Hydrogen absorption, desorption and embrittlement of Zn and ZnNi-electrodeposited bolts

The H contents and H embrittlement (HE) of Zn- and ZnNi-electrodeposited SCM435 bolts were quantitatively evaluated before and after baking. The Zn-coated bolt possessed higher H contents than the ZnNi-coated bolt in as-electrodeposited and baked states. H atoms were strongly trapped inside the coating layers. The Zn-coated bolt underwent flaking of coating layer during baking at temperatures above 200 °C due to H effusion through the brittle δ phase. The Zn-coated bolt exhibited no HE regardless of baking despite of its high H content due to no permeation of H into the steel substrate during electrodeposition and tensile deformation.