Aluminium Welding
Since there is no solid state phase change when aluminium alloys are welded, they should be much easier to weld than steel. However, there are several problems and in many respects aluminium is more difficult to weld than steel. The main problem is the presence of a tenacious surface oxide film that must be removed before welding. The material is also much less tolerant to surface contamination, such as dirt, oil, grease or water, and cleaning the material just prior to welding is very important.
The arc processes most suitable for welding aluminium are MIG, TIG, and plasma, and while MMA can be used it does not give high quality welds and is difficult to use. Gas welding is still used but is much less common now. Friction stir welding is a new process with much promise but equipment costs are very high.
When MIG welding aluminium a totally inert shielding gas must be used or weld oxidation will result, and pure argon or argon-helium mixtures are generally used. This also applies to TIG and plasma welding.
Consumables for MIG, TIG, and plasma welding are solid wires based on pure aluminium, aluminium-magnesium, (Al-5%Mg), or aluminium-silicon, (Al-5%Si or Al-12%Si) compositions. MMA electrodes additionally have active, aggressive coatings. Gas fluxes are aggressive and must be cleaned off after welding. Friction stir needs no consumables.
The main welding problems encountered are porosity and cracking in sensitive alloys. Attention to cleaning, preheat, heat input control and correct choice of filler is essential if they are to be overcome.
Electric arc welding aluminium can produce considerable amounts of particulate and gaseous fume.
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