The development of Fe–Zn intermetallic compounds in solid Fe/Zn and Fe/Zn–Al diffusion couples during short-term annealing at 400°C

The effect of aluminium alloying additions of up to 0.2wt.%Al to zinc in the early-stage formation of Fe–Zn intermetallic compounds was studied by means of diffusion couple experiments. Diffusion annealing was employed on Fe/Zn, Fe/Zn–0.1wt.%Al and Fe/Zn–0.2wt.%Al couples at 400°C for times ranging from 10 to 50 min. It was found that aluminium additions to the zinc alloy initially inhibited intermetallic compound formation. Furthermore, a localised phase was noted at the δp/ζ interface in the ternary couples at short times (<30 min) which also inhibited phase growth. However, this phase was noted to have dissolved on further annealing (≥40 min), with the intermetallic phases that formed growing more rapidly than the binary couple at these times. It was also noted that intermetallic phase growth in the binary couple was dominated by the ζ phase at short times, but δp growth dominated at times greater than 30 min. In contrast, the relative rate of growth of the ζ and δp phases in the ternary couples remained almost constant with annealing time.