Phase Equilibria In The Al-Si-Cu-Fe Quaternary System At650℃

Compared with other protection technology of steel, hot-dip aluminizing steelhas many excellent properties, such as superior high-temperature corrosion resistance,abrasion resistance, reflective properties of light and heat. Especially, it has goodcorrosion resistance in harsh environments. For this reason, in the1960s, manystudies on hot-dip aluminizing have been done at home and many achievements havebeen obtained. However, there are some problems in the process of the actualproduction and using. For example, as the intermetallic compound layer is too thick,the processability and forming property of hot-dip aluminizing steel is poor and thebrittle phase alloy layer can cause stress concentration and crack easily. Adding alloyelements, such as Cu，Si，Ti，Cr and RE et al., in the bath to change the sort and sharpof intermetallics in the alloy layer is a feasible solution to these problems. Thepurpose of this study was to explore the effects of Cu and Si on hot-dip aluminized,which involves the phase equilibria of Al-Si-Cu-Fe quaternary system. In this work,the Al-Si-Cu-Fe quaternary system and related ternary system are investigated to laythe theoretical fundament of analyzing the effect of Cu and Si on the bath and thequality of coating.In this work, equilibrated alloys were utilized with the help of scanning electronmicroscope equipped with dispersive X-ray spectroscope and X-ray power diffractionto determine the phase relations in the isothermal section of Cu-Fe-Si and the Al-richcorners of the Al-Cu-Fe, Al-Si-Fe and Al-Si-Cu systems, and the isothermal section ofthe Al-Si-Cu-Fe system with Al being fixed at85at.%at650°C. Isothermal section ofthe Cu-Fe-Si ternary system at650°C contains seven three-phase regions:(αFe)+(Cu)+FeSi; FeSi2+η+FeSi;(Si)+η+FeSi2; FeSi+ε+η; γ+FeSi+κ; ε+FeSi+γ;FeSi+(Cu)+κ. Two three-phase regions, i.e., L+λ+(Al), L+λ+ω are found in theAl-rich corner of Al-Cu-Fe system. Three ternary-phase regions, i.e., L+λ+τ5, L+τ5+τ6, L+λ+(Al) are found in the Al-rich corner of the Al-Si-Fe system. The Al-richcorner of the Al-Si-Cu system contains only the L phase. Two four-phase regions, i.e.,L+τ5+τ6+ω, L+τ5+τ6+λ exist in the isothermal section of the Al-Si-Cu-Fequaternary system at650°C with Al being fixed at85at.%. No quaternary compoundis detected in the quaternary system and the L phase is in equilibrium with all phasesin this section.