XRD studies of the phase composition of the electrodeposited copper-rich Cu–Sn alloys

Studies of the phase and chemical compositions as well as of the surface morphology of Cu–Sn alloys electrodeposited in the sulphate solution containing laprol were carried out using the XRD, SEM, and EDX techniques. The multiphase composition—pure copper, the α-CuSn phase and the intermediate hcp phase were determined to be present in the deposits obtained at cathode potentials positive to that of the reversible of the Sn/Sn2+electrode. When the content of Sn in the deposit was higher than 12–13 at.%, the β and/or δ phases were determined to be present along with that mentioned above. The deposit obtained at the potentials negative to that of the reversible of the Sn/Sn2+ electrode presented the δ phase with low quantities of the pure Cu and α-CuSn phases. The grain size of deposits increased with the cathode potential until it was positive to that of the reversible of the Sn/Sn2+ electrode. The presence of Br− ions in the solution hindered the granular electrocrystallization and reduced the Sn proportion in the alloy. It was assumed that underpotential deposition (UPD) of Sn on copper could be responsible for the formation of the multiphase composition and the intermediate hcp phase. It was concluded that the brightness of the studied Cu–Sn coatings was conditioned by the surface morphology.