging in Example 3. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the accompanying drawings are an integral part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the invention, but do not imply limitation on the scope of protection of the present invention.

[0042] Figure 1 The diagram shows the process flow of the present invention, illustrating the control of the forming and toughening heat treatment of Al-Cu-Mg-Ag alloy forgings. The Al-Cu-Mg-Ag alloy forgings sequentially undergo stress-relief annealing, multi-stage homogenization heat treatment, deformation blanking, die forging, solution treatment, staged controlled cooling water quenching, cold pressing deformation, room temperature storage, and artificial aging. In the diagram, V0 represents the solution treatment heating rate, T0 represents the solution treatment temperature, and after the solution treatment holding period, the forging temperature decreases from T0 to T1 at an average cooling rate V1, and then decreases from temperature T1 to room temperature at an average cooling rate V2.

[0043] The multi-stage homogenization heat treatment employed in this invention aims to dissolve the low-melting-point eutectic phase in the ingot in a stepwise manner, significantly reducing dendrite segregation and laying the foundation for obtaining a homogeneous matrix. Combined with fully deformed blanking processes such as multi-directional forging, not only is the casting structure broken up, but a uniform, high-density dislocation structure is also introduced into the alloy. This uniform solute distribution and high dislocation density provide superior chemical driving force and nucleation sites for the high-density, uniform nucleation of the Ω phase during subsequent aging.

[0044] During the deformation forging and die forging processes, strict control of preheating temperature, holding time, forging method, and forging process parameters ensured uniform deformation of the ingot and blank, resulting in a more regular shape and higher dimensional accuracy of the final forging, reducing subsequent machining. Nitriding the contact surfaces of the forging anvil or die and uniformly applying lubricant to the die surface improved interfacial contact conditions, reduced frictional resistance and the risk of die sticking, further guaranteeing the regularity of the forging shape. A precise graded controlled cooling quenching process suppressed the precipitation of coarse equilibrium phases in the high-temperature region through high-speed cooling (V1), followed by low-speed cooling (V2) to reduce thermal stress, thus maintaining a supersaturated vacancy concentration in the matrix. The subsequent room-temperature cold pressing effectively reduced residual stress within the forging, minimizing the risk of deformation and cracking caused by residual stress, and improving the dimensional stability and service life of the forging. Simultaneously, cold compression further introduced crystal defects such as dislocations. The subsequent room temperature resting period allows vacancies and solute atoms (such as Cu, Mg, and Ag) to diffuse and aggregate around dislocation lines, forming solute-rich clusters. These clusters, acting as pre-precipitated phases, effectively promote heterogeneous nucleation of the Ω phase during subsequent artificial aging, increasing the precipitation sites and number density of the aging-strengthening phase. This, in turn, enhances the density and refines the size of the precipitated phase, which is crucial for achieving a synergistic improvement in strength and toughness.

[0045] Comparative Example 1

[0046] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 4.8, Mg: 0.9, Ag: 0.55, Mn: 0.5, Fe: 0.1, Ti: 0.06, Cr: 0.15, Zn: 0.3, Si: 0.08, with impurity content (total) < 0.15, and the remainder being Al.

[0047] After stress-relief annealing (340℃ / 3h) and single-stage homogenization annealing ((↑10h) 500℃ / 24h), the alloy ingot was surface-finished with a surface-finishing depth of 10mm. The surface-finished ingot was reheated to 420℃ and held for 7 hours before being extruded. During the extrusion process, the extrusion cylinder and die were preheated to 430℃. The extruded ingot was then sawn to length and surface-finished, before being reheated to 420℃ and held for 6 hours before being die-formed. The die-formed forging was heated to 500℃ at a rate of 11℃ / min and held for 2 hours, followed by a two-stage controlled-cooling water quenching treatment (V1=60℃ / s, T1=190℃, V2=12℃ / s), with a quenching transfer time of 3s. The forging was then left to rest at room temperature for 2 hours before cold-pressing deformation, with a cold-pressing deformation amount of 1.5%. The cold-pressed forgings were left to stand at room temperature for 2 days. Then, they underwent artificial aging treatment at 160℃ for 16 hours.

[0048] Comparative Example 2

[0049] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 5.0, Mg: 0.85, Ag: 0.58, Mn: 0.7, Fe: 0.2, Ti: 0.08, Cr: 0.18, Zn: 0.2, Si: 0.06, with impurity content (total) < 0.15, and the remainder being Al.

[0050] After stress-relief annealing (360℃ / 4h) and three-stage homogenization annealing ((↑9h) 450℃ / 4h + (↑2h) 475℃ / 4h + (↑1.5h) 505℃ / 24h), the alloy ingot was surface-finished with a surface-finishing depth of 12mm. The surface-finished ingot was reheated to 400℃ and held for 7 hours before being directly upset. The anvil preheated to 400℃ during upseting. The upset ingot was then sawn to length and machined, then reheated to 440℃ and held for 6 hours before being die-formed. The die-formed forging was heated to 500℃ at a heating rate of 13℃ / min and held for 3 hours, followed by a two-stage controlled-cooling water quenching treatment (V1=70℃ / s, T1=200℃, V2=9℃ / s), with a quenching transfer time of 3s. The forgings were then left to stand at room temperature for 2 hours before undergoing cold pressing deformation, with a deformation amount of 1.5%. The cold-pressed forgings were then left to stand at room temperature for 2.5 days. Subsequently, they underwent artificial aging treatment at an aging temperature of 170℃ for 16 hours.

[0051] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 4.9, Mg: 0.95, Ag: 0.52, Mn: 0.6, Fe: 0.15, Ti: 0.08, Cr: 0.14, Zn: 0.25, Si: 0.07, with impurity content (total) < 0.15, and the remainder being Al.

[0052] After stress-relief annealing (360℃ / 6h) and three-stage homogenization annealing ((↑10h) 450℃ / 5h + (↑2.5h) 480℃ / 4h + (↑1.5h) 505℃ / 20h), the alloy ingot is surface-finished with a machining depth of 12mm. The machined ingot is then reheated to 440℃ and held for 8 hours before being upset and drawn using a cross-forging method. The anvil is preheated to 440℃ during the drawing process. After finishing the surface of the ingot, it is reheated to 440℃ and held for 8 hours before die forming. The contact surface of the die is nitrided to a thickness of 65μm. Before die forming, molybdenum disulfide lubricant is uniformly applied to the contact surface of the die. The forgings, after being die-formed, were heated to 505℃ at a heating rate of 12℃ / min and held at that temperature for 2.5 hours. They were then subjected to a two-stage controlled-cooling water quenching treatment (V1=80℃ / s, T1=200℃, V2=7℃ / s), with a quenching transfer time of 3 seconds. After being left to rest at room temperature for 1.5 hours, the forgings underwent cold pressing deformation treatment, with a deformation amount of 2.5%. The cold-pressed forgings were then left to rest at room temperature for 3 days. Subsequently, they underwent artificial aging treatment at an aging temperature of 165℃ for 20 hours.

[0053] Example 2

[0054] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 5.2, Mg: 0.8, Ag: 0.5, Mn: 0.4, Fe: 0.45, Ti: 0.12, Cr: 0.13, Zn: 0.21, Si: 0.05, with impurity content (total) < 0.15, and the remainder being Al.

[0055] After stress-relief annealing (360℃ / 5h) and three-stage homogenization annealing ((↑12h) 450℃ / 4h + (↑3.5h) 480℃ / 4h + (↑2.5h) 505℃ / 19h), the alloy ingot is surface-finished with a machining depth of 12mm. The machined ingot is then reheated to 450℃ and held for 8 hours before upsetting using multi-directional forging. The anvil is preheated to 450℃ during the upsetting process. After surface finishing, the ingot is reheated to 450℃ and held for 8 hours before die forming. The die contact surface is nitrided to a thickness of 90μm. Boron nitride lubricant is uniformly sprayed onto the die contact surface before die forming. The forgings, after being die-formed, were heated to 510℃ at a heating rate of 12℃ / min and held at that temperature for 2.5 hours. They were then subjected to a two-stage controlled-cooling water quenching treatment (V1=80℃ / s, T1=195℃, V2=8℃ / s), with a quenching transfer time of 3 seconds. After being left to stand at room temperature for 2.5 hours, the forgings underwent cold pressing deformation treatment, with a deformation amount of 3.0%. The cold-pressed forgings were then left to stand at room temperature for 3.5 days. Subsequently, they underwent artificial aging treatment at 170℃ for 16 hours.

[0056] Example 3

[0057] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 4.7, Mg: 0.9, Ag: 0.55, Mn: 0.8, Fe: 0.06, Ti: 0.08, Cr: 0.17, Zn: 0.3, Si: 0.04, with impurity content (total) < 0.15, and the remainder being Al.

[0058] After stress-relief annealing (360℃ / 6h) and three-stage homogenization annealing ((↑16h) 450℃ / 3.5h + (↑4h) 480℃ / 3h + (↑4h) 510℃ / 18h), the alloy ingot is surface-finished with a machining depth of 13mm. The machined ingot is then reheated to 460℃ and held for 10 hours before upsetting using multi-directional forging. The anvil is preheated to 460℃ during the upsetting process. After surface finishing, the ingot is reheated to 460℃ and held for 10 hours before die forming. The die contact surface is nitrided to a thickness of 115μm. Molybdenum disulfide lubricant is uniformly applied to the die contact surface before die forming. The forgings, after being die-formed, were heated to 510℃ at a heating rate of 12℃ / min and held at that temperature for 3 hours. They were then subjected to a two-stage controlled-cooling water quenching treatment (V1=75℃ / s, T1=190℃, V2=5℃ / s), with a quenching transfer time of 3 seconds. After being left to stand at room temperature for 2 hours, the forgings underwent cold pressing deformation treatment, with a deformation amount of 3.5%. The cold-pressed forgings were then left to stand at room temperature for 3 days. Subsequently, they underwent artificial aging treatment at an aging temperature of 165℃ for 20 hours.

[0059] Example 4

[0060] The alloy chemical composition of the forging is (by mass percentage, wt%): Cu: 5.1, Mg: 0.84, Ag: 0.58, Mn: 0.66, Fe: 0.12, Ti: 0.07, Cr: 0.12, Zn: 0.18, Si: 0.07, with a total impurity content of <0.15, and the remainder being Al.

[0061] After stress-relief annealing (360℃ / 6h) and three-stage homogenization annealing ((↑10h) 450℃ / 5h + (↑2.5h) 480℃ / 4h + (↑1.5h) 505℃ / 20h), the alloy ingot is surface-finished with a machining depth of 11mm. The machined ingot is then reheated to 460℃ and held for 9 hours before upsetting using multi-directional forging. The anvil is preheated to 460℃ during the upsetting process. After surface finishing, the ingot is reheated to 440℃ and held for 8 hours before die forming. The die contact surface is nitrided to a thickness of 104μm. Before die forming, a graphite-machine-oil mixture is uniformly applied to the die contact surface. The forgings, after being die-formed, were heated to 505℃ at a heating rate of 11℃ / min and held at that temperature for 3 hours. They were then subjected to a two-stage controlled-cooling water quenching treatment (V1=75℃ / s, T1=195℃, V2=6℃ / s), with a quenching transfer time of 3 seconds. After being left to stand at room temperature for 2.5 hours, the forgings underwent cold pressing deformation treatment, with a deformation amount of 3.0%. The cold-pressed forgings were then left to stand at room temperature for 3 days. Subsequently, they underwent artificial aging treatment at an aging temperature of 165℃ for 18 hours.

[0062] Figure 2 The image shown is a scanning electron microscope (SEM) image of the microstructure of the alloy ingot in Comparative Example 1. Figure 3 The image shows a scanning electron microscope (SEM) image of the microstructure of the alloy ingot in Example 3. As can be seen from the image, after single-stage homogenization heat treatment, a considerable amount of the second phase in the matrix of the sample of Comparative Example 1 was not dissolved back into the matrix. After multi-stage homogenization heat treatment, the second phase in the ingot sample of Example 3 was more fully dissolved back into the matrix. Figure 4 The image shown is a photograph of the aged microstructure of the alloy forging in Comparative Example 1. Figure 5 This is a photograph of the aged microstructure of the alloy forging from Example 3. Figure 4 and Figure 5 It can be seen that the internal structure of the forgings is mainly deformed, with fine grains accompanying the deformed grains, and the grain size of the sample in Comparative Example 1 is relatively large.

[0063] Table 1 Comparison of mechanical properties of Al-Cu-Mg-Ag alloy forgings obtained in the comparative examples and embodiments

[0064]

[0065] As can be seen from the comparison results of the mechanical properties of the alloys shown in Table 1:

[0066] (1) The tensile strength and yield strength of the comparative forging samples at room temperature and 150℃ are relatively low. Figure 2It can be seen that a large number of undissolved second phases still exist in the matrix after single-stage homogenization. This leads to uneven subsequent deformation and affects the final precipitate distribution, which is an important factor causing its low performance. In contrast, the forging samples of the opposite examples have higher strength levels (e.g., the room temperature tensile strength of Example 3 reaches 538 MPa) and higher fracture toughness (e.g., the fracture toughness K of Example 3 is also higher). Q The value is as high as 32.7 MPa·m 1 / 2 Furthermore, the residual stress level in the quenched state is low, combined with Figure 3 It can be seen that after multi-stage homogenization treatment, the second phase in the ingot is dissolved more completely, which provides a better chance of obtaining... Figure 5 The uniform deformation and precipitation structure, along with ideal properties, lay the foundation for this invention. Therefore, the alloy forgings obtained through the method of this invention possess both high strength and ideal fracture toughness, as well as a low residual stress level.

[0067] (2) In the comparative example, the multi-stage homogenization heat treatment with reasonable process parameters was not adopted during the homogenization heat treatment of the ingot, and the deformation and blanking process was relatively simple. In addition, the die surface was not treated during the die forming process, and the severe shearing action from the die surface during the metal flow process resulted in excessive localization, die sticking, and insufficient filling of high rib positions. The solution quenching process of the forging was not effectively controlled-cooling water quenching, which led to high levels of residual stress inside and coarse grains at the locations of large shear deformation, weakening the overall performance of the forging. In contrast, the alloy forging obtained by the method of this invention, due to the more reasonable homogenization annealing, multi-directional forging deformation blanking, nitriding and lubricant spraying on the die surface, staged controlled-cooling quenching and room temperature storage treatment, improved the room temperature and high temperature tensile properties of the forging, improved the fracture toughness of the forging, reduced the overall residual stress level of the forging, and greatly improved the yield of the forging.

[0068] The above description is only a more optimized specific embodiment of the present invention. However, it should be noted that the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the general scope of the present invention. All such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings, characterized in that, The method includes the following steps: (1) According to the composition of the alloy material, the ingot is obtained by feeding, melting and casting. Then the obtained ingot is subjected to stress relief annealing treatment. The stress relief annealing temperature is 350℃~400℃ and the holding time is 2h~8h. (2) The stress-relief annealed ingot is subjected to multi-stage homogenization heat treatment. The process parameters for multi-stage homogenization heat treatment are as follows: First, the ingot is heated to 440℃~460℃ within 6h~15h and held for 3h~8h; then, the ingot is further heated to 470℃~490℃ within 2h~5h and held for 3h~8h; finally, the ingot is further heated to 505℃~520℃ within 1h~3h and held for 12h~36h. (3) The ingot is deformed and opened by extrusion, forging or a combination of both. Before opening, the ingot temperature is preheated to 400℃~480℃ and kept at this temperature for 3h~12h. (4) After the alloy blank is deformed and the oxide scale and impurities are removed by machining, it is preheated to 400℃~480℃ and held at this temperature for 3h~12h before die forging. The surface of the forging anvil or forging die is nitrided and the thickness of the nitrided layer is 50μ~150μm. Before forging, the forging anvil or forging die is preheated to 350℃~450℃ and lubricant is evenly applied to the surface of the forging anvil or forging die during the forging process. (5) The forgings after deformation are subjected to solution heat treatment. The heating rate is 10℃ / min≤V0≤15℃ / min and the solution temperature is 480℃~520℃. After the heat treatment is completed, the alloy is immediately subjected to graded controlled cooling water quenching treatment. The alloy is cooled from the solution temperature point to T1 at an average cooling rate V1, where V1=60℃ / s~80℃ / s and T1=160℃~200℃. Then, the alloy is cooled from the T1 temperature point to room temperature at a cooling rate V2, where V2=3℃ / s~12℃ / s. (6) Perform 1% to 5% cold pressing deformation treatment on the quenched forgings at room temperature; (7) The forgings after cold pressing deformation are left to stand at room temperature for 24h~96h; (8) Artificial aging treatment is performed on the forgings after they have been left to stand at room temperature. The aging temperature is 145℃~190℃ and the treatment time is 8h~72h. Then the forgings are taken out of the furnace and air-cooled to room temperature.

2. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1, characterized in that, In step (3), the surface depth of the ingot is 10mm~15mm; the billet temperature is preheated to 400℃~480℃ and kept at that temperature for 3h~12h before deformation and billet opening; In step (4), the forging billet is first turned or milled before forging, and then preheated to 400℃~480℃ and held for 3h~12h before forging. In step (5), the process parameters for solution heat treatment are: temperature 490℃~515℃, holding time 1~5h; after the holding treatment is completed, the alloy is immediately subjected to graded controlled cooling water quenching treatment, cooled from the solution temperature point to T1 at an average cooling rate V1, where V1=65℃ / s~80℃ / s, T1=170℃~200℃; then cooled from the T1 temperature point to room temperature at a cooling rate V2, where V2=3℃ / s~9℃ / s; In step (6), the cold compression deformation of the forging at room temperature is 1.5% to 5%; In step (7), the room temperature storage time of the cold-compressed forging is 48h~96h; In step (8), the artificial aging temperature of the forging is 150℃~180℃, the treatment time is 12h~60h, and then it is taken out of the furnace and air-cooled to room temperature.

3. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (1), the annealing temperature is 360℃~380℃, the holding time is 3h~8h, and the ingot is taken out of the furnace and air-cooled to room temperature.

4. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (2), the process parameters for multi-stage homogenization heat treatment are as follows: First, the ingot is heated to 440℃~460℃ within 9h~13h and held for 4h~6h; second, the ingot is further heated to 470℃~480℃ within 2h~4h and held for 4h~6h; finally, the ingot is further heated to 505℃~520℃ within 1h~2h and held for 12h~24h before being air-cooled to room temperature.

5. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, After the homogenization heat treatment of the ingot is completed in step (2), the ingot is air-cooled to room temperature and then the surface of the ingot is machined with a depth of 10mm~15mm.

6. The method for strengthening and toughening Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (3), the ingot after the car body is reheated to 410℃~480℃ and kept at that temperature for 6h~12h before deformation and blanking.

7. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 6, characterized in that, In step (3), the deformation blanking method is selected from one or more combinations of extrusion, cross forging or multi-directional forging.

8. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 7, characterized in that, The preheating temperature of the extrusion cylinder, extrusion die, gasket, or anvil is 380℃~450℃.

9. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (4), the forging billet is first turned or milled before forging, and then preheated to 410℃~480℃ and held for 6h~12h before forging.

10. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (4), before forging begins, the forging anvil or forging die is preheated to 380°C to 450°C and its surface is uniformly coated with a mixture of graphite machine oil, molybdenum disulfide or boron nitride lubricant.

11. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (5), the solution heat treatment temperature of the forging is 500℃~515℃, the furnace heating rate is 11℃ / min≤V0≤13℃ / min, and the holding time is 3h.

12. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (5), the quenching method is spray quenching, immersion quenching or a combination of the above two methods. During the quenching cooling process, the average cooling rate V1 is from the solution temperature point to T1, where V1 = 70℃ / s~80℃ / s and T1 = 180℃~200℃; then, the temperature is cooled from T1 to room temperature at a cooling rate V2, where V2 = 3℃ / s≤V2≤6℃ / s.

13. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (6), the time interval between the quenched forging and the start of the cold pressing deformation process is 1h≤t1≤4h; the cold pressing deformation amount is 1.5%~4.0%.

14. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In the graded controlled cooling water quenching process, the average cooling rate V1 is 70℃ / s to 80℃ / s, and the amount of cold pressing deformation is 2.0% to 3.5%.

15. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (7), the alloy forgings are left to stand at room temperature for 48h~72h after cold pressing deformation treatment.

16. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, In step (8), the artificial aging temperature is 160℃~170℃ and the processing time is 12h~32h.

17. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, The room temperature storage time is 48h to 72h, and the artificial aging treatment temperature is 160℃ to 170℃.

18. The method for strengthening and toughening heat treatment of Al-Cu-Mg-Ag heat-resistant alloy forgings according to claim 1 or 2, characterized in that, The applicable Al-Cu-Mg-Ag heat-resistant alloy forgings have the following composition: Cu: 0.6~5.2wt%, Mg: 0.3~1.0wt%, Ag: 0.3~0.6wt%, Mn: 0.3~0.8wt%, Fe: 0.06~0.35wt%, Ti: 0.04~0.12wt%, Cr: 0.1~0.2wt%, Zn: 0.2~0.4wt%, Si: 0.05~1.1wt%, with a total impurity content of <0.15wt%, and the remainder being Al.

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