GB1080291A - Plating metal - Google Patents

Abstract

The surface of a basis metal having a positive electrode potential of less than 2.37 volts, e.g. Al, Mg, Be, U, Mn, Ti, Te, Zn, Cr, Fe, Cd, In, Th, Co, Ni, Mo, Sn, Pb, Cu, is plated by contacting it with an activating bath containing only a single platable metal more noble than the basis metal and in the form of a soluble salt, e.g. Sn (as sodium stannate or stannous chloride), Cu or Cd (as cyanide), Zn (as cyanide or sodium zincate), Ni (as sulphate or pyrophosphate), Ag (as nitrate or cyanide) or Pb (as carbonate), to activate the surface of the basis metal, withdrawing and immersing it into a strike bath containing in solution a plate metal and at least one alloying plate metal, e.g. Cu, Sn, Zn, Ag, Ni, Au, Cd, and electro-depositing on to the activated surface a plate containing the two plate metals. Commercial aluminium alloys are specified for the basis metal; other alloys may be used for the basis metal, including those of Mg, Sn-Pb (pewter), Zn-Sn, Zn-Cu, Cu-Sn or Zn-Ni. For an Al surface, e.g. steel coated with an Al layer, a typical activating bath contains 10-70 g/1 stannate ion e.g. K2Sn(OH)6 with free KOH, and examples of alkaline strike baths are: (a) solution of K2Sn(OH)6, 2 KCN. CuCn or Zn(CN)2, free KCN and KOH, for plating bronze or Sn-Zn; (b) solution of AgCN, CdO and NaCN for Cd-Ag; (c) solution of K2Sn(OH)6, Ni3(PO4)2, K2P2O7 and NH4OH for Sn-Ni. Additions for the baths may be Rochelle salt, sodium gluconate or gluconic acid, glucoheptonic or saccharic acid, E.D.T.A., N, N-bis (hydroxyethyl) glycine. The Al bearing the alloy plate may be further plated with Cr, Ni, Sn, Cu.