Abstract Pulsed current (PC) electrodeposition has become an essential tool for producing coatings in a wide range of industries. The pulsed current can have a significant influence on the composition, morphology and properties of electrodeposited coatings and this is particularly true when plating an alloy. In this study, the mechanism for the development of Sn-Cu alloy coatings produced by PC electrodeposition was investigated. Sn-Cu alloy coatings produced by PC electrodeposition were essentially composed of a dual layer of Sn-Cu electrodeposits and Cu6Sn5 intermetallic compounds (IMCs). In addition, it was observed that pulsed Sn-Cu electrodeposits exhibited an increased Cu content. Experiments were carefully designed to elucidate the mechanism for this important finding and based on their results a theory is proposed which explains the increased Cu content in terms of a metal displacement reaction occurring during the ‘relaxation’ time of PC electrodeposition.