Study on the Inhomogeneous Defect and Corrosion Resistance Characteristic of 55%Al-43.4%Zn-1.6%Si Alloy Coating on the Steel Substrate

Spangle characteristic and distribution of alloying elements coating on the steel substrate of 55% Al-43.4% Zn-1.6% Si alloy are carried out by using OM,SEM and EDS testing means.Coating corrosion resistance behavior of different areas was studied by polarization curve,and the formation process of hot dip and evolution of microstructures in the process of corrosion has been discussed.The results show that the different sizes of spangle microstructures consist of vertical grid dendrites arms with same spacing and and the composition of the different size of spangle surface contains Al,Zn and trace amounts of Si element where the ratio of Al/Zn is about 2:1.It is found out that inhomogeneous distribution of spangle size is mainly caused by the different number of α-{Fe,Al,Si} in the metal compounds layer.The smaller spangle size generates more τ5 phase in the IMC layerand hence more shape nucleolinus in the solidification process,and the resulting spangle is much more fine.Multi-point statistical collection indicates that the different sizes of spangle have the same corrosion resistance behavior.