New generation of acid Zn-Ni electrolyte for barrel application (Part 2)

Fig. 24: M8x70 bolts tested according to Cyclic Corrosion Test VDA 233-102; as received (a), after 10 cycles (b), after 15 cycles (c)
Tab. 7: Current efficiencies of different Zn-Ni processes measured electrochemically in a fresh M-up during deposition at 2.5 and 0.7 A/dm2
Fig. 23: M10 bolts coated with Zinni® 220, passivated with Tridur DB and sealed with two different sealers (Corrosil® Plus 501 – left and Corrosil® Plus 315L – right); samples before NSS test (a) after 240 h in NSST (b) and after 1055 h in NSST (c); test according to ASTM B-117
Fig. 22: M10 bolts coated with Zinni® 220 and passivated with Tridur DB, heat treated (hydrogen de-embrittlement) at 210 °C for 4 hours after passivation; samples before NSS test (a) and after 504 h in NSS chamber (b); test according to ASTM B-117
Fig. 20: ALSV of galvanostatically deposited Zn-Ni coating. Deposition was done from Zinni® 220 and the conventional acid Zn-Ni electrolyte with 0.1 A/dm2 (a) and 0.7 A/dm2 (b) at 35 °C with rotation speed of the RDE of 1000 rpm. The ALSV was done in metal ion free electrolyte at 35 °C with 1000 rpm and potential scan rate of 10 mV/s
Fig. 16: Comparison of deposition potentials recorded during Zn-Ni deposition from Zinni® 220, conventional alkaline Zn-Ni process and conventional acid Zn-Ni process at 2.5 A/dm2

The demand for Zinc Nickel coatings continuously increases in the automotive industry. Especially interesting are zinc nickel alloys with a nickel incorporation of 12–16 %, due to their high corrosion protection as well as superior wear and heat resistance as compared to pure zinc and other zinc alloy coatings.
Despite many advantages of acid Zn-Ni electrolytes there are still some areas of application, like barrel plating or plating of complex-shaped parts, believed to be reserved for alkaline processes. In this paper zinc nickel coatings deposited from ammonium and boric acid-free acid zinc nickel electrolytes, with improved throwing power for rack and barrel applications are investigated. Their corrosion resistance, ductility and hardness will be presented. Moreover, their texture and morphology will be investigated using SEM, XRD and FIB methods. In the end thickness distribution and Ni-incorporation will be presented and compared to alkaline systems.

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