A method for processing large-diameter thin-walled aluminum alloy tubing of 2A14-T4 for aerospace applications

Abstract

This invention belongs to the field of high-precision aluminum alloy tube processing technology, specifically relating to a processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubes. The method includes: preparing an ingot; subjecting the ingot to a primary extrusion, specifically: the extrusion cylinder temperature is specified as 410-430℃, the die heating temperature in the bogie furnace is 430-450℃, the billet heating temperature is 410-430℃, and the extrusion speed is 0.45-0.75 mm / s, to produce a first extruded tube blank; performing full annealing on the first extruded tube blank and machining the outer skin and boring the inner hole to obtain a second extruded ingot, wherein the annealing temperature is 390-410℃ and the holding time is 1-3 hours; subjecting the second extruded ingot to a secondary hot extrusion, specifically: the second extruded ingot is extruded at an extrusion speed of 0.25-0.75 mm / s, to produce a second extruded tube blank; pickling and repairing the second extruded tube blank to obtain a cold-drawn tube blank; performing multiple cold-drawing deformation cycles on the cold-drawn tube blank to obtain a tube; and solution treating and finishing the tube to obtain the finished tube.

Description

Technical Field

[0001] This invention belongs to the field of high-precision aluminum alloy tube processing technology, specifically relating to a processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubes. Background Technology

[0002] Aluminum alloys are the preferred material for lightweighting aircraft and spacecraft, and are widely used in the aerospace industry. The main characteristics of aluminum alloy tubing for aerospace applications are high surface quality requirements, stringent dimensional accuracy requirements, and strict guarantees of microstructure and mechanical properties.

[0003] 2A14 aluminum alloy is a heat-treatable aluminum alloy with Cu and Mg as the main alloying elements. It is widely used in key components such as rocket fuel tubes in the aerospace industry. Currently, many aluminum alloy processing plants have low yield rates and poor surface quality in the production of large-diameter, thin-walled aluminum alloy tubes, making it difficult to meet national military standards. Summary of the Invention

[0004] Purpose of the invention: To provide a processing method for large-diameter, thin-walled, high-precision aluminum alloy tubes for aerospace applications, so as to improve the yield of large-diameter, thin-walled 2A14 aluminum alloy tubes and the quality of the inner and outer surfaces of the tubes.

[0005] Technical solution:

[0006] A method for processing large-diameter thin-walled aluminum alloy tubing of 2A14-T4 for aerospace applications includes:

[0007] Preparation of ingots;

[0008] The ingot is extruded once, specifically: the extrusion cylinder temperature is specified as 410-430℃, the die heating temperature in the bogie furnace is 430-450℃, the billet heating temperature is 410-430℃, and the extrusion speed is 0.45-0.75mm / s, to produce the first extruded tube billet;

[0009] The first extrusion billet is subjected to full annealing and the outer skin is machined and the inner hole is bored to obtain a second extrusion billet. The annealing temperature is 390-410℃ and the holding time is 1-3h.

[0010] The secondary extrusion billet is subjected to secondary hot extrusion, specifically: the secondary extrusion billet is extruded at a speed of 0.25-0.75 mm / s to produce a secondary extrusion tube blank;

[0011] The secondary extrusion tube blank is pickled and repaired to obtain a cold-drawn tube blank.

[0012] The tube is obtained by performing multiple cold drawing deformation cycles on the cold-drawn tube blank;

[0013] The pipe material is solution treated and finished to obtain the finished pipe material.

[0014] Furthermore, the cold-drawn tube blank is subjected to multiple cold-drawing deformation cycles to obtain the tube material, specifically including:

[0015] Install the drawing die on the cold drawing equipment and the drawing head on the mandrel; operate the chuck to move forward and start the cold drawing. The cold drawing adopts the fixed short mandrel drawing method, and the deformation of each cold drawing is controlled at 10%-20%.

[0016] After cold drawing, use a hydrocarbon solution to clean the lubricating oil from the inner and outer surfaces of the pipe.

[0017] After degreasing and cleaning, roller straightening is performed;

[0018] After roller straightening, the product undergoes annealing treatment. The intermediate annealing temperature is 340-395℃, the holding time is 40-130min, and the cooling method is air cooling.

[0019] After annealing, pickling or sanding is performed on the surface of the pipe to remove the oxide scale generated on the inner and outer surfaces of the pipe due to annealing.

[0020] Furthermore, after degreasing and cleaning, roller straightening is performed, specifically using a 10-roll hyperbolic roller straightener, and the straightness of the pipe reaches 2mm / m after straightening.

[0021] Furthermore, the pipe is subjected to solution treatment, specifically including: hoisting the pipe onto a heat treatment rack, heating it to 480-490℃, holding it at that temperature for 30-70 minutes, and then quickly immersing it in a water tank, requiring a quenching transfer time of ≤10 seconds.

[0022] Further finishing of the pipes includes: air drawing, tension straightening, straightness measurement, bending straightening, rounding and repair of damage, wherein air drawing does not require pulling the mandrel.

[0023] Further, the preparation of the billet includes:

[0024] Hot-top casting method is adopted: aluminum and 2A14 primary scrap are used, Mn and Ti are added in the form of intermediate alloys, and Ti element is added after the furnace using Al-Ti-B wire; the refining process is carried out for 10-15 minutes in a melting furnace and a holding furnace respectively using a mixture of nitrogen and chlorine gas. The refining process must be smooth and without dead corners, and finally cast into ingots.

[0025] After casting, the ingot is subjected to homogenization annealing.

[0026] After homogenization annealing, the ingot is peeled and drilled. The outer skin of the machine is controlled to be 2-5mm on one side of the machine frame. The flaw detection level reaches A grade, the structure is uniform, and finally the extruded billet is produced.

[0027] Furthermore, after casting, the ingot is subjected to homogenization annealing, specifically including: two-stage heat preservation: the first stage temperature is 450℃, and the heat preservation time is 4 to 7 hours; the second stage temperature is 480 to 500℃, and the heat preservation time is 27 to 35 hours.

[0028] Furthermore, after homogenizing the ingot with annealing, the process also includes: performing 100% Class A flaw detection on the ingot.

[0029] Beneficial effects:

[0030] The processing method for this type of aerospace-grade 2A14-T4 high-precision aluminum alloy tubing involves precise control of alloy composition; determination of extrusion billet specifications; control of deformation amount in each pass; surface treatment and tubing finishing processes; and regulation of microstructure through heat treatment. The resulting tubing achieves a precision of ±10% tmm, exhibiting excellent overall performance and superior surface quality.

[0031] By adjusting the casting composition of the billet, performing two-stage extrusion, and multi-stage cold drawing, along with surface treatment and heat treatment of intermediate-sized tubes, aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubes are produced. These tubes possess high dimensional accuracy, excellent surface quality, and a good balance between process performance and mechanical properties. Stable mass production is possible, and the yield rate for subsequent tube manufacturing can reach over 92%. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0033] This invention relates to a method for extruding and cold drawing aluminum alloy tubing for aerospace applications. Currently, many aluminum alloy processing plants are producing large-diameter, thin-walled aluminum alloy tubing with low yields and poor surface quality.

[0034] This invention provides a manufacturing method for 2A14 cold-drawn tubing for aerospace applications, which solves the problems of poor surface quality, low dimensional accuracy, poor mechanical properties, and easy cracking and low yield in most 2A14 aluminum alloy tubing.

[0035] This invention provides a technical solution: a method for processing large-diameter thin-walled aluminum alloy tubing (2A14-T4) for aerospace applications, comprising the following steps:

[0036] (1) Ingot preparation

[0037] (2) Ingot machining and flaw detection

[0038] (3) One-time extrusion blanking

[0039] (4) One-time extrusion billet mill

[0040] (5) Secondary extrusion

[0041] (6) Heat treatment, repair and straightening of extruded tube blanks

[0042] (7) Cold drawing deformation cycle

[0043] (8) Solution treatment of finished product

[0044] (9) Finishing of finished products

[0045] (10) Inspect the quality of finished pipes

[0046] The composition of the ingot prepared in this way is as follows:

[0047]

[0048] (1) Hot-top casting is used during casting. Pure Al and 2Al4 grade 1 scrap can be used, but composite materials cannot be used. Mn and Ti are added as intermediate alloys, and Ti is added after the furnace using Al-Ti-B wire. Refining is performed for 10-15 minutes using a nitrogen and chlorine mixture in a melting furnace and a settling furnace. The refining process must be smooth and without dead zones. The final casting is... Casting ingots.

[0049] (2) After casting, the ingot is subjected to homogenization annealing using a two-stage heat treatment process. The first stage temperature is 450℃, and the heat treatment time is 4-7 hours; the second stage temperature is 480-500℃, and the heat treatment time is 27-35 hours. The ingot is subjected to 100% Class A flaw detection.

[0050] After homogenization annealing, the ingot is machined and bored, with the machined outer skin controlled to have a single-sided frame beam of 2-5mm. The flaw detection level reaches Grade A, and the microstructure is uniform. Finally, an extruded billet is produced.

[0051] (3) The ingot is extruded once using a 3600T horizontal reverse double-acting hot extrusion press. The extrusion cylinder temperature is set at 410-430℃, the die heating temperature in the trolley furnace is 430-450℃, and the billet heating temperature is 410-430℃. The extrusion speed is 0.45-0.75mm / s, producing... Larger diameter thick-walled tube blanks.

[0052] When hot extruding aluminum alloy tubes, the selection of billet preheating temperature generally follows these principles: ① The selected billet preheating temperature range should minimize the metal's deformation resistance; ② Within this temperature range, metal oxidation is not severe; ③ Ensure that the metal has good plasticity within the selected billet preheating temperature range, and that the extruded thin-walled tube has a relatively uniform structure and good performance.

[0053] Extrusion speed also significantly affects the uniformity of billet deformation, thermal effects, and the microstructure, mechanical properties, and surface roughness of extruded thin-walled tubes during hot extrusion. In actual production, a higher extrusion speed can effectively reduce heat transfer between the billet and the die, piercing needle, and extrusion cylinder during hot extrusion, thus improving the uniformity of billet temperature distribution. It also reduces the coefficient of friction, lowering the billet's deformation resistance and facilitating hot extrusion. However, excessively high extrusion speeds can lead to excessively rapid billet deformation. The heat generated during deformation can cause the die surface temperature to rise too quickly, resulting in reduced die strength and fatigue resistance, thus shortening the die's service life. Extruded thin-walled tubes may also exhibit cracks and orange peel-like defects. The principle for determining the extrusion speed is to maximize production efficiency while ensuring product quality and equipment capacity (tonnage, speed), but excessively high extrusion speeds can easily cause cracks.

[0054] (4) Then perform full annealing at a temperature of 390-410℃ for 1-3 hours.

[0055] The outer surface of the extruded tube blank is machined again, the inner hole is bored, and defects on the inner and outer surfaces are removed.

[0056] (5) Then, a 2000T vertical forward double-acting hot extrusion press is used to perform a secondary extrusion on the primary extruded billet. The extrusion cylinder temperature is specified as 410-430℃, the die heating temperature in the trolley furnace is 430-450℃, the billet heating temperature is between 410-430℃, and the extrusion speed is 0.25-0.75mm / s. The resulting product... Extruded tube blanks.

[0057] (6) Before cold drawing, extrusion defects on the inner and outer surfaces of the tube must be removed; otherwise, during the cold drawing process, a continuous cold drawing scratch will be generated along the tube axis starting from the defect. The removal method involves pickling the extruded tube blank and repairing the scratch with an angle grinder. After removing the extrusion scratches and other defects on the inner and outer surfaces of the extruded tube blank, it is then subjected to necking or twisting treatment.

[0058] (7) Perform multiple cold drawing deformation cycles. The process of a single cycle is as follows:

[0059] Before cold drawing, the inner surface of the pipe is lubricated with 38# wear-resistant hydraulic oil. First, the drawing outer die is installed on the equipment and the drawing mandrel is installed on the mandrel. The equipment clamps the constricted or twisted section of the pipe, and the clamps are moved forward to start cold drawing. The cold drawing adopts the fixed short mandrel drawing method.

[0060] The tube blank undergoes diameter and wall reduction through the gap between the die and the mandrel. The deformation amount in each cold drawing pass is controlled between 10% and 20%. If the deformation amount is too large (>20%), the friction between the tube and the die will be very intense, easily causing defects such as wrinkles and cracks, and even tube breakage. If the deformation amount is too small (<10%), the diameter and wall reduction in each cold drawing pass will be too small, affecting production efficiency.

[0061] After cold drawing, use a hydrocarbon solution to clean the lubricating oil on the inner and outer surfaces of the pipe.

[0062] To avoid strength reduction after heat treatment and the appearance of straightening marks during straightening, roller straightening is performed after degreasing and cleaning using a 10-roll hyperbolic roller straightener. The straightened pipe achieves a straightness of 2 mm / m.

[0063] After roller straightening, intermediate annealing is performed. The intermediate annealing temperature is 340-395℃, the holding time is 40-130min, and the cooling method is air cooling.

[0064] After annealing, the pipe surface is pickled or sanded to remove the oxide scale generated by annealing on the inner and outer surfaces of the pipe. At the same time, defects generated in the previous cold drawing are repaired to avoid cold drawing damage caused by surface defects affecting the lubrication of the contact between the pipe and the mold during the next cold drawing.

[0065] Repeat small cycles of cold drawing, degreasing and cleaning, roller straightening, annealing, and surface treatment. Gradually reduce the wall size and diameter of the pipe until it reaches the final dimensions before finishing.

[0066] (8) After the final drawing, solution treatment is performed. The pipe is hoisted on the heat treatment rack. The solution temperature of the finished product is 490-510℃, the holding time is 45-60min, and the quenching transfer time is ≤10s.

[0067] (9) After solution treatment, air drawing is performed. The processing method is the same as that for cold drawing, but no drawing mandrel is required. This process is to further reduce the outer diameter of the pipe and increase the internal stress of the pipe to improve the mechanical properties of the finished pipe.

[0068] After the air drawing is completed, the constricted or twisted section is cut off, and the pipe is stretched and straightened to release the internal stress of the pipe, improve the straightness of the pipe, and improve the mechanical properties of the pipe.

[0069] The straightness of the pipe is measured, and the pipe is bent and straightened according to the measurement data. The three-point bending method is used to ensure that the straightness of the finished pipe is less than or equal to 0.6 mm / m.

[0070] The outer diameter of the pipe is measured using an outside micrometer. Based on the distribution of outer diameter values ​​and the required outer diameter tolerance range for the finished pipe, a rounding plan is developed. A bench vise is used to clamp the points where the outer diameter exceeds the tolerance, causing plastic deformation to bring the outer diameter of the finished pipe into compliance with the tolerance specifications.

[0071] Visually inspect the inner and outer surfaces of the pipe for any defects that do not meet standards. Remove these defects using an angle grinder, ensuring the minimum wall thickness tolerance is maintained. After removal with the angle grinder, continue polishing with polishing cotton until the surface roughness of the repaired area meets the standards.

[0072] The dimensional accuracy, performance testing, and surface quality requirements for the finished pipes mentioned above refer to:

[0073] Dimensional accuracy: Outer diameter tolerance reaches D±0.41mm, and wall thickness tolerance can reach ±10%tmm (D is the outer diameter, t is the wall thickness).

[0074] Room temperature mechanical properties: Under T4 conditions, tensile strength Rm≥370MPa; specified non-proportional tensile strength Rp0.2≥205MPa; elongation after fracture≥10%.

[0075] Surface Quality: The inner and outer surfaces of the pipes should be smooth and clean, free from cracks, bubbles, peeling, foreign inclusions, corrosion spots, delamination, and folds. Minor defects such as blemishes, dents, scratches, abrasions, and graphite stains are permissible, but their depth must not exceed the negative wall thickness deviation and must ensure the minimum thickness. However, dents must not exceed the negative diameter deviation. The permissible surface defect area should not exceed 3% of the surface area. Longitudinal and transverse scratches on the pipe surface are permissible with a depth not exceeding 0.05 mm. Oxidation discoloration, non-rough black and white spots, and straightening rings and spirals that do not affect the pipe wall thickness are permissible. Slight longitudinal wrinkles are permissible on the inner surface of the pipe.

[0076] Implementation Example 1: Pipe cold drawing process

[0077]

[0078] Solution treatment of intermediate and finished products: intermediate annealing temperature: 340~395℃, holding time: 40-130min, cooling method: air cooling; solution treatment temperature of finished products: 490~510℃, holding time: 45-60min, quenching transfer time ≤10s.

[0079] Finished product mechanical properties: tensile strength Rm≥370MPa; specified non-proportional tensile strength Rp0.2≥205MPa; elongation after fracture≥10%.

[0080] Surface treatment: The extruded tube blank undergoes external machining and internal boring. The machining allowance on one side is 5mm, and the boring allowance is 3mm.

[0081] The yield rate of this type of pipe produced subsequently reached over 90%.

[0082] Example 2: Cold drawing process for aluminum alloy tubes

[0083]

[0084] Solution treatment of intermediate and finished products: intermediate annealing temperature: 340~395℃, holding time: 45-60min, cooling method: air cooling; solution treatment temperature of finished product: 495℃, holding time: 45-60min, quenching transfer time ≤10s.

[0085] Finished product mechanical properties: tensile strength Rm≥370MPa; specified non-proportional tensile strength Rp0.2≥205MPa; elongation after fracture≥10%.

[0086] Surface treatment: The extruded tube blank undergoes external machining and internal boring. The machining allowance on one side is 5mm, and the boring allowance is 3mm.

[0087] The yield rate of this type of pipe produced subsequently reached over 90%.

[0088] All standard parts used in this invention can be purchased from the market, and irregular parts can be customized according to the description in the specification. The specific connection methods of each part adopt conventional methods such as bolts, rivets, and welding that are mature in the prior art. The machinery, parts and equipment adopt conventional models in the prior art. In addition, the circuit connection adopts conventional connection methods in the prior art, which will not be described in detail here. The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0089] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing large-diameter thin-walled aluminum alloy tubing of 2A14-T4 for aerospace applications, characterized in that, include: Preparation of ingots; The ingot is extruded once, specifically: the extrusion cylinder temperature is specified as 410-430℃, the die heating temperature in the bogie furnace is 430-450℃, the billet heating temperature is 410-430℃, and the extrusion speed is 0.45-0.75mm / s, to produce the first extruded tube billet; The first extrusion billet is subjected to full annealing and the outer skin is machined and the inner hole is bored to obtain a second extrusion billet. The annealing temperature is 390-410℃ and the holding time is 1-3h. The secondary extrusion billet is subjected to secondary hot extrusion, specifically: the secondary extrusion billet is extruded at a speed of 0.25-0.75 mm / s to produce a secondary extrusion tube blank; The secondary extrusion tube blank is pickled and repaired to obtain a cold-drawn tube blank. The process involves multiple cold drawing deformation cycles on a cold-drawn tube blank to obtain the tube material. Specifically, this includes: installing a drawing die on the cold drawing equipment and a drawing mandrel on the mandrel; advancing the chuck to begin cold drawing, using a fixed short mandrel drawing method, with the deformation amount controlled at 10%-20% per pass; cleaning the lubricating oil on the inner and outer surfaces of the tube with a hydrocarbon solution after cold drawing; straightening the tube by rollers after degreasing and cleaning; annealing after roller straightening, with an intermediate annealing temperature of 340~395℃, a holding time of 40-130min, and air cooling; after annealing, pickling or sanding the tube surface to remove the oxide scale generated on the inner and outer surfaces of the tube due to annealing. The pipe material is solution treated and finished to obtain the finished pipe material.

2. The processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, After degreasing and cleaning, the pipe is straightened by roller straightening, specifically by using a 10-roll hyperbolic roller straightening machine. After straightening, the straightness of the pipe reaches 2mm / m.

3. The processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, The solution treatment of the pipes includes: hoisting the pipes onto the heat treatment rack, heating them to 480~490℃, holding them at that temperature for 30min~70min, and then quickly immersing them in a water tank, requiring a quenching transfer time of ≤10s.

4. The processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, The finishing process for the pipes includes: air drawing, tension straightening, straightness measurement, bending straightening, rounding and repair of defects. Air drawing does not require pulling the mandrel.

5. The processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, The preparation of billets specifically includes: Hot-top casting method is adopted: aluminum and 2A14 primary scrap are used, Mn and Ti are added in the form of intermediate alloys, and Ti element is added after the furnace using Al-Ti-B wire; the refining process is carried out for 10-15 minutes in a melting furnace and a holding furnace respectively using a mixture of nitrogen and chlorine gas. The refining process must be smooth and without dead corners, and finally cast into ingots. After casting, the ingot is subjected to homogenization annealing. After homogenization annealing, the ingot is peeled and drilled. The outer skin of the machine is controlled to be 2-5mm on one side of the machine frame. The flaw detection level reaches A grade, the structure is uniform, and finally the extruded billet is produced.

6. The processing method for aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, After casting, the ingot is subjected to homogenization annealing, which includes two-stage heat treatment: the first stage temperature is 450℃ and the heat treatment time is 4~7h; the second stage temperature is 480~500℃ and the heat treatment time is 27~35h.

7. The method for processing aerospace-grade 2A14-T4 large-diameter thin-walled aluminum alloy tubing according to claim 1, characterized in that, After homogenization annealing of the ingot, the process also includes: 100% Class A flaw detection of the ingot.

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