Seven Fe–Si binary alloys with different silicon concentrations ranging from 0.10 to 2.84 mass% were immersed in a pure zinc bath in the temperature range between 713 K and 873 K for 600 s. The thickness of the alloy layer and the quantities of iron having reacted with zinc were measured, and the structure of the alloy layer was observed. These observations were compared with those of pure iron to offer information about the effect of silicon in galvanizing. Results obtained are as follows:
(1) The alloy layer consists of a gamma layer existing next to steel, followed by a delta 1 layer under all the conditions studied. The alloy layer formed next to the delta 1 varies with the silicon concentration of the Fe–Si alloy and the immersion temperature, and four areas are seen in the area map depending on the silicon concentration and the immersion temperature.
(2) The reactivity of the Fe–Zn reaction is higher in the region of 0.10 mass%Si and 713 K–733 K, and also in the region of 1–1.15 mass%Si and 773 K–793 K. The former high reactivity is due to the formation of a thicker zeta layer, and the latter is due to the formation of a thicker (delta 1+eta) layer. On the other hand, this reactivity is low in the region of 0.2–0.3 mass%Si, 713 K–793 K, and in the region of 813 K.
(3) The Fe–Zn reaction above 833 K does not depend on the silicon concentration of the Fe–Si alloy.