Tailorable deposition of Sn-Ni alloy from a pyrophosphate bath with an adjustable Sn:Ni molar ratio

Tailorable deposition was carried out by varying the Sn:Ni molar ratio of a pyrophosphate bath to adjust the deposition rate as well as the phase composition, morphology and corrosion resistance of the as-deposited Sn-Ni alloy. The nickel content of the resultant Sn-Ni alloy decreases gradually from 50 wt% to 28 wt% when the Sn:Ni molar ratio of electrolytes increases from 0.2 to 2.0 and remains reasonably constant at 31-37 wt% when the ratio is in the range of 0.6-1.8. Codeposition of a reasonable content of Ni with tin refines the crystal grains of the alloy and produces a compact coating. The phase composition of the Sn-Ni alloy deposition changes along with the Sn:Ni molar ratio, and alloys with low nickel content are composed of Ni4Sn, Ni3Sn2 or Ni3Sn4 phases. A single-phase homogeneous intermetallic compound of Ni4Sn appears in alloys containing 31-37 wt% nickel. Compared to pure deposited Sn, the electrochemical measurements reveal that the Sn-Ni alloys containing single-phase Ni4Sn have a smaller corrosion current density, smaller blunt current and larger electrochemical charge transfer resistance in 10% H2SO4 solution, indicating that the nearly equiatomic alloy Sn-Ni exhibits excellent corrosion resistance in sulfuric acid solution.