The culprit behind pores in aluminum welding – hydrogen

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During aluminum welding, hydrogen can be generated in many places, including moisture in the surrounding air, moisture trapped within or on the oxide layer of the weldment, or contamination caused by hydrocarbon-containing greases. Compared to welding steel plates, the solubility of hydrogen increases significantly during the welding of aluminum, which means that there is a greater chance of hydrogen getting trapped within the weld. Furthermore, due to aluminum’s high thermal conductivity, the solidification of the molten pool occurs more rapidly, which in turn increases the likelihood of hydrogen being trapped. To ensure that the porosity of welds meets industry standards, welding engineers should refer to the EN970 standard during visual inspections, and radiographic testing of welds should be carried out in accordance with the EN1435 standard. 　　How can the risk associated with pores be minimized? The most effective approach is to reduce the hydrogen content prior to welding by following these steps: 1. Before carrying out the welding process, thoroughly remove any grease/solvents from the surface of the aluminum material and ensure it is fully dried. 2 If the design permits, use a stainless steel brush to wipe the aluminum in order to remove the oxide layer on its surface. 3 When cutting, sawing, or machining aluminum that requires welding, do not use cutting fluid. 4 After cleaning the aluminum, start welding as soon as possible (within 4 hours). 5 Try to use wire with the largest diameter. 6 Ensure that the welding wire and base material are stored in a warm, dry environment; it is advisable to heat them as well. 7 Preheat the connecting parts and their surrounding area to remove all residual moisture. 8 After welding, remove the welding wire from the welder and store it in an area with a specific temperature. 9 Use wire with three-sided polishing to ensure a low hydrogen content. 10 The wire feeding speed during MIG welding is crucial. It should be balanced with current, voltage, and travel speed, as this affects irregular deposition and atmospheric absorption. The welding wire should be cut before starting the arc. 11 When performing TIG welding manually, do not remove the tip of the welding wire from the protective gas surrounding the weld pool; otherwise, the wire will oxidize, and the oxides will be introduced into the weld pool. 　　What if there are still pore problems after taking all obvious preventive measures? If pore problems persist, it may be due to residual moisture inside the welding gun or in the connection pipes between the welder and the gas supply points. Such problems are often caused by air entering the welding gun when it is not in use, or by air entering through leaks in the gas supply pipes or connections. Therefore, in such cases, pipes may not be suitable, and leakage may occur, allowing water to seep in and diffuse within the gas. 　　All shielding gases must comply with BS14175 standards; whether supplied as a gas or a liquid, their water content is guaranteed to be below 10 ppm.