Magnesium alloy welding process is a very common but complex technology in the welding industry. Generally speaking, tungsten inert gas maintenance arc welding (GTAW ΠTIG) and molten inert gas maintenance arc welding (GMAW Π MIG) It is a common welding method for magnesium alloys. In addition, magnesium alloys can also be welded by resistance spot welding (RSW), conflict welding (FW), stir friction welding (FSW), laser welding (LBW), electron beam welding (EBW) and other processes. Because of the small specific heat capacity and latent heat of fusion of magnesium, less heat input is required for welding and the welding speed is high. In most cases, magnesium alloy parts can be welded by fusion welding, such as arc welding, laser welding, electron beam welding and gas welding. see below Magnesium alloy welding The introduction of performance, I hope to help everyone!

Because magnesium alloys have the characteristics of low density and melting point, large thermal conductivity, electrical conductivity and thermal expansion coefficient, strong chemical activity, easy oxidation and high melting point of oxides, it is necessary to deal with the following series of problems in the welding of magnesium alloys:

1. Coarse crystals

Magnesium has a low melting point and high thermal conductivity. High-power welding heat sources are required for welding. Overheating, grain growth, and crystal segregation are prone to occur in the weld and near seam areas, which reduce the joint function.

2. Oxidation and transpiration

Magnesium is very oxidizing and easy to combine with oxygen. It is easy to form MgO in the welding process. MgO has a high melting point (2500 ° C) and a high density (3.2g/cm-3). It is easy to form small flake solid slag inclusions in the weld. Not only severely prevents the weld from forming, but also reduces the weld performance. Magnesium is also easy to combine with nitrogen in the air to form magnesium nitrides at high welding temperatures, and magnesium nitride slag inclusions will also cause the plasticity of the weld metal to decrease, making the joint function worse. The boiling point of magnesium is not high (1100 ° C), and it is easy to transpiration under the high temperature of the arc.

3. Burn-through and fall of thin parts

When welding thin parts, because the melting point of magnesium alloy is low, and the melting point of magnesium oxide is high, the two are not easy to fuse, and it is difficult to investigate the melting process of the weld during welding operations. When the temperature increases, the color of the molten pool does not change significantly, and the phenomenon of burn-through and collapse is very easy to occur.

4. Thermal stress and cracks

The thermal expansion coefficient of magnesium and magnesium alloys is large, which is about 2 times that of steel and 1.2 times that of aluminum, which is easy to cause large welding stress and deformation during the welding process. Magnesium is easy to form a low melting point eutectic with some alloying elements (such as Cu, Al, Ni, etc.) The temperature is 508 °C), the brittle temperature range is wide, and it is easy to form hot cracks. After research, it was found that when w(Zn)>1%, it will increase hot brittleness and may lead to welding cracks. Adding w(Al)≤10% in magnesium can refine the grain of the weld and improve the weldability. Magnesium alloys containing a small amount of Th have excellent weldability and no tendency to crack.

5. Stomata

Hydrogen pores are prone to occur when welding magnesium, and the solubility of hydrogen in magnesium also decreases sharply with the decrease of temperature.

6. Magnesium and its alloys are easy to be oxidized and burned when welded in the air environment, and need to be maintained with inert gas or flux during fusion welding.