A method for reducing the coarse grain ring in 2219 aluminum alloy extruded rods using a pre-heat treatment

Abstract

The present application relates to the technical field of aluminum alloy processing, and particularly relates to a method for reducing coarse grain ring of 2219 aluminum alloy extruded rod by preheating treatment, the composition of the 2219 aluminum alloy is as follows: Si≤0.20%; Fe≤0.30%; Cu 5.8~6.8%; Mn 0.20~0.25%; Mg≤0.02%; Zn≤0.10%; Ti 0.02~0.10%; Zr 0.1~0.13%; V 0.07~0.10%, and the rest is Al and some inevitable impurity elements; the present application adds a preheating treatment process with a temperature lower than the solid solution temperature before solid solution quenching, the preheating treatment process is to slowly heat the rod to 380~480 DEG C at a heating rate of 5-8 DEG C / h, keep warm for 3-8 h, and cool to room temperature in the furnace. Under the premise of reducing the addition amount of Mn and Zr elements, the added preheating treatment process can reduce the distortion energy accumulated in the deformation process of the extruded rod, reduce the recrystallization power, achieve the purpose of reducing the coarse grain ring of the 2219 aluminum alloy extruded rod, and avoid the element segregation caused by Mn and Zr elements, thus reducing the material rejection rate, and improving the production efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy processing, and particularly relates to a method for reducing coarse grain ring of 2219 aluminum alloy extruded rods by preheating treatment. BACKGROUND

[0002] The 2219 aluminum alloy has the characteristics of high specific strength, heat resistance, good welding performance, high fracture toughness, etc., and in particular, the heat-treated state has very high stress corrosion cracking resistance, and the 2219 forged piece is widely used in aerospace structural parts. There is a big defect in the 2219 aluminum alloy extruded rod as a forged piece blank, that is, the 2219 aluminum alloy will produce a large-size extruded coarse grain ring during extrusion. The root cause of the coarse grain ring is recrystallization. During the extrusion process, the blank is constrained and strongly rubbed by the inner wall of the extrusion cylinder, causing uneven deformation of the metal, and the degree of deformation of the outer layer metal is much greater than that of the inner layer. The high-density dislocations and distortion energy accumulated in the outer layer metal cause the recrystallization temperature of the outer layer metal to decrease, and the grains recrystallize and grow during the solid solution process, forming a coarse grain ring. The coarse grain ring has a negative impact on the mechanical properties, corrosion resistance, reaction during anodic oxidation treatment, bendability, and machinability of the extruded product: for example, the existence of the coarse grain ring will increase the sensitivity of welding cracking, reduce the fracture toughness, and reduce the corrosion resistance; and the extruded rod with the coarse grain ring is prone to cracking during subsequent forging, resulting in the rejection of the forged piece. Therefore, this microstructure defect is particularly detrimental to the extruded profile of the structural part used in transportation. In the existing preparation process, some adopt the method of removing the coarse grain ring by turning before forging, but this will cause a large amount of material waste, and the depth of the coarse grain ring is not uniform, so it is not possible to guarantee that the size of the turned rod meets the forging requirements, which is not conducive to efficient production.

[0003] In the existing technical solution, patent CN114908264A discloses a method for eliminating the coarse grain ring of 2219 alloy extruded rods. The patent utilizes the effect of Mn and Zr elements in increasing the recrystallization temperature of aluminum alloy, substantially increases the content of Mn and Zr elements (Mn 0.3~0.4%, Zr 0.20~0.25%), suppresses the generation of coarse grain ring, and achieves the purpose of reducing coarse grain ring. However, high content of Mn and Zr elements is prone to segregation to form defects, which will cause unqualified detection and forging cracking, resulting in material rejection. SUMMARY

[0004] The purpose of the present application is to provide a method for reducing the coarse grain ring of 2219 aluminum alloy extruded rods by preheating treatment, which overcomes the defects of high generation rate of coarse grain ring of alloy extruded rods, and the unqualified detection and forging cracking caused by increasing the content of Mn and Zr elements in the prior art to suppress the generation of coarse grain ring, resulting in material rejection.

[0005] To achieve the above object, the application provides a method for reducing coarse grain ring of 2219 aluminum alloy extruded rod by preheating treatment, which comprises the following steps: batching, smelting and casting, soaking, sawing and skinning, casting ingot heating, extruding, on-line cooling, preheating treatment, solid solution quenching, sawing, testing and packaging.

[0006] The 2219 aluminum alloy comprises the following components in mass percentage:

[0007] Si ≤0.20%

[0008] Fe ≤0.30%

[0009] Cu 5.8~6.8%

[0010] Mn 0.20~0.25%

[0011] Mg ≤0.02%

[0012] Zn ≤0.10%

[0013] Ti 0.02~0.10%

[0014] Zr 0.1~0.13%

[0015] V 0.07~0.10%

[0016] The rest are Al and some inevitable impurity elements, and each of the inevitable impurity elements is ≤0.05%, and the total amount of the inevitable impurity elements is ≤0.15%.

[0017] The preheating treatment process is to slowly heat the rod to 380~480℃ at a heating rate of 5~8℃ per hour, keep warm for 3~8h, and then cool down to room temperature with the furnace.

[0018] The root cause of the coarse grain ring is recrystallization, and the driving force of recrystallization is the distortion energy storage generated by the deformation of the extruded rod. During the subsequent solid solution process, the driving force is provided by the distortion energy storage to promote the recrystallization and growth of the grains, and finally form the coarse grain ring. During the solid solution process, in addition to recrystallization, recovery also occurs, and the driving force of recovery is also the distortion energy storage. The present application utilizes the characteristics that the driving forces of recovery and recrystallization are both distortion energy storage, and adds a preheating process at a temperature lower than the solid solution temperature before the solid solution quenching of the 2219 aluminum alloy extruded rod, so that more recovery occurs before recrystallization, consumes the distortion energy storage, reduces the power of recrystallization, reduces the recrystallization, and thus achieves the purpose of reducing the coarse grain ring. At the same time, only a small amount of Mn and Zr elements (Mn 0.20-0.25%, Zr 0.1-0.13%) are added, the element segregation caused by Mn and Zr elements is reduced, and the risk of material scrap caused by flaw detection unqualified and forging cracking is reduced. The preheating treatment needs to be slowly heated to 380-480℃ at a rate of 5-8℃ / h, the heating rate is too slow, the time is too long, and the energy consumption is wasted; if the heating rate is too fast, the recovery time is insufficient, and the coarse grain ring suppression effect is not good. At the same time, if the preheating treatment temperature is too low, the recovery effect is not good; if the temperature is too high, the grains will coarsen in the preheating process. Therefore, it is appropriate to control the preheating treatment temperature range to be 380-480℃ and the heating rate to be 5-8℃ / h. The inventors of the present application have verified through many experiments that the preheating treatment can reduce the coarse grain ring regardless of whether the rod is heated to 200℃ in the early stage, so the rod can be first heated to 200℃ at a high speed and then slowly heated to 380-480℃ at a rate of 5-8℃ / h to improve production efficiency.

[0019] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the melting and casting process, first, the 2219 aluminum alloy composition is dosed, then half of the total input amount of aluminum ingots or return materials is added to the melting furnace, melted, and then Cu, Mn, V, and Zr intermediate alloys are added, stirred until the alloy is completely melted, and then heated to 780-850℃ and kept for 10-30min; after the holding is completed, the remaining aluminum ingots or return materials are added, and the temperature is lowered to 720-760℃ in the furnace, and then refined by online chlorine and argon mixed gas in the furnace, and further, in the melting and casting process, a straight cooling type semi-continuous casting is used for production, and the cooling water flow is 20-60m 3 / h; no auxiliary tooling such as water scraping ring is used during casting to ensure the molding, and the ingot is molded in the whole process of strong cooling.

[0020] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the soaking process, the prepared aluminum alloy ingot is soaked at a temperature of 300-350 DEG C for 8-42 hours, and the temperature rising rate is 50-80 DEG C / h.

[0021] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the ingot heating process, the ingot heating temperature is 400-420 DEG C; the mold is heated to 380-410 DEG C in the heating furnace and is kept for 10-30 hours; and the extrusion cylinder heating temperature is controlled to be 390-420 DEG C.

[0022] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the extrusion process, the extrusion speed is controlled to be 0.3-1.5 m / min, and the extruded rod specification is phi 100 mm.

[0023] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, the on-line cooling process adopts on-line water mist cooling.

[0024] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the solid solution quenching process, the solid solution temperature is 530-538 DEG C, and the holding time is 150-250 min.

[0025] Further, in the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, in the solid solution quenching process, after the rod solid solution holding is finished, quenching is carried out in a vertical quenching furnace, the water temperature is 20-35 DEG C, and the quenching transfer time is 10-30 s.

[0026] Compared with the prior art, the method has the following beneficial effects:

[0027] 1. The method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment increases a preheating process with a temperature lower than the solid solution temperature before solution quenching, slowly rises to 380-480 DEG C at a temperature rising rate of 5-8 DEG C / h, and keeps for 3-8 hours, so that the accumulated distortion energy in the deformation process of the extruded rod can be effectively reduced, the recrystallization power is reduced, and the purpose of reducing the coarse grain ring of the 2219 aluminum alloy extruded rod is achieved.

[0028] 2. The method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment provided by the present application, the content of Mn element in the composition of the 2219 aluminum alloy is 0.20-0.25%, the content of Zr element is 0.1-0.13%, the addition amount of Mn and Zr elements is reduced, the element segregation caused by Mn and Zr elements can be reduced, the risk of disqualification in flaw detection and forging cracking to cause material scrap is reduced, and thus the production efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The macrostructure image of the 2219 aluminum alloy extruded rod prepared in Example 1 of the present application.

[0030] Figure 2 The macrostructure image of the 2219 aluminum alloy extruded rod prepared in Example 2 of the present application.

[0031] Figure 3 The macrostructure image of the 2219 aluminum alloy extruded rod prepared in Example 3 of the present application.

[0032] Figure 4 The macrostructure image of the 2219 aluminum alloy extruded rod prepared in Comparative Example 1 of the present application.

[0033] Figure 5 The macrostructure image of the 2219 aluminum alloy extruded rod prepared in Comparative Example 2 of the present application.

[0034] Figure 6 The cracking phenomenon image of the 2219 aluminum alloy extruded rod prepared in Comparative Example 2 of the present application. EMBODIMENT

[0035] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments. Example 1

[0036] The present embodiment provides a method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment, which comprises the following steps: batching, melting and casting, soaking, sawing and skinning, ingot heating, extruding, online cooling, preheating treatment, solid solution quenching, sawing, detection and packaging.

[0037] (1) Batching: the composition of the 2219 aluminum alloy in the present embodiment is as follows in terms of mass percentage:

[0038] Si: 0.038%

[0039] Fe: 0.084%

[0040] Cu: 6.19%

[0041] Mn: 0.21%

[0042] Mg ≤ 0.02%

[0043] Zn ≤ 0.01%

[0044] Ti: 0.03%

[0045] Zr: 0.12%

[0046] V: 0.077%

[0047] The rest is Al and some inevitable impurity elements, and each inevitable impurity element is ≤ 0.05%, and the total amount of inevitable impurity elements is ≤ 0.15%.

[0048] (2) Melting and casting: according to the mass percentage of the 2219 aluminum alloy in step (1), the ingredients are prepared, half of the total input amount of aluminum ingots or return materials is added in the melting furnace, after melting, Cu, Mn, V, Zr element intermediate alloy is added, after fully stirring until the alloy is completely melted, the temperature is raised to 815℃, and the temperature is kept for 20 min. After the end of the heat preservation, the remaining aluminum ingots or return materials are added, and after the temperature is cooled to 740℃ in the furnace, the on-line mixed gas refining of chlorine and argon is carried out, and the straight cooling type semi-continuous casting is used for production, the cooling water flow is 22m 3 / h, without using the water ring and other auxiliary tools for sacrificial cooling to ensure the molding during the casting process, ensuring that the ingot is molded in the whole process of strong cooling, and a φ582mm specification round ingot with a grain size of ≤3 levels (determined according to GB / T 3246.2-2012 “Deformed aluminum and aluminum alloy product organization test method Part 2: Low magnification organization test method”) is cast.

[0049] (3) Soaking: the prepared aluminum alloy ingot is soaked at a temperature of 325℃ for 25h, the heating rate is 60℃ / h, and after air cooling to room temperature, the head and tail are sawn and the segregation layer is removed;

[0050] (4) Ingot heating: the prepared aluminum alloy ingot is preheated, the preheating temperature is 410℃; the mold is heated to 395℃ in the heating furnace and kept for 20h; the extrusion cylinder is heated, and the temperature is controlled at 405℃.

[0051] (5) Extrusion cold cutting: the preheated ingot is extruded, the extrusion speed is controlled at 1.0m / min, the extrusion rod specification is φ100mm, and the extrusion rod is cooled by online water mist;

[0052] (6) Preheating treatment: first, the rod temperature is quickly raised to 200℃, then slowly raised to 380℃ at a heating rate of 6℃ / h, kept for 8h, and then cooled to room temperature with the furnace;

[0053] Solution treatment: the pre-treated bar was solution treated at 535℃ for 200 min, and then quenched in a vertical quenching furnace with water temperature of 20℃, and quenching transfer time of 20s. Finally, the bar was sawed, sampled and tested. Example 2

[0054] This example was prepared according to the preparation method of Example 1, except that (6) pre-treatment: the bar was first rapidly heated to 200℃, then slowly heated to 430℃ at a heating rate of 5℃ / h, and held for 5h, and then cooled to room temperature with the furnace; the other steps were the same as Example 1. Example 3

[0055] This example was prepared according to the preparation method of Example 1, except that (6) pre-treatment: the bar was slowly heated to 480℃ at a heating rate of 8℃ / h, and held for 3h, and then cooled to room temperature with the furnace; the other steps were the same as Example 1.

[0056] Comparative Example 1

[0057] This comparative example was prepared according to the preparation method of Example 1, except that step (6) pre-treatment was not performed, and step (7) solution treatment was directly performed; the other steps were the same as Example 1.

[0058] Comparative Example 2

[0059] This comparative example was prepared according to the preparation method of Example 1, except that the content of Mn and Zr in the composition of 2219 aluminum alloy was high, and step (6) pre-treatment was not performed, and step (7) solution treatment was directly performed; the other steps were the same as Example 1.

[0060] The composition of 2219 aluminum alloy in this comparative example was as follows:

[0061] Si: 0.056%

[0062] Fe: 0.091%

[0063] Cu: 6.25%

[0064] Mn: 0.38%

[0065] Mg≤0.02%

[0066] Zn≤0.01%

[0067] Ti: 0.03%

[0068] Zr: 0.23%

[0069] V: 0.077%

[0070] Other is Al and some inevitable impurity elements, and each inevitable impurity element is ≤0.05%, and the total amount of inevitable impurity elements is ≤0.15%.

[0071] The macrostructure images of the 2219 bars obtained in examples 1~3 and comparative examples 1~2 are shown in Figures 1 to 5 , and the detection results after sampling detection are shown in table 1.

[0072] Table 1 is the detection results of the macrostructure of the 2219 bars obtained in examples 1~3 and comparative examples 1~2

[0073]

[0074] In combination with Figures 1-5 and table 1, it can be seen that, by using the method for reducing the coarse grain ring of the 2219 aluminum alloy extruded bar by adopting the preheating treatment according to the application in examples 1, 2 and 3, the content of the added Mn element is 0.21%, and the content of the added Zr element is 0.12%, and a small amount of Mn and Zr elements will not cause element segregation, so as to reduce the risk of material scrap caused by detection failure and forging cracking; before solid solution quenching, a preheating process at a temperature lower than the solid solution temperature is added, so that more recovery of the grains occurs before recrystallization, the distortion energy is consumed, the recrystallization power is reduced, and the recrystallization is inhibited, so as to achieve the purpose of reducing the coarse grain ring, and the coarse grain ring of the prepared 2219 aluminum alloy extruded bar is 0~2.8mm, while in comparative example 1, no preheating process is performed before solid solution quenching, and the coarse grain ring of the prepared 2219 aluminum alloy extruded bar is 5.5~5.6mm, and in comparative example 2, the contents of Mn and Zr are increased (Mn: 0.38%, Zr: 0.23%), and the prepared 2219 aluminum alloy extruded bar almost does not have coarse grain ring, but due to the increase of the contents of Mn and Zr elements during preparation, the Mn and Zr elements are prone to segregation to form defects (such as Figure 6 ), so as to cause detection failure and forging cracking, and lead to material scrap. Therefore, by adding a preheating process at a temperature lower than the solid solution temperature before solid solution quenching, the purpose of reducing the coarse grain ring can be achieved without greatly increasing the contents of Mn and Zr elements, and the risk of material scrap caused by element segregation, detection failure and forging cracking due to the Mn and Zr elements can be reduced.

[0075] The method for reducing the coarse grain ring of the 2219 aluminum alloy extruded rod by preheating treatment provided by the application reduces the distortion energy accumulated in the deformation process of the extruded rod and reduces the recrystallization power by adding a small amount of Mn and Zr elements and adding a preheating process at a temperature lower than the solid solution temperature before the solid solution quenching, so that the coarse grain ring of the 2219 aluminum alloy extruded rod is reduced, the coarse grain ring is reduced from 5.5-5.6 mm to 0-2.8 mm, and the production efficiency is improved because the element segregation defects caused by the Mn and Zr elements can be avoided due to the reduction of the addition amount of the Mn and Zr elements, and the material rejection rate is reduced.

[0076] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application and to allow others skilled in the art to understand the application for various exemplary embodiments with various modifications being applicable. The scope of the application is intended to be defined by the claims and their equivalents.

Claims

1. A method for reducing the coarse grain ring in an extruded rod of 2219 aluminum alloy using a pre-heat treatment, characterized by, It comprises the following procedures: batching, smelting and casting, soaking, sawing and skinning, ingot heating, extrusion, on-line cooling, preheating treatment, solid solution quenching, sawing, detection and packaging. The 2219 aluminum alloy has the following component mass percentages: Si ≤0.20% Fe ≤0.30% Cu 5.8~6.8% Mn 0.20~0.25% Mg ≤0.02% Zn ≤0.10% Ti 0.02~0.10% Zr 0.1~0.13% V 0.07~0.10% The rest is Al and some inevitable impurity elements. The preheating treatment procedure is to slowly heat the rod to 380~480℃ at a heating rate of 5~8℃ / h, keep for 3~8h, and then cool to room temperature in the furnace.

2. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, The smelting and casting procedure is to add half of the total input amount of aluminum ingots or return materials in a smelting furnace, melt, then add intermediate alloy and stir until the alloy is completely melted, then heat to 780~850℃, keep for 10~30min; after the end of the heat preservation, add the remaining aluminum ingots or return materials and reduce the temperature to 720~760℃.

3. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 2, characterized in that, The intermediate alloy refers to Cu, Mn, V and Zr elements.

4. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, The smelting and casting process is produced by using direct cooling semi-continuous casting, and the cooling water flow is 20-60 m 3 / h.

5. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, In the soaking procedure, the soaking temperature is 300~350℃, the soaking treatment heat preservation time is 8~42h, and the heating rate is 50~80℃ / h.

6. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, In the ingot heating procedure, the ingot heating temperature is 400~420℃; the mold is heated to 380~410℃ in the heating furnace, and the heat preservation time is 10~30h; the extrusion cylinder heating temperature is controlled at 390~420℃.

7. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, In the extrusion procedure, the extrusion speed is controlled at 0.3~1.5m / min, and the extrusion rod specification is φ100mm.

8. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, The on-line cooling procedure adopts on-line water mist cooling.

9. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, In the solid solution quenching procedure, the solid solution temperature is 530~538℃, and the heat preservation time is 150~250min.

10. The method for reducing the coarse grain ring in an extruded 2219 aluminum alloy rod by pre-heat treatment according to claim 1, characterized in that, In the solid solution quenching procedure, after the end of the solid solution heat preservation, quenching is carried out in a vertical quenching furnace, the water temperature is 20~35℃, and the quenching transfer time is 10~30s.

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