The Challenges of Welding Aluminum
Aluminum has certain properties which make it more challenging to weld than other metals. Its relatively high thermal conductivity (approx. 209 W/m K) and low melting point (1,221°F/660.3°C) make it such that only fusion welding processes can be used to weld it.
Fusion welding processes, such as MIG, TIG, Laser, and Electron Beam, generate intense heat in small area to melt the material in the desired weld area. This small heat affected zone is essential as aluminum’s high thermal conductivity tends to result in heat traveling throughout the work piece, either melting too much material or deforming the entire part. The amount of heat applied and the location to which it is applied must be controlled very precisely. Manual welding processes, such as MIG and TIG, rely on operator skill and heat sinking to control these factors. Because aluminum doesn’t change in appearance as it approaches its melting point, welding processes which require visual judgment of material readiness can be unreliable. Automated methods, such as Laser and Electron Beam, which use computers to control feed rate, power, and weld location, offer more precise and consistent weld quality.
Another challenge of welding aluminum involves the formation of oxide film on the work surface. The melting point of aluminum oxide is approximately 3x the melting point of pure aluminum, which can result in particles of aluminum oxide contaminating the weld and leading to porosity issues. In most cases, oxide film must be removed either by mechanical or chemical means prior to welding. Aluminum oxide can affect laser welding: oxide films can change the reflectivity of the parts surface, which negatively impacts the amount of laser energy making it to the base metal.
Hydrocarbon contamination of aluminum during storage and preparation of the material can cause problems when welding. Aluminum parts are frequently formed, sheared, sawed and machined prior to the welding operation. If a lubricant is used during any of these pre-weld operations, complete removal of the lubricant prior to welding is essential to avoid bad welds. Prudence dictates that aluminum parts which are to be welded should be pre-weld processed in a such a manner that minimal to no lubricants are used — sawing and machining of aluminum should be performed dry, if possible, and if not, the parts must be throughly cleaned.