Acoustic emission from 7075 aluminum during tensile deformation or cyclic loading has been the subject of investigations by many authors [1–9]. The acoustic emission source mechanism during fatigue crack propagation was initially believed to be the fracture of.Mg2Si intermetallic inclusions which play a strong role in the crack propagation process. Recent work has clearly demonstrated, however, that the mechanism is related to localized yielding or incremental separation of the crack face surfaces as the fatigue crack advances [7, 8, 9].