What are the difficulties in aluminum welding?
Aluminum and aluminum alloy are lightweight and non-corrosive metals. They are becoming popular in the recent fifty years. However, when welders talk about aluminum welding, they all think of it as tough work to deal with.
Why is aluminum welding so difficult?
1) Aluminum alloy is easy to oxidize.
In the air, aluminum will combine with oxygen, developing a layer of dense aluminum oxide film, calls aluminum oxidation.
It is about 0.1-0.2 μm in thickness, and has a high melting point of about 2050C, far exceeding the melting point of aluminum and aluminum alloys (about 600C).
Its density is 3.95-4.10g/cm, about 1.4 times that of aluminum. Besides, the surface of the oxidation film is easy to absorb moisture.
During welding, it could prevent the fusion of base metals. Besides, it will result in pores, slag, incomplete fusion, and other welding defects. That caused a decline in weld performance.
(2) Porosity is a big problem in aluminum welding.
Hydrogen is the main cause of porosity in Aluminum welding. Liquid aluminum can dissolve a large amount of hydrogen, while solid aluminum almost dissolves no hydrogen.
When the puddle temperature cooled and solidified rapidly, hydrogen cannot escape. It will gather in the weld and form pores.
Hydrogen porosity is difficult to avoid completely. There are many sources of hydrogen, such as moisture in the air, damp base metal, and even water in argon.
The practice has proved that when the moisture content reaches 20 ppm, there will be a large number of dense pores. When the relative humidity of the air exceeds 80%, there will be obvious pores in the weld.
We suggest welders use argon gas with a purity of 99.99% or more.
(3) Aluminum welding Tend to form deformation and cracks
Aluminum and its alloy have properties of high linear expansion and crystallization shrinkage. They are about twice as large as steel, and prone to make greater welding deformation and cracks.
(4) High thermal conductivity of Aluminum
Aluminum and aluminum alloy has high thermal conductivity.
It is about four times that of steel.
Therefore, aluminum welding needs more heat input, especially compared with steel welding.
(5) No color change in aluminum welding.
During aluminum welding, when we heat the base aluminum metal, it will melt and become liquid.
But unlike regular metals, there is no obvious color change. It is very difficult for welders to check what the heating temperature is.
(6) Alloying elements Loss during aluminum welding.
Some alloying elements, such as Magnesium, Zinc, Manganese, etc, are low boiling points. Under high temperatures, those elements will change into a gas.
It results in elements loss in the joint metal.
It will greatly decrease the weld performance and joint chemical composition.
For more information, please click here to form a clean joint.
In the welding industry, aluminum and aluminum alloy are really difficult to deal with, and not as easy as most people thought. The properties of aluminum itself make aluminum difficult to weld.