Aluminum Workshop: Common porosity problems (and how to fix them)

Q: I’m having a lot of problems with porosity in my aluminum welds. Can you tell me what’s causing it?

A: As we’ve said before, all porosity in aluminum welds is caused by hydrogen, which is very soluble in molten aluminum but insoluble in solid aluminum. Generally, hydrogen comes from two sources—water vapor and residual hydrocarbons, which are usually residual oils, greases, lubricants, or solvents. So where specifically should you look? Following are some of the culprits and how to correct them.

• Residual water in the shielding gas. Remember, the dew point of the gas should be -76 F or lower.
• Incorrect contact tip-to-work distance. Give yourself a contact tip-to-work distance of about 15 mm. Any longer than 15 mm can let air into the shielding gas blanket.
• Contamination on the plate surface. This usually is caused by oils and greases. You need to remove these with a good degreasing solvent. Wire brushing alone will not remove them.
• Incorrect gun angle. Always use a push angle, and never drag the torch.
• Incorrect shielding gas flow rate. Use at least 35 SCFH for GMAW and 25 SCFH for GTAW.
• Spatter buildup in the gun nozzle. Even a small amount can disturb the gas flow and cause porosity. Keep it clean.
• Small gas nozzle. Try using a larger nozzle.
• Antispatter sprays on aluminum or on the welding torch. Never use them, as these products contain hydrocarbons.
• Filler wire with residual drawing lubricant on it. Try a different spool of wire.
• Aluminum storage environment. If the aluminum is stored outside and moved into a warm shop, you may get water condensing on it.
• Water leakage in a water-cooled torch. This will cause porosity long before you can visually detect the leak.
• Drafty welding area. This can blow away the shielding very easily. If you can feel a breeze in the area, that’s too much. Turn off all fans in the area.

I have listed these in random order. Some are common, some are not (for instance, bad shielding gas and bad filler wire). However, I will end by making an emphatic statement: The welding power source cannot cause porosity unless there is a water leak in the torch.