1995 Volume 81 Issue 10 Pages 995-1000
The growth of the alloy layer formed in a hot-dip Zn-530 mass%Al coating has been studied by gas-reducing coating and fluxing coating methods. The growth of the alloy layer occured at a bath temperature above 520°C even in a short time immersion (15s), and is accelerated with increasing the Al content in the bath and raising the bath temperature. The grown alloy layer consists of Al-Fe intermetallic compounds (mainly Al5Fe2 phase containing 6.77.8 at%Zn), and Zn phase (94 95 at%Zn) solidified at cavities in Al-Fe intermetallic compounds. In similar to Al5Fe2 phase formed in a hot-dip aluminizing, this Zn-containing Al5Fe2 phase formed in the hot-dip Zn-5-30 mass%Al coating has also a strong orientation of (002) plane and grows even in a vertical direction to the steel surface. However, in the hot-dip Zn-530 mass%Al coating, Al-Fe intermetallic compounds grow preferentially at ferrite grain boundaries of the steel substrate where Zn has diffused.
It is considered that the grain boundary diffusion of Zn to the steel substrate has a great influence on the growth of the alloy laver.
