This study determines the correlation between microstructure, fracture mechanism and formability of Al tailor-welded blanks (TWBs). It is found that porosity in the welds is detrimental to the formability of non-vacuum electron beam (NVEB) welded AA5754-O temper Al TWBs. It is also found that the degree of influence of the weld characteristics on formability can be minimal in one test condition, but critical in another, depending on the loading condition, strain state (related to blank geometry) and relative position of the weld seam to the major strain during forming.Metallography, microhardness measurement, electron probe chemical analysis and fractography for 1-2 mm NVEB AA5754-O temper of Al TWBs were used to analyze precipitation, porosity, grain structure, microhardness profile and microchemistry profile across the weld of Al TWBs and their fracture mechanisms during forming tests. Formability of the NVEB welded AA5754 Al TWBs has been previously evaluated. In this study, observations of the failure location are carried out on those specimens subjected to transverse tensile, longitudinal tensile, transverse dome and longitudinal dome tests.