The mechanical properties of Al-Cu-Mn casting alloy mainly depend on the morphology,distribution,size,and number ofθ′(Al2Cu)precipitates.In this study,we have analyzed the effect of rare earth samarium(Sm)addition on the kinetics of precipitation in the Al-Cu-Mn casting alloy by using differential scanning calorimetry(DSC)and high-resolution transmission electron microscopy.Thermal effect peaks that are attributed to the formation and the dissolution of Guinier-Preston(GP)zone andθ′phase were identified from the DSC curves.The activation energy ofθ′formation was calculated by using both the Kissinger method and the analytical model,and the corresponding results were compared.Results suggest that the activation energy ofθ′formation in Al-Cu-Mn alloy is dramatically higher than that in Al-Cu-Mn-Sm alloy.Accordingly,it is concluded that the addition of rare earth Sm decreases the activation energy ofθ′formation and promotes the formation ofθ′precipitates. The mechanical properties of Al-Cu-Mn casting alloy mainly depend on the morphology, distribution, size, and number of θ ’(Al2Cu) precipitates. In this study, we have analyzed the effect of rare earth samarium (Sm) addition on the kinetics of precipitation in the Al-Cu-Mn casting alloy by using differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy. Thermo effect peaks that are attributed to the formation and the dissolution of Guinier-Preston (GP) zone and theta’phase were identified from the DSC curves. The activation energy of θ’formation was calculated by using both the Kissinger method and the analytical model, and the corresponding results were compared. Results suggest that the activation energy of θ’formation in Al-Cu-Mn alloy is dramatically higher than that in Al-Cu-Mn-Sm alloy. Accordially, it is concluded that the addition of rare earth Sm decreases the activation energy of θ’formation and promotes the formation of θ’precipitates.