Repairs that come into the shop can sometimes be really challenging. In almost all automotive repairs, the part has been exposed to, or immersed in oil - which is a real problem for a quality weld repair. Irrespective of the metal type concerned, this oil and or grime needs to be cleaned properly to enable a sound weld repair.
In the case of aluminium, the oil is absorbed into the pores of the metal and this is where a lot of the repair time is spent. Most repairs done are not pretty - not because of a 'could care less' attitude on my part, but because of the condition of the metal, the amount of impurities still trapped inside and dirt or oil that just cannot be removed at the time of welding. A large percentage of parts have to be re-machined after welding to bring mating surfaces or part clearances back into tolerance. This machining is done in house.
In the majority of cases, the repair is being done to save money on the cost of a new part or because a new part is just not available. Generally, on cheaper more common parts or articles, it is often more cost effective to replace it with a second hand part (or sometimes even a new part) than it is to repair the original broken part.