JP5336802B2 - Seamless aluminum alloy tube manufacturing method - Google Patents

Description

  The present invention provides an aluminum heat exchanger and an aluminum alloy tube material used as its piping material, in particular, an aluminum alloy tube material used under high pressure conditions, by performing continuous drawing and solution treatment, thereby reducing the cost. The present invention relates to a method for producing a seamless aluminum alloy tube material having high dimensional accuracy and excellent end workability.

  In recent years, due to environmental problems such as global warming and the sudden rise in crude oil prices, especially for automotive piping materials, both reducing weight and improving strength by reducing the thickness of pipe materials to reduce the size and weight of heat exchangers. In addition, there is a demand for high formability that enables high-difficult processing to reduce the size and increase the degree of freedom of piping and to save labor in piping work.

  In such a situation, a 3003 seamless pipe (mandrel extrusion pipe) generally used, for example, is inferior to a porthole pipe in terms of dimensional accuracy and formability represented by thickness deviation accuracy. This is derived from the conventional method for manufacturing a mandrel extruded tube. That is, the current method for manufacturing a mandrel extruded tube is to extrude a large ingot and manufacture it by artificial aging treatment after cold working by continuous drawing. However, since the original material of the mandrel extrusion tube is thick, the cross-section reduction rate from the raw tube size to the final product size must be 70% or more. Inferior to. In addition, since the cross-section reduction rate is high, it is necessary to cold work multiple times. Therefore, even if aging treatment is performed afterwards, elongation due to work hardening during cold working is insufficient, and the formability is also porthole tube. It will be inferior. In particular, it is difficult to use for high-pressure piping because of the inferior thickness accuracy. Therefore, the high-pressure pipe is preferably a mandrel pipe that originally has no welded part and does not worry about breakage, but currently, a porthole pipe having excellent formability and high dimensional accuracy compared to a mandrel pipe, for example, A port hole tube equivalent to 6063-T83 having a maximum tube expansion ratio of 70 to 80% and a total elongation of 14 to 15% at a wall thickness of 1 mm is generally used.

  As described above, the porthole pipe is a pipe material with high dimensional accuracy, but a welded portion is formed in the manufacturing process. The welded part of the porthole tube formed by this porthole extrusion has different formability than the normal part. Therefore, when performing the process of expanding the tube by applying an internal pressure, the welded part is preferentially deformed and easily breaks, so that there is a problem that a process with a high expansion rate cannot be performed. One factor that causes the welded portion to break preferentially during processing is the difference in texture between the welded portion and the normal portion. Since the metal flow in the extrusion tool is different between the welded portion and the other normal portion, the processing history between the heat is different, resulting in different textures of the tube material after forming. This can be said to be an unavoidable phenomenon in porthole extrusion in which a hollow material is obtained by welding the metal once cut in the extrusion die at the welded portion.

  In order to solve this problem with porthole pipes, there is no welded part in the mandrel extrusion pipe manufacturing method by continuous drawing, so there is no need to consider the difference in texture between the welded part and the normal part. Works in an advantageous manner. However, as described above, the conventional mandrel extruded tube has a problem that the thickness deviation accuracy and formability are inferior to those of the conventional porthole tube.

  On the other hand, in recent years, the connection method of automobile piping materials has mainly been adopted as a mechanical connection method with a connector by VA or the like represented by process cut. For example, the degree of difficulty such as tube expansion processing of a terminal portion or shaft shield bead processing High and severe processing is increasing. When processing with different combinations of tube expansion, rolling and punching, such as shaft shield bead processing, cracks may occur at the welded portion of the porthole tube, so the porthole tube is thick enough to withstand the cracking. Is required. In other words, since there is no reliability of the welded part in the porthole pipe, it is necessary to increase the thickness of the pipe, and for example, a heat exchanger for an automobile using the porthole pipe is large and heavy. .

  Therefore, in order to produce an aluminum alloy tube material excellent in corrosion resistance and formability, for example, used as a pipe connecting a radiator or a heater of an automobile, an extruded tube obtained by hot extruding an aluminum alloy ingot A method for producing an aluminum alloy pipe material that is annealed after cold drawing at a workability of 30% or more is known. According to this manufacturing method, it is said that cracks and rough skin are less likely to occur during bending or bulging (Patent Document 1).

  However, in the above prior art, even if the formability of the aluminum alloy pipe material for automobile piping is improved to some extent, it is not possible to reduce the diameter of the piping material and reduce the weight of the heat exchanger.

On the other hand, reducing the size and weight of a heat exchanger for automobiles will become more important in the future because it can reduce the space on the vehicle and greatly contribute to the weight reduction and fuel consumption improvement of the vehicle body. Therefore, as a means for reducing the size and weight, and further as a means for reducing the size of the pipe and increasing the degree of freedom of the pipe, the pipe material is required to have a small diameter and a thin wall and high formability.
JP 2002-348624 A

  The present invention has been made to solve such problems of the prior art, and uses a mandrel extruded tube having no welded portion and high quality reliability, and has high dimensional accuracy and excellent formability. Seamless aluminum alloy with mechanical properties equivalent to or better than conventional porthole pipes, which is manufactured at low cost and has a maximum tube expansion ratio of 70 to 80% and a total elongation of 14 to 15% at a thickness of 1 mm. It aims at providing the manufacturing method of a pipe material.

  In the course of conducting various experiments and studies to develop a method for producing a seamless aluminum alloy pipe material in which the dimensional accuracy and mechanical properties such as elongation and bending have characteristics similar to those of a porthole pipe, Solved. Specifically, by performing solution treatment on the coil that has been wound after continuous drawing, and then performing cold drawing and artificial aging treatment, heat treatment alloy 6063- It was discovered that an aluminum alloy tube material having mechanical properties similar to those of a T83 porthole tube can be obtained.

The first aspect of the method for producing an aluminum alloy tube material of the present invention is the first cold-worked tube obtained by subjecting a mandrel extruded tube of JIS6063 aluminum alloy to a first cold working with a cross-section reduction rate of 70% or more by a continuous drawing method. It is characterized in that after the drawing tube is subjected to solution treatment, second cold working is performed by drawing with a cross-sectional reduction rate of 10 to 40%, and then artificial aging treatment is performed. Here, continuous drawing refers to continuous drawing processing, also called bull block, and cross-section reduction rate is the percentage of the value obtained by dividing the difference between the cross-sectional area before processing and the cross-sectional area after processing by the cross-sectional area before processing. That is, [(cross-sectional area before processing−cross-sectional area after processing) / cross-sectional area before processing] × 100. The solution treatment refers to a heat treatment for dissolving the alloy components in aluminum crystals and a subsequent cooling treatment, and softens the structure of the first drawn tube that has been excessively worked and hardened by the first cold working. Can be made. The artificial aging treatment is a heat treatment for giving a predetermined strength and formability to the aluminum alloy tube material.

  A second aspect of the method for producing an aluminum alloy pipe according to the present invention is characterized in that the first drawn pipe is continuously coiled by a coil before the solution treatment.

  A third aspect of the method for producing an aluminum alloy pipe according to the present invention is characterized in that a cooling temperature of the solution treatment is 1.5 ° C./second or more.

  According to a fourth aspect of the method for producing an aluminum alloy tube of the present invention, the second cold working has a cross-sectional reduction rate of 10 to 40%.

  According to the first aspect of the method for producing an aluminum alloy tube of the present invention, since the solution treatment is performed after the first cold working by the continuous drawing method with a cross-section reduction rate of 70% or more, the first cold working is performed. The work-hardened first drawn tube can be softened, and the formability and workability of the aluminum alloy tube material are improved.

  According to the second aspect of the method for producing an aluminum alloy tube of the present invention, since the first drawn tube obtained by the first cold working is coiled and then subjected to solution treatment, The capacity can be reduced, the energy consumption of the solution treatment furnace can be reduced, and the production cost can be reduced. Further, by twisting the first drawn tube, the twist generated in the first drawn tube is corrected and the first drawn tube is straightened. Therefore, in the subsequent second cold working, Uneven thickness of the drawn tube, especially in the longitudinal direction, can be greatly reduced.

  According to the third aspect of the method for producing an aluminum alloy tube of the present invention, if the cooling temperature of the solution treatment is 1.5 ° C./second or more, the amount of solid solution of quenching and alloy components becomes sufficient. Variations in the strength of the alloy tube can be suppressed.

  According to the fourth aspect of the method for producing an aluminum alloy tube of the present invention, the second cold working with a cross-sectional reduction rate of 10 to 40% is performed after the solution treatment and before the artificial aging treatment. It is possible to increase the dimensional accuracy by reducing the uneven thickness in the longitudinal direction and the radial direction of one drawn tube.

  Next, a method for manufacturing a seamless aluminum alloy tube according to an embodiment of the present invention will be described. The method for producing a seamless aluminum alloy tube according to an embodiment of the present invention includes: (1) a first cold-drawn mandrel extruded tube having a cross-section reduction rate of 70% or more by a continuous drawing method; A step of machining, (2) using a level winder to coil the first cold-worked first drawn tube while untwisting, and (3) a solution of the coiled first drawn tube A step of heat treatment, (4) a step of stretching the solution-treated coiled first drawn tube while straightening and drawing by the second cold working, and (5) after the second cold working, And an artificial aging treatment.

  In the first cold working step (1), a continuous drawing machine called a bull block is used to continuously draw the mandrel extruded tube a plurality of times so that the cross-section reduction rate becomes 70% or more. 1 A drawn tube is prepared. By setting the cross-sectional reduction rate to 70% or more, even a mandrel extruded tube that is thicker than the porthole tube can be thinned to some extent. Therefore, the final product can be obtained through the steps (2) to (5). A certain aluminum alloy tube can be thinned, and dimensional accuracy and formability can be improved. Further, in the first cold working process, continuous drawing is performed a plurality of times, so that uneven thickness can be reduced and dimensional accuracy can be increased to some extent in the process of continuous drawing. However, when the cross-section reduction rate is 70% or more, excessive work hardening has occurred in the first drawn tube, and the formability and workability are inferior to those of the conventional porthole tube.

  On the other hand, if the cross-section reduction rate is less than 70%, the thickness of the aluminum alloy tube material is not sufficient for reducing the size and weight of the heat exchanger. It is difficult to achieve high moldability. In addition, the continuous drawing machine has a structure in which when the continuously drawn pipe is wound around the drum of the continuous drawing machine, it is dropped as it is into the container provided under the drum by its own weight. If the cross-sectional reduction rate of the mandrel extrusion tube is small at the time of continuous drawing, the tube material after drawing cannot be wound around the drum of the continuous drawing machine, and therefore continuous drawing using the continuous drawing machine cannot be performed.

  In the coiling step of the first drawing tube (2), the first drawing tube is coiled using a level winder. As described above, when the first drawing tube is wound around the drum of the continuous drawing machine, the first drawing tube falls into the container under the drum as it is by its own weight, so that twist occurs in a direction substantially perpendicular to the longitudinal direction of the first drawing tube. Yes. However, by using a level winder, the first drawn tube can be coiled while eliminating this twist. By coiling the first drawn tube, the first drawn tube can be made compact, so that the efficiency of the solution treatment can be improved in terms of both space and energy, and productivity is improved. In addition, since twisting is eliminated during coiling, not only radial deviation but also longitudinal deviation is reduced in the second cold working process, and dimensional accuracy of the final product, aluminum alloy tube material is reduced. Can be increased.

  In the solution treatment step (3), since the first drawn tube is softened, excessive work hardening in the first cold working can be reduced. The heat treatment temperature is preferably 500 ° C. or higher and 550 ° C. or lower. Below 500 ° C, the amount of solid solution of the alloy components is insufficient, so even if the artificial aging treatment is performed after the second cold working, the strength and elongation of the final aluminum alloy tube are insufficient, and the required quality Can't meet. On the other hand, if it exceeds 550 ° C., local melting occurs at the grain boundaries, which is not preferable in that the strength may be lowered. In particular, a heat treatment temperature of 530 to 540 ° C. is preferable in that a sufficient amount of solid solution is obtained and local melting is surely avoided.

  The cooling rate after the heat treatment in the solution treatment is preferably 1.5 ° C./sec or more from the viewpoint of suppressing variation in strength of the first drawn tube. Since the first drawn tube is coiled, each portion of the first drawn tube is in contact with other portions that are adjacent vertically. Therefore, in order to set the cooling rate in the vicinity of the coiled first drawing tube central portion to 1.5 ° C./sec or more, it is preferable to perform cooling by a fan from the outer surface of the coil, and further, the coil inner tube The cooling efficiency may be improved by purging air. When the first drawn tube is not coiled, the surface area in contact with the outside air becomes larger than when coiled, so that the cooling rate may be 1.5 ° C./sec or more only by cooling.

  In the second cold working step (4), the coiled first drawing tube is stretched while being straightened and drawn. In this step, for example, the drawing is performed using a continuous drawing machine such as a combined machine. At this time, since the first drawn tube is drawn in a straightened state with the twist removed, the direction of feeding the first drawn tube into the continuous drawing machine is constant, and not only the radial thickness deviation but also the longitudinal direction The uneven thickness of can also be reduced. In the second cold working step, the strength is improved by work hardening. Usually, the number of drawing operations in the second cold working is one time, but may be performed a plurality of times as necessary.

  Regarding the degree of processing in the second cold working step, the cross-sectional reduction rate is preferably in the range of 10 to 40%. When the cross-section reduction rate is less than 10%, there is no difference in structure at the welded portion, so work cracks are not induced. However, the average crystal grain size after recrystallization is coarsened, so the formability is reduced. Moreover, since the work hardening is insufficient, the strength equivalent to 6063-T8 of the porthole tube cannot be obtained. On the other hand, when the cross-section reduction rate exceeds 40%, the crystal grain size after recrystallization does not become coarse, but the work hardening becomes excessive because the cold work degree is high, and then the artificial aging treatment step Even if it performs, softening of a structure | tissue will become inadequate and moldability will run short.

  The artificial aging treatment (5) is also called tempering, and is a heat treatment for imparting toughness to the aluminum alloy tube material. Formability is improved by increasing toughness. The heat treatment temperature is preferably 120 to 200 ° C. in terms of the precipitation process by artificial aging treatment, and particularly preferably 150 to 180 ° C. in terms of generating fine precipitates and further improving toughness. The heat treatment time is 2 to 24 hours, and after the heat treatment is completed, it is gradually cooled.

  Examples of the present invention will be described below in comparison with comparative examples. In all of the examples, evaluation was performed using a drawing tube of the same size. The evaluation of the present invention is not limited as long as the continuous drawing tube can be manufactured, and can be applied.

  The manufacturing method of the aluminum alloy pipe material which concerns on an Example and a comparative example is demonstrated. First, using JIS6063 alloy, with a mandrel extruded tube with a total length of 170m, an outer diameter of 50mm, and a wall thickness of 4mm as the base material, the first cold working is performed by a continuous drawing method using a continuous drawing machine. A tube (hereinafter referred to as BB drawn tube) was produced. In order to change the cross-sectional reduction rate of the final product, the BB drawn tube was produced in several sizes. In order to coil the BB drawn tube, winding was performed by aligned winding with a level winder. At this time, the winding length of each BB drawn tube was fixed. Thereafter, the coiled BB drawn tube was heat-treated at a predetermined solution temperature and a cooling rate. After the heat treatment, the second cold working is drawn with a continuous drawing machine (combined machine) while the coil is straightened, artificially aged at 150 ° C. for 13 hours, and test materials 1 to 7 for the mandrel tube Got. The test materials 1 to 4 as examples and the test materials 5 to 7 as comparative examples were 8 mm in outer diameter and 1 mm in thickness.

  Next, as a reference example, a method for manufacturing a conventional porthole tube corresponding to 6063-T83 will be described. First, using JIS6063 alloy, a porthole extruded tube having a total length of 4000 mm, outer diameters of 10 and 11.05 mm, and a wall thickness of 1.1 mm is drawn with a draw bench that is a general drawing method, and artificially processed at 150 ° C. for 13 hours. Aging treatment was performed to obtain test materials 8 and 9. The test materials 8 and 9 which are reference examples have an outer diameter of 8 mm and a wall thickness of 1 mm as in the above-described examples and comparative examples.

  About the said various test materials, the maximum pipe expansion rate was measured as a shaping | molding limit, and the mechanical property was investigated by evaluating U bend bendability. Table 1 shows the measurement and evaluation results. In addition, the cross-sectional reduction rate of the test materials 1 to 4 and 10 to 13 which are examples described in Tables 1 and 2 and the test materials 5 to 7 and 14 to 16 which are comparative examples is the second cold working. The cross-section reduction rate is shown.

Measurement of the maximum tube expansion rate: Place one end of the open end of the test material, which is a straight material cut to a length of 50 mm, at the tip of the conical die, and fix the test material perpendicularly to the conical die. Then, pressure is applied to the opening end from above by a hand press with a maximum load of 60 kgf, and the opening end is expanded by pushing the test material until cracking occurs in the opening end, and the diameter of the maximum diameter portion Was measured. The maximum tube expansion rate of each test material was measured with the difference between the diameter of the maximum diameter portion and the diameter before tube expansion processing being 100% in the test material 3 where the maximum tube expansion processing was completed.
U-bend bendability: A rotating pull bending method was used in which a test material cut to a length of 500 mm on a bending die was pressed with a holding die to bend the test material. The test material was bent at a constant bending speed, and the bending angle was 90 °. U-bend bendability is evaluated by observing the surface state of the outer R section, and processing that has a smooth surface without rough surface, and that can be processed and has rough or wrinkled surface. The thing which a crack generate | occur | produced was made into the crack.

  As shown in Table 1, the test material 8 of the reference example, which is a conventional porthole tube not subjected to solution treatment, had a maximum tube expansion rate of 80%. On the other hand, all of the test materials 1 to 4 as examples had a maximum tube expansion ratio of 90% or more, and a measured value equal to or higher than that of the test material 8 was obtained. About the porthole tube of the test material 9 of the reference example whose cross section reduction rate is higher than that of the test material 8, wrinkles are generated by the U-bend bending, and the maximum tube expansion rate is only 70%, which is higher than that of the test materials 1-4. The characteristics were inferior. Thus, all of the test materials 1 to 4 having a solution temperature of 500 to 530 ° C. and a cooling rate of 1.5 ° C./sec or more are maximum in comparison with the porthole tube of the reference example which is a conventional material. Formability equal to or better than that of a conventional porthole tube was obtained in that the expansion ratio and U-bend bending were equivalent or better.

  On the other hand, the test material 5 having a solution temperature of 500 ° C. and a cooling rate of 1.0 ° C./sec has a lower cross-sectional reduction rate than the test materials 1 to 4 of the examples, and the work hardening in the second cold drawing occurs much. As a result, the maximum tube expansion ratio was 80%, which was the same as that of the reference example, but wrinkles were generated by U-bending. The test material 6 having a solution temperature of 500 ° C. and a cooling rate of 0.5 ° C./sec had a low maximum value of 50%. Since the test materials 5 and 6 had a low cooling rate during the solution treatment and the solution formation was insufficient, it is considered that the formability was lowered as compared with the test materials 1 to 4 of the examples. Since the test material 7 had a cross-sectional reduction rate higher than that of the test materials 1 to 4 of the example and had a higher workability, the maximum tube expansion rate was only 30%, and wrinkles were generated in U-bend bending.

  Test materials 10 to 18 were produced in the same manner as test materials 1 to 9 described in Example 1, respectively, and subjected to molding for high-pressure piping. About these test materials 10-18, the mechanical property was investigated by measuring the total elongation after a process, evaluating a rolling workability by the surface state of a process part after a rolling process. Table 2 shows the measurement and evaluation results. Here, the high-pressure piping molding process is a molding process typified by pipe bending and a rolling process with high processing difficulty that requires terminal connection reliability, assuming actual automotive piping materials. Means.

Measurement of total elongation: It was carried out using a No. 11 test piece specified by seamless pipe JISH4080 specified in Z2241 (metal material tensile test method), and the total elongation was measured.
Rolling workability: Using a rolling test apparatus equipped with a die for grooved shape, the test material was rolled with the roll rotation speed, roll feed amount, and rolling pressure fixed. . Rolling workability is evaluated by observing the surface condition of the processed part, processing and satisfying the dimension and shape, and having a smooth surface without rough surface, and processing and satisfying the dimension and shape, but rough surface. Alternatively, those having wrinkles were roughened and processed, but those that did not satisfy the dimensional shape were determined to be defective in dimension, and those that cracked during processing were determined to be cracked.

  As shown in Table 2, the test material 17 of the reference example, which is a conventional porthole extruded tube not subjected to a solution treatment, had a total elongation of 15% and a good rolling process. On the other hand, all of the test materials 10 to 13 of the examples had a total elongation of 15% or more, and the rolling process was good. Compared with the test material 17, the same or better results were obtained. About the porthole pipe of the test material 18 of the reference example having a higher cross-sectional reduction rate than the test material 17, the total elongation is 14%, and cracks are generated during the rolling process. Compared with the characteristics. Thus, also about the test material which performed the shaping | molding process for high voltage | pressure piping, all the test materials 10-13 of the Example which are solution treatment temperature 500-530 degreeC and the cooling rate 1.5 degree C / sec or more, Formability equal to or better than that of the porthole pipe was obtained in that the total elongation and rolling processability were equivalent or better compared to the porthole pipe of the reference example which is a conventional material.

  On the other hand, the test material 14 having a solution temperature of 500 ° C. and a cooling rate of 1.0 ° C./sec had a total area of only 8% although the cross-sectional reduction rate was lower than that of the test materials 10 to 13 of the examples. The test material 15 having a solution temperature of 500 ° C. and a cooling rate of 0.5 ° C./sec had a low total elongation of 6%. Since the test materials 14 and 15 had a slow cooling rate during solution treatment and solution formation was insufficient, it is considered that the moldability was lowered as compared with the test materials 10 to 13 of the examples. Since the test material 16 had a cross-sectional reduction rate higher than that of the test materials 10 to 13 of the example and had a strong workability, the total elongation was a low value of 6%, and cracking occurred in the rolling process.

  Thus, according to the present invention, a seamless aluminum alloy tube having a dimensional accuracy and high formability equivalent to or higher than that of a porthole tube equivalent to 6063-T83, no welded portion, and high quality reliability can be obtained at low cost. Can be provided.

  According to the method for producing an aluminum alloy tube of the present invention, an aluminum alloy tube that is thin and has excellent strength and formability can be produced from a mandrel extruded tube having no welded portion and high quality reliability. It is highly useful in the field of automobiles that use complicatedly processed piping under high pressure conditions.

Claims (3)

A mandrel extruded tube of JIS6063 aluminum alloy is subjected to a first cold working with a cross-section reduction rate of 70% or more by a continuous drawing method, and the obtained first drawn tube is subjected to a solution treatment, and then a cross-section reduction rate of 10 to 40%. A method for producing an aluminum alloy pipe material, characterized in that the second cold working is performed by drawing, and then an artificial aging treatment is performed.   2. The method for producing an aluminum alloy pipe according to claim 1, wherein the first drawn pipe is continuously coiled by a coil before the solution treatment. 3.   The method for producing an aluminum alloy pipe according to claim 1, wherein a cooling temperature of the solution treatment is 1.5 ° C / second or more.