Effects of 0.1 and 0.2 wt.% aluminium addition to zinc on the interdiffusion between zinc and iron at 400°C

This paper reports the interdiffusion behaviour between iron and zinc in Fe/Zn, Fe/Zn–0.1 wt.% Al, and Fe/Zn–0.2 wt.% Al couples annealed at 400°C for times ranging from 1 to 30 h. Under steady-state growth conditions, the interdiffusion zone in the Fe/Zn and Fe/Zn–Al alloy couples consisted of intermetallic layers of the Fe–Zn phases Γ-Fe3Zn10, δk-FeZn7, δp-FeZn10, and ζ-FeZn13. The intermetallic layers grew at a more rapid rate in the Fe/Zn–Al alloy couples than in the Fe/Zn couple. The thickening kinetics of the total interdiffusion zone in all couples were parabolic for annealing times greater than 3 h. The compact δ structure (δk) appeared at the Γ/δp interface of the Fe/Zn couples after about 7 h annealing; whereas, the same structure in either of the Fe/Zn–Al alloy couples was not observed until after about 13 h annealing. Enrichment of aluminium was detected at the δp/ζ and ζ/η-zinc interfaces in the Fe/Zn–Al couples. The extent of this enrichment was highest in the Fe/Zn–0.2 wt.% Al couple. The aluminium enrichment is believed to have contributed to the increase in the thickening kinetics of the intermetallic layers in the Fe/Zn–Al alloy couples owing to a negative thermodynamic interaction between aluminium and zinc.