Study of surface treatment effects in galvanizing iron single crystals

Single crystals of iron with basic low-index surface orientations were given various pretreatments to produce a range of surface roughness and hardness conditions and then galvanized in pure zinc in a purified hydrogen atmosphere. Significantly different reaction effects previously found on electropolished (110), (100) and (111) surfaces of commercial single crystals were confirmed in tests involving pretreatment by thermal faceting and mechanical polishing. A relationship between galvanizing reactivity and crystallographic orientation of the iron surface was thereby more conclusively established. Increasing the roughness of the crystal surfaces by grit blasting, and to a lesser extent by chemical etching, significantly reduced the dependence of the reactivity on crystallographic orientation. Fine surface irregularities and larger-scale uneveness, especially as produced by grit blasting, in combination with the growth habit of the iron-zinc alloy layers, were the predominant factors determining the galvanizing behaviour. Surface work-hardening by the mechanical polishing and grit-blasting pretreatments had no apparent effect on the galvanizing reaction.