During aluminum welding, the weld metal solidifies and traps hydrogen, creating porosity. Hydrogen is the primary cause of porosity.
Hydrogen can be generated from a variety of sources during aluminum welding, including moisture in the ambient air, moisture trapped in or on the weld metal oxide layer, and contamination from hydrocarbon-containing oils and greases.
Compared to welding steel, for example, the solubility of hydrogen is significantly higher when welding aluminum, which increases the chance of hydrogen being trapped in the weld. Furthermore, due to aluminum’s high thermal conductivity, the weld pool solidifies more quickly, further increasing the chance of hydrogen being trapped.
To ensure weld porosity meets industry standards, welding engineers should consult EN970 for visual inspections and EN1435 for radiographic testing.
How can the risk of porosity be minimized?
The most effective method is to minimize hydrogen content before welding:
1. Thoroughly remove all grease/solvents from the aluminum surface and thoroughly dry it before welding.
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2. If the design permits, wipe the aluminum with a stainless steel brush to remove any surface oxide.
3. Do not use cutting fluids when cutting, sawing, or machining aluminum to be welded.
4. After cleaning the aluminum, begin welding as soon as possible (within 4 hours).
5. Use the largest possible wire diameter.
6. Ensure that the wire and base material are stored in a warm, dry environment, preferably heated.
7. Preheat the parts being joined and the surrounding area to remove any residual moisture.
8. After welding, remove the wire from the welder and store it in a temperature-controlled area.
9. Use wire that is ground on three sides to ensure it has a low hydrogen content.
10. Wire feed speed is critical during MIG welding. It should be balanced with the current, voltage, and feed speed, as it affects irregular deposition and atmospheric absorption. Wire should be cut before starting the arc. 11. When manually welding TIG welding, do not remove the wire tip from the shielding gas between weld pools; otherwise, the wire will oxidize, introducing oxides into the weld pool.
What if porosity persists after taking all obvious precautions?
If porosity persists, it may be due to residual moisture in the welding torch or in the tubing connecting the welding machine to the gas supply point. This problem often occurs when air enters the welding torch when not in use, or through leaks in the gas supply tubing or connections. In these cases, the tubing may be unsuitable and permeation may occur, allowing moisture to seep in and diffuse into the gas.
All shielding gases should comply with BS14175, and the moisture content, whether supplied as a gas or liquid, must be below 10 ppm.
Post time: Jul-29-2025
