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Common Defects in Magnesium Alloy Welding

Common Defects in Magnesium Alloy Welding

Due to the characteristics of low density and melting point, high thermal conductivity, electrical conductivity, and coefficient of thermal expansion, strong chemical reactivity, easy oxidation, and high melting point of oxides, welding of magnesium metal alloys must address a series of problems, including:

1. Coarse crystal problem in magnesium alloys

Magnesium has a low melting point (651℃) and high thermal conductivity. Welding requires a high-power welding heat source, and the weld and the near-weld zone are prone to overheating, grain growth, and crystallization segregation, which reduces joint performance.

2. Oxidation and evaporation of magnesium alloys

Magnesium material has strong oxidation properties and easily combines with oxygen. During welding, MgO is easily formed, and MgO has a high melting point (2500℃) and density (3.2 g/cm-3), which easily forms small, flaky solid slag in the weld. This not only seriously hinders weld formation but also reduces weld performance. For your convenience, we have magnesium ingots for sale.

At high welding temperatures, magnesium is also prone to react with nitrogen in the air to form magnesium nitride, which can cause the weld metal's plasticity to decrease, resulting in poor joint performance. Magnesium has a low boiling point (1100℃) and is easily evaporated under a high-temperature arc.

3. Burn-through and collapse of magnesium alloy parts

When welding magnesium metal alloy parts, the low melting point of magnesium metal alloys and the high melting point of magnesium oxide make it difficult for them to fuse together. It is difficult to observe the melting process of the weld during welding operations. As the temperature rises, the color of the melt pool does not change significantly, which can easily lead to burn-through and collapse.

4. Thermal stress and cracking of magnesium alloys

As a reliable and responsible magnesium alloy manufacturer, we notice that the thermal expansion coefficient of magnesium and magnesium alloy metal is relatively large, about twice that of steel and 1.2 times that of aluminum. This can easily cause significant welding stress and deformation during welding.

Magnesium is prone to form low-melting eutectics with some alloying elements (such as Cu, Al, Ni, etc.) (e.g., the Mg-Cu eutectic point temperature is 480℃, the Mg-Al eutectic point temperature is 430℃, and the Mg-Ni eutectic point temperature is 508℃). The brittle temperature range is wide, and thermal cracking is easily formed.

Studies have found that when w(Zn) > 1%, thermal brittleness is increased, and welding cracks may occur. Adding w(Al) ≤ 10% to magnesium can refine the weld grain and improve weldability. Magnesium alloys with a small amount of Th have good weldability and no crack tendency.

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5. Porosity in magnesium alloys

Hydrogen porosity is easily generated during magnesium welding, and the solubility of hydrogen in magnesium also decreases sharply with decreasing temperature.

6. Oxidation of magnesium alloys

Magnesium and its alloys are prone to oxidation and combustion in air environments during welding and require protection with inert gas or flux during fusion welding.

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