Establishing industrial Zn‑Ni brush electroplating process without post-plating hydrogen embrittlement relief baking

Abstract

Transitioning from carcinogenic cadmium (Cd) to zinc‑nickel (Zn‑Ni) coating in aircraft components to prevent corrosion poses a challenge of hydrogen embrittlement (HE) of the substrate. While post-plating baking addresses HE in Zn‑Ni coated components, the economic repair of damaged coatings using the Zn‑Ni brush plating process without baking remains problematic. Therefore, in this work, the HE susceptibility of Zn‑Ni brush electroplating, both with and without baking has been investigated by subjecting plated notched specimens to a sustained load test (SLT) in accordance with ASTM F519. Baked specimens after plating passed the SLT, while unbaked specimens exhibit severe HE and fail. Adjusting electroplating parameters alone, such as plating current density and total plating electric charge, did not reduce HE vulnerability of the Zn‑Ni brush plating process without baking. However, optimizing the pre-plating grit blasting process (pressure, working distance), along with reducing the total plating electric charge, and introducing a 72 h delay between electroplating and subsequent SLT, enable plated specimens to exhibit no HE and to pass SLT without requiring baking.