In-situ observation of the fracture process in Al–Zn–Mg–Cu alloys

Abstract In order to investigate the fracture behaviour of highly-alloyed Al–Zn–Mg–Cu alloys as a function of alloy purity, in-situ observations using scanning electron microscopy were performed during tensile testing. The observations were used to verify proposed fracture mechanisms in conjunction with microstructural and fractographic analyses along with fracture toughness tests. It was found that the fracture process is complex. The nucleation, growth, and coalescence of voids precede ductile fracture of the alloys. The decohesion and fracture of intermetallic particles (generally >1 μm in diameter) appears to be the initial event in the fracture process, while mechanism and propagation rate of fracture depend on the alloy chemistry. A tortuous crack path and reduced crack propagation rate in the least pure alloy can be closely related to a strong interaction of the crack front with intermetallic particles.

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