Thermodynamic and Morphlogical Investigations of Dross in Molten Zn Bath

Abstract

A study was conducted on the formation of Zn-Fe and Fe-Al crystals in a molten Zn bath. Baths similar in composition to that of a CGL, were prepared in the laboratory and attention was paid on the cooling rate in Zn bath sampling.
When samples were cooled at lower cooling rates than 100°C/s, crystallization and crystal growth were observed in the Zn bath sample ingots. Higher cooling rates than 10⁵°C/s inhibited the crystallization and crystal growth during cooling. In order to evaluate the presence of crystals in the Zn bath, it is necessary to employ a rapid cooling.
The type of crystal changed with the Al content of the bath. In a bath containing above 0.13mass% Al, Fe₂Al₅ formed. Below 0.13mass%, FeZn₇, formed. From the results obtained with the rapid cooling technique, an equilibrium solubility curve for Fe and Al was estimated in the region where Fe₂Al₅ was crystallized. The curve was expressed as Log [Fe]²[Al]⁵=5.37-9354/T for Fe+5/2Al=1/2Fe₂Al₅. With this equation, the available Zn-Al-Fe ternary phase diagram in the literature was corrected at the Zn corner.