Clean Aluminum is Weldable Aluminum
As one of the most abundant naturally occurring metals on the planet, aluminum is used everywhere. From pocket electronics to skyscrapers, aluminum is part of our everyday world—which means it is also a major part of the welding industry. This lightweight metal conducts heat exceptionally well, making it tricky to weld, especially at higher thicknesses. While a clean surface is important in every weld, it is especially important when welding aluminum. Failing to clean the surface properly can lead to sheet metal defects such as porosity, weld cracks, and other problems leading to rework or scrapping the piece altogether. This blog delves into this topic in more detail.
Pre-Weld Aluminum Preparation
As part of Australia’s cutting-edge aluminum fabrication enhancements, it is necessary to preheat or bevel aluminum anytime the material is more than 3/16 in. thick. Beveling allows for full penetration without overheating the person welding, burning through parts, or exceeding the duty cycle of the machine. Good joint design and planning go a long way to ensuring a quality weld. An industrial solvent such as acetone or a citrus-based degreaser can be used to break down oils without leaving a residue. One has to be careful when using chemicals because they can harm the skin or be toxic when inhaled. One should also never use a wire brush before degreasing as it will simply push oils into small depressions and scratches and cause problems later.
Oxides form on the surface of aluminum when it is exposed to air and can cause porosity if not removed. Most often the oxides are removed with an alkaline solution or by grinding away a small amount of material. If one chooses grinding, it is necessary to avoid consumables such as a grinding wheel or sandpaper that can embed foreign material into the base metal. If a brush is used that has been used previously on steel, it can deposit tiny particles in the softer aluminum surface. In pressure vessel welding, the grinding can go all the way into the base material to ensure all contaminants are removed. In most other welding, the tolerances are not as strict, and an alkaline solution or small amount of grinding is all that is needed.
Challenge of Repair Welding
Making new aluminum welds is tricky enough, but repair welding adds unique challenges. The clean area around the weld needs to be much larger in repair welding applications for steel fabrication Australia. Once the aluminum heats it can act as a sponge, pulling in any nearby contaminants. Knowing how large the heat-affected zone of the repair weld could be will help determine how large of an area needs to be cleaned. If the material or part is porous or heavily pitted, use a torch to help remove inaccessible contaminants. One may have to repeat the grinding and cleaning processes more than once to mitigate embedded contaminants.
Once the area is as clean as possible, plan the repair weld carefully. If it is suspected that cracks are present within the weld, it is necessary to heat the area with a torch for a few seconds. The metal will expand as it heats and contract as it cools, possibly revealing cracks. If one is using TIG welding (gas tungsten arc welding (GTAW)), a positive AC balance can help break up surface contaminants on dirty parts. Low amperage and slow travel speed are important, but it is important to make sure that proper heat input and penetration is reached. Adjusting the shielding gas also can help one achieve a clean repair weld.
Final Thoughts
Sometimes getting the surface perfectly clean is not possible, especially with repair welding. In that case, having a power source with upgraded technology can be extremely beneficial. At the end of the day, it boils down to the fact that, while new welding technology can make up for a lot of problems, it can never do its best work on a dirty surface. To get the best possible weld, starting with a properly prepped surface will work wonders!
