Analysis of laser welding process for aluminum alloy

1 overview of aluminum alloy and its welding

Aluminum and aluminum alloys have very good properties, such as high specific strength and strong corrosion resistance. They are widely used in many industries, especially in national defense industry, machinery and other industries. Aluminum alloys are non-ferrous metals and need to be welded in the process of application. Therefore, with the rapid development of science and technology, The research of aluminum alloy welding technology is more and more in-depth. Therefore, laser welding technology is a great progress in science and technology.

Overview of laser welding technology: as a new type of welding technology, laser welding is directly used as the welding heat source, which can not only avoid the waste of energy, but also greatly improve the efficiency of welding. At the same time, laser welding robot or CNC machine as a motion system, reduce the participation of personnel, can reduce the waste of labor, improve the efficiency of welding. In addition to the advantages of renewable, clean and pollution-free, laser heat source can also be highly focused and have good performance of transmission, so it can concentrate all the energy in one point to avoid heat loss and waste. Therefore, laser welding can improve the efficiency, speed and quality of welding. Because the laser beam of laser welding is realized by pulse or continuous laser beam, when the laser beam directly irradiates the surface of the aluminum alloy, the heat of the metal surface can quickly diffuse to the interior of the aluminum alloy, so that the aluminum alloy can quickly melt to form a weld, and form a reaction force on the melted metal, Finally, the surface of molten aluminum alloy is depressed to form small holes. This small hole has a powerful effect, which can absorb all the energy generated by laser beam irradiation, and generate high-temperature steam at the same time. The steam pressure and the wall surface tension form a dynamic balance.

1.1 laser welding power

Laser welding has a certain power. Only when the welding power reaches a certain height, can the welding be carried out stably and continuously. Otherwise, the welding can only be carried out on the surface of aluminum alloy, making the surface of aluminum alloy melt, so that the welding can not be carried out successfully. The power of laser welding can reach the height of welding aluminum alloy surface and interior, even higher than that, so laser welding aluminum alloy can improve efficiency, speed and quality.

1.2 speed of laser welding

Because of the high power of laser welding, the welding speed is also improved. The continuous improvement of the welding speed can reduce the penetration. On the contrary, if the speed slows down, the aluminum alloy will be excessively welded or even penetrated by welding. Therefore, the selection of laser welding can reduce the proportion of welding failure and greatly reduce the welding cost.

1.3 advantages of laser welding

It can improve the energy density, improve the welding quality, increase the accuracy and density of welding, improve the efficiency and speed of welding, reduce the welding cost, and can be welded under special conditions.

Application of laser welding in various fields

2.1 application in oil pipeline

In the oil pipeline, the application of aluminum alloy pipeline can increase the diameter of the pipeline, thicken the wall of the oil pipeline, so that the pipeline can transport more oil in a certain period of time. Oil transportation has a very high risk, such as oil leakage, which will cause incalculable property losses, casualties, environmental pollution and groundwater pollution. Therefore, special attention must be paid to aluminum alloy pipeline welding to improve the quality of welding. Laser welding can play a huge role at this time, Can control the welding process, can be in the premise of no groove welding operation, welding forming, high quality weld, fully avoid the risk of oil leakage, improve the safety of oil transportation.

2.2 application in automobile manufacturing industry

With the rapid development of the times and the increasing high-speed of people's living standards, it has been used to going out and taking cars, and people's requirements for the quality of cars are also higher and higher. Therefore, the automobile industry is constantly looking for new materials and technical means to improve the quality of cars, and laser welding technology is more and more widely used in the automobile industry. The United States is the first to introduce the laser welding aluminum alloy technology into the automobile manufacturing industry. After a series of experiments, the automobile made of laser welding aluminum alloy will be made into thin aluminum alloy after laser welding, which not only greatly reduces the weight of the body, but also reduces the process of manufacturing automobile, and improves the production efficiency, It is welcomed and favored by the automobile manufacturing industry.

2.3 Application in aerospace industry

As we all know, the aerospace industry needs highly accurate materials to manufacture a series of spacecraft, such as aircraft, and the weight of the machine itself is also very strict. Using laser welded aluminum alloy to manufacture aircraft and other machines can reduce the fuselage by about 20% than usual, and the manufacturing cost has been greatly reduced. For example, the A350 series aircraft parts produced by the German common tube parts factory using laser welding aluminum alloy technology have achieved great success.

3. Difficulties in laser welding of aluminum alloy

3.1 the surface of aluminum alloy is reflective of laser

Because aluminum alloy is a kind of non-ferrous metal, it has strong reflectance to all kinds of light. As a more intense beam, laser is more likely to cause reflection on the surface of aluminum alloy. In other words, aluminum alloy, a non-ferrous metal, has high reflectivity and low absorptivity for laser. In addition, all metals have thermal conductivity, so aluminum alloy also has strong thermal conductivity. When using laser welding, it is easy to reflect the laser or quickly transfer the heat of the laser, which eventually leads to the failure of aluminum alloy welding. Therefore, in the laser welding of aluminum alloy, we should pay attention to and quickly improve the laser power density to prevent reflection or conduction, and strive to weld aluminum alloy with high density in extreme time, so as to avoid the occurrence of reflection and other problems.

3.2 make full preparation for laser welding of aluminum alloy

Because aluminum alloy is active and easy to be oxidized, it is easy to attach a large amount of dust and water on its surface. Therefore, in the process of welding, if sufficient preparation is not made, the things attached on the surface are easy to stay on the surface of aluminum alloy with the rapid welding of laser, thus affecting the quality of aluminum alloy and welding effect. Therefore, before welding the aluminum alloy, it is necessary to clean the surface of the aluminum alloy and remove the oil stains on the surface. At the same time, it is necessary to thoroughly clean the oxide film on the metal surface and remove the oxide film completely to prevent the explosion caused by oxidation during welding.

4 defects in laser welding of aluminum alloy

Although laser welding has high efficiency, high speed and can greatly reduce the cost, laser welding also has many shortcomings. Only when these defects are clear and solved, can laser welding technology of aluminum alloy be more widely used.

4.1 porosity defects

As mentioned above, moderate porosity can maintain the internal and external balance of aluminum alloy, but excessive bubbles will cause a large number of defects, so it is difficult to avoid a large number of pores. When there are a large number of pores, the pores are unstable, and they are channeling in the aluminum alloy, which is easy to cause cracks in the welding position, Therefore, the removal of pores will be an important defect in laser welding of aluminum alloy.

4.2 hot crack defects

When using laser technology, it is necessary to increase the temperature and density to achieve the purpose of rapid welding, which is easy to appear special cracks on the surface of aluminum alloy, thus making the welding failure. In order to deal with the hot cracks, scientists have come up with a solution, that is, using filling materials in laser welding, but this method is easy to lead to a waste of resources and a lot of labor. Taking a more simple way to deal with hot cracks is also a major problem to be solved by this technology.