Explanation of laser beam welding method for aluminum magnesium manganese aluminum plate

Laser beam welding technology takes high-energy density beam (electron beam, laser, plasma, etc.) as heat source, and melts the parent metal under the action of vacuum or shielding gas to realize material welding. Compared with traditional welding technology, this high-flow welding technology has the advantages of high energy density, high weld depth-width ratio, fast welding speed, small thermal deformation of weldments and good weld performance. At present, plasma welding and laser welding are the main laser beam welding methods used in aluminum-magnesium-manganese aluminum plate welding.

A, plasma welding:

A method of welding using compressed arc (transfer arc) between tungsten electrode and workpiece or compressed arc (non-transfer arc) between tungsten electrode and nozzle. The gas is dissociated by electric arc heating, and is compressed when it passes through the water-cooled nozzle at high speed, which increases the energy density and dissociation degree, and forms a plasma arc. Its stability, calorific value and temperature are higher than those of ordinary electric arc, so it has greater penetration force and welding speed. The gas forming the plasma arc and its surrounding protective gas are generally gas. According to the material properties of each workpiece, ammonia or mixed gases such as argon nitrogen and argon hydrogen are also used. When this method is applied to the welding of Al-Mg-Mn-Al plate, the joint can be defect-free. However, due to its low welding efficiency, this method can only achieve vertical position welding at present.

Second, laser welding:

Laser welding is a welding method that uses a laser beam with high energy density as a heat source and focuses the laser to a small point through a lens, thus forming a molten pool. Because of the high energy density of laser, the weld seam obtained by welding Al-Mg-Mn plate can obtain a small heat affected zone. During laser welding, due to the effect of laser heating, some parent materials will generate airflow waves on the surface of the substrate after vaporization, which will clean the welding parts. At the same time, a small cavity is formed in the middle of the molten pool. When the laser beam moves forward for welding, the melt velocity around the concave cavity flows to the cavity. At the same time, due to the effect of surface tension, when the welding gun moves forward at a uniform speed for welding, the cavity is continuously filled, thus forming a uniform weld.

Laser welding belongs to non-contact welding, which has the characteristics of no electromagnetic interference, no pollution in air, rapid temperature rise and high heating temperature, and can realize the welding of high melting point substances. In addition, the laser beam used in welding has good directionality, convenient focusing and easy automation, thus achieving high production efficiency.

Al-Mg-Mn-Al plate can monitor the welding process by using sensors such as inductance, capacitance, sound wave, photoelectricity and vision, and can easily realize seam tracking, defect detection and adjustment of welding process, and realize fully automatic production.

Analysis of Difficulties in Welding Technology of Al-Mg-Mn Aluminum Plate

Al-Mg-Mn aluminum plate has the characteristics of high specific strength, low density, good formability, corrosion resistance and low cost, and has a wide application prospect in aerospace, equipment manufacturing, shipbuilding and nuclear industry. The use of Al-Mg-Mn materials in the structural parts of aviation equipment can achieve the purpose of reducing weight and saving energy. Welding is a stable connection method between metal materials. Under the traction of the development of aerospace engineering, aluminum alloys in China have been greatly developed. Aluminum-magnesium-manganese materials widely used in the aerospace field are mainly aluminum alloys containing copper series 2, zinc series 7, manganese series 3, magnesium series 5 and lithium series 8.

For the welding technology of aviation aluminum alloy structural parts, the traditional fusion welding, such as inert gas shielded welding and plasma arc welding, often leads to the casting structure harmful to the performance of aluminum alloy weld, and the shrinkage after welding between weld and heat affected zone will cause great deformation of aluminum alloy joint. The dense oxide layer on the surface of Al-Mg-Mn-Al plate, large deformation and welding defects during arc welding limit its further popularization. In addition, a wide range of softening in the heat affected zone of the joint will greatly reduce the mechanical properties of the welded joint. Al-Mg-Mn welding mainly has the following difficulties:

(1) The Al-Mg-Mn welded joint is severely softened and its strength coefficient is low, which is also a big obstacle to the application of aluminum alloy.

(2) Refractory oxide film (AAO) is easy to form on the surface of Al-Mg-Mn, and its melting point is 2060℃, which requires high power density welding process.

(3) Aluminum-magnesium-manganese welding is easy to produce blowholes and hot cracks, and the linear expansion coefficient is large, which is easy to produce welding deformation.

With the progress of welding technology, scientific research institutions and some enterprises have developed a variety of welding methods suitable for aviation aluminum-magnesium-manganese-aluminum plate structures, mainly including tungsten inert gas welding (IC welding), metal inertia gas welding (MIC welding), laser welding (LBW), plasma arc welding, electron beam welding and solid-state welding. Friction stir welding method has changed the limitation of traditional fusion welding methods that need to melt materials and use other filler solders because of its advantages of phase welding. When the materials are in viscoplastic state, the parent metal is connected by stirring method, which greatly improves the comprehensive performance of aluminum alloy weldments.

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