Quasi-Static and High-Strain-Rate Experimental Microstructural Investigation of a High-Strength Aluminum Alloy

The damage mechanisms associated with the deformation and failure of high-strength Al 2139-T8 were investigated by optical and scanning electron microscopy at strain rates ranging from the quasi-static, 10⁻³ s⁻¹, to the high strain rate, at approximately 2350 s⁻¹. Deformation was more uniform at the lowest strain rate of 10⁻³ s⁻¹, where nanocracking nucleated at coarse inclusions and clustered dispersed particles. Deformation was more localized as the strain-rate increased, with microvoid nucleation, resulting from particle-matrix interfacial decohesion and particle cracking, observed at higher strain rates. Dispersed particles and coarse inclusions were observed on the fracture surfaces of the deformed samples subjected to high rates of strain. Coarse inclusions were associated with inclusion cracking and shear deformation. The dispersed particles were associated with dimpled rupture, and the orientation of the particles determined the amount of plasticity prior to failure of the alloy.