The Research On Solid Zn/Fe And Zn/Fe-Si Diffusion Couples And Phase Diagram Of Zn-Fe-S

Hot-dip galvanizing is an economic and effective way of metal surface protection. Silicon in the steel results in the Sandlin effect and affects the coating's quality seriously. Despite for the piles of work done by the researchers of the world, the cause of the microstructural development in the coating layer on Si steels is a subject of controversy and debate.Due to the complexity of galvanizing, it is hard to control and understand the reaction mechanism and growth dynamics for it. So, studying the problem by the means of diffusing-couples is significant.After a number of experimental methods were tryed, The Zn/Fe and Zn/Fe-Si diffusion couples made by clamps were adopted. By analysing the morphology of the diffusion coatings at 380℃, the rule of Zn-Fe alloy layers'growth dynamics as well as the influence induced by silicon were studied. The experimental results show that different layers are formed by clamping method, and the first layer is theζphase,no matter in the Zn/Fe or in the Zn/Fe-Si diffusion couples.The total thickness of the diffusion layers , the thickness of theζphase and the thickness of theδphase increase with the time.Especially, theГphase which appears between theδphase and the steel, has been thin all the time. In the Zn/Fe couples, the growth rate of theδphase accelerates remarkably with the time, but theζphase and theГphase are samdwich continuousely. When the annealing time is less than 5h, the inter-diffusion zone is consist of theζphase, theδphase and theГphases. After annealling for 5h, theζphase is too thin to observe and the inter-diffusion zone is formed by theδphase merely. In the Zn/Fe-Si couples, the addtion of silicon promotes the growth of theζphase enormously and restrains the growth of theδphase. At the beginning, there are only a few overhangs,and the continuous saw tooth-like layers are formed only after annealling for 5h.When the annealing time is less than 2h and the content of silicon in the steels is about 0.1wt%,the inter-diffusion zone is thicker than the steels free of silicon. But when the content of silicon is around 0.3wt%, the thickness of the layers are as the same as the Zn/Fe diffusion couples'.Otherwise,when the annealing time is more than 2h, the addtion of silicon increases the total thickness of the interdiffusion zone obviously, and the layers are thicker more than 10μm.Based on the SEM-EDS and X-ray diffractometry analyses, the Zn-Fe-S ternary...