Application Status of Friction Stir Welding of Aluminum Alloys

Friction stir welding technology has many unique advantages. It has incomparable advantages over other welding methods in welding methods, mechanical properties and production efficiency for the connection of light alloy materials (such as aluminum, copper, magnesium, zinc, etc.). Friction stir welding is a solid phase connection method. The weld joint has excellent mechanical properties and small welding deformation. No shielding gas and welding wire are required during the welding process. There is no melting, smoke, splashing and arc. It is an environmentally friendly new connection technology. The actual situation is indeed the case. In just a few years after the advent of FSW technology, great progress has been made in welding mechanism, applicable materials, welding equipment and engineering applications. Friction stir welding technology was originally used to solve the welding of materials such as aluminum alloys, magnesium alloys and zinc alloys. The British Welding Institute has conducted a lot of research on the characteristics and applications of friction stir welding technology, and applied for worldwide patent protection in 1993 and 1995. At present, the institute mainly cooperates with welding equipment manufacturers and international large companies such as aviation, aerospace, shipbuilding, high-speed trains and automobiles to research and develop stir friction welding technology in the form of group sponsorship or cooperation (TWI's GSP project) to continuously expand its application scope.

Currently, the research projects sponsored by industrial enterprises include: stir friction welding of thick aluminum alloys, stir friction welding of steel, stir friction welding of titanium alloys, stir friction welding of lightweight automotive components, etc. The Edison Welding Institute (EWI) in the United States works closely with TWI and is also conducting research on FSW technology. Lockheed Martin Aerospace Corporation, Marshall Space Flight Center, U.S. Naval Research Institute, Dartmuth University, Stuttgart University in Germany, Adelaide University in Australia and Australian Welding Institute have all conducted special research on stir friction welding from different angles.

1. Application of stir friction welding of aluminum alloys in the field of aerospace

As the research on stir friction welding goes deeper, stir friction welding equipment is gradually moving from the laboratory to commercial use. TWI has used this technology to produce three 2000 series aluminum alloy space shuttle fuel tanks for Boeing; Lockheed Martin, Boeing-McDonnell Douglas, Rockwell Group, Edison Welding Institute and many other institutions are currently working on the research, application evaluation and development of stir friction welding. In the aerospace field, structures suitable for FSW welding include: skins of military or civilian aircraft, cryogenic fuel tanks in spacecraft, aircraft fuel tanks, auxiliary fuel tanks of military aircraft, military or scientific exploration rockets, etc.; Lockheed Martin Aerospace Corporation of the United States used this technology to weld cryogenic containers for storing liquid oxygen outside the space shuttle; at the Marshall Space Flight Center, this technology has also been used to weld large cylindrical containers.

Boeing invested several million dollars to manufacture a large-scale special friction stir welding machine for large cryogenic fuel containers for Delta launch vehicles. BAE Airbus is verifying the method, performance and feasibility of FSW technology for the purpose of producing medium and large commercial passenger aircraft. The friction stir welding machine used is manufactured by GRAWFORD-SWIFT in Austria and is said to be the most powerful welding machine in Europe. The American ECLIPSE (Eclipse) Airlines will use FSW to manufacture a medium-sized aircraft with a length of 10.86m and a wingspan of 11.88m. Figure 1 is the E500 new energy-saving small jet high-service aircraft successfully developed by the American ECLIPSE company at a cost of US$300 million. The company estimates that the use of FSW can reduce the assembly time of the reinforcing ribs and frames on the fuselage wall panels by 80%, reducing the cost of the aircraft to US$837,000. The main structural parts and skins of this aircraft are all manufactured using the latest international connection technology - stir friction welding technology. The fuselage of the passenger aircraft is basically manufactured using stir friction welding, including aircraft skins, wing ribs, chord supports, aircraft floors and assembly of structural parts.

The application of stir friction welding is mainly used to improve production efficiency and reduce manufacturing costs. The stir friction welding process for aviation structural parts was jointly developed by TWI and ALCOA of the United States and then applied to the welding of ECLIPSE500 aircraft structural parts. The company passed the preliminary design evaluation and certification of the Aircraft Safety Committee in September 2000, determined the feasibility of stir friction welding in aircraft manufacturing in June 2001, began to manufacture stir friction welding aircraft structural parts in 2001, made its first flight in June 2002, and demonstrated this new type of aircraft to the public from June 29 to July 1. Currently, hundreds of customers are scrambling to order this new type of affordable and energy-saving business aircraft.

2. Application of aluminum alloy friction stir welding in the field of shipbuilding

At present, based on the great advantages of friction stir welding in welding methods, mechanical properties, manufacturing costs and environment and its potential industrial application prospects, friction stir welding has been deeply and meticulously studied and developed in the field of shipbuilding. Shipbuilding requires not only an increase in speed, but also an improvement in unit price load performance, so shipbuilding should use aluminum alloy materials as much as possible to reduce the weight of ships. However, the traditional connection methods of aluminum alloy materials are rivet connection and arc welding connection. Riveting increases the manufacturing time, manpower and material usage, and aluminum alloy is prone to deformation, defects and smoke during fusion welding, which also limits the use of arc welding on aluminum alloy components. Therefore, with the development of friction stir welding technology, using friction stir welding to achieve high-integration preformed modular manufacturing to replace the traditional ship plate-reinforcement structure manufacturing is an inevitable and revolutionary progress in the development of shipbuilding technology.

The application of friction stir welding on light alloy preformed structural parts of ships has obvious advantages in appearance, weight, performance, cost and manufacturing time. It can not only be used for the manufacture of light alloy structural parts of ships, but also for on-site assembly, providing a new connection method for modern shipbuilding. The use of friction stir welding instead of fusion welding to realize the manufacture of light alloy structural parts is another leap in the development of modern welding technology.

FSW technology has broad application prospects in shipbuilding, marine industry and aerospace industry. Structures suitable for welding with FSW technology include: welding of decks, wall panels, partitions and other plates, welding of aluminum extrusions, welding of hulls and reinforcements, welding of helicopter landing platforms, etc. At present, this technology has been used to weld aluminum alloy structural parts with a length of 20m in speedboats, and the total length of welds exceeds 500km.

As a solid-phase connection method, it overcomes the shortcomings of previous fusion welding such as pores, cracks, and deformation, and makes materials that could not be welded by traditional fusion welding methods in the past available for FSW welding. It is known as "another revolutionary welding technology after laser welding".

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