1. INTRODUCTION Friction stir welding is a solid-state joining method proposed by The Welding Institute (TWI) in 1991 [1-5], and developed in 1993 and 1995 in the world. Developing countries applied for intellectual property protection [1,2,6,7]. This technical principle is simple, and the control parameters are small and easy to automate, which can minimize the human factors in the welding process. Friction stir welding technology has many advantages compared with traditional fusion welding, which makes it have a wide range of industrial applications and development potential. The study of the friction stir welding head's microstructure, mechanical properties (including fracture, fatigue, and corrosion properties), non-destructive testing, and the influence of process parameters on the quality of welds is the basis for promoting the use of friction stir welding. The research on these aspects is this Research hotspots in the field. Friction stir welding technology is a magical solid-phase connection technology with the shortest time span and fastest development in the history of world welding technology from invention to industrial application [8]. As of September 15, 2002, there were 78 users worldwide licensed by the United Kingdom Welding Research Institute (TWI) for friction stir welding patent technology, and 551 patents related to friction stir welding technology [8,9, 10,11], Users have covered 24 countries and regions. Famous Boing, NASA, BAE, HONDA, GE, HITACHI, MARTIN and other companies have purchased this technology and have been successfully applied in aerospace, aviation, vehicle, shipbuilding and other industries [10,12]. 2. Principle and process of friction stir welding The welding principle of friction stir welding is shown in Fig. 1 [13-30]. The mating workpiece placed on the mat is clamped by a clamp to prevent the mating joint from loosening during welding. A stirring head with a special stirring finger rotates and slowly inserts the stirring finger into the weld between the two opposing plates. In general, the length of the stirring finger is close to the depth of the weld. When the rotating stirring finger contacts the surface of the workpiece, the frictional heat generated by the rapid friction with the workpiece surface causes the temperature of the contact point material to increase and the strength decreases. Stir the fingers under the action of the external force to continuously forge and squeeze the material on both sides of the seam until the shoulders are in close contact with the surface of the workpiece. At this time, the frictional heat generated by the rotating shoulder and the stirring finger forms a large amount of plasticized layer under the shoulder and around the stirring finger. When the workpiece moves relative to the stirring finger or the stirring finger moves relative to the workpiece, the front surface of the stirring finger transfers the plasticized material to the rear surface of the stirring finger under the action of mechanical stirring and upsetting generated on the side and rotational direction of the stirring finger. As the stirring finger advances along the seam, the butt joint surface of the head of the stirring horn is frictionally heated to a superplastic state. Stir the finger and shoulder to rub the joint, break the oxide film, stir and recombine the grind material behind the mixing finger. After the material behind the stirring finger cools, a weld seam is formed. It can be seen that the weld seam is a solid weld formed under the action of a thermal-machine joint. This method can be regarded as a self-locking hole connection technology. During the welding process, a small hole is formed at the point where the stirring finger is located. The small hole is filled again during the subsequent welding process. It should be noted that when the friction stir welding end Leave a keyhole in the terminal. Usually this keyhole can be cut off or it can be sealed by other welding methods [8,27]. The main heating element in the welding process is the stirring finger and shoulder. When welding thin plates, friction between the shoulder and the workpiece is the main source of heat [13].
Friction Stir Welding Schematic Friction stir welding welding process parameters are: the speed of the stirring finger welding, stirring finger rotation speed and pressing force. These parameters determine the heat generated around the finger during the welding process and directly affect the microstructure and properties of the weld. 3. Technical advantages of friction stir welding In addition to the advantages of friction welding technology, friction stir welding can also be used for connection of various joint types and welding positions.
Several types of friction stir welding joints using friction stir welding technology can not only weld almost all of the welding can weld metal, but also can weld a lot of welding and poor welding of metals, such as: aluminum alloy, titanium alloy, copper alloy and so on. In the case of aluminum alloys, aluminum alloys tend to adsorb hydrogen when they are melted at a high temperature, resulting in pores after solidification, which are prone to thermal cracking and deformation. Therefore, the welding defect rate is high, and as the content of alloying elements in the aluminum alloy increases, these welding defect rates. Will greatly increase. If friction stir welding is used, the above disadvantages are overcome because there is no metal melting in the welding process, so the friction stir welding can make a reliable connection of metals that are not suitable for welding. In addition, friction stir welding can be used not only for connection between homogeneous alloys, but also for connection between different alloys. The use of friction stir welding to replace the traditional fusion welding can also improve the weld microstructure and greatly improve the mechanical properties of welded joints, and eliminate the possibility of welding defects. Friction stir welding weld zone organization shown in Figure 3: Welds can be divided into A, B, C, D four areas: A area for the base metal (basic metal, referred to as BM); B area for the heat effect In the heat affected zone (HAZ), the material in this area is affected by the thermal cycle, and the microstructure and mechanical properties are all changed, but no plastic deformation occurs; area C is the hot-mechanically affected zone (abbreviated as TMAZ), material in the area has undergone severe plastic deformation. In the case of aluminum alloys, there is usually a clear demarcation between the recrystallized region and TMAZ, but in other materials that have no thermally induced phase transitions, such as pure titanium, beta titanium alloys, austenitic stainless steels, and copper, TMAZ seems to be The whole has been recrystallized, resulting in strain-free recrystallization, which may make the HAZ/TMAZ boundary difficult to accurately divide; D zone is a weld zone (dynamically recrystallized zone, DXZ for short), and the weld nugget is the area closest to the shoulder, the organization The structure usually has big changes. In the heat affected zone of the welded joint, except that the corrosion reaction is faster than the base metal, the metallurgical structure is not much different from the base metal; in the area of ​​thermal deformation of the welded joint, the welding process causes long grain bending and slight Recrystallization; the weld nuclei are made up of fine, dynamically recrystallized equiaxed grains with a grain size much smaller than the grain size of the base metal. Friction stir welding experiments of 5083 aluminum alloy show that the weakest link of the weld is not in the weld zone, but in the heat affected zone. After the solution treatment and artificial aging treatment, friction stir welding welds of 2 series and 6 series aluminum alloys are aged, and their strength is close to that of the matrix material [18].
Friction Stir Welding Weld Zones Schematic Diagram 4. Industrial Applications Based on the obvious advantages of this solid-phase joining technology, for example: a wide range of weldable metals, excellent mechanical properties of the joints, no need to fill the welding material, no welding fumes and splashing, very With less pre-weld preparation and welding deformation, a large amount of research and development work has been carried out in international cooperation worldwide. In particular, friction stir welding can weld a variety of aluminum alloy materials, and even the former so-called non-weldable aluminum alloy materials can be welded, such as the 2000 series (Al-Cu), 5000 series (Al-Mg), used in the aviation and aerospace fields, The 6000 series (Al-Mg-Si), 7000 series (Al-Zn), and 8000 series (Al-Li) high-strength aluminum alloys [33, 34] can also be used to obtain high-quality connections using this advanced welding method. Therefore, friction stir welding has a wide range of industrial applications. Many universities, research institutes, and companies are continuing to conduct research related to this technology, with a view to using the technology more widely in aircrafts, lightweight energy-saving automobiles, high-speed trains, ships, etc. to reduce structural weight and improve their overall performance. To promote the development of aerospace, automotive, marine and other industries [5,36-40]. Taken together, the applications of friction stir welding in the world's industrial fields mainly include the following: â— Ships and marine industry: decks, side plates, waterproof partitions, hull shells, main structural parts, helicopter platforms, offshore waters of speed boats, cruise ships, etc. Observing stations, marine freezers, sailing masts and structural components; â— Aerospace: carrier rocket fuel tanks, engine bearing frames, aluminum alloy containers, space shuttles outside the tank, manned return warehouse, etc.; â— Aviation: Aircraft skin, Beams, connections between reinforcements, frame connections, aircraft panels and floor connections, aircraft door preforms, landing gear covers, and external fuel tanks; â— Vehicle industry: high-speed trains, rail cars, subway cars, light rail trams â—Auto Industry: Automotive Engine Engines, Chassis Brackets, Car Wheels, Door Preforms, Body Frames, Lifting Platforms, Fuel Tanks, Escape Tools, etc. â— In the Construction Industry: Panels Made of Aluminum, Copper, Titanium, etc. , door and window frames, reactors for power plants and chemical plants, aluminum pipes, heat exchangers and air conditioners, etc.; â— other industries: engines Body refrigerator cooling plate, electrical sub-package, natural gas, liquefied petroleum gas tank, light alloy container, home decoration, magnesium alloy products. 5. Development prospects Due to the good microstructure of friction stir welding welds and excellent mechanical properties of joints, it has been widely used in many industrial fields. In the aerospace industry, the promotion and application of friction stir welding technology in the manufacture of aircraft aluminum alloy structures has demonstrated strong technological innovation in foreign countries, bringing a revolutionary transformation to traditional manufacturing processes. In 1998, Boeing’s Space and Defense Laboratories introduced friction stir welding technology for the welding of certain rocket components; McDonnell Douglas also used this technology to manufacture propellant tanks for Delta rockets [41]; NASA Excel Mather is evaluating the feasibility of this process for connecting the 2195A1-Li alloy. In the shipbuilding and vehicle industry, several companies in Europe have used this technology to produce large-scale prefabricated aluminum panels. The friction stir welding equipment used for research and production has been commercialized and the length of the weldable sheet has reached 16m [42]. In equipment development and manufacturing, Norway has established the world's first friction stir welding commercial equipment, which can weld 3-15mm thick, 6×16m2 Al boat; ESAB is manufacturing friction stir welding for commercial applications. The machine, which is planned to be installed on the TWI, is used to weld workpieces with a size of 8 m × 5 m. The expected weldable workpiece thickness is 1.5 to 18 mm. From the above examples of industrial applications and equipment development, it can be seen that friction stir welding has shown strong innovation vigor and broad application prospects in the light structure manufacturing of aerospace, shipbuilding, high-speed trains, automobiles and other manufacturing fields, and has been widely application. In 1995, the United Kingdom Welding Research Institute (TWI) applied for patent protection on friction stir welding and stirring heads (patent number: ZL95192193.2), and it was approved by the Chinese Intellectual Property Office in 1999 (Grant No. 51451); On April 18, 2002, Beijing Aeronautical Manufacturing Engineering Institute and the British Welding Research Institute formally signed the patent license and technical cooperation agreement for friction stir welding in Beijing, and they were registered on the basis of the establishment of the China Friction Stir Welding Center. China's first professional friction stir welding technology company - Beijing Forster Technology Co., Ltd. Beijing Forster Technology Co., Ltd. is responsible for all friction stir welding operations of the China Friction Stir Welding Center in China (including: Hong Kong, Macau and Taiwan): mainly engaged in friction stir welding technology research, FSW engineering application development, FSW equipment Manufacturing and sales and full responsibility for the distribution and management of FSW "secondary licenses" for FSWC in China. The establishment of the China Friction Stir Welding Center and the professional Beijing Forste Technology Co., Ltd. marks the official start of the development and engineering application of friction stir welding technology in the Chinese market, and is a highlight in the development of China's welding technology in the new century. milestone. Some domestic institutions and research institutes have also begun research work in this area. There is reason to believe that friction stir welding technology also has application prospects in China. 6. Conclusion As the Friction Stir Welding technology has advantages that other welding technologies cannot match, it has a wide range of industrial applications and will become a research hotspot in the 21st century. In addition, with the study of the plastic flow behavior in the friction stir welding process, the finite element analysis of the thermo-mechanical coupling of the welding process, the optimization of the process parameters of friction stir welding of various typical materials and the evaluation of the joint performance, the design and optimization of the shape of the mixing head and Further research work on the connection between dissimilar metals will be further improved, and its application will be more extensive.
Friction Stir Welding Schematic Friction stir welding welding process parameters are: the speed of the stirring finger welding, stirring finger rotation speed and pressing force. These parameters determine the heat generated around the finger during the welding process and directly affect the microstructure and properties of the weld. 3. Technical advantages of friction stir welding In addition to the advantages of friction welding technology, friction stir welding can also be used for connection of various joint types and welding positions.
Several types of friction stir welding joints using friction stir welding technology can not only weld almost all of the welding can weld metal, but also can weld a lot of welding and poor welding of metals, such as: aluminum alloy, titanium alloy, copper alloy and so on. In the case of aluminum alloys, aluminum alloys tend to adsorb hydrogen when they are melted at a high temperature, resulting in pores after solidification, which are prone to thermal cracking and deformation. Therefore, the welding defect rate is high, and as the content of alloying elements in the aluminum alloy increases, these welding defect rates. Will greatly increase. If friction stir welding is used, the above disadvantages are overcome because there is no metal melting in the welding process, so the friction stir welding can make a reliable connection of metals that are not suitable for welding. In addition, friction stir welding can be used not only for connection between homogeneous alloys, but also for connection between different alloys. The use of friction stir welding to replace the traditional fusion welding can also improve the weld microstructure and greatly improve the mechanical properties of welded joints, and eliminate the possibility of welding defects. Friction stir welding weld zone organization shown in Figure 3: Welds can be divided into A, B, C, D four areas: A area for the base metal (basic metal, referred to as BM); B area for the heat effect In the heat affected zone (HAZ), the material in this area is affected by the thermal cycle, and the microstructure and mechanical properties are all changed, but no plastic deformation occurs; area C is the hot-mechanically affected zone (abbreviated as TMAZ), material in the area has undergone severe plastic deformation. In the case of aluminum alloys, there is usually a clear demarcation between the recrystallized region and TMAZ, but in other materials that have no thermally induced phase transitions, such as pure titanium, beta titanium alloys, austenitic stainless steels, and copper, TMAZ seems to be The whole has been recrystallized, resulting in strain-free recrystallization, which may make the HAZ/TMAZ boundary difficult to accurately divide; D zone is a weld zone (dynamically recrystallized zone, DXZ for short), and the weld nugget is the area closest to the shoulder, the organization The structure usually has big changes. In the heat affected zone of the welded joint, except that the corrosion reaction is faster than the base metal, the metallurgical structure is not much different from the base metal; in the area of ​​thermal deformation of the welded joint, the welding process causes long grain bending and slight Recrystallization; the weld nuclei are made up of fine, dynamically recrystallized equiaxed grains with a grain size much smaller than the grain size of the base metal. Friction stir welding experiments of 5083 aluminum alloy show that the weakest link of the weld is not in the weld zone, but in the heat affected zone. After the solution treatment and artificial aging treatment, friction stir welding welds of 2 series and 6 series aluminum alloys are aged, and their strength is close to that of the matrix material [18].
Friction Stir Welding Weld Zones Schematic Diagram 4. Industrial Applications Based on the obvious advantages of this solid-phase joining technology, for example: a wide range of weldable metals, excellent mechanical properties of the joints, no need to fill the welding material, no welding fumes and splashing, very With less pre-weld preparation and welding deformation, a large amount of research and development work has been carried out in international cooperation worldwide. In particular, friction stir welding can weld a variety of aluminum alloy materials, and even the former so-called non-weldable aluminum alloy materials can be welded, such as the 2000 series (Al-Cu), 5000 series (Al-Mg), used in the aviation and aerospace fields, The 6000 series (Al-Mg-Si), 7000 series (Al-Zn), and 8000 series (Al-Li) high-strength aluminum alloys [33, 34] can also be used to obtain high-quality connections using this advanced welding method. Therefore, friction stir welding has a wide range of industrial applications. Many universities, research institutes, and companies are continuing to conduct research related to this technology, with a view to using the technology more widely in aircrafts, lightweight energy-saving automobiles, high-speed trains, ships, etc. to reduce structural weight and improve their overall performance. To promote the development of aerospace, automotive, marine and other industries [5,36-40]. Taken together, the applications of friction stir welding in the world's industrial fields mainly include the following: â— Ships and marine industry: decks, side plates, waterproof partitions, hull shells, main structural parts, helicopter platforms, offshore waters of speed boats, cruise ships, etc. Observing stations, marine freezers, sailing masts and structural components; â— Aerospace: carrier rocket fuel tanks, engine bearing frames, aluminum alloy containers, space shuttles outside the tank, manned return warehouse, etc.; â— Aviation: Aircraft skin, Beams, connections between reinforcements, frame connections, aircraft panels and floor connections, aircraft door preforms, landing gear covers, and external fuel tanks; â— Vehicle industry: high-speed trains, rail cars, subway cars, light rail trams â—Auto Industry: Automotive Engine Engines, Chassis Brackets, Car Wheels, Door Preforms, Body Frames, Lifting Platforms, Fuel Tanks, Escape Tools, etc. â— In the Construction Industry: Panels Made of Aluminum, Copper, Titanium, etc. , door and window frames, reactors for power plants and chemical plants, aluminum pipes, heat exchangers and air conditioners, etc.; â— other industries: engines Body refrigerator cooling plate, electrical sub-package, natural gas, liquefied petroleum gas tank, light alloy container, home decoration, magnesium alloy products. 5. Development prospects Due to the good microstructure of friction stir welding welds and excellent mechanical properties of joints, it has been widely used in many industrial fields. In the aerospace industry, the promotion and application of friction stir welding technology in the manufacture of aircraft aluminum alloy structures has demonstrated strong technological innovation in foreign countries, bringing a revolutionary transformation to traditional manufacturing processes. In 1998, Boeing’s Space and Defense Laboratories introduced friction stir welding technology for the welding of certain rocket components; McDonnell Douglas also used this technology to manufacture propellant tanks for Delta rockets [41]; NASA Excel Mather is evaluating the feasibility of this process for connecting the 2195A1-Li alloy. In the shipbuilding and vehicle industry, several companies in Europe have used this technology to produce large-scale prefabricated aluminum panels. The friction stir welding equipment used for research and production has been commercialized and the length of the weldable sheet has reached 16m [42]. In equipment development and manufacturing, Norway has established the world's first friction stir welding commercial equipment, which can weld 3-15mm thick, 6×16m2 Al boat; ESAB is manufacturing friction stir welding for commercial applications. The machine, which is planned to be installed on the TWI, is used to weld workpieces with a size of 8 m × 5 m. The expected weldable workpiece thickness is 1.5 to 18 mm. From the above examples of industrial applications and equipment development, it can be seen that friction stir welding has shown strong innovation vigor and broad application prospects in the light structure manufacturing of aerospace, shipbuilding, high-speed trains, automobiles and other manufacturing fields, and has been widely application. In 1995, the United Kingdom Welding Research Institute (TWI) applied for patent protection on friction stir welding and stirring heads (patent number: ZL95192193.2), and it was approved by the Chinese Intellectual Property Office in 1999 (Grant No. 51451); On April 18, 2002, Beijing Aeronautical Manufacturing Engineering Institute and the British Welding Research Institute formally signed the patent license and technical cooperation agreement for friction stir welding in Beijing, and they were registered on the basis of the establishment of the China Friction Stir Welding Center. China's first professional friction stir welding technology company - Beijing Forster Technology Co., Ltd. Beijing Forster Technology Co., Ltd. is responsible for all friction stir welding operations of the China Friction Stir Welding Center in China (including: Hong Kong, Macau and Taiwan): mainly engaged in friction stir welding technology research, FSW engineering application development, FSW equipment Manufacturing and sales and full responsibility for the distribution and management of FSW "secondary licenses" for FSWC in China. The establishment of the China Friction Stir Welding Center and the professional Beijing Forste Technology Co., Ltd. marks the official start of the development and engineering application of friction stir welding technology in the Chinese market, and is a highlight in the development of China's welding technology in the new century. milestone. Some domestic institutions and research institutes have also begun research work in this area. There is reason to believe that friction stir welding technology also has application prospects in China. 6. Conclusion As the Friction Stir Welding technology has advantages that other welding technologies cannot match, it has a wide range of industrial applications and will become a research hotspot in the 21st century. In addition, with the study of the plastic flow behavior in the friction stir welding process, the finite element analysis of the thermo-mechanical coupling of the welding process, the optimization of the process parameters of friction stir welding of various typical materials and the evaluation of the joint performance, the design and optimization of the shape of the mixing head and Further research work on the connection between dissimilar metals will be further improved, and its application will be more extensive.