Al-Mg alloys exhibit remarkable hot and warm ductilities, which have made the 5000-series alloys a critical part of commercial hot gas-pressure forming operations for the transportation industry. A review of the metallurgical and practical engineering reasons for this success is presented, and new understanding for behaviors in these materials, expected to impact future advances in hot- and warm-forming technology, are described. The excellent formabilities in this material class are fundamentally attributable to two deformation mechanisms, grain-boundary-sliding and solute-drag creep. However, a number of failure mechanisms ultimately limit final ductility and formability. These include cavitation, flow localization and microstructure evolution. The interplay of these mechanisms is discussed in terms of the potential to improve processing windows in forming operations.