Aluminum alloy laser welding quality assurance measures
[China Aluminum Network] Introduction This article briefly describes the application characteristics of aluminum alloys and welding characteristics, from the preparation of welding, welding seam protection gas, the use of double spot laser welding, laser filler wire welding or laser-MIG hybrid welding, process parameter adjustment, etc. The aspect describes the quality assurance method of aluminum alloy laser welding. In the industrial production, the existing high-end laser head can also be used to stabilize the welding quality.
Key words: aluminum alloy; welding; laser welding; dual spot; composite welding aluminum alloy application characteristics:
Aluminum alloy is widely used in many fields such as aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industry due to its light material, corrosion resistance, low temperature performance and good mechanical performance. With the pursuit of energy-saving economy in recent years, the need for aluminum alloys has reached a new level. At present, there are three major series of Al-Mg (5000 series), Al-Mg-Si (6000 series) and Al-Mg-Zn (7000 series) aluminum alloys for automotive applications. Alloys are used, and parts with high strength such as beams and columns are made of 6000 series or 7000 series alloys. Studies have shown that the use of aluminum alloy materials to properly reduce the weight of the car can reduce fuel consumption by 37%; the load on the suspension device is reduced by 18%; vibration intensity is reduced by 5%. While the major automobile plants have increased investment in aluminum alloy processing R&D and manufacturing, welding of aluminum alloys has become a fundamental problem that has to be solved.
Aluminum alloy welding characteristics:
Currently, aluminum alloys are mainly welded by conventional methods such as TIG welding and MIG welding. With conventional methods of welding, large heat input leads to large weld widths and shallow depths of penetration. Aluminum alloys conduct heat quickly. When metallurgy, high temperatures dissolve large amounts of hydrogen, and hydrogen holes are not generated by overflow (holes formed by hydrogen dissolved in the molten pool are precipitated.) For the metallurgical pores, the moisture in the incompletely oxidized oxide film is formed by hydrogen decomposition and hydrogen is formed as pores, which are called oxide film pores; due to the rapid metallurgical speed of the weld metal grains, the strength of the welded joints can be reduced to 40 %; Aluminum alloy has a low melting point and rapid heat conduction, and the molten metal has poor fluidity to make the weld bead unsightly; the heated area is large, and the processed material is easily deformed to affect the processing dimensional accuracy. The conventional welding quality of aluminum alloy is difficult to guarantee, and the welding speed is difficult to meet the requirements of mass production.
With the increasing popularity of laser processing applications, the use of laser welding aluminum alloy, the heat input is small and the heat source is concentrated, especially after the advent of fiber lasers, the laser welding aluminum alloy energy density is more concentrated, the laser wavelength is shorter, the high reflection is improve. Through laser-filled wire, laser-MIG hybrid welding, dual-spot laser welding and other processes, the forming effect of aluminum alloy welding can be significantly improved, and the welding quality is improved.
No matter what kind of welding method, the preparation work of aluminum alloy before welding is indispensable, and it has great influence on the welding quality of aluminum alloy. Before the welding, the surface of the aluminum alloy pieces was subjected to absolute alcohol or acetone wiping to remove impurities such as water or oil adsorbed on the surface. In order to prevent the workpiece from being oxidized in the air, the workpiece needs to be mechanically polished or chemically treated and dried to complete the welding as soon as possible. In order to accelerate the molten pool fluidity during the welding of aluminum alloys, the back surface of aluminum alloy workpieces can be brazed to improve the weld seam formation. During welding, Ar gas is used to protect against air and reduce the generation of air holes.
Laser welding aluminum alloy optimization quality specific measures:
At the beginning of laser welding of aluminum alloys, there is a high reflection phenomenon, which seriously affects the absorption of laser energy by the material. The shorter the wavelength, the better the light absorption of the material. Therefore, the fiber laser is better than the CO2 laser to absorb the aluminum alloy. The fiber laser beam mode is also better than the CO2 laser, and the energy density is more concentrated. Once the material begins to absorb light energy, the reflectivity of the liquid metal to light decreases significantly.
The use of dual-spot laser welding can significantly improve the porosity, mainly because when two beams are used for welding, the two beams form a relatively large keyhole, which improves the stability of the keyhole and facilitates the escape of gas; Compared with the serial double beam, when the parallel two-beam welding is used, the temperature gradient inside the weld pool is smaller, the solidification speed of the liquid metal is reduced, and the escape time of the bubbles is prolonged, which is advantageous to reduce the tendency of the blowhole; parallel dual beam laser welding can also Improve the stability of wire feeding, and it is beneficial to stabilize the welding quality.
Laser-filled wire welding can achieve better molding than aluminum alloy laser self-welding. Laser filler wire welding can be compatible with the high energy density of laser welding and the high bridging ability of filler wire welding. For a weld with a certain gap, it can ensure a good molding result. Moreover, through the choice of different filler materials, the parent metal can be subjected to different chemical metallurgy, and the effect of certain alloy elements can be supplemented and enhanced.
The use of laser hybrid welding, through the combination of laser and arc, can effectively eliminate the influence of plasma formed by laser welding. Through the adjustment of the parameters such as the distance between the light wire, air blowing and the angle of the welding gun, it is possible to obtain a beautiful weld seam, and it is also possible to form a good weld seam for a thick plate without a groove or a small groove.
With proper welding process parameters, welding quality can be guaranteed. Fig. 8 is a graph showing the relationship between the laser power and the welding speed of the 6061 aluminum alloy laser filler wire. It can be seen from the figure that the optimized matching parameter curve of laser power and welding speed rises linearly, and the slope remains basically unchanged. For each given laser power value, there is an optimized welding speed corresponding to the optimized parameter curve, and the welding speed can be changed within a certain range and a good quality weld can be obtained. This area belongs to the welding stability area. . At a certain power value, when the welding speed is too large, the heat input becomes smaller, and the aluminum alloy plate cannot be penetrated. At this time, when the welding speed is too large, it exceeds the range of the stable zone upwards, which belongs to the unmelted zone; when the welding speed is too small, If the heat input is too large, the molten pool will fall down and this will be the collapse zone of the molten pool. To obtain stable weld formation, it is necessary to match the appropriate welding process parameters.
(This article was provided by Shen Yi, Senior Engineer of Wuhan Farililai Welding System Engineering Co., Ltd. Thanks to the author for their great support!)
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