Microstructure and corrosion resistance of electrodeposited zinc alloy coatings

A heat treatment effect on the microstructure and corrosion properties of electrodeposited Zn, Zn-Co, Zn-Fe and Zn-Ni alloy coatings was studied. Surface morphology examinations were carried with AFM, while XRD was used to determine metal lattice parameters, texture and phase composition. Low-temperature annealing ( at 225 degreesC) caused the formation of intermetallic Fe/Zn compounds, a transformation of amorphous oxide inclusions to the crystalline form and a decrease in the Zn lattice parameter for Zn-Co and Zn-Fe alloys. The mentioned structural modi. cations were not accompanied, however, by corrosion behavior changes of these coatings. On the Zn-Ni alloy, the annealing caused a significant reduction in the diffraction peak width and simultaneous considerable augmentation of the corrosion current. This effect is related to the formation of a less disordered lattice for this alloy.