Effects of θ′ precipitates on the mechanical performance and fracture behavior of an Al–Cu alloy subjected to overaged condition

Abstract

In this work, the effects of shear-resistant plate-shaped θ′ (Al2Cu) precipitates on mechanical performance and fracture behavior of a heat-treatable Al–Cu alloy were studied. The precipitates, dislocations and micro-voids around grain boundaries were observed using transmission electron microscope and scanning electron microscope equipped with electron backscatter diffraction. The Al–Cu alloy was overaged to ensure that the θ′ phase was the only precipitate in the material. The results show that concentration of local strain and pile-up of dislocations occurred along grain boundaries during tensile deformation. A method was developed to calculate the total dislocation density nearby the grain boundaries in the deformed alloy, from which a quantitative relation was established between precipitate number density and void areal density on intergranular fracture surface. The effect of precipitates on the mechanical properties of Al–Cu alloy was also discussed qualitatively. The precipitate number density of the over-aged Al–Cu alloy acted as the dominating factor that influenced the dislocation density and void density on grain boundaries, which thus determined the mechanical properties and fracture behaviors of the alloy.