Age-hardening behavior and related changes were studied to elucidate the hardening mechanism of an Ag–Cu–Pd alloyby Differential Scanning Calorimetry (DSC), hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and energy dispersive spectrometer (EDS). The results showed that hardness of the alloy was raised to 90% and 68% of its solution state value by isothermal aging at 300 ◦C and 400 ◦C, respectively. However, aging at 500 ◦C led to a decrease in the hardness of the alloy. Moreover, while age hardening at 300◦C occurred due to coherency strains between the (111) plane of Ag-rich and the (111) plane of Cu3Pd phases, the mechanism of aging at 400◦C was the formation ofCu3Pd superlattice with the L12-type crystal structure. In contrast, reduction of Cu3Pd phase and formation of Cu solid solution decreased hardness during aging at 500oC. Manuscript profile