<p>Laser-powder bed fusion (L-PBF)-based additive manufacturing (AM) of pure Fe and two alloys in the Fe-Cu system (FeCu2.5 and FeCu5&#xa0;wt.%) was used to understand the role of Cu in the microstructure and resulting mechanical properties at strain rates between 10⁻³&#xa0;s⁻¹ and 10³&#xa0;s⁻¹. Small amounts of Cu were found to significantly increase yield strength at all strain rates because of a combination of grain refinement and the presence of nanoscale Cu precipitates within the Fe grains. The strengthening increments are interpreted in terms of Hall–Petch strengthening from Fe grain boundaries, strengthening from dislocations introduced via processing, and precipitation hardening from Cu precipitates. Enhancements in yield strength were accompanied by slight reductions in strain rate sensitivity and tensile ductility. Fracture surface analysis revealed that Fe and FeCu2.5 showed similar ductile fracture features at all strain rates, whereas FeCu5 exhibited a shear-dominated slanted fracture surface. The absence of solidification defects in these alloys can be rationalized in terms of CALPHAD-based Scheil and Clyne–Davies solidification simulations. The simulations show that the propensity for solidification cracking is expected to increase rapidly for Cu contents exceeding ~ 8%. This demonstrates the potential of rapid solidification simulations in aiding alloy design.</p>