CN112474871B - Push rolling process of high-performance short-flow ribbed magnesium alloy seamless pipe - Google Patents

Abstract

The invention provides a push rolling process of a high-performance short-flow ribbed magnesium alloy seamless tube blank, wherein the tube blank is heated and then inserted into a grooved mandrel, and a small part of the tube blank is clamped into the mandrel in a mode of sleeve head necking; the core rod drives the compacted pipe blank to be sent into a roller, and the pipe blank is subjected to plastic processing of reducing diameter and reducing wall; then the steel bar enters the groove type with the groove to roll the outer rib. And (4) continuously feeding the rolled pipe into a quick cooling device for quick cooling, and obtaining a finished product after entering a rod stripping process. The invention adopts the hole pattern with the transition arc, greatly improves the pipe forming efficiency, reduces the rolling pass, effectively prevents the generation of lugs in the rolling process and greatly improves the surface quality of the pipe; the mandrel with the groove is adopted, the clamping force is increased, and a subsequent mandrel releasing mechanism is not required to be added for subsequent mandrel releasing, so that the rolling process is reduced, and the production efficiency is improved; meanwhile, the mechanical property of the magnesium alloy is greatly improved by adopting a ribbed rolling and quick cooling device.

Description

A push-rolling process for a high-performance short-flow reinforced magnesium alloy seamless pipe

technical field

The invention relates to the field of preparation of magnesium alloy pipes, in particular to a push-rolling process for high-performance short-flow ribbed magnesium alloy seamless pipes.

technical background

As the lightest engineering metal material, magnesium alloy has the advantages of high specific strength, high specific stiffness, good damping and shock absorption, good dimensional stability, convenient machining, and easy recycling. ".

At present, the preparation process of commercial magnesium alloy pipes is mainly casting and extrusion. The above processes all have their shortcomings. Although the extrusion and cast pipes have high production efficiency and relatively mature technology, they have obvious defects in the performance of the pipes, which are difficult to be used in occasions requiring high strength, and still have structural properties. There is a lot of room for improvement. Although ordinary rolling can meet the above defects, in the process of multi-pass rolling, because the magnesium alloy material is very sensitive to temperature, it is difficult to control the elongation of the material, and the matching of roll speed is still a big problem. Produce pulling or stacking, which will adversely affect the quality and performance of the pipe.

In the industry, especially in the automotive industry and aerospace, which have high requirements on weight and strength, in order to achieve the purpose of light weight, energy saving and emission reduction, mainly from two perspectives, one is to use lightweight materials, and the other is to pass the strength. Designed to strengthen the mechanical properties of lightweight structural parts, this patent designs a push-rolling process for high-performance short-flow reinforced magnesium alloy seamless pipes from these two perspectives.

This patent solves the problems in the prior art that the magnesium alloy material is difficult to process and the performance of the processed pipe is poor.

SUMMARY OF THE INVENTION

In view of the above technical situation, the purpose of the present invention is: starting from the plasticity optimization of the rolled billet, using the push-rolling process to process the as-cast or extruded magnesium alloy pipe, and then rolling the pipe through the three-roll push-rolling process. To provide a short-flow, high-performance, high-yield magnesium alloy pipe preparation process.

In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is to provide a high-performance short-flow ribbed magnesium alloy pipe rolling process, which specifically includes the following process flow:

(1) Billet pre-heating process, place the tube blank in a heating furnace to heat it, the heating rate is 50°C/s~70°C/s, and after heating the temperature to 250°C~500°C, the mandrel is sent to Into the blank, the mandrel is preheated to 250 ℃;

(2) Shrinking process: insert the heated tube blank into the mandrel and hold it with clamps, then send it to the shrinking die for shrinking. The amount of reduction is determined by the thickness of the tube wall and the diameter of the tube blank. Press down 2mm~7mm to ensure that the front end of the tube blank is in contact with the mandrel after shrinking and has a certain one-way tensile force, and then release the clamp to enter the next process;

(3) Rough rolling process: push the mandrel bar to drive the tube blank after shrinkage into the roll, the pushing speed is 0.5m/s~1m/s, reduce the diameter and wall of the tube blank to enhance its microstructure and properties;

(4) Rounding process: push the mandrel to drive the tube blank into the roll, the pushing speed is 0.7m/s~1.5m/s, and the tube blank is pressed down slightly to return to a round shape, which is convenient for entering the next pass for external reinforcement. rolling;

(5) Rolling process of external reinforcement: Continue to push the mandrel into the roll with a pass at a pushing speed of 0.5m/s~1.5m/s, and roll the outer reinforcement of the tube blank to enhance its mechanical properties;

(6) Quick cooling process: the rolled tube blank is quickly passed through the liquid nitrogen quick cooling device;

(7) Loosening process: After the pipe that has undergone the rapid cooling process is loosened by the loosening process, the shrinkage section of the tube blank is cut off, and the finished product is completed.

The shrinking device performs shrinking by clamping and biting, and is composed of clamps, a shrinking die and a special mandrel. The clamp clamps the tube blank, and sends the tube blank and the mandrel as a whole into the shrinking die to complete the shrinking process.

The shape of the mandrel at the constriction is spoon-shaped, the front end of the spoon-shaped inclination angle α is between 25° and 45°, and the rear end arc radius R is 12% to 17% of the radius of the mandrel.

In the shrinking process of the pipe, the clamp and the shrinking die need to be preheated, and the shrinking die and the clamp need to be loosened after the shrinking process is completed.

The rolling pass is an ellipse-circle-oval pass, and the ovality of the elliptical pass is 1.03-1.08.

In the push rolling process, the pushing speed of the first four passes, that is, the wall-reducing passes, is 0.5m/s~1.5m/s, and the pushing speed of the last four passes, that is, the outer bar rolling passes, is 0.5m/s ~1.5m/s. Since there is a certain gap between the tube blank and the mandrel in the initial state, the front end plane of the tube should be kept perpendicular to the rolling centerline during the first rolling process.

The invention improves the performance of the pipe on the basis of the as-cast and extruded pipes, and there are mainly three forms: one is to use a large reduction to refine the crystal grains to enhance the performance of the material itself; the other is to roll the outer reinforcement. , significantly enhance the mechanical properties of the pipe; the third is to carry out a rapid cooling process to prevent grain coarsening and significantly improve the strength and stiffness of the material.

The necking method adopted in the present invention changes the beating and shrinking method in the traditional sense, and adopts the method of clamping and biting. The eccentric load of the force caused by the point contact or line contact between the billets and the difficulty of loosening the bar after rolling; and during the push rolling process, thanks to the ring-shaped shrinkage, the billet can be automatically aligned. There is no need for an additional holding device; its one-way scoop-shaped shrinkage can not only ensure the reliability of the connection between the pipe and the mandrel during the mandrel rolling process, but also ensure the smooth stripping in the subsequent stripping process.

This process adopts the push-rolling method. Compared with the Y-rolling method, the push-rolling method has a simplified transmission, smaller size, and a more compact pass arrangement, which will not cause defects such as pulling and stacking, and can be used in No roll gap pass is used in the rolling process to suppress the generation of ears. Adjustable between passes, with great flexibility to adapt to a variety of sizes.

The present invention adopts ellipse-circle-ellipse hole type in the rolling stage, which well avoids the situation that the mandrel is locked due to the action of concentrated load when the reduction amount is large.

The beneficial effects of the invention are as follows: adopting the process of clamping and biting into the necking, effectively solves the shortcomings of unstable necking and difficulty in loosening the rod in the conventional necking method; adopts the method of actively pushing the mandrel rod, and reasonably solves the problem of the conventional rolling During the process, the roller speed does not match and the problem of pulling and stacking occurs; the method of external reinforcement rolling solves the problem of light weight but general strength of magnesium alloy pipes, which can be used in various occasions; the rapid cooling process is adopted to suppress the The coarsening of the grains enhances the mechanical properties of the tube blank.

Description of drawings

Fig. 1 is a schematic diagram of the rolling principle of magnesium alloy push pipe;

Fig. 2 is a schematic diagram of a shrinking process;

Fig. 3 is the front view of the section of the necking process;

Figure 4 is a cross-sectional oblique view of the necking process;

Fig. 5 is a schematic diagram of a necking die;

6 is a schematic diagram of a mandrel;

Figure 7 is an enlarged view of the mandrel necking;

Fig. 8 is a schematic diagram of all the passes in the rolling process;

Fig. 9 is the schematic diagram of rolling pass under high pressure;

Figure 10 is a schematic diagram of a rolling pass under high pressure;

Figure 11 is a schematic diagram of the rounding pass and pass;

Figure 12 is a schematic diagram of the rolling pass of the outer bar;

Fig. 13 is a schematic diagram of a rolling pass of the outer bar;

In the figure: 1. Mandrel; 2. Tube blank; 3. Clamp; 4. Narrowing die; 5. High-reduction rolling pass; 6. Rounding pass; 7. External reinforcement rolling pass; 8. Fast cooling device.

specific embodiment

The application is described below with examples

Example 1

The tube blank used is as-cast AZ61 magnesium alloy, and the original size is φ50mm in outer diameter and φ32mm in inner diameter. The length is 200mm, the outer diameter of the mandrel used is φ30mm, the surface of the mandrel is coated with powdered graphite lubricant, and the roll is preheated with hot roll material to prevent the plasticity of the tube from being reduced due to the sudden temperature drop. The mandrel and the tube blank are heated to 300°C at the same time, and then the tube blank is shrunk by the rear end clamping the front groove and gradually biting in, and the single side is pressed down by 2mm. Then push the mandrel bar for rolling at a speed of 2m/s. After the first four passes of rolling, a tube with an outer diameter of 40 mm and an inner diameter of 30 mm is obtained, and the mandrel is continued to be rolled at 1.2 m/s for the next four passes, and the rapid cooling process is carried out immediately after the rolling process is completed. Then, the mandrel is taken out to obtain a high-strength magnesium alloy pipe with a wall thickness of 3.5 mm and a height of 1 mm of outer ribs.

The mechanical properties of the pipe after rolling in this example are as follows: the tensile strength is: 290Mpa~315Mpa.

Embodiment 2:

The tube material used is an extruded AZ31b magnesium alloy tube blank, the original size is the outer rib φ150mm, the inner diameter φ100mm, and the length 1500mm. The inner diameter of the mandrel used is φ95mm. The surface of the mandrel is coated with MoS ₂ lubricant, and the roll is preheated by flame spraying. The mandrel and tube blank are heated to 350°C with the furnace, and then the tube blank is shrunk by clamping the front bevel at the rear end, and the unilateral pressing is 3mm. After the first four passes of rolling, the unilateral pressing The sizes are 4mm, 3mm, 2.5mm, and 2mm, respectively. The last four passes are rolled at a speed of 1.5 m/s, followed by a rapid cooling process. After stripping, a pipe with an outer diameter of φ115mm, an inner diameter of φ95mm and a rib height of 4mm is obtained.

The mechanical properties of the pipe after rolling in this example are as follows: the tensile strength is: 315Mpa~325Mpa.

The above are only some specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Based on the solutions in the present invention, those of ordinary skill in the art can obtain all the Other solutions fall within the protection scope of the present invention.

Claims (3)

1. a push-rolling process for a high-performance short-flow ribbed magnesium alloy seamless pipe, characterized in that: The specific steps include the following processes: Billet preheating process: place the tube blank in a heating furnace to heat it, the heating rate is 50℃/s~70℃/s, after heating the temperature to 250℃~500℃, send the mandrel into the billet, The mandrel is preheated to 250℃; Nrinking process: After inserting the heated tube blank into the mandrel, clamp it with clamps, send it to the shrinking die for shrinking, and press down 2mm~7mm on one side to ensure that the front end of the tube blank and the mandrel after shrinking contact, and then release the clamp to enter the next process; Rough rolling process: push the mandrel to drive the necked tube blank into the roll, and the pushing speed is 0.5m/s~1m/s; Rounding process: push the mandrel to drive the tube blank into the roll, and the pushing speed is 0.7m/s~1.5m/s; External rib rolling process: continue to push the mandrel into the roll with a hole type, the pushing speed is 0.5m/s~1.5m/s, and the outer rib is rolled on the tube blank; Fast cooling process: the rolled tube blank is quickly passed through the liquid nitrogen fast cooling device; Loosening process: After the pipe that has undergone the rapid cooling process is loosened by the loosening process, the shrinking section of the tube blank is cut off, and the finished product is completed; The shape of the mandrel at the constriction is a spoon-shaped, the front end of the spoon-shaped inclination angle α is between 25° and 45°, and the rear end arc radius R is 12% to 17% of the radius of the mandrel; The shrinking process is performed by clamping and biting; the shrinking process needs to preheat the clamp and the shrinking mold, and after the shrinking process is completed, the shrinking mold and the clamp need to be released. 2. The push-rolling process of a high-performance short-flow ribbed magnesium alloy seamless pipe according to claim 1, wherein the rough rolling process pass is an ellipse-circle-elliptical pass without a roll gap, wherein the ellipse The ovality of the hole type is 1.03~1.08. 3 . The push-rolling process for a high-performance short-flow ribbed magnesium alloy seamless pipe according to claim 1 , wherein: the outer rib rolling process has a pass without a roll gap. 4 .

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