Keys and tools for Hydrogen Embrittlement minimization during ZnNi plating on Ultra High Strength Steels

Ultra-High Strength Steels (UHSS) are highly used in the aeronautic sector in critical components, like landing gears. For these applications corrosion protection through sacrificial metallic coatings is needed, since Hydrogen produced during plating and pickling may diffuse to the steel and cause hydrogen embrittlement. Cd plating has been widely applied for enhancing corrosion performance of high performing components manufactured on UHSS, but this is a harmful substance for human health (toxic, mutagenic, carcinogenic).

As an alternative, ZnNi plating, a REACH(*) compliant coating, offers a superior corrosion performance for UHSS, also acting as a sacrificial coating for corrosion protection on UHSS. But this plating shows low efficiency (20-50%) depending on plating conditions. Developing LHE electrolytes for minimizing hydrogen generation can increase ZnNi plating efficiency (>50%).

Applying ZnNi coatings to complex parts leads to areas with different local current densities leading to different H content based on current density distribution, different coating morphology and different effusion kinetics.

H2Free project consortium has investigated and modelled hydrogen effusion in electrochemically plated ultra-high-strength-steels used for landing gears structures. This presentation focuses on the evaluation of the correlation among base material, ZnNi coating structure, Hydrogen uptake and degassing efficiency of electroplated ZnNi coatings on four UHSS: 300M, E35NCD16H, EZ2NKD18 and Custom465.

As a result, a model to predict H intake and effusion has been developed for 4 targeted UHSS coated with 3 different morphologies. The model has been coupled to ELSYCA´s Plating Manager Software to correlate plating parameters and H uptake and effusion. The model has been validated both in laboratory and at the industrial scale regarding H intake and main coating features (thickness and composition).

(*) REACH (Regulation on the registration, evaluation, authorisation and restriction of chemicals) regulation is the main EU law to protect human health and the environment from the risks that can be posed by chemicals. 

Funding: This research has been developed within H2Free Project funded under the Clean Sky 2 Joint Undertaking (JU) with the grant agreement Nº 101007712. The JU receives support from the EU Horizon 2020 research and innovation programme and the Clean Sky 2 JU members.