Aluminum Workshop: Preweld cleaning - a friendly reminder

Instead of the standard question/answer format, this month I thought it might be time to review preweld cleaning, both why it’s important and which methods to employ. It is a topic that we must address periodically because it is so important in making acceptable weldments.

Adequate preweld cleaning is one of the most important actions you can take to ensure that the welds you make are of acceptable geometry and are defect-free. For instance, most people who have problems with porosity encounter it because they haven’t cleaned the weld area properly before they weld. Don’t automatically blame bad shielding gas or bad wire. While either can cause porosity, it is far more likely that the problem is lack of preweld cleaning.

Two separate aspects are key to cleaning aluminum before welding. The first is removing all oils, greases, lubricants, solvents, and other hydrocarbons from the base material in the weld area. These contaminants contain hydrogen. If they get into the welding arc, they are dissociated into hydrogen and other substances by the heat of the arc. This hydrogen causes weld porosity.

These contaminants can be removed from the weld area by one of two methods. The first, and most common, removal method is to saturate a clean, lint-free rag with a degreasing solvent and wipe down the area to be welded thoroughly. Good degreasing solvents include acetone, toluene, and MEK. If you don’t have access to these, carburetor cleaner or liquid-penetrant cleaner works well also. Do not use any sort of alcohol as a preweld cleaner as it simply spreads the contaminants around.

The second common degreasing method you can use is immersing or power washing the parts in a mild alkaline solution. This is a common practice in high-volume applications, such as automotive parts, but it is not commonly done in fabricating industries.

The second important step in preweld cleaning is to remove any oxides from the weldable surfaces. You can do this by hand using a clean stainless steel wire brush or by using a powered stainless steel brush. Be sure the brush is relatively soft (i.e., fine bristles) and use it with a light touch. Applying excessive pressure on the brush will actually burnish the oxide and drive it into the surface of the soft aluminum.

If you follow these simple practices, you should see an improvement in your weld quality.