Aluminum alloy thick plate single-shaft-shoulder stirring head and manufacturing and welding method thereof

Abstract

The invention belongs to the technical field of aluminum alloy solid phase welding, and particularly relates to an aluminum alloy thick plate single-shaft-shoulder stirring head and a manufacturing and welding method thereof. Comprising a clamping handle, a stirring needle and a shaft shoulder, and two annular inner grooves are formed in the bottom of the shaft shoulder around the center; the stirring needle is integrally conical, the cross section of the stirring needle is of a hexagonal structure, and the hexagonal structure is formed by alternately arranging planes and cambered surfaces; the side walls of the three cambered surfaces of the stirring needle are provided with conical threads, and the side walls of the three planes are smooth surfaces; an aluminum alloy plate with the thickness of 20 mm is adopted for welding, and the downward rolling speed, the rotating speed and the welding speed of a stirring head are determined; continuous and stable welding of the butt joint of the thick aluminum alloy plate with the thickness being 15 mm or above can be achieved; the problems that holes, flashes and burrs exist in welding seams of aluminum alloy thick plates are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy solid phase welding, and specifically relates to an aluminum alloy thick plate single-shaft shoulder stirring head and a welding method thereof. Background Art

[0002] Friction stir welding technology is increasingly used in aluminum alloy welding, and high-quality and stable welding of aluminum alloy thick plates is still a difficult problem in welding production. Friction stir welding of aluminum alloy thick plates relies on the local friction between the stirring head and the material to be welded to generate heat to soften the material. The friction heat between the stirring head and the material to be welded will drive the softened metal material to undergo plastic flow, and the plastic deformation of the metal material will also generate heat. The metal material undergoing plastic flow is wrapped and squeezed by the shoulder behind the stirring head to form a weld. A reasonable stirring head structure can provide sufficient heat input to allow the material to flow and mix fully, which is the key to obtaining defect-free high-quality welds. Controlling the heat generated during the welding process and promoting the flow of materials during the welding process are the purpose of improving welding quality and optimizing the welding process. Optimizing and improving the stirring head structure is a strategy with minimal changes to the welding process, the lowest cost, and significant results.

[0003] The existing friction stir welding process and stirring head are suitable for welding aluminum alloy plates with smaller thickness (usually less than 10mm in thickness). However, for thicker aluminum alloy plates (more than 15mm in thickness), due to the influence of the strength, wear resistance, fracture toughness and thickness of the materials to be welded, the stirring head cannot exert its welding capacity, resulting in defects such as holes, flash and burrs in the weld. Summary of the invention

[0004] The present invention overcomes the shortcomings of the prior art and proposes a single-axis shoulder stirring head for thick aluminum alloy plates and a welding method thereof; the continuous and stable welding of butt joints of aluminum alloy plates with a thickness of more than 15 mm can be achieved. The present invention is achieved through the following technical solutions: A single-shoulder stirring head for aluminum alloy thick plate, comprising a clamping handle, a stirring needle and a shoulder, the clamping handle is connected to a stir friction welding device, a shoulder is provided at the bottom of the clamping handle, and the center of the bottom of the shoulder is connected to the root of the stirring needle; two annular inner grooves are provided around the center of the bottom of the shoulder; the stirring needle is tapered as a whole, and the cross-section of the stirring needle is a hexagonal structure, and the hexagonal structure is an alternating arrangement of plane arc surfaces; the side walls of the three arc surfaces of the stirring needle are provided with conical threads, and the side walls of the three planes are smooth surfaces.

[0005] Preferably, the material is die steel 4Cr5MoSiV1.

[0006] Preferably, the diameter of the shoulder is 30-34 mm.

[0007] Preferably, the root diameter of the stirring needle is 15-18 mm.

[0008] A method for manufacturing a single-shaft shoulder stirring head for an aluminum alloy thick plate comprises the following steps: 1) Rough turning; 2) Heat treatment: The quenching and tempering process is divided into two steps: quenching and tempering. During the quenching process, the heating temperature is 520±10℃, and the heat preservation time is 90-120min. The heating temperature is increased to 820±10℃, and the heat preservation time is 90-120min. The heating temperature is increased to 1020±10℃, and the heat preservation time is 120-150min. Then the oil cooling is carried out for 7-12h. Tempering is carried out within 2h after quenching. The tempering temperature is 560±10℃, and the heat preservation time is 150-180min.

[0009] 3) Forming size processing: The finishing process processes two annular inner grooves of the shaft shoulder and the tapered thread of the side wall of the stirring needle; 4) Mill the three planes of the stirring needle.

[0010] Preferably, a 1.5 mm margin is left on one side during rough turning, and hardness testing is performed after rough turning.

[0011] More preferably, the heat treatment is performed in a vacuum furnace.

[0012] Based on a welding method of a single-axis shoulder stirring head for aluminum alloy thick plates, an aluminum alloy plate with a thickness of 20 mm is used for welding. The stirring head plunge speed is 12-18 mm / min; the rotation speed is 300-340 r / min; and the welding speed is 90-120 mm / min.

[0013] Preferably, the stirring head plunge speed is 15mm / min; the rotation speed is 320r / min; and the welding speed is 100mm / min.

[0014] Preferably, the dwell time is 2 s.

[0015] The beneficial effects of the present invention compared with the prior art are as follows: The structure of the stirring head shoulder and the stirring needle directly affects the heat input of the weld and the flow behavior of the plasticized material in the stirring zone. A reasonable stirring head structure can broaden the process parameter range of friction stir welding, improve weld strength and product qualification rate. Suitable stirring head materials and heat treatment processes can extend the service life of the stirring head, improve the stability of the welding process, and reduce welding production costs.

[0016] In the present invention, for 20mm thick aluminum alloy friction stir welding butt joints, hot working die steel materials are used for the structural design and production of single-axis shoulder stirring heads, welding parameter debugging and test verification are carried out, the rotation speed and welding speed fluctuations during the welding process are stable, the flash on both sides are continuous, the pressure feedback is normal, the welding life of the stirring head meets the welding production requirements, and the continuous and stable welding of long welds can be achieved. The quality of the welded joint can meet the requirements of Class I. According to welding test verification and life test verification, at a certain rotation speed and welding speed, the continuous and stable welding length of the stirring head is not less than 30 meters.

[0017] The present invention adopts a concave shoulder to increase the friction contact area and improve the heat input, and at the same time, the plasticized metal is gathered together under the wrapping of the shoulder, and the cavity generated when the stirring head moves is filled under the traction of the stirring needle, which can reduce the generation of flash. The present invention adopts a double-circular concave shoulder. During the friction stir welding process, the shoulder of this structure is in close contact with the surface of the weldment, providing sufficient wrapping for the plasticized weld metal, and providing sufficient axial pressure, so that the plasticized metal cannot overflow the weld, and cools as the weld moves to form a welded joint.

[0018] During the friction stir welding process, the stirring needle penetrates deep into the welded material and generates intense friction stirring with the welded material. As the spindle moves, the plastically deformed metal in front of the welded workpiece is brought to the rear of the stirring needle by the friction rotation of the stirring head, filling the instantaneous cavity generated by the forward movement of the stirring head. The morphology of the stirring needle can directly affect the fluidity and heat generation efficiency of the plastically deformed material of the welded workpiece. The use of a three-plane stirring needle and a conical thread stirring needle structure can significantly improve the morphology of the cross-section of the welded joint. The size of the welded joint in the material thickness direction shows a uniform transition change trend, which is conducive to ensuring the uniformity and continuity of the mechanical properties of the welded joint.

[0019] The present invention uses a mold steel grade 4Cr5MoSiV1, which implements the standard GB / T1299, has a medium chromium content, contains alloy elements tungsten, molybdenum, and vanadium that are easy to form carbides, and has good resistance to high-temperature softening. The alloy has a low carbon content and a low total alloy content, which can improve the toughness at a working hardness of 40 to 55HRC, has a high tungsten content and molybdenum content, which can improve the thermal strength, but its toughness is slightly reduced; the vanadium element can improve the corrosion resistance at high temperatures; the silicon element can improve the oxidation resistance at temperatures below 800°C. The material has high hardenability and high toughness, excellent thermal cracking resistance, can be water-cooled during the process, has medium wear resistance, small heat treatment deformation, and medium and high cutting processability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a front view of the single-shoulder stirring head for aluminum alloy thick plate of the present invention; Figure 2 This is a real photo of the aluminum alloy thick plate single-shaft shoulder stirring head before machining the stirring pin plane of the present invention; Figure 3 This is a real photo of the stirring pin of the present invention before the stirring pin plane is processed; Figure 4 This is a real photo of the bottom of the stirring needle of the present invention; Figure 5 This is a metallographic diagram of a cross section of a joint in the embodiment; Figure 6 It is a three-dimensional diagram of the stirring needle and the shoulder described in the present invention.

[0021] In the figure: 1. Clamping handle; 2. Stirring needle; 3. Shoulder; 4. Annular inner groove. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings, but the scope of protection is not limited thereto.

[0023] Example 1 See also Figures 1 to 6 This embodiment provides a single-shoulder stirring head for thick aluminum alloy plates and a manufacturing and welding method thereof; The single-shoulder stirring head for thick aluminum alloy plate includes a clamping handle 1, a stirring needle 2 and a shoulder 3 of an integrated structure. The clamping handle 1 is connected to the friction stir welding equipment, and the stirring head is driven to move by the rotation of the equipment. A shoulder 3 is provided at the bottom of the clamping handle 1, and the center of the bottom of the shoulder 3 is connected to the root of the stirring needle 2; two annular inner grooves 4 are provided around the center of the bottom of the shoulder 3; the stirring needle 2 is conical as a whole, and the cross-section of the stirring needle 2 is a hexagonal structure, and the hexagonal structure is an alternating arrangement of plane arc surfaces; the side walls of the three arc surfaces of the stirring needle 2 are provided with conical threads, and the side walls of the three planes are smooth surfaces. The stirring head is made of die steel 4Cr5MoSiV1.

[0024] During the working process of the stirring head, the stirring head is subjected to a large forging force. The melting point of aluminum alloy is 660°C. During the stir friction welding process, the plasticizing temperature of the material is generally around 500°C. In the present invention, hot working die steel 4Cr5MoSiV1 is selected as the stirring head material. The material has the characteristics of thermal strength, high hardness, wear resistance, creep resistance, impact resistance, easy processing, material inertia, excellent friction effect, etc. It has the ability to withstand dynamic loads without breaking at high temperatures and is suitable for stir friction welding conditions. The stirring needle 2 is located at the end of the stirring head and acts on the workpiece during welding to break the metal-based oxide film and drive the metal to flow. The shoulder 3 is connected to the root of the stirring needle 2 and contacts and acts on the surface of the workpiece during welding. The shoulder 3 contacts and rubs with the material to be welded to provide sufficient heat generation. At the same time, the wrapping effect of the shoulder makes it difficult for the plasticized metal to overflow, and the material to be welded forms a forging structure through the action of the downward pressure. The main parameters of the stirring head are summarized in Table 1.

[0025] In this embodiment, the concave shoulder 3 is used to increase the friction contact area and improve the heat input. At the same time, the plasticized metal is gathered together under the wrapping of the shoulder 3, and the cavity generated when the stirring head moves is filled under the traction of the stirring needle 2, which can reduce the generation of flash. The present invention adopts a double-circular concave shoulder 3, and the diameter of the shoulder 3 is 32mm. During the friction stir welding process, the shoulder 3 of this size is in close contact with the surface of the weldment, providing sufficient wrapping for the plasticized weld metal, and at the same time providing sufficient axial pressure, so that the plasticized metal cannot overflow the weld, and cools as the weld moves to form a welded joint.

[0026] During the friction stir welding process, the stirring needle 2 penetrates deep into the material to be welded, and a violent friction stirring action occurs with the material to be welded. As the spindle moves, the plastically deformed metal in front of the welded workpiece is brought to the rear of the stirring needle 2 by the friction rotation of the stirring head, filling the instantaneous cavity generated by the forward movement of the stirring head. The morphology of the stirring needle 2 can directly affect the fluidity and heat generation efficiency of the plastically deformed material of the welded workpiece. The use of a three-plane stirring needle and a conical thread stirring needle structure can significantly improve the morphology of the cross-section of the welded joint. The size of the welded joint in the material thickness direction shows a uniform transition change trend, which is conducive to ensuring the uniformity and continuity of the mechanical properties of the welded joint.

[0027] Single-axis shoulder stir friction welding is used to weld 20mm thick 5A06 aluminum alloy. The material of the stirring head must comprehensively consider the strength, wear resistance, fracture toughness, creep and creep fatigue, thermal fatigue characteristics, machinability, oxidation resistance, whether it reacts with the workpiece, service life, etc. The thermal conductivity of the stirring head will also affect the distribution of the temperature field during the process and thus affect the welding quality.

[0028] The present invention uses a mold steel grade 4Cr5MoSiV1, which implements the standard GB / T1299, has a medium chromium content, contains alloy elements tungsten, molybdenum, and vanadium that are easy to form carbides, and has good resistance to high-temperature softening. The alloy has a low carbon content and a low total alloy content, which can improve the toughness at a working hardness of 40 to 55HRC, has a high tungsten content and molybdenum content, which can improve the thermal strength, but its toughness is slightly reduced; the vanadium element can improve the corrosion resistance at high temperatures; the silicon element can improve the oxidation resistance at temperatures below 800°C. The material has high hardenability and high toughness, excellent thermal cracking resistance, can be water-cooled during the process, has medium wear resistance, small heat treatment deformation, and medium and high cutting processability.

[0029] Example 2 See also Figures 1 to 6 , this embodiment proposes a method for manufacturing a single-shoulder stirring head for an aluminum alloy thick plate as described in Embodiment 1; The stirring head is a rotary structure with a hardness of no less than 45HRC. The hardness increases after heat treatment, and the difficulty of removing the excess increases. When planning the process route, rough turning is performed to remove most of the excess before heat treatment, and then heat treatment is performed to obtain the required hardness, and then the shoulder part and the stirring needle part are processed to the required size. The manufacturing process route of the stirring head: rough turning → tempering → hardness testing (HRC48~55) → fine turning → milling → marking and storage.

[0030] 1. Leave 1.5mm margin on one side during rough turning.

[0031] 2. Heat treatment: The quenching and tempering process is divided into two steps, quenching and tempering, which are completed in a vacuum furnace. During the quenching process, the heating temperature is 520±10℃, and the insulation time is 90-120min. The heating temperature is increased to 820±10℃, and the insulation time is 90-120min. The heating temperature is increased to 1020±10℃, and the insulation time is 120-150min. Then the oil cooling is performed for 7-12h. Tempering is performed within 2h after quenching. The tempering temperature is 560±10℃, and the insulation time is 150-180min.

[0032] 3. Forming size processing: Finishing process processes the double ring of the shoulder, stirring needle and thread.

[0033] 4. Mill the three planes of the stirring needle.

[0034] 5. After processing, the stirring head has a metallic luster, and the shoulder morphology and stirring needle features are clear.

[0035] Example 3 See also Figures 1 to 6 , this embodiment proposes a welding method for a single-shoulder stirring head for an aluminum alloy thick plate as described in Embodiment 1; A 20mm butt joint test plate of aluminum alloy 5A06-H112 was used for welding parameter debugging test. The preliminary judgment was based on the appearance quality being smooth and flat, without flash burrs, closed tail hole, and no visually visible hole defects. The load and pressure values ​​during welding were relatively stable and did not fluctuate violently. During the test, when the stirring head rotated and penetrated downward, material was gradually discharged from the periphery of the stirring needle. As the penetration depth increased, the discharged material increased. When the shaft shoulder contacted the parent material, the shaft shoulder began to participate in the plasticization process. The shaft shoulder continued to be squeezed out from the periphery of the shaft shoulder, and the pressure value reached the maximum, generally 85KN~95KN. Within the range of 30mm, it gradually began to move to the normal welding speed and started welding. The normal welding pressure value was 60KN~70KN.

[0036] According to the size of the stirring head shoulder and the stirring needle, the matching and debugging parameters during the test, and the quality inspection results, the recommended welding parameter range is confirmed in Table 2. By using the stirring head of the present invention to weld within the parameter range of Table 2, a joint with better appearance quality can be obtained.

[0037] The best welding parameters are shown in Table 3. The 20mm thick butt joint of 5A06 aluminum alloy is welded with the parameters in Table 3. The joint quality can meet the requirements of Class I. The mechanical properties of the joint can reach the same strength as the parent material. The metallographic section of the joint shows good fusion and no microscopic defects ( Figure 5 ).

[0038] Stirring head life test: The stirring head in Example 1 was used to perform continuous welding life assessment on a 5A06 aluminum alloy 35 mm plate using the optimal welding parameters in Table 3, and the expected life was not less than 30 meters. The test results showed that when the welding length reached 30 meters, there was no visual defect on the appearance of the stirring head. When the welding length reached 33 meters, the threaded profiling near the root began to wear, and the continuous welding wear gradually increased. When the welding reached 63 meters, the profiling wear of about 4 to 5 circles of the stirring needle increased, and no further testing was performed.

[0039] The life test results show that by using hot working die steel 4Cr5MoSiV1 as the stirring head material and adopting appropriate heat treatment process, the welding length of the stirring head can achieve the welding requirement of not less than 30 meters, and a continuous and stable stir friction welding process can be obtained.

[0040] The present invention designs and manufactures a stirring head suitable for single-axis shoulder stir friction welding of 5A06 aluminum alloy 20mm thick plate butt joints, which can realize continuous welding and complete the welding of a single long weld. The stirring head has reliable quality and a stable welding service life of up to 30 meters.

[0041] The stirring head can achieve continuous high-quality and stable welding. The pressure value feedback during the welding process is stable, the parameter fluctuation range is small, and the quality is stable during continuous welding.

[0042] Through welding tests, a reliable welding parameter range and optimal matching parameters were obtained, which can achieve 20mm full penetration on one side of the butt joint, uniform weld structure, and the joint quality and tensile properties meet Level I requirements.

[0043] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. A single-shoulder stirring head for thick aluminum alloy plates, comprising a clamping handle (1), a stirring needle (2) and a shoulder (3), wherein the clamping handle (1) is connected to a friction stir welding device, a shoulder (3) is provided at the bottom of the clamping handle (1), and the center of the bottom of the shoulder (3) is connected to the root of the stirring needle (2); characterized in that: The bottom of the shaft shoulder (3) is provided with two annular inner grooves (4) around the center; the stirring needle (2) is tapered as a whole, the cross section of the stirring needle (2) is a hexagonal structure, and the hexagonal structure is a planar arc surface arranged alternately; the side walls of the three arc surfaces of the stirring needle (2) are provided with conical threads, and the side walls of the three planes are smooth surfaces.

2. The single-shaft shoulder stirring head for thick aluminum alloy plate according to claim 1, characterized in that: The material is mold steel 4Cr5MoSiV1.

3. The single-shaft shoulder stirring head for thick aluminum alloy plate according to claim 1, characterized in that: The diameter of the shaft shoulder (3) is 30-34 mm.

4. The single-shaft shoulder stirring head for thick aluminum alloy plate according to claim 3, characterized in that: The root diameter of the stirring needle (2) is 15-18 mm.

5. A method for manufacturing a single-shoulder stirring head for thick aluminum alloy plates according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) Rough turning; 2) Heat treatment: The quenching and tempering process is divided into two steps: quenching and tempering. During the quenching process, the heating temperature is 520±10℃, and the temperature is kept for 90-120min. The heating temperature is 820±10℃, and the temperature is kept for 90-120min. The heating temperature is 1020±10℃, and the temperature is kept for 120-150min. Then, the oil is cooled for 7-12h. Tempering is performed within 2h after quenching. The tempering temperature is 560±10℃, and the temperature is kept for 150-180min. 3) Forming size processing: The finishing process processes two annular inner grooves of the shaft shoulder and the tapered thread on the side wall of the stirring needle (2); 4) Milling three flat surfaces of the stirring needle (2).

6. The method for manufacturing a single-shoulder stirring head for thick aluminum alloy plates according to claim 5, characterized in that: Leave a 1.5mm margin on one side during rough turning, and perform hardness testing after rough turning.

7. The method for manufacturing a single-shoulder stirring head for aluminum alloy thick plate according to claim 5, characterized in that: The heat treatment is performed in a vacuum furnace.

8. A welding method for a single-shoulder stirring head for an aluminum alloy thick plate according to any one of claims 1 to 4, characterized in that: Aluminum alloy plates with a thickness of 20 mm are used for welding. The stirring head plunge speed is 12 to 18 mm / min; the rotation speed is 300 to 340 r / min; and the welding speed is 90 to 120 mm / min.

9. The welding method based on a single-shoulder stirring head for thick aluminum alloy plates according to claim 8 is characterized in that: The stirring head plunge speed is 15mm / min; the rotation speed is 320r / min; the welding speed is 100mm / min.

10. The welding method based on a single-shoulder stirring head for thick aluminum alloy plates according to claim 8, characterized in that: The dwell time is 2s.

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