The best process to joining aluminum to itself or to other materials such as copper accurately must be in a vacuum because the alloy is so dirty and quick to oxidize. Vacuum furnace brazing does a great job of de-oxidizing metals as well as vaporizing undesirable high vapor pressure elements that might be seen as contaminants to ensure a strong braze joint. Unlike dip-brazing, vacuum brazing is not plagued with salts that invariably leach out over time and contaminate the vacuum systems in which those assemblies are used. Also, if welding versus brazing is a concern, please take a look at the photo below showing the difference of a homogenous joint versus a welded joint.