Black Deposits Formed After Aluminum Welding

In many applications—particularly in products such as pallets, ladders, and scaffolding used in the chemical and food industries—black residue can be quite problematic. While a simple brushing process is usually sufficient to remove this residue, it may require additional manual steps in areas with limited access.

Black residue is caused by evaporation followed by magnesium oxide spatter. Magnesium is an alloying element that significantly increases the strength of aluminum, and this increase is generally not overlooked.

Although magnesium oxide is generally known to be white, an EDS analysis dispels any doubt regarding the presence of MgO, which can appear not only in white but also in gray, yellow, brown, or black forms.

The following measures can be taken to prevent MgO formation:

• Use of wire electrodes with low or no magnesium content (e.g., AlMg3, AlSi5).
• Optimized pulse parameters to minimize metal vapor formation.
• Avoiding unfavorable torch positions due to insufficient access.
• Ensuring adequate shielding gas coverage to keep oxygen intake as low as possible.