Three-dimensional particle cracking damage development in an Al–Mg-base wrought alloy

Experiments have been performed to quantitatively characterize the three-dimensional (3-D) microstructural damage due to cracking of Fe-rich intermetallic particles in an Al–Mg-base extruded 5086(O) alloy as a function of strain under uniaxial compression and tension. The 3-D number density and average volume of the cracked particles are estimated using the unbiased and efficient large area disector (LAD) stereological technique. In each specimen, the two-dimensional (2-D) number fraction of cracked particles is significantly lower than the corresponding 3-D number fraction. Therefore, the conventional 2-D damage measurements considerably underestimate the true 3-D damage due to particle cracking in this alloy. Comparison of the 3-D damage data on the 5086(O) alloy and earlier data on 6061(T6) alloy reveals that at all tensile/compressive stress levels higher than the yield stress of both alloys, the 3-D number fraction of cracked Fe-rich intermetallic particles in the 5086(O) alloy is significantly lower than its corresponding value in the 6061(T6) alloy. Therefore, the 5086(O) alloy is less prone to damage progression due to particle cracking compared to the 6061(T6) alloy. In both the alloys, significant rotations of the Fe-rich intermetallic particles occur during deformation under uniaxial compression. These rotations tend to align the particles along the direction of induced tensile stretch. The particle rotations in turn affect the progression of damage due to particle cracking. For deformation under uniaxial compression, the average volume of cracked Fe-rich particles increases with the increase in the strain. These observations are explained on the basis of the particle rotations.