Al alloys with Mg as the major alloying element constitute a group of non-heat treatable alloys with
medium strength, high ductility, excellent corrosion resistance and weldability. However, the segregation of Mg
may adversely affect the performance of these materials if they are exposed to rapid heating and cooling
environments such as resistance spot welding. The formation and migration of vacancy is an important factor
affecting Mg segregation. In this paper, the amount and distribution of Mg were measured by electron probe
microanalysis and the vacancy formation energy in AA5754 alloys was measured by positron annihilation
lifetime spectroscopy. The results indicated that the segregation of Mg at cracks, occurring under suitable
temperature and stress conditions, is related to the formation and migration of vacancies, and may promote crack
initiation and propagation.
