亜鉛と鉄との合金化反応と拡散現象

抄録

Fundamental research for the alloying reaction in the galvannealing process was made using the multiple marker technique which enables us to investigate atomic movement due to diffusion. 0.1 mass%Al was added to both solid and molten zinc employed. After anneal of the iron-solid zinc diffusion couples, intermetallic compounds were detected in the couple. Bends of the multiple marker arrays were observed at both iron/intermetallic compound and intermetallic compound/zinc interfaces. From these results we can deduce that iron atoms leave an iron lattice and then be included in a crystal lattice of the intermetallic compound together with zinc atoms at the iron/compound interface. At the same time vacancies are created at the interface and then move toward the compound/zinc interface by exchange of positions with zinc atoms. Consequently, growth of the compounds is controlled by the diffusion of zinc atoms.
The reaction of a solid iron specimen with molten zinc in the high temperature range of more than about 780 K yields thin coherent compound layers over the iron substrate. The outer compound, δ₁, layer, however, is disrupted by attack of the molten zinc, in place of a coherent layer. The marker experiment also shows that iron and zinc atoms are included in the intermetallic compound at the iron/compound interface. Hence, a cause for rapid proceeding of the alloying reaction in the galvannealing can be ascribed to the short distance pass for zinc atom diffusion.