Aluminum alloy products should have high quality, good tensile properties and large-scale wide-body profiles, which has become a hot research topic in various countries. Since the aluminum alloy has a large thermal expansion coefficient and a small elastic modulus, the welding deformation problem is particularly serious, which greatly affects the manufacturing precision and the use performance of the structure. The aluminum alloy sheet used for the structure has a small degree of restraint, and the aluminum alloy has a large expansion coefficient, and the conventional heat input amount is liable to be left and burned, resulting in wave deformation which is difficult to correct. Therefore, research on the welding technology of aluminum alloy sheets is very important.
The aluminum alloy thin plate welded structure is widely used in the box body and the vehicle body because of its light weight, corrosion resistance, excellent processing performance, and easy connection. In some aviation equipment and high-speed trains, aluminum alloy sheets are mainly used in skins, floors, end walls, etc. The main aluminum alloy grades used are: 5754 and 5083 non-heat treated reinforced aluminum alloys. The main methods of welding aluminum alloy sheets are:
Tungsten Arc Welding (TIG)
Tungsten argon arc welding is widely used in the welding of aluminum alloys, which is a relatively mature welding method. Compared with manual TIG, automatic TIG, pulse TIG automatic welding, the long seam of aluminum alloy sheet is ideal for pulsed TIG automatic welding. After welding, the weld has good performance on the street, and the production efficiency is more than three times higher than manual TIG.
In the case of aluminum alloy TIG welding, in order to effectively remove the oxide film on the surface of the aluminum alloy and reduce the burning loss of the tungsten electrode, it is preferable to use an alternating current TIG welding method. Since the pulsed square wave AC TIG welding of the aluminum alloy sheet is used, the pulse current amplitude and the ER half-wave time determine the ability of the cathode to clean the oxide film.
Since the use of TIG welding of aluminum alloy sheets is prone to weld defects and cannot meet the requirements of high quality and high quality, in high-volume production, TIG welding is difficult to meet the needs of a wide range of applications. At present, a large number of domestic aluminum alloy sheet welding uses argon-shielded arc welding. The problem of defects such as pores and poor forming defects in the welding process of 1 to 3 mm aluminum alloy sheets has been successfully solved. By optimizing the welding process parameters, the 2mm aluminum alloy sheet is welded by MIG, the productivity is more than twice that of TIG, and the quality can reach international standards. When using a double-pulse MIG welding for a 2.5mm 1060 aluminum alloy sheet, the low-energy pulse phase arc length correction value should be higher than the high-energy pulse phase value to obtain a good weld. However, the use of pulsed MIG welding of aluminum alloy sheets, the weldments are easily burned through, and the welding process is difficult to control. Therefore, the operator is required to be proficient in operational skills. Otherwise, the stability of the quality of the welded product will be difficult to guarantee. To this end, modern welders are equipped with expert systems to ensure optimum welding process parameters, and then a fool welder can be used to properly reduce the skill level of the operator.
Laser welding (LBW)
Laser welding is a welding method on the high level. It has the advantages of advanced nature, concentrated energy, small welding deformation, excellent weld quality and high production efficiency. It is an ideal welding method for welding aluminum alloy. For laser filler wire welding, the wire feeding method, the filament spacing, and the welding heat input are the main factors affecting the weld formation. Compared with laser single spot welding, laser double spot welding of aluminum alloy can significantly improve the quality of the weld. Increasing the wire can improve the surface quality of the laser single spot welded aluminum alloy weld, but will increase the tendency of the weld to create atmospheric holes. In laser welding, a multi-optical system can be used to weld aluminum alloy sheets, which can improve the quality of laser welding and obtain high-quality welds. However, in general, the mechanical properties of the welded aluminum alloy sheet are not ideal. The mechanical properties of the weld are usually only about 60% of the base metal, and the laser welding has strict requirements on the joint clearance. The welding process is not very stable and it is easy to cause welding. defect. Therefore, laser welded aluminum alloy sheets can only be used in applications where it is not very important.
Friction stir welding (FSW)
The British invented the friction stir welding in 1991 and was soon used by Boeing for the welding of aircraft and rockets, which is sufficient to illustrate the superiority of the welding method. The biggest characteristic of this welding method is that the welding process has a short duration, the reliability of the welded joint is higher, and the operation skill is low. Friction stir welding is a new type of solid phase welding technology, which can avoid common defects in fusion welding such as pores and solidification cracks, small welding deformation and high joint strength. The 1.4 mm thick LF2 aluminum alloy sheet is subjected to friction stir welding, and the joint strength reaches 80 to 85% of the base material. The 6061-T6 aluminum alloy with a thickness of 1mm is friction stir welded. After the welding parameters are optimized, the tensile strength of the joint reaches 105% of the base metal. Friction stir welding is better than other conventional welding methods in the welding of aluminum alloy sheets.