Production method for reducing metal extrusion welding lines

Abstract

According to the production method for reducing the metal extrusion welding line, key parameters such as the extrusion ratio, the extrusion speed, the extrusion pressure and the extrusion breakthrough pressure are controlled, and optimal design is conducted on a mold again. According to the produced metal extrusion product, the defects of welding lines are greatly reduced, the grain size of the product is smaller, and the performance of the product is more excellent.

Description

Technical Field

[0001] The invention relates to the technical field of metal material processing, in particular to a production method for reducing metal extrusion welding lines. Background Art

[0002] When metal materials are extruded to produce complex cavity materials such as pipes and profiles, forward extrusion is generally used for products with high requirements such as dimensional accuracy, and a diversion combination mold is used for the extrusion mold. Due to the diversion effect of the diversion bridge in the mold, the metal flow is diverted and then welded together, and the final product forms a longitudinal weld line. Since many metal extrusion products need to undergo subsequent surface treatments such as oxidation and electrophoresis, if the product weld line is too large or too deep, the surface of the product after surface treatment will easily show visible weld line marks, and even form a concave and convex feel, especially for square tubes with a large width-to-thickness ratio: large curved tubes, round tubes, etc. It is difficult to avoid the weld line problem from the profile section design. Therefore, reducing or alleviating the formation of weld lines during the extrusion stage is a technical problem that needs to be solved in this field.

[0003] In actual production, technicians have proposed some improvement methods based on practical experience for the problem of extrusion weld line stripes. The key technology to solve the problem of extrusion weld line stripes is die design. Some scholars believe that during the extrusion of the split die, the metal deforms violently at the weld and the temperature rises sharply, resulting in coarse grains at the weld of the profile. Or the die design is unreasonable, the welding is not sufficient, resulting in the cast structure being brought into the extruded product. Or impurities and segregation tumors on the surface of the ingot are brought into the weld during the extrusion process. However, after efforts, this problem cannot be solved well. The problem of batch scrapping of profiles due to quality problems of weld line stripes occurs from time to time.

[0004] In addition to the design of the internal structure of the mold, metal casting and extrusion processes are also important factors in controlling the weld line. How to reduce the impact of the weld line from the source through production technology is also a goal that technical personnel in this field continue to explore. Summary of the invention

[0005] The present invention provides a production method for reducing metal extrusion welding lines. By adjusting the production process parameters and optimizing the structure of the mold flow channel, the metal extrusion products produced have greatly reduced the defects of the welding lines, the grain size of the products is smaller, and the product performance is better.

[0006] In order to achieve the above objectives, the technical solution of the present invention is as follows: A production method for reducing metal extrusion welding lines comprises the following steps: A. Batching and smelting: Aluminum ingots and master alloys are placed in a smelting furnace according to a predetermined alloy ratio standard. The alloy percentage weight content is: Si is 0.2-0.6, Fe is ≤0.35, Cu is ≤0.10, Mn is ≤0.10, Mg is 0.45-0.9, Cr is ≤0.10, Zn is ≤0.10, Ti is ≤0.10, and the balance is Al.

[0007] B. Casting: The molten metal is purified through a holding furnace and a launder, and then enters a casting machine to be cast into cylindrical rods; C. Soaking: The cast bars are put into the soaking furnace for soaking, and then taken out of the furnace for rapid air cooling; D. Ingot sawing and lathing: saw the long ingot into a suitable length for extrusion, and lathe the surface of the ingot; E. Billet heating: Gradient heating is adopted, starting from the ingot head temperature of 530℃, the temperature is reduced by 5-15℃ every 100mm; F. Extrusion: The speed of the profile flowing out of the die hole is maintained at 1.5-10m / min; G. Quenching: Control the extrusion outlet temperature to 510-520℃ and start quenching, using strong air cooling quenching; H. Stretching: Insert the pads into the inner cavity at both ends of the tube profile for online stretching, with a stretching rate of 0.3-0.6%; I. Sawing and aging: After the pipe profile is cut to size, it enters the aging furnace for aging; In the step A, alloys are also added: La and Ce; the weight percentage of the above elements accounts for 0.1-10% of the total; wherein La<Ce50%.

[0008] Adding rare earth elements La and Ce to aluminum alloys can increase component supercooling, refine grains during casting, reduce secondary crystal spacing, reduce gas and inclusions in the alloy, and make the inclusion phase tend to spheroidize. On the other hand, the addition of rare earth elements can increase melt fluidity, which is beneficial to casting and molding, and at the same time increase the extrudability of aluminum alloys, which can provide high-quality raw materials for the subsequent pipe oxidation process.

[0009] The best temperature range for quenching is 510-520℃. If the temperature is too low, the alloy elements cannot be fully dissolved; if the temperature is too high, a coarse recrystallized structure will be formed, which will reduce the strength of the profile. After the extrusion starts, the billet near the die end face and the working belt will generate heat due to plastic deformation and friction. The thermal effect can increase the temperature by 50-80℃. In order to make the profile extrusion close to the isothermal extrusion state, the best heating method before extrusion of aluminum alloy ingots is gradient heating, that is, the temperature is reduced by 5-15℃ every 100mm.

[0010] The alloy weight content percentages in step A are: Si is 0.2-0.6, Fe is ≤0.35, Cu is ≤0.10, Mn is ≤0.10, Mg is 0.45-0.9, Cr is ≤0.10, Zn is ≤0.10, Ti is ≤0.10, and the balance is Al.

[0011] In the step F, the extrusion pressure is kept constant before and after extrusion, the speed is controlled by variable speed control, and the pressure difference between the head and the tail of extrusion is ≤5MPa.

[0012] In step F, the extrusion ratio λ is controlled at 40-70%; λ=S / S 筒， Where S is the cross-sectional area of ​​the profile, S 筒 is the cross-sectional area of ​​the extrusion cylinder.

[0013] For the formation of the weld seam, the pressure of the metal fluid in the welding cavity of the mold is an important factor affecting the size of the weld seam. The extrusion ratio and the extrusion pressure act on the welding pressure of the metal fluid in the mold cavity at the same time. The higher the material pressure during metal fluid welding, the more conducive to the welding effect of the weld seam. However, excessive extrusion pressure will damage the diversion structure of the mold. Therefore, during the extrusion process, the extrusion speed is controlled to affect the welding pressure of the metal fluid in the welding cavity. The isobaric environment in the welding cavity is more conducive to the formation of the weld line.

[0014] In the step I, the aging process is to keep the temperature at 170° C. for 5 hours.

[0015] The extrusion die is divided into a male die and a female die. A diverter bridge and a die core are arranged on the male die, and a welding chamber is arranged on the female die. The front shape of the welding chamber is petal-shaped. The diverter bridge and the welding chamber are both evenly distributed in a radial shape. After the two are relatively combined, a complete diverter welding structure is formed.

[0016] The traditional welding chamber is trapezoidal or gear-shaped. The defect of the welding chamber is that the metal fluid is filled with too little fluid, and the pressure of the metal fluid does not increase rapidly when the metal fluid flows from the molding flow channel to the molding flow channel. Instead, it smoothly enters the mold working zone, resulting in unsatisfactory turbulent welding of the metal fluid. The petal-shaped welding chamber changes the defects of the traditional chamber. The cavity volume is larger at the edge of the petal, and the chamber cross-sectional area is smaller as it is closer to the working zone. With this design, the metal fluid is gradually pressurized when it flows to the molding flow channel working zone, which makes the welding effect better.

[0017] A drainage groove is set between the bottoms of the welding chambers, and the position of the drainage groove corresponds to the position of the diverter bridge. Initially, after the metal fluid is cut by the diverter bridge, a fluid vacuum zone is formed at the rear, and the vacuum zone is the reason for the formation of the weld; the design of the drainage groove makes the metal fluid that originally had a vacuum zone gather to the drainage groove, making up for and eliminating the original vacuum zone, and trying to eliminate the phenomenon of the weld.

[0018] The drainage groove is in a Y-shape, and the bottom of the Y-shape is connected to the working belt of the side wall of the die outlet. The Y-shaped drainage groove gathers the metal fluids on both sides to the middle to supplement the metal amount at the weld seam.

[0019] A stop is provided between adjacent drainage grooves.

[0020] The baffle makes the metal fluid flow turbulent when it flows to the forming flow channel. The formation of turbulence stirs the fluid in the original neat vacuum area, intensifies the fusion between the metals, and reduces the degree of weld formation. At the same time, the baffle also reduces the cross-sectional area of ​​the metal flow channel, further increases the fluid pressure in the welding chamber, and improves the welding effect.

[0021] The shape of the baffle is arc-shaped, which matches the shape of the working zone of the side wall of the die outlet. The arc-shaped baffle is also conducive to the flow of metal fluid to the drainage grooves on both sides.

[0022] Advantages of the invention: 1. In the present invention, in the key step of extrusion, by controlling key parameters such as extrusion ratio, extrusion speed, extrusion pressure, extrusion breakthrough pressure, etc., the control and reduction of the profile welding line is achieved, and the effect is obvious.

[0023] 2. The present invention optimizes the design of the extrusion splitter combined die welding confluence channel, and the produced metal extrusion products greatly reduce the defects of the welding line. The welding line in the product is not only invisible to the naked eye, but also cannot be seen in the metal microstructure photos.

[0024] 3. The product extruded by the extrusion die of the present invention has more complete turbulence, so the metal grain size of the product is smaller and the mechanical properties of the product are better.

[0025] 4. The present invention optimizes the alloy composition and adds rare earth elements La and Ce, which also greatly reduces the metal grain size and improves the mechanical properties of the metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow chart of the present invention; Figure 2 It is a schematic diagram of the exploded side view structure of the extrusion die; Figure 3 This is a schematic diagram of the main structure of the punch; (extrusion direction) Figure 4 This is a schematic diagram of the main structure of the die; (extrusion direction) Figure 5 The sample cut at 1.8 m from the tail end in Example 1 shows the microstructure photos of the welding position and the non-welding position and the grain size picture of the anode coating. It can be seen from the figure that there is not much difference between the microstructures of the welding position and the non-welding position, the grain structure is evenly distributed, and the grain size is about 100 μm. In fact, the grain and second phase precipitation at the welding position is slightly better than that at the non-welding position. This is because the turbulent stirring effect of the welding position passing through the mold is more intense, and the grain breakage is higher.

[0027] Figure 6 The figure is a comparison of the ingot grain refinement effect (film coating) and the profile microstructure of Example 1 and Comparative Example 6; after the alloy composition is optimized, the ingot grains are finer, broken from >200μm to about 100μm, and the grain morphology is spheroidized. In the subsequent extrusion process, the spheroidized grains will be uniformly elongated, the deformation is relatively stable, and no excessive coarse second phase will remain; After alloy optimization, the second phase in the microstructure of the profile is obviously finer and more evenly distributed. The second phase in the microstructure of conventional products is coarse and disorderly distributed, which will lead to the aggregation of the second phase at the welding site during the subsequent oxidation process, resulting in an obvious welding line.

[0028] The names of the components in the figure are: 1-punch; 11-diverter bridge; 12-core; 13-diverter hole; 2-die; 21-welding chamber; 22-drainage groove; 23-blocking platform. DETAILED DESCRIPTION Example 1

[0029] A 2800-ton extruder was selected for production, with a 6063-T4 aluminum alloy round tube with a diameter of 120 mm, a wall thickness of 3 mm, and an extrusion ratio of 58.9; The steps include: Batching and smelting: Put aluminum ingots and master alloy into the smelting furnace according to the predetermined alloy ratio standard; The percentage weight content of the alloy is: Si is 0.4868, Fe is 0.205, Cu is 0.0133, Mn is 0.06, Mg is 0.6578, Cr is 0.0104, Zn is 0.0287, Ti is 0.0175, La is 0.04261, Ce is 0.11846, and the balance is Al; B. Casting: The molten metal is purified through a holding furnace and a launder, and then enters a casting machine to be cast into cylindrical rods; C. Soaking: The cast bars are put into the soaking furnace for soaking, and then taken out of the furnace for rapid air cooling; D. Ingot sawing and lathing: saw the long ingot into a suitable length for extrusion, and lathe the surface of the ingot; E. Billet heating: Gradient heating is adopted, starting from the ingot head temperature of 530℃, the temperature is reduced by 10℃ every 100mm; F. Extrusion: The speed of the profile flowing out of the die hole is maintained at 1.5-10m / min; G. Quenching: Control the extrusion outlet temperature to 515℃ and start quenching, using strong air cooling quenching; H. Stretching: Insert the pads into the inner cavity at both ends of the tube profile and perform online stretching with a stretching rate of 0.5%; I. Sawing and aging: After the pipe profile is cut to size, it enters the aging furnace for aging; The ingredients in step A are: In the step F, the extrusion pressure is kept constant before and after extrusion, and the speed is controlled by variable speed control.

[0030] In the step F, the extrusion ratio λ is 58.9; λ=S / S 筒， Where S is the cross-sectional area of ​​the profile, S 筒 is the cross-sectional area of ​​the extrusion cylinder.

[0031] In the step I, the aging process is to keep the temperature at 170° C. for 5 hours.

[0032] The extrusion die is divided into a male die 1 and a female die 2. The male die 1 is provided with a diverter bridge 11 and a mold core 12. The female die 2 is provided with a welding chamber 21. The front shape of the welding chamber 21 is petal-shaped. The diverter bridge 11 and the welding chamber 21 are both radially evenly distributed. After the two are relatively combined, a complete diverter welding structure is formed.

[0033] A drainage groove 22 is provided between the bottoms of the welding chambers 21 , and the position of the drainage groove 22 corresponds to the position of the diverter bridge 11 .

[0034] The drainage groove 22 is in a Y-shape, and the bottom of the Y-shape is connected to the working zone of the side wall of the mold outlet.

[0035] A stop 23 is disposed between adjacent drainage grooves 22 .

[0036] The shape of the baffle 23 is arc-shaped, which matches the shape of the working zone of the side wall of the mold outlet.

[0037] Comparative Example 1 Compared with Example 1, under the same conditions of other parameters, the extrusion pressure was kept constant and the extrusion speed was changed to constant speed, and the extrusion speed was 3m / min; Comparative Example 2 Compared with Example 1, under the same conditions of other parameters, the extrusion pressure was kept constant and the extrusion speed was changed to constant speed, and the extrusion speed was 5m / min; Comparative Example 3 Compared with Example 1, under the same conditions of other parameters, the extrusion pressure was kept constant and the extrusion speed was changed to constant speed, and the extrusion speed was 7m / min; The obtained profile product was subjected to welding and fracturing tests by taking multiple samples at different positions of the tail end. The press used for the pressure test was a 100T press.

[0038] After analysis, it is believed that the temperature in the mold cavity rises rapidly due to the high extrusion pressure at the head of the ingot when the product is produced by isobaric extrusion, and soon exceeds 530°C. The high-temperature metal has a great impact on the working belt of the mold, resulting in aluminum sticking to the working belt of the mold after a long extrusion time, and the nitride layer of the working belt is worn, which ultimately leads to unqualified product surface quality. Due to the use of isobaric extrusion, the pressure in the mold welding cavity is always kept equal.

[0039] Comparative Example 4 Compared with Example 1, under the condition of the same other parameters, the design of the drainage groove in the mold is cancelled.

[0040] Comparative Example 5 Compared with Example 1, under the condition of the same other parameters, the design of the stopper in the mold is cancelled.

[0041]

[0042]

[0043] It can be seen that the surface welding line, product yield, mechanical strength and other aspects of Example 1 have better comprehensive effects. In particular, in Example 1, the head and tail pressure difference of extrusion is smaller, the extrusion pressure is more stable, and the metal flow is more uniform, which is conducive to the smooth progress of welding and the comprehensive benefits are more optimized.

[0044] Comparative Example 6 Compared with Example 1, under the same other parameters, the addition of elements La and Ce was eliminated.

[0045] It can be seen from the above that the addition of La and Ce alloy elements has a great influence on the mechanical properties of the product, especially the elongation. The reason is that after the grains are spheroidized and refined, the probability of microcracks in the metal is greatly reduced, which greatly increases the elongation.

Claims

1. A production method for reducing metal extrusion welding lines, characterized in that: The steps include: A. Batching and smelting: Aluminum ingots and master alloys are placed in a smelting furnace according to a predetermined alloy ratio standard, and the alloy weight content is as follows: Si is 0.2-0.6, Fe is ≤0.35, Cu is ≤0.10, Mn is ≤0.10, Mg is 0.45-0.9, Cr is ≤0.10, Zn is ≤0.10, Ti is ≤0.10, and the balance is Al; B. Casting: The molten metal is purified through a holding furnace and a launder, and then enters a casting machine to be cast into cylindrical rods; C. Soaking: The cast bars are put into the soaking furnace for soaking, and then taken out of the furnace for rapid air cooling; D. Ingot sawing and lathing: saw the long ingot into a suitable length for extrusion, and lathe the surface of the ingot; E. Billet heating: Gradient heating is adopted, starting from the ingot head temperature of 530℃, the temperature is reduced by 5-15℃ every 100mm; F. Extrusion: The speed of the profile flowing out of the die hole is maintained at 1.5-10m / min; G. Quenching: Control the extrusion outlet temperature to 510-520℃ and start quenching, using strong air cooling quenching; H. Stretching: Insert the pads into the inner cavity at both ends of the tube profile for online stretching, with a stretching rate of 0.3-0.6%; I. Sawing and aging: After the pipe profile is cut to size, it enters the aging furnace for aging.

2. The production method for reducing metal extrusion welding lines according to claim 1, characterized in that: In step A, alloys: La and Ce are also added; the weight percentage of the above elements accounts for 0.1-10% of the total; Among them, La<Ce50%.

3. The production method for reducing metal extrusion welding lines according to claim 1, characterized in that: In the step F, the extrusion pressure is kept constant before and after extrusion, the speed is controlled by variable speed control, and the pressure difference between the head and the tail of extrusion is ≤5MPa.

4. The production method for reducing metal extrusion welding lines according to claim 1, characterized in that: In the step F, the extrusion ratio λ is controlled at 40-70; λ=S / S 筒， Where S is the cross-sectional area of ​​the profile, S 筒 is the cross-sectional area of ​​the extrusion cylinder.

5. The production method for reducing metal extrusion welding lines according to claim 1, characterized in that: In the step I, the aging process is to keep the temperature at 170° C. for 5 hours.

6. The production method for reducing metal extrusion welding lines according to claim 1, characterized in that: The extrusion die is divided into a male die (1) and a female die (2); a shunt bridge (11) and a die core (12) are arranged on the male die (1); a welding chamber (21) is arranged on the female die (2); the front face of the welding chamber (21) is in the shape of a petal; the shunt bridge (11) and the welding chamber (21) are both evenly distributed in a radial shape; after the two are relatively combined, a complete shunt welding structure is formed.

7. The die structure for reducing metal extrusion welding line according to claim 5, characterized in that: A drainage groove (22) is provided between the bottoms of the welding chambers (21), and the positions of the drainage grooves (22) correspond to and match the positions of the diverter bridges (11).

8. The die structure for reducing metal extrusion welding line according to claim 5, characterized in that: The drainage groove (22) is in a Y-shape, and the bottom of the Y-shape is connected to the working zone of the side wall of the mold outlet.

9. The die structure for reducing metal extrusion welding line according to claim 6, characterized in that: A stopper (23) is provided between adjacent drainage grooves (22).

10. The die structure for reducing metal extrusion welding line according to claim 6, characterized in that: The baffle (23) is in an arc shape, matching the shape of the working zone of the die outlet side wall.

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