Zincate mechanism on cast Al-Si alloy in non-cyanide multi-metal zincate solutions
(Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Arrhenius formula was applied to calculate the apparent activation energy of zincate reaction. The standard electrode potential of all the metal coordinating ions and the order of galvanic couple of different metals in zincate solution were also calculated. Electrochemical behavior of zincate process was studied by Tafel polarization curves, E—t curves, and electrochemical impedance spectroscopy(EIS). The results show that the apparent activation energy of zincate reaction in non-cyanide multi-metal zincate solution is smaller than that in simple zincate solution, and precipitation sequence of all the metals in zincate solution is Cu, Ni, Fe and Zn. Relationship between the potential at 30 s before zincate and coverage was attained according to the change of potential of zincate. EIS shows that inductive reactance is produced during zincate.
Key words: cast Al-Si alloy; non-cyanide multi-metal zincate; zincate solution; zincate mechanism; apparent activation energy