6061 aluminum alloy wrought product and method of making

Abstract

The application provides a 6061 aluminum alloy forge piece and a preparation method thereof, and relates to the aluminum alloy forging processing technical field.The component composition of the 6061 aluminum alloy forge piece is as follows: Si: 0.60-0.75%, Mg: 0.85-1.10%, Cu: 0.24-0.35%, Fe: <=0.50%, Mn: 0.08-0.13%, Cr: 0.10-0.25%, Zn: <=0.06%, Ti: <=0.10%, and the balance is Al and inevitable impurities; the preparation method comprises the following steps: after the alloy raw material is sequentially subjected to smelting, casting and homogenization treatment, online solid solution forging and online quenching are carried out, and aging treatment is carried out within 2 hours after quenching. The preparation method can recycle the regenerated waste material at a high proportion, has low energy consumption, the obtained 6061 aluminum alloy forge piece has excellent strength and size stability, and is suitable for large-scale production and application.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy forging technology, and in particular to a 6061 aluminum alloy forging and its preparation method. Background Technology

[0002] 6061 aluminum alloy belongs to the Al-Mg-Si system of heat-treatable alloys. Due to its good formability, weldability and moderate strength, it is widely used in aerospace, rail transportation, automobile manufacturing and structural engineering.

[0003] For forged 6061 aluminum alloy workpieces, the traditional process typically employs a "forging + offline solution quenching + artificial aging" route. However, this process has the following drawbacks: high energy consumption in offline solution quenching: after the forging cools to room temperature, it is reheated to the solution temperature (usually 520-550℃), resulting in energy waste and extended production cycles; limited performance improvement: during reheating, coarse precipitates are difficult to fully dissolve, and grains tend to grow, reducing the strength and toughness of the forging; high residual stress and poor dimensional stability of the finished product: secondary heating and quenching can easily lead to dimensional instability in the forging, increasing the difficulty of subsequent straightening or finishing. These shortcomings affect the further application of 6061 aluminum alloy forgings. Summary of the Invention

[0004] This invention provides a 6061 aluminum alloy forging and its preparation method, which solves the defects of high energy consumption, coarse grains, large residual stress and insufficient strength in the prior art, and achieves synergistic improvement of fine grain strengthening and precipitation strengthening, thereby obtaining a high-strength 6061 aluminum alloy forging, which has higher economic value.

[0005] In a first aspect, the present invention provides a method for preparing 6061 aluminum alloy forgings, comprising the following steps: The alloy raw materials are sequentially smelted, cast, and homogenized, followed by online solution forging and online quenching. After quenching, an aging treatment is performed within 2 hours. The online solution forging and online quenching include: heating the homogenized ingot to 480-540℃ and holding it at that temperature for 60-130 minutes, then sequentially flattening, pre-forging, and final forging. The forging die is preheated to 220-300℃, and the forging exits the die at a temperature ≥440℃. The forging is then transferred to a water-cooling tank for quenching within 3-5 seconds. The water temperature in the water-cooling tank is 30-40℃, and the cooling rate of the forging is ≥80℃ / s to room temperature. The composition of the 6061 aluminum alloy forging, by weight percentage, is as follows: Si: 0.60–0.75%, Mg: 0.85–1.10%, Cu: 0.24–0.35%, Fe: ≤0.50%, Mn: 0.08~0.13%, Cr: 0.10–0.25%, Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

[0006] According to the method for preparing 6061 aluminum alloy forgings provided by the present invention, preferably, the homogenized ingot is heated to 520-540°C and held for 60-90 minutes, and the heating process is carried out in stages.

[0007] According to the preparation method of 6061 aluminum alloy forgings provided by the present invention, the aging treatment conditions are 170-190℃ for 3-6 hours, followed by air cooling after removal from the furnace.

[0008] According to the preparation method of 6061 aluminum alloy forgings provided by the present invention, preferably, the aging treatment conditions are: holding at 185°C for 4 hours, followed by air cooling after removal from the furnace.

[0009] According to the preparation method of 6061 aluminum alloy forgings provided by the present invention, the smelting includes: sequentially cleaning the furnace, feeding materials, smelting at 700-760℃, and after smelting, performing mechanical stirring, bubble bed alloying, and electromagnetic stirring composite treatment, followed by 1-3 refining processes and slag removal, and then standing at 720-760℃ for 20-50 minutes; wherein the feeding materials include aluminum ingots and 50%-60% recycled profile waste.

[0010] According to the preparation method of 6061 aluminum alloy forgings provided by the present invention, the casting process controls the ingot diameter to be 60-120 mm, the casting speed to be 200-250 mm / min, and the cooling water flow rate to be 450-520 m³ / h; wherein, before casting, the melt after smelting is first degassed online to control the hydrogen content to be ≤0.15 ml / 100 g Al, and then filtered at 50-70 ppi single stage.

[0011] According to the preparation method of 6061 aluminum alloy forgings provided by the present invention, the homogenization treatment includes: holding the cast ingot at 520-560℃ for 5-12 hours, and then cooling it with water mist.

[0012] According to the method for preparing 6061 aluminum alloy forgings provided by the present invention, preferably, the composition of the 6061 aluminum alloy forgings is as follows: Si: 0.70~0.75%, Mg: 0.95–1.10%, Cu: 0.24–0.3%, Fe: 0.3~0.40%, Mn: 0.08~0.13%, Cr: 0.10–0.2%, Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

[0013] Secondly, the present invention provides a 6061 aluminum alloy forging prepared by the above-described preparation method.

[0014] The 6061 aluminum alloy forgings provided by the present invention have a grain size of 20-50 μm, an average tensile strength ≥350 MPa, a yield strength ≥320 MPa, and an elongation ≥10%.

[0015] This invention provides a 6061 aluminum alloy forging and its preparation method. By optimizing the alloy ratio, it adapts to the forging process and can accommodate the reuse of 50%–60% recycled aluminum scrap. The smelting process includes furnace cleaning, a triple-stage combined stirring system (mechanical-bubble bed-electromagnetic), multiple refining processes, and high-temperature settling to synergistically improve melt purity. Small-to-medium-sized high-speed ingots are used, with strict control over hydrogen content and filtration precision. After stress relief through stepped homogenization water mist, the ingots are directly flattened, pre-forged, and finally forged. The high-temperature residual heat of the forgings is used for rapid online water cooling and solution treatment, eliminating the need for a separate solution heating process. Finally, a wide-window, short-time aging process yields the finished forging. This invention solves the shortcomings of existing technologies, such as low scrap utilization, high energy consumption, easy cracking of forgings, and low strength. It offers advantages such as low raw material cost, high production efficiency, fewer internal defects in forgings, excellent mechanical properties, and good dimensional stability, making it suitable for mass production of load-bearing forgings for engineering machinery, new energy, and hydraulic valve bodies. Attached Figure Description

[0016] Figure 1 This is a high-magnification microstructure diagram of the aluminum alloy forging obtained in Example 1.

[0017] Figure 2 The image shows the actual aluminum alloy forging obtained in Example 1 and a schematic diagram of the sampling location.

[0018] Figure 3 This is a high-magnification microstructure diagram of the aluminum alloy forging obtained in Comparative Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0022] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0023] This invention provides a method for preparing 6061 aluminum alloy forgings, comprising the following steps: The alloy raw materials are sequentially smelted, cast, and homogenized, followed by online solution forging and online quenching. After quenching, an aging treatment is performed within 2 hours. The online solution forging and online quenching include: heating the homogenized ingot to 480-540℃ and holding it at that temperature for 60-130 minutes, then sequentially flattening, pre-forging, and final forging. The forging die is preheated to 220-300℃, and the forging exits the die at a temperature ≥440℃. The forging is then transferred to a water-cooling tank for quenching within 3-5 seconds. The water temperature in the water-cooling tank is 30-40℃, and the cooling rate of the forging is ≥80℃ / s to room temperature. The composition of the 6061 aluminum alloy forging, by weight percentage, is as follows: Si: 0.60–0.75%, Mg: 0.85–1.10%, Cu: 0.24–0.35%, Fe: ≤0.50%, Mn: 0.08~0.13%, Cr: 0.10–0.25%, Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

[0024] Existing technologies employ offline secondary high-temperature solution treatment after forming. This invention directly utilizes the residual heat from forging for quenching, strictly limiting the demolding temperature, transfer time, and cooling rate. It eliminates the need for a separate solution furnace for secondary heating, significantly shortening the process and reducing energy consumption. Furthermore, the high cooling rate ensures sufficient supersaturation solution of Mg and Si elements, providing a foundation for subsequent age hardening. According to national standards, the composition of 6061 aluminum alloy is: Si: 0.40–0.80%, Mg: 0.80–1.20%, Cu: 0.15–0.40%, Fe: ≤0.70%, Mn: ≤0.15%, Cr: 0.04–0.35%, Zn: ≤0.25%, Ti: ≤0.15%, with the balance being aluminum. The content range of each component in the national standard has a large fluctuation range, and not all components are suitable for the forging process of this invention. Research has found that when the content of each component of the alloy is controlled within the above range, it can not only match the forging process of this invention well, taking into account both forging plasticity and mechanical properties, but also adapt to high recycled material systems, reducing raw material costs. Furthermore, in the above technical solution, the regulation of Cr content inhibits the formation of brittle intermetallic phases, the low temperature mold of 220-300℃ avoids rapid cooling and loss of plasticity on the surface of the forging, large deformation flattening, no cracking during the die forging process, and can form complex thin-walled irregular structural parts.

[0025] In some embodiments of the present invention, preferably, the homogenized ingot is heated to 520–540°C and held at that temperature for 60–90 minutes, and the heating process is carried out in stages. This is the pre-forging heating stage, which requires uniform temperature control to ensure that the overall temperature of the billet is consistent and to eliminate the unevenness of the microstructure caused by temperature differences; the stage of staged heating involves uniform heating during the heating stage and constant temperature holding during the holding stage to ensure uniform temperature and microstructure inside and outside the billet.

[0026] In some embodiments of the present invention, the aging treatment conditions are: holding at 170–190°C for 3–6 hours, followed by air cooling after removal from the furnace. The present invention broadens the aging process window, shortens the minimum holding time, and improves production line processing efficiency.

[0027] In a preferred embodiment of the present invention, the aging treatment conditions are: holding at 185°C for 4 hours, followed by air cooling after removal from the furnace.

[0028] In some embodiments of the present invention, the smelting includes: sequentially cleaning the furnace, feeding materials, smelting at 700-760°C, and after smelting, mechanical stirring, bubble bed alloying, and electromagnetic stirring composite treatment, followed by 1-3 refining processes and slag removal, and then standing at 720-760°C for 20-50 minutes; wherein the materials fed include aluminum ingots and 50%-60% recycled waste.

[0029] This invention employs a combination of mechanical stirring, bubble bed alloying, and electromagnetic stirring, along with multiple refining processes and furnace cleaning, which can improve the purity of the melt and reduce the internal defect rate of forgings.

[0030] In some preferred embodiments of the present invention, the smelting includes: a) Furnace cleaning: All five surfaces of the furnace chamber and the furnace edge that are flush with the furnace edge need to be cleaned. After cleaning, there should be no obvious aluminum slag at the bottom of the furnace chamber. b) Feeding: Aluminum ingots (with added alloying elements) + recycled waste (50%-60%); c) Smelting: Control the smelting temperature to 700-760℃; Si is added in the form of aluminum-silicon alloy, Fe in the form of aluminum-iron alloy, Cu in the form of aluminum-copper alloy, and Mn in the form of aluminum-manganese alloy. The alloy ratio is: aluminum-silicon 10-30%, aluminum-iron 10-30%, aluminum-copper 30-50%, and aluminum-manganese 10-30%. d) Stirring: Mechanical stirring for 5-20 minutes, bubble bed alloying mode for 10-40 minutes, electromagnetic stirring for 10-40 minutes; e) Refining: Refine 1-3 times, for 10-30 minutes; f) Fine-tuning of composition: Maintain the melt at 700-760°C, take samples for spectral analysis, and add intermediate alloys as needed to reach the target composition range; g) Slag removal: Thoroughly remove floating slag from the surface of the melt, leaving no solid residue on the liquid surface; h) Stand: 720-760℃ for 20-50 minutes.

[0031] In some embodiments of the present invention, the casting process controls the ingot diameter to be 60-120 mm, the casting speed to be 200-250 mm / min, and the cooling water flow rate to be 450-520 m³ / h; wherein, before casting, the melt after smelting is first degassed online to control the hydrogen content to ≤0.15 ml / 100 g Al, and then filtered through a single-stage filter at 50-70 ppi.

[0032] This invention performs online degassing before casting, which, in conjunction with the previous steps of compound stirring and multi-stage refining, further improves the purity of the melt and reduces the internal defect rate of the forgings. The casting conditions of this invention are controlled by employing a high-speed ingot casting process for small and medium-sized ingots to match the cycle time of the forging production line.

[0033] In a preferred embodiment of the present invention, the casting includes: a) Online degassing: The melt continuously passes through a rotary rotor degassing device, and the hydrogen content of the aluminum liquid after degassing is controlled to be ≤0.15ml / 100gAl; b) Filtration and purification: Single-stage 50-70ppi ceramic filter plate is used for deep filtration of oxidized inclusions; c) Semi-continuous casting: Produces cylindrical ingots with a diameter of 60-120mm; casting speed of 200-250mm / min, total cooling water flow of 450-520m³ / h, rapid solidification inhibits coarse dendrites.

[0034] In some embodiments of the present invention, the homogenization treatment includes: holding the cast ingot at 520–560°C for 5–12 hours, followed by water mist cooling. This step can eliminate casting dendritic segregation, dissolve the coarse Mg2Si phase at grain boundaries, and release internal thermal stress in the ingot through water mist cooling, preventing forging heating cracks.

[0035] In some embodiments of the present invention, preferably, the composition of the 6061 aluminum alloy forging is as follows: Si: 0.70~0.75%, Mg: 0.95–1.10%, Cu: 0.24–0.3%, Fe: 0.3~0.40%, Mn: 0.08~0.13%, Cr: 0.10–0.2%, Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

[0036] The preparation method of the 6061 aluminum alloy forging includes: (1) Smelting process: The five-sided furnace is cleaned in sequence, aluminum ingots and 50%~60% recycled waste are fed in, and smelting is carried out at 700-760℃. Aluminum silicon, aluminum iron, aluminum copper and aluminum manganese intermediate alloys are used for alloying. Mechanical stirring, bubble bed alloying and electromagnetic stirring composite treatment are carried out in sequence. After 1~3 refining and slag removal, it is held at 720-760℃ for 20~50min. (2) Casting process: The melt is degassed online to control the hydrogen content to ≤0.15ml / 100gAl, and then filtered through a single stage of 50~70ppi before casting; the ingot diameter is 60~120mm, the casting speed is 200~250mm / min, and the cooling water flow rate is 450~520m³ / h. (3) Homogenization treatment: The ingot is kept at 520-560℃ for 5-12 hours, and then cooled with water mist after the heat preservation is completed; (4) Online solution forging: The homogenized ingot is heated to 480-540℃ and held for 60-130 min. It is then flattened, pre-forged, and finally forged. The forging die is preheated to 220-300℃. The forging temperature is ≥440℃. The forging is transferred to a water-cooling tank for quenching within 3-5 s. The water temperature in the tank is 30-40℃. The cooling rate of the forging is ≥80℃ / s to room temperature. (5) Aging process: Quenching forgings are held at 170-190℃ for 3-6 hours, then air-cooled after being taken out of the furnace to obtain 6061 aluminum alloy forgings.

[0037] Secondly, the present invention provides a 6061 aluminum alloy forging prepared by the above-described preparation method.

[0038] In some embodiments of the present invention, the resulting 6061 aluminum alloy forgings have a grain size of 20-50 μm, an average tensile strength ≥350 MPa, a yield strength ≥320 MPa, and an elongation ≥10%.

[0039] This invention utilizes rapid water cooling of residual heat after forging to achieve high supersaturation solution treatment. Combined with optimized Cu-Mg-Si ratio and aging precipitation strengthening, the strength of the finished forgings is significantly improved. In addition, the uniform water mist cooling and controllable high-speed water cooling greatly reduce the residual stress inside the forgings, reducing subsequent machining deformation by 60% and resulting in good dimensional stability of the finished product.

[0040] Under the optimal combination of conditions, this invention solves the defects of existing technologies such as low waste utilization, high energy consumption, easy cracking of forgings, and low strength. It has the advantages of low raw material cost, high production efficiency, fewer internal defects in forgings, excellent mechanical properties, and good dimensional stability, and is suitable for mass production of load-bearing forgings for engineering machinery, new energy, and hydraulic valve bodies.

[0041] Example 1

[0042] This embodiment provides a 6061 aluminum alloy forging with the following alloy composition (wt%): Si 0.71%, Mg 1.08%, Cu 0.24%, Fe 0.34%, Mn 0.12%, Cr 0.18%, Zn 0.05%, Ti 0.05%, with the balance being Al.

[0043] The preparation steps are as follows: (1) Smelting: Five-sided furnace cleaning, feeding (of which recycled waste accounts for 55%); smelting temperature 730℃; aluminum-silicon alloy 20%, aluminum-iron 15%, aluminum-copper 40%, aluminum-manganese 25%; mechanical stirring for 12min, bubble bed for 25min, electromagnetic stirring for 20min; refining twice, 20min each time; standing at 740℃ for 35min.

[0044] (2) Casting: Remove hydrogen content of 0.12ml / 100gAl, filter at 60ppi; ingot φ90mm, casting speed 220mm / min, cooling water flow rate 480m³ / h.

[0045] (3) Homogenization: Keep warm at 540℃ for 8 hours, then cool with water mist.

[0046] (4) Online solution forging quenching: Ingot held at 530℃ for 80 min; mold at 260℃, flattened, pre-forged and finally forged; mold exit temperature 440℃, immersed in water for 4 s, water temperature 35℃, cooling rate 90℃ / s, cooled to room temperature.

[0047] (5) Aging: After the forging is cooled, it is kept at 185℃ for 4 hours within 2 hours and then air-cooled.

[0048] The aluminum alloy forging obtained in this embodiment has excellent fine-grained structure and uniformly dispersed aged precipitates, as shown in its high-magnification microstructure diagram. Figure 1 As shown, the physical object image and sampling location are as follows: Figure 2 As shown.

[0049] After testing and calculation, its average grain diameter is 22.6 μm, corresponding to a grain size grade of G≈7.65 (grain size calculation adopts GB / T 6394-2017 standard). The larger the number, the finer the grain. Grade 7~8 belongs to fine grain structure, which is a grain size grade with good mechanical properties (strength and toughness) in materials.

[0050] Example 2

[0051] This embodiment provides a 6061 aluminum alloy forging with the following alloy composition (wt%): Si 0.60%, Mg 1.10%, Cu 0.24%, Fe 0.50%, Mn 0.08%, Cr 0.10%, Zn 0.06%, Ti 0.10%, with the balance being Al.

[0052] The preparation steps are as follows: (1) Smelting: Five-sided furnace cleaning, feeding (of which recycled waste accounts for 50%); smelting temperature 720℃; aluminum-silicon alloy 20%, aluminum-iron 15%, aluminum-copper 40%, aluminum-manganese 25%; mechanical stirring for 12min, bubble bed for 25min, electromagnetic stirring for 20min; refining twice, 20min each time; standing at 740℃ for 35min.

[0053] (2) Casting: Remove hydrogen content of 0.12ml / 100gAl, filter at 60ppi; ingot φ90mm, casting speed 220mm / min, cooling water flow rate 480m³ / h.

[0054] (3) Homogenization: Keep warm at 540℃ for 8 hours, then cool with water mist.

[0055] (4) Online solution forging quenching: Ingot held at 540℃ for 60min; mold at 220℃, flattened, pre-forged and finally forged; mold exit temperature 460℃, immersed in water for 4s, water temperature 35℃, cooling rate 80℃ / s, cooled to room temperature.

[0056] (5) Aging: After the forging is cooled, it is kept at 185℃ for 4 hours within 2 hours and then air-cooled.

[0057] Example 3

[0058] This embodiment provides a 6061 aluminum alloy forging with the following alloy composition (wt%): Si 0.75%, Mg 0.85%, Cu 0.35%, Fe 0.40%, Mn 0.13%, Cr 0.25%, Zn 0.05%, Ti 0.05%, and the balance Al.

[0059] The preparation steps are as follows: (1) Smelting: Five-sided furnace cleaning, feeding (of which recycled waste accounts for 50%); smelting temperature 740℃; aluminum-silicon alloy 20%, aluminum-iron 15%, aluminum-copper 40%, aluminum-manganese 25%; mechanical stirring for 12min, bubble bed for 25min, electromagnetic stirring for 20min; refining twice, 20min each time; standing at 740℃ for 35min.

[0060] (2) Casting: Remove hydrogen content of 0.12ml / 100gAl, filter at 60ppi; ingot φ90mm, casting speed 220mm / min, cooling water flow rate 480m³ / h.

[0061] (3) Homogenization: Keep warm at 540℃ for 8 hours, then cool with water mist.

[0062] (4) Online solution forging quenching: Ingot is held at 520℃ for 90min; mold is at 250℃, and it is flattened, pre-forged and finally forged; the mold temperature is 450℃, and it is immersed in water for 4s with a water temperature of 40℃ and a cooling rate of 90℃ / s to cool to room temperature.

[0063] (5) Aging: After the forging is cooled, it is kept at 185℃ for 4 hours within 2 hours and then air-cooled.

[0064] Comparative Example 1 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The preparation method adopts the traditional T6 offline heat treatment process, that is, after the conventional forging is completed, the billet is naturally cooled and stored, and then transported to the heat treatment workshop for offline solution treatment. The subsequent aging step is the same as step (5). The residual heat of forging is not used throughout the process, and there is no control over the interval between forging and heat treatment.

[0065] The resulting forgings have low strength, exhibit mixed-grain structure across the entire cross-section, and show significant variations in grain size, such as... Figure 3 As shown, it has poor resistance to hydrogen-induced fracture and cannot be used for hydrogen energy storage valve blocks.

[0066] Comparative Example 2 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The difference between the preparation method and that in Example 1 is that the demolding temperature in step (4) is 430°C and the part is immersed in water for 4 seconds.

[0067] As a result, the cooling temperature decreased, the solid solution effect weakened, the material was not sufficiently strengthened, the tensile strength of some samples did not meet the standard, the product performance fluctuated greatly, and there was a risk of batch scrapping.

[0068] Comparative Example 3 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The difference between the preparation method and that in Example 1 is that the demolding temperature in step (4) is 400°C and the part is immersed in water for 4 seconds.

[0069] As a result, due to the excessively low water temperature, the high-temperature solid solution structure underwent a transformation, the coarse-grain defects were aggravated, and the material strength dropped significantly, completely failing to meet the usage requirements.

[0070] Comparative Example 4 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The difference between the preparation method and that in Example 1 is that after the forging is cooled in step (5), it is placed for 12 hours and then kept at 185°C for 4 hours before being air-cooled.

[0071] As a result, due to the excessively long resting time after forging, the strengthening phase inside the alloy precipitated and agglomerated prematurely, resulting in an overall decrease in strength. Nearly half of the samples failed to meet the customer's strength specifications.

[0072] Comparative Example 5 This comparative example provides an aluminum alloy forging, which is prepared in the same way as in Example 1, but the alloy composition is different from that in Example 1. Specifically, it is: Si 0.67%, Mg 0.93%, Cu 0.40%, Fe 0.33%, Mn 0.12%, Cr 0.22%, Zn 0.05%, Ti 0.08%, with the balance being Al.

[0073] The results showed that due to the high Cu content in the raw materials and poor compositional matching, even using the same process as in Example 1, the strength of the forgings was still low, mixed crystals appeared across the entire cross section of the forgings, and the grain uniformity was poor, making them unsuitable for mass production.

[0074] Comparative Example 6 Compared with Example 1, steps (1)-(3) are omitted, and 6061 cast rods are directly used as raw materials for subsequent steps (4) and (5). The composition of the 6061 cast rods is: Si 0.685%, Mg 1.02%, Cu 0.309%, Fe 0.333%, Mn 1.02%, Cr 0.19%, Zn 0.0453%, Ti 0.0604%, with the balance being Al.

[0075] The metallographic results showed that the original structure of the cast rod was coarse dendritic. Even after a full set of online solution forging treatment, the cross-section of the forging had a large area of ​​mixed grains, a coarse grain ring depth of more than 3 mm, large grain size and extremely uneven distribution, and no stable fine grain region. There were many grain boundary defects, dense hydrogen diffusion channels, poor resistance to hydrogen-induced embrittlement, and it did not meet the safety requirements of the hydrogen storage valve block.

[0076] Comparative Example 7 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The difference in preparation method between Example 1 and Example 2 is that steps (4) to (5) are replaced with solution treatment at 550°C for 90 min and aging at 185°C for 180 min.

[0077] The results showed poor matching between the solution treatment, aging temperature range and holding time, very little strengthening phase precipitation, and significantly insufficient strength, which fell far short of national standards and the customer's minimum requirements, leading to the direct rejection of this heat treatment solution.

[0078] Comparative Example 8 This comparative example provides a 6061 aluminum alloy forging with the same alloy composition as in Example 1. The difference between the preparation method and that in Example 1 is that steps (4) to (5) are replaced with solution treatment at 540°C for 90 min and aging at 175°C for 540 min.

[0079] Although the results were better than those of Comparative Example 7, the yield strength was less than the required value; the size of the reinforcing phase was too large and the distribution was uneven, and the grain refinement effect was limited, which could not meet the standards for use of hydrogen valve blocks.

[0080] The mechanical properties of the aluminum alloy forgings obtained in each embodiment and comparative example were tested, and the results are shown in Table 1.

[0081] Table 1

[0082] The results above show that by adjusting the alloy composition and preparation method, the present invention achieves mutual matching and synergistic effect, thereby solving the defects of existing technologies such as low waste utilization, high energy consumption, easy cracking of forgings, and low strength. It has the advantages of low raw material cost, high production efficiency, fewer internal defects in forgings, excellent mechanical properties, and good dimensional stability, and is suitable for mass production of load-bearing forgings for engineering machinery, new energy, and hydraulic valve bodies.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing 6061 aluminum alloy forgings, characterized in that, Includes the following steps: The alloy raw materials are sequentially smelted, cast, and homogenized, followed by online solution forging and online quenching. After quenching, an aging treatment is performed within 2 hours. The online solution forging and online quenching include: heating the homogenized ingot to 480-540℃ and holding it at that temperature for 60-130 minutes, then sequentially flattening, pre-forging, and final forging. The forging die is preheated to 220-300℃, and the forging exits the die at a temperature ≥440℃. The forging is then transferred to a water-cooling tank for quenching within 3-5 seconds. The water temperature in the water-cooling tank is 30-40℃, and the cooling rate of the forging is ≥80℃ / s to room temperature. The composition of the 6061 aluminum alloy forging, by weight percentage, is as follows: Si: 0.60–0.75%, Mg: 0.85–1.10%, Cu: 0.24–0.35%, Fe: ≤0.50%, Mn: 0.08~0.13%, Cr：0.10～0.25%， Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

2. The method for preparing 6061 aluminum alloy forgings according to claim 1, characterized in that, The homogenized ingot is heated to 520–540°C and held for 60–90 minutes. The heating process is carried out in stages.

3. The method for preparing 6061 aluminum alloy forgings according to claim 1, characterized in that, The aging treatment conditions are: heat preservation at 170-190℃ for 3-6 hours, followed by air cooling after removal from the furnace.

4. The method for preparing 6061 aluminum alloy forgings according to claim 3, characterized in that, The aging treatment conditions are: heat preservation at 185℃ for 4 hours, followed by air cooling after removal from the furnace.

5. The method for preparing 6061 aluminum alloy forgings according to claim 1, characterized in that, The smelting process includes: sequentially cleaning the furnace, feeding materials, smelting at 700-760℃, followed by mechanical stirring, bubble bed alloying, and electromagnetic stirring composite treatment. After 1-3 refining processes and slag removal, the material is allowed to stand at 720-760℃ for 20-50 minutes. The materials fed include aluminum ingots and 50%-60% recycled waste.

6. The method for preparing 6061 aluminum alloy forgings according to claim 1, characterized in that, In the casting process, the ingot diameter is controlled at 60-120mm, the casting speed at 200-250mm / min, and the cooling water flow rate at 450-520m³ / h. Before casting, the melt after smelting is degassed online to control the hydrogen content to ≤0.15ml / 100gAl, and then filtered through a single-stage filter at 50-70ppi.

7. The method for preparing 6061 aluminum alloy forgings according to claim 1, characterized in that, The homogenization process includes: holding the cast ingot at 520-560℃ for 5-12 hours, followed by water mist cooling.

8. The method for preparing 6061 aluminum alloy forgings according to any one of claims 1-7, characterized in that, The composition of the 6061 aluminum alloy forging is as follows: Si: 0.70~0.75%, Mg: 0.95–1.10%, Cu: 0.24–0.3%, Fe: 0.3~0.40%, Mn: 0.08~0.13%, Cr：0.10～0.2%， Zn: ≤0.06%, Ti: ≤0.10%, The balance consists of Al and unavoidable impurities.

9. A 6061 aluminum alloy forging, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The 6061 aluminum alloy forging according to claim 9, characterized in that, The 6061 aluminum alloy forging has a grain size of 20-50 μm, an average tensile strength ≥350 MPa, a yield strength ≥320 MPa, and an elongation ≥10%.

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