Sn microalloying Al–Cu alloys with enhanced fracture toughness

Effect of minor Sn additions (0.05, 0.10 wt%) on the microstructure and room-temperature mechanical properties of Al-3.0 wt%Cu alloy was studied by using transmission electron microscopy (TEM), atom probe tomography (APT), tensile testing, and fracture toughness measurement, respectively. TEM experimental results showed that the Sn addition promoted the dispersion of θ′ -Al2Cu precipitates with refined size and increased number density. APT examinations revealed that the Sn microalloying mechanism was mainly the heterogeneous nucleation of θ′ precipitates on Sn particles. The microstructural evolution with Sn addition resulted in a decrease in ductility but an increase in both yield strength and fracture toughness. In particular, the fracture toughness was increased by over 60% at 0.1 wt% Sn addition, indicative of a significant microalloying effect. The ductility inversely scaled with the strength, while the fracture toughness simultaneously increased with the strength. These relationships are rationalized by considering a competition between dislocation-precipitate interaction and precipitate-matrix deformation discrepancy as the dominant strain localization mechanism, which is modulated by the Sn-affected precipitation as well as the constraint condition.