Summary: The use of aluminum alloys to replace steel on traditional cars is one of the important ways to achieve lightweight cars. However, due to the characteristics of good thermal conductivity and large linear expansion coefficient of aluminum alloy, there are some problems in welding.

The use of aluminum alloys to replace steel on traditional cars is one of the important ways to achieve lightweight cars. However, due to the characteristics of good thermal conductivity and large linear expansion coefficient of aluminum alloy, there are some problems in welding:
1) The welded joints of aluminum alloy are severely softened and the strength coefficient is low;
2) Aluminum alloy is easily oxidized to form a refractory oxide film (Al2O3, melting point is 2060°C), which requires a high-power-density welding process;
3) easy to produce pores;
4) The linear expansion coefficient is large, and welding deformation and welding cracks are easy to occur;
5) The thermal conductivity and specific heat capacity are large, and the heat input is 2 to 4 times larger than that of welded steel.

Therefore, in order to obtain high-performance aluminum alloy welded joints, welding methods with high energy density, low welding heat input and high welding speed are required, among which laser welding is one of the most promising aluminum alloy welding technologies.

1. Aluminum alloy laser welding technology

1.1 Aluminum alloy laser self-fluxing welding 

Laser self-fluxing welding refers to a welding method in which a high-energy-density laser beam is used as a heat source to impact the surface of the base metal to melt the base metal itself to form a welded joint. For aluminum alloy laser welding, the aluminum alloy surface has a high reflectivity to the laser, and a large laser power is required for welding; the laser spot diameter is small, the precision of the welding tooling is high, and the tolerance value of the part gap is low, usually requiring parts The gap value is below 0.2mm; the heating and cooling speed is fast during the welding process, there are many welding porosity defects, the laser energy density is concentrated, and the keyhole effect can easily lead to the phenomenon of weld sinking and undercutting. Therefore, the welding process parameters have higher requirements.

Laser self-fluxing welding has the advantages of good welding quality, fast welding speed and easy automation in aluminum alloy welding, and is widely used in the automotive industry. In the electric vehicle industry, aluminum alloy laser self-fluxing welding is mainly used for sealing the power battery case. In the aluminum body of a new energy automobile company in China, the welding of the door assembly and the side wall structural parts also uses aluminum alloy laser self-fluxing welding.

1.2 Aluminum Alloy Laser Filler Welding  

In laser wire filling welding, the laser is still used as the main heat source to melt the metal to be welded, but the automatic wire feeding device is used to continuously feed the filler metal into the molten pool to realize the metallurgical connection process. Compared with laser self-fluxing welding, laser wire filling welding relaxes the requirements for the gap precision of the welding process. By filling the welding wire with different components, the metallurgical properties of the weld can be improved, welding thermal cracks and pores can be prevented, and the stability of the welding process can be improved. and joint mechanical properties.

Aluminum alloy laser filler wire welding has the characteristics of good appearance quality and looser process gap precision than laser self-fluxing welding. It is usually used on the exterior surface of the car body, such as between the top cover and the side wall, and between the upper and lower panels of the trunk lid outer panel. There are also some models that use laser filler wire welding to weld aluminum alloy doors in order to obtain higher welding quality.

1.3 Aluminum alloy laser-arc hybrid welding

Laser-arc hybrid welding combines laser and arc heat sources with completely different physical properties and energy transmission mechanisms, and acts on the workpiece to be welded together. It not only fully exerts the respective advantages of the two heat sources, but also complements each other. lack of. In aluminum alloy laser-arc hybrid welding, the arc can guide the laser heat source, improve the aluminum alloy's ability to absorb the laser and the energy utilization rate during the welding process, and the weld surface formability is better than that of laser self-fluxing welding.

In addition, the introduction of the arc can greatly reduce the clamping accuracy of the welding workpiece. At the same time, the arc has a dilution effect on the plasma of laser welding, which can reduce the shielding effect of the plasma on the laser. The laser plays an important role in the stability of the arc, so that the arc can stably act on the joint during high-speed welding, which can improve the welding quality of the joint and increase the welding speed.