Q: I am having a problem with porosity in my aluminum welds. The porosity is being detected in groove welds that are radiographic inspected. It is fairly extensive porosity and well outside the acceptance criteria. How can I reduce or remove this porosity problem? A: Producing low porosity levels in aluminum welds is not always straightforward and often proves to be a challenge when working in applications that are subjected to radiographic inspection. Porosity can range from very small microporosity to large pores. In all cases, porosity in aluminum welds results from gas dissolved in the molten weld metal becoming trapped as it solidifies and forming bubbles in the solidified weld metal — Figs. 1, 2. The Cause of Porosity in Aluminum Welds The cause of porosity in aluminum welds is hydrogen, which has a high solubility in molten aluminum but very low solubility in the solid (Fig. 3), and for this reason, the potential for excessive porosity during arc welding of aluminum is high. During the welding operation, it is easy to introduce hydrogen unintentionally through contaminants within the welding area. It is important to understand the many sources of these contaminants to detect the cause and take the necessary action to resolve porosity problems. Understanding the Potential Sources of Contamination That Can Cause Porosity When we have a problem with porosity in aluminum welds, the one thing that we can be sure of is that we had a source of hydrogen in or around the welding area during the welding operation. To remove the porosity problem, we must identify the source of hydrogen and reduce or remove it. The two most common sources of hydrogen contamination during welding aluminum are hydrocarbons and moisture, which we will first consider separately. ALUMINUM Q&A 24 WELDING JOURNAL / APRIL 2015 BY TONY ANDERSON Fig. 1 — Porosity in an aluminum weld ranging from very small microporosity to large pores. This porosity is the result of gas (hydrogen) dissolved in the molten weld metal becoming trapped as it solidifies and forming bubbles in the solidified weld metal. For info, go to www.aws.org/adindex
Welding Journal | April 2015
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