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 rapid diffusional phase transformation in the vicinity of 150-degrees-C. For bulk iron contents of 8-13 wt %, eta transforms to 100% G phase. The G phase subsequently transforms at 240-degrees-C to zeta’ phase, which in turn transforms to delta or GAMMA1 phase near 300-degrees-C by depletion of iron from the surrounding matrix. The decomposition process may be driven by supersaturation of eta with iron.