Cleaning and Preparing Aluminum Filler and Base Metals Before Welding

A welding solutions specialist with a local welding supply, when recently asked what the most important factor was for a successful aluminum weld, replied “clean, clean, clean, clean . . . and clean.”

Welding aluminum poses its own unique set of challenges – trying to weld with dirty base and filler metals adds unnecessary difficulty and can lead to poor weld quality. You also have to deal with the natural oxidation that takes place with aluminum.

Suitable preparation prior to welding is important, especially when fabrications are required to meet the weld quality requirements of industry codes, such as AWS D1.2 that governs the structural welding of aluminum.

There are key steps you can take in the treatment and preparation of filler and base metals to ensure that you don’t face problems associated with dirt, grease and airborne shop dust – as well as the natural oxidation process that takes place when aluminum is exposed to the air. We’ll cover these steps and present you with best practices to make sure you’re not sabotaging your aluminum welding processes before you even begin.

THE NATURAL CHALLENGES OF ALUMINUM
Aluminum presents immediate challenges versus steel. Aluminum has a greater potential to develop problems such as lack of fusion due to the tough oxide layer, lack of penetration due to high thermal conductivity, and porosity due to the high solubility of hydrogen in molten aluminum.

As such, all moisture and hydrocarbons must be eliminated, and the thickness of the oxide film must be controlled and prevented from hydrating due to the presence of excessive moisture.

PROPER STORAGE AND HANDLING OF ALUMINUM FILLER AND BASE METALS
Oxides on aluminum TIG filler metal can be introduced directly into the weld puddle and lead to porosity. Oxides on MIG filler metals can lead to a number of problems, including an erratic arc, added resistance, sooting and poor feeding. And thicker oxide layers on aluminum base metals must either be removed mechanically or face the risk of contaminating the weld.

Here are a few things you can do in storage to prevent this from happening:

• Store all welding filler metals and base metals in a dry location with minimum temperature fluctuation (to minimize condensation). Welding filler metals should be stored in a dry and heated room or cabinet.
• Store aluminum pieces vertically to minimize condensation and absorption of water contamination between layers.
• When possible, bring all filler and base metals into the welding area 24 hours prior to welding to allow them to reach room temperature (minimizing condensation).
• Keep filler metals covered at all times prior to welding. This would include a sealed case for TIG rods and a spool cover for MIG wire.

OPTIMAL JOINT PREPARATION FOR WELDING ALUMINUM
There are two key steps in preparing the joint for welding: (1) mechanically removing the oxide layer to make it manageable (the oxide layer has a higher melting point than the base metal) and (2) removing any oil, grease, dirt or moisture that could contaminate the weld.