Study On The Micromechanism And Reaction Between Low Carbon Steel Containing Si And Liquid Zn-Ni Alloy

In this thesis, the reaction between low carbon steel containing Si and liquid Zn or Zn-Ni alloy, the formation and the growth kinetics of Fe-Zn and Fe-Ni-Zn intermetallic compounds are studied. The composition, phase structure and formation mechanism of zinc dross are also studied. The formation and growth kinetics of the intermetallic compounds through reaction between liquid Zn and low carbon steel containing Si which is treated by electroless pre-plating Ni are analyzed.The results on the reaction between low carbon steel containing Si and liquid Zn or Zn-Ni alloy show that the relation between Fe-Zn reaction and Si content in steel below 480℃abides by Sandelin effect, which owes to the abnormal growth ofζ(FeZn13). Adding Ni to liquid Zn bath can restrain the abnormal growth ofζlayer on the low carbon steel containing 0.04~0.18wt%Si. However, Ni has little influence on the growth ofζlayer between 480~500℃. Ni restrain the growth ofζlayer mainly by two reasons. First, the growth of coarseζcrystals is blocked by high concentration Ni region, and Fe-Ni-Zn ternary intermetallic compoundζsmall crystals are formed by dissolving Fe from coarseζcrystals and combining Fe with Ni and Zn in liquid under conditions of low Ni content in the Zn bath. Second, the Fe-Ni-Zn ternary intermetallic compoundΓ2 particles emerge in the front ofζcrystals so as to restrain effectively the growth ofζcrystals under conditions of high Ni content in the Zn bath. It is found thatζis the first intermetallic compound that appears during the Fe-Zn reaction. The preferential nucleation and growth ofζcrystal on the Fe substrate mainly depend on Fe concentration gradient ahead of solid/liquid interface and high match betweenζand special crystal orientation ofα-Fe.The research on the Fe-Ni-Zn ternary intermetallic zinc dross indicates that Ni content in theζand theΓ2 in the zinc dross increases with increasing of Ni content in the zinc bath. Zinc dross is compose ofη+ζ,η+ζ+Γ2 andη+Γ2.ζandΓ2 particles in the zinc dross are new phases, which formed due to the enhancing of Ni concentration in the Zn bath after Zn-Ni master alloy completely dissolve into Zn bath.