EFFECT OF ANNEALING UPON DECOMPOSITION OF ELECTRODEPOSITED IRON ZINC ALLOY COATINGS

As-deposited electrodeposited iron-zinc alloy coatings containing eta phase, decompose upon heating through a sequence of metastable phases. The hcp eta phase transforms to bcc G, or GAMMA-like phase via a rapi d diffusional phase transformation in the vicinity of 150-degrees-C. F or bulk iron contents of 8-13 wt %, eta transforms to 100% G phase. Th e G phase subsequently transforms at 240-degrees-C to zeta' phase, whi ch in turn transforms to delta or GAMMA1 phase near 300-degrees-C by d epletion of iron from the surrounding matrix. The decomposition proces s may be driven by supersaturation of eta with iron.