Cleaning and Preparing Aluminum Filler and Base Metals Before Welding

• Do not use cutting methods that leave a ground or smeared surface. For example, a high-speed circular saw is suitable for cutting aluminum whereas a band-sawed surface can lead to smearing. Grinders should be avoided when possible, but use a coarse disc grinder over a wheel grinder if it’s your only option.

The goal is to use as fast and sharp of a method as possible that quickly cuts away the material rather than smearing it. A wheel grinder, for instance, can embed pieces of stone into the aluminum that may become a contaminant or inclusion. A smeared surface may cause lack of fusion and should be filed to remove any smeared metal prior to welding.

• Do not use oxy-fuel gas cutting, carbon arc cutting or gouging processes, or oxy-fuel flames to preheat. These processes damage the heat affected areas and promote the growth and hydration of the oxide film present on the surface.
• Use plasma arc cutting and gouging, and laser cutting, as these processes are less likely to introduce hydrogen and moisture to the oxide layer.
• Mechanically remove the plasma arc and laser cut edges from 2xxx, 6xxx and 7xxx series alloys. The melted edges of these alloys contain detrimental solidification cracks and heat affected zone conditions. Remove a minimum of 1/8 in of metal from the cut edge. Use mechanical methods, such as milling or a coarse burr grinder, to cut and remove metal chips.
• When possible, do not use lubricants in aluminum cutting applications. Any petroleum-based lubricant contains hydrocarbons, which will break down during the welding process and introduce hydrogen into the joint, leading to porosity and cracking.
• Most aluminum will come from the factory with oil and grease on it. To clean the joint prior to assembly, first degrease the surfaces with a solvent, and then use a cheesecloth or paper towel to clean and dry the welding joint (these are preferred because they are porous and will absorb more oils/moisture). Also wipe the opposite side of the joint clean so that not impurities are pulled through the aluminum and into the weld puddle.

Look for a solvent that leaves behind no residue, and do not use chlorinated solvents in the welding area because these substances may form toxic gases in the presence of a welding arc.

• Do not use shop rags to clean welding joints as these rags can easily transfer oil and dirt to the welding surface.
• Do not use compressed air to blow off the joint. Compressed air contains moisture and oil contaminants.
• Clean the joint with a stainless wire brush only after solvent cleaning. Wire brushing prior to cleaning embeds hydrocarbons and other contaminants in the metal surface, as well as transfers these undesirable elements to the brush – which then makes the brush unsuitable for cleaning.
• Use a stainless steel wire brush to clean all metal that has been etched. The by-product residuals from etching must be removed prior to welding.
• Clean all wire brushes and cutting tools frequently to prevent the transfer of contaminants to the weld joint and, if possible, keep dedicated brushes solely for welding aluminum to minimize opportunities for contamination.